Muyiwa Adaramola - Academia.edu (original) (raw)
Papers by Muyiwa Adaramola
Energy Exploration Exploitation, Aug 1, 2012
ABSTRACT The technical and economic assessment of using hybrid energy system for electricity gene... more ABSTRACT The technical and economic assessment of using hybrid energy system for electricity generation in rural communities in the south-west of Nigeria is investigated in this study. Renewable resources (wind and solar data) in Ibadan located on the latitude of 7.43 °N and longitude 3.91 °E are used. Hybrid Optimization Model for Electric Renewable software has been employed to carry out the present study. It was found that Wind-PV-Generator-Battery hybrid system is most suitable option as stand-alone electricity generating system in Ibadan. The optimal simulation results indicate that the levelised cost of energy for this hybrid energy system varies between 0.437/kWhand0.437/kWh and 0.437/kWhand0.606/kWh depending on the diesel price. These costs are significantly lower than the cost of using diesel generator only (without battery) which varies between 0.607and0.607 and 0.607and0.940 per kWh. It was further observed that there is a significant reduction in emission produced if hybrid energy system is used instead of only generator based energy system. The most suitable hybrid systems in other locations in southwest Nigeria can be identified from the optimal energy system plots provided.
The performance of a 0.9m diameter model wind turbine using the NREL s826 airfoil profile has bee... more The performance of a 0.9m diameter model wind turbine using the NREL s826 airfoil profile has been investigated both experimentally and numerically. The geometry was laid out using Blade Element Momentum theory (BEM). The design was tested experimentally and gave a peak power coefficient of C P = 0.448 at the design tip speed ratio of λ = 6. It was found that the BEM had correctly predicted the power coefficient curve very well giving virtually identical results to the measurements, except when the turbine is operating in a deep stall mode. The thrust predicted was however consistently too low by a shift of the order of ∆C T ∼ 0.1. After the model tests had been undertaken, numerical calculations were performed by means of fully 3D CFD simulations using a k − ω turbulence model. The high resolution CFD predictions (using about 3.5 × 10 6 grid points) reproduced the model thrust coefficient almost perfectly. The predicted power coefficients were also very close to the measurements, but somewhat overestimated at high tip speed ratios. At the design tip speed ratio the CFD over-predicted the power coefficient by merely 2%.
Latvian Journal of Physics and Technical Sciences
Solar Energy, 2015
In this study, global solar radiation over Nigeria was simulated under an enhanced atmospheric CO... more In this study, global solar radiation over Nigeria was simulated under an enhanced atmospheric CO 2 level using the International Centre for Theoretical Physics (ICTP) Regional Climate Model version 3 (RegCM3) for the period 1981 to 2100 with ECHAM5 GCM as the lateral boundary conditions. The simulated seasonal global solar radiation bias for the RegCM3 with NIMET and NASA observed datasets in the control period are of similar magnitudes and showed a mixture of persistent positive and negative biases ranging between À10% and 30%. The model generally underestimates solar radiation (biases À10% to À30%) across the whole country in most of the months. In addition, it overestimates radiation (biases +2-30%) over the northern region of the country. Alongside the present climate , three future periods were considered viz: period 1 (2011-2040), period 2 (2041-2070) and period 3 (2071-2100) for the potential future changes. The seasonal potential future changes in period 1 (i.e. potential future changes with respect to 2040) showed a reduction in the range of 0% (North) to 3.27% (South) whereas more reduction in global solar radiation is observed in period 2 (i.e. 2041-2070 minus present climate) having general decrease ranging from 0.11% to 3.39% with the least value in April (Middle-belt) and the largest in the South zone (March). Potential future changes in period 3 (i.e. 2071-2100 minus present climate) is generally characterized with mixed increase and decrease in global solar radiation across the country than the previous two periods (1 and 2). For the annual potential future changes, RegCM3 model predicted a decrease in solar radiation towards the end of the century with more reduction found in the South zone and the least in the North region. Furthermore, future changes in global solar radiation across the zones in all the periods are however found to be insignificant at p 6 0.01.
Volume 9: 6th FSI, AE and FIV and N Symposium, 2006
ABSTRACT The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake of a cylind... more ABSTRACT The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake of a cylindrical stack of AR = 9 was investigated with two-component thermal anemometry. The cross-flow Reynolds number was ReD = 2.3×104 , the jet Reynolds number ranged from Red = 7×103 to 4.6×104 , and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-height ratio of δ/H = 0.5 at the location of the stack. The flow around the stack was broadly classified into three flow regimes depending on the value of R, which were the downwash (R < 0.5), cross-wind dominated (0.5 < R < 1.5), and jet-dominated (R > 1.5) regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields.
International Journal of Fluid Mechanics Research, 2007
Thermophysics and Aeromechanics, 2011
ABSTRACT The paper considers the evolution of turbulent kinetic energy in a turbulent boundary la... more ABSTRACT The paper considers the evolution of turbulent kinetic energy in a turbulent boundary layer perturbed by suction. The results show that the boundary layer equilibrium is altered in a non-linear manner due to suppression of the structures near the wall. The behavior, however, suggests that the wavelength of alteration of the equilibrium of the layer is unaffected by a change in Reynolds number and suction rate.
Thermophysics and Aeromechanics, 2007
Hot-wire measurements have been undertaken in a turbulent boundary layer which is subjected to an... more Hot-wire measurements have been undertaken in a turbulent boundary layer which is subjected to an impulse in form of a short roughness strip with the aim of examining its influence on the structure of the turbulent boundary layer. The results indicate that, while the energy containing motion is shifted from low wave number to high wave number near the wall due to the interfering of the roughness strip with the near-wall structure, the reverse is the case in the outer region. While the anisotropy at small scale changes appreciably, there is no discernable change at the large scale when distance from the wall is increased as reflected in the collapses of spectra shear correlation coefficient at the low wave number. It further shows that the roughness strip alters the flow dynamics of the boundary layer as shown in the changes in the mixing length distribution.
Volume 9: 6th FSI, AE and FIV and N Symposium, 2006
ABSTRACT The influence of the jet-to-cross-flow velocity ratio, R, on vortex shedding from a cyli... more ABSTRACT The influence of the jet-to-cross-flow velocity ratio, R, on vortex shedding from a cylindrical stack of aspect ratio AR = 9 was investigated using hot-wire anemometry. The cross-flow Reynolds number was ReD = 2.3×104 and R was varied from 0 to 3. The stack was partially immersed in a flat-plate boundary layer, where the boundary layer thickness-to-height ratio at the location of the stack was δ/H = 0.5. In the downwash flow regime, when R < 0.7, a single Strouhal number (e.g., St = 0.167 at R = 0) was measured along the entire stack height. In the crosswind-dominated flow regime, when 0.7 ≤ R < 1.5, a higher Strouhal number was obtained (e.g., St = 0.185 at R = 1.0). In the transitional and jet-dominated flow regimes, a jump in Strouhal number (e.g., from St = 0.176 to 0.193 at R = 2.0), occurred within the flat-plate boundary layer. The power spectra showed that the shape and strength of the vortex shedding peak changed along the stack height. In general, the peak was more broad-banded near the base of the stack, became sharper and more distinct within the middle of the combined stack and jet wakes, and then reduced in strength in the jet wake and jet regions. In the transitional and jet-dominated flow regimes, the jump in Strouhal number was seen as a gradual change in dominance between two closely spaced peaks, with both peaks co-existing near the edge of the boundary layer.
Latvian Journal of Physics and Technical Sciences, 2008
Studies of the flow conditions of natural gases in pipelines have led to the development of compl... more Studies of the flow conditions of natural gases in pipelines have led to the development of complex equations for relating the volume transmitted through a gas pipeline to the various factors involved, thus deciding the optimum pressures and pipeline dimensions to be used. From equations of this type, various combinations of pipe diameter and wall thickness for a desired rate
International Journal of Energy and Environmental Engineering, 2012
In this study, the wind speed characteristics and energy potential in three selected locations in... more In this study, the wind speed characteristics and energy potential in three selected locations in the southeastern part of Nigeria were investigated using wind speed data that span between 24 and 37 years and measured at a height of 10 m. It was shown that the annual mean wind speed at a height of 10 m for Enugu, Owerri and Onitsha are 5.42, 3.36 and 3.59 m/s, respectively, while the annual mean power densities are 96.98, 23.23 and 28.34 W/m 2 , respectively. It was further shown that the mean annual value of the most probable wind speed are 5.47, 3.72 and 3.50 m/s for Enugu, Owerri and Onitsha, respectively, while the respective annual value of the wind speed carrying maximum energy are 6.48, 4.33 and 3.90 m/s. The performance of selected commercial wind turbine models (with rated power between 50 and 1,000 kW) designed for electricity generation and a windmill (rated power, 0.36 kW) for water pumping located in these sites was examined. The annual energy output and capacity factor for these turbines, as well as the water produced by the windmill, were determined. The minimum required design parameters for a wind turbine to be a viable option for electricity generation in each location are also suggested.
International Journal of Photoenergy, 2014
Computer simulation of buildings and solar energy systems are being used increasingly in energy a... more Computer simulation of buildings and solar energy systems are being used increasingly in energy assessments and design. This paper evaluates the typical meteorological year (TMY) for Sokoto, northwest region, Nigeria, using 23-year hourly weather data including global solar radiation, dew point temperature, mean temperature, maximum temperature, minimum temperature, relative humidity, and wind speed. Filkenstein-Schafer statistical method was utilized for the creation of a TMY for the site. The persistence of mean dry bulb temperature and daily global horizontal radiation on the five candidate months were evaluated. TMY predictions were compared with the 23-year long-term average values and are found to have close agreement and can be used in building energy simulation for comparative energy efficiency study.
Energy Conversion and Management, 2014
ABSTRACT Due to advances in renewable energy technologies and increase in oil price, hybrid renew... more ABSTRACT Due to advances in renewable energy technologies and increase in oil price, hybrid renewable energy systems are becoming increasingly attractive for power generation applications in remote areas. This paper presents an economic analysis of the feasibility of utilizing a hybrid energy system consisting of solar, wind and diesel generators for application in remote areas of southern Ghana using levelized cost of electricity (LCOE) and net present cost of the system. The annual daily average solar global radiation at the selected site is 5.4 kW h/m2/day and the annual mean wind speed is 5.11 m/s. The National Renewable Energy Laboratory’s Hybrid Optimization Model for Electric Renewable (HOMER) software was employed to carry out the present study. Both wind data and the actual load data have been used in the simulation model. It was found that a PV array of 80 kW, a 100 kW wind turbine, two generators with combined capacity of 100 kW, a 60 kW converter/inverter and a 60 Surrette 4KS25P battery produced a mix of 791.1 MW h of electricity annually. The cost of electricity for this hybrid system is found to be $0.281/kW h. Sensitivity analysis on the effect of changes in wind speed, solar global radiation and diesel price on the optimal energy was investigated and the impact of solar PV price on the LCOE for a selected hybrid energy system was also presented.
Wind Energy, 2012
ABSTRACT The performance characteristics and the near wake of a model wind turbine were investiga... more ABSTRACT The performance characteristics and the near wake of a model wind turbine were investigated experimentally. The model tested is a three‐bladed horizontal axis type wind turbine with an upstream rotor of 0.90 m diameter. The performance measurements were conducted at various yaw angles, a freestream speed of about 10 m s −1, and the tip speed ratio was varied from 0.5 to 12. The time‐averaged streamwise velocity field in the near wake of the turbine was measured at different tip speed ratios and downstream locations. As expected, it was found that power and thrust coefficients decrease with increasing yaw angle. The power loss is about 3% when the yaw angle is less than 10° and increases to more than 30% when the yaw angle is greater than 30°. The velocity distribution in the near wake was found to be strongly influenced by the tip speed ratio and the yaw angle. At the optimum tip speed ratio, the axial velocity was almost uniform within the midsection of the rotor wake, whereas two strong peaks are observed for high tip speed ratios when the yaw angle is 0°. As the yaw angle increases, the wake width was found to be reduced and skewed towards the yawed direction. With increasing downstream distance, the wake velocity field was observed to depend on the tip speed ratio and more pronounced at high tip speed ratio. Copyright © 2011 John Wiley & Sons, Ltd.
Renewable Energy, 2011
The wake interference effect on the performance of a downstream wind turbine was investigated exp... more The wake interference effect on the performance of a downstream wind turbine was investigated experimentally. Two similar model turbines with the same rotor diameter were used. The effects on the performance of the downstream turbine of the distance of separation between the turbines and the amount of power extracted from the upstream turbine were studied. The effects of these parameters on the total power output from the turbines were also estimated. The reduction in the maximum power coefficient of the downstream turbine is strongly dependent on the distance between the turbines and the operating condition of the upstream turbine. Depending on the distance of separation and blade pitch angle, the loss in power from the downstream turbine varies from about 20 to 46% compared to the power output from an unobstructed single turbine operating at its designed conditions. By operating the upstream turbine slightly outside this optimum setting or yawing the upstream turbine, the power output from the downstream turbine was significantly improved. This study shows that the total power output could be increased by installing an upstream turbine which extracts less power than the following turbines. By operating the upstream turbine in yawed condition, the gain in total power output from the two turbines could be increased by about 12%.
Renewable Energy, 2011
ABSTRACT The wind speed distribution and wind energy potential are investigated in three selected... more ABSTRACT The wind speed distribution and wind energy potential are investigated in three selected locations in Oyo state using wind speed data that span between 12 and 20 years measured at 10 m height. In addition, the performance of selected small to medium size wind turbines in these sites were examined. The annual energy output and capacity factor for these turbines were determined. It was found that the monthly mean wind speeds in Oyo state ranges from 2.85 m/s to 5.20 m/s. While the monthly mean power density varies between 27.08 W/m2 and 164.48 W/m2, while the annual mean power density is in the range of 67.28 W/m2 and 106.60 W/m2. Based on annual energy output, wind turbines with cut-in wind speed of about 2.5 m/s and moderate rated wind speeds will be best suited for all the sites.
Journal of Physics: Conference Series, 2011
The effect of jet velocity relative to the crossflow velocity on the higher-order moments of velo... more The effect of jet velocity relative to the crossflow velocity on the higher-order moments of velocity fluctuations characteristics in the wake of stack is reported in this study. The cross-flow Reynolds number was Re D = 2.3×10 4 , and the jet-to-cross-flow velocity ratio was varied from R = 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-stack-height ratio of δ/H = 0.5 at the location of the stack. The skewness factor, flatness factor and triple correlations are found to be influenced by the flow regime. The deviation of skewness and flatness factors from the Gaussian fluctuation values of zero and 3 are more pronounced outside the wake centre region due to the presence of the separated shear layers and vortex structures. The high values of the skewness and flatness factors for all values of velocity ratio within the vicinity of the stack free end are related to the tip vortex structures near the stack free end which decrease in strength as the value of R increases. In addition, the separated shear layers from both sides of the stack contribute to the high values observed away from the wake centreline.
Journal of Fluids and Structures, 2007
The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake and Ka´rma´n vortex ... more The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake and Ka´rma´n vortex shedding for a cylindrical stack of aspect ratio AR ¼ 9 was investigated in a low-speed wind tunnel using thermal anemometry. The cross-flow Reynolds number was Re D ¼ 2.3 Â 10 4 , the jet Reynolds number ranged from Re d ¼ 7.6 Â 10 3 to 4.7 Â 10 4 , and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-stack-height ratio of d/H ¼ 0.5 at the location of the stack. From the behaviour of the turbulent wake and the vortex shedding, the flow around the stack could be classified into three regimes depending on the value of R, which were the downwash (Ro0.7), cross-wind-dominated (0.7pRo1.5), and jet-dominated (RX1.5) flow regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields, as well as the variation of the Strouhal number and the power spectrum along the stack height. r
Journal of Fluids and Structures, 2010
The time-averaged velocity and streamwise vorticity fields within the wake of a stack were invest... more The time-averaged velocity and streamwise vorticity fields within the wake of a stack were investigated in a low-speed wind tunnel using a seven-hole pressure probe. The experiments were conducted at a Reynolds number, based on the stack external diameter, of Re D ¼ 2.3 Â 10 4 . The stack, of aspect ratio AR ¼ 9, was mounted normal to a ground plane and was partially immersed in a flat-plate turbulent boundary layer, where the ratio of the boundary layer thickness to the stack height was d/HE0.5. The jet-to-cross-flow velocity ratio was varied from R ¼ 0 to 3, which covered the downwash, crosswind-dominated and jet-dominated flow regimes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip vortex pair located close to the free end of the stack, and the base vortex pair located close to the ground plane within the flat-plate boundary layer, were similar to those found in the wake of a finite circular cylinder, and were associated with the upwash and downwash flow fields within the stack wake, respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair had the same orientation as the base vortex pair and was associated with the jet rise. The peak vorticity and strength of the streamwise vortex structures were functions of the jet-to-cross-flow velocity ratio. For the tip vortex structures, their peak vorticity and strength reduced as the jet-to-cross-flow velocity ratio increased. r
Journal of Fluids and Structures, 2006
The turbulent wake of a finite circular cylinder mounted normal to a wall and partially immersed ... more The turbulent wake of a finite circular cylinder mounted normal to a wall and partially immersed in a turbulent boundary layer was studied experimentally using two-component thermal anemometry in a low-speed wind tunnel. Four circular cylinders of aspect ratios AR=9, 7, 5, and 3 were tested at a Reynolds number of ReD=6×104. The cylinders were either completely or partially immersed in the wall boundary layer, where the boundary layer thickness relative to the cylinder diameter was δ/D=3.0. A similar turbulent wake structure (mean velocity, turbulence intensity, and Reynolds shear stress distributions) was found for cylinders of AR=9, 7, and 5, while a distinctly different turbulent wake structure was found for the cylinder of AR=3. This was consistent with the results of a previous study that focused on the time-averaged streamwise vortex structures in the wake.
Energy Exploration Exploitation, Aug 1, 2012
ABSTRACT The technical and economic assessment of using hybrid energy system for electricity gene... more ABSTRACT The technical and economic assessment of using hybrid energy system for electricity generation in rural communities in the south-west of Nigeria is investigated in this study. Renewable resources (wind and solar data) in Ibadan located on the latitude of 7.43 °N and longitude 3.91 °E are used. Hybrid Optimization Model for Electric Renewable software has been employed to carry out the present study. It was found that Wind-PV-Generator-Battery hybrid system is most suitable option as stand-alone electricity generating system in Ibadan. The optimal simulation results indicate that the levelised cost of energy for this hybrid energy system varies between 0.437/kWhand0.437/kWh and 0.437/kWhand0.606/kWh depending on the diesel price. These costs are significantly lower than the cost of using diesel generator only (without battery) which varies between 0.607and0.607 and 0.607and0.940 per kWh. It was further observed that there is a significant reduction in emission produced if hybrid energy system is used instead of only generator based energy system. The most suitable hybrid systems in other locations in southwest Nigeria can be identified from the optimal energy system plots provided.
The performance of a 0.9m diameter model wind turbine using the NREL s826 airfoil profile has bee... more The performance of a 0.9m diameter model wind turbine using the NREL s826 airfoil profile has been investigated both experimentally and numerically. The geometry was laid out using Blade Element Momentum theory (BEM). The design was tested experimentally and gave a peak power coefficient of C P = 0.448 at the design tip speed ratio of λ = 6. It was found that the BEM had correctly predicted the power coefficient curve very well giving virtually identical results to the measurements, except when the turbine is operating in a deep stall mode. The thrust predicted was however consistently too low by a shift of the order of ∆C T ∼ 0.1. After the model tests had been undertaken, numerical calculations were performed by means of fully 3D CFD simulations using a k − ω turbulence model. The high resolution CFD predictions (using about 3.5 × 10 6 grid points) reproduced the model thrust coefficient almost perfectly. The predicted power coefficients were also very close to the measurements, but somewhat overestimated at high tip speed ratios. At the design tip speed ratio the CFD over-predicted the power coefficient by merely 2%.
Latvian Journal of Physics and Technical Sciences
Solar Energy, 2015
In this study, global solar radiation over Nigeria was simulated under an enhanced atmospheric CO... more In this study, global solar radiation over Nigeria was simulated under an enhanced atmospheric CO 2 level using the International Centre for Theoretical Physics (ICTP) Regional Climate Model version 3 (RegCM3) for the period 1981 to 2100 with ECHAM5 GCM as the lateral boundary conditions. The simulated seasonal global solar radiation bias for the RegCM3 with NIMET and NASA observed datasets in the control period are of similar magnitudes and showed a mixture of persistent positive and negative biases ranging between À10% and 30%. The model generally underestimates solar radiation (biases À10% to À30%) across the whole country in most of the months. In addition, it overestimates radiation (biases +2-30%) over the northern region of the country. Alongside the present climate , three future periods were considered viz: period 1 (2011-2040), period 2 (2041-2070) and period 3 (2071-2100) for the potential future changes. The seasonal potential future changes in period 1 (i.e. potential future changes with respect to 2040) showed a reduction in the range of 0% (North) to 3.27% (South) whereas more reduction in global solar radiation is observed in period 2 (i.e. 2041-2070 minus present climate) having general decrease ranging from 0.11% to 3.39% with the least value in April (Middle-belt) and the largest in the South zone (March). Potential future changes in period 3 (i.e. 2071-2100 minus present climate) is generally characterized with mixed increase and decrease in global solar radiation across the country than the previous two periods (1 and 2). For the annual potential future changes, RegCM3 model predicted a decrease in solar radiation towards the end of the century with more reduction found in the South zone and the least in the North region. Furthermore, future changes in global solar radiation across the zones in all the periods are however found to be insignificant at p 6 0.01.
Volume 9: 6th FSI, AE and FIV and N Symposium, 2006
ABSTRACT The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake of a cylind... more ABSTRACT The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake of a cylindrical stack of AR = 9 was investigated with two-component thermal anemometry. The cross-flow Reynolds number was ReD = 2.3×104 , the jet Reynolds number ranged from Red = 7×103 to 4.6×104 , and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-height ratio of δ/H = 0.5 at the location of the stack. The flow around the stack was broadly classified into three flow regimes depending on the value of R, which were the downwash (R < 0.5), cross-wind dominated (0.5 < R < 1.5), and jet-dominated (R > 1.5) regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields.
International Journal of Fluid Mechanics Research, 2007
Thermophysics and Aeromechanics, 2011
ABSTRACT The paper considers the evolution of turbulent kinetic energy in a turbulent boundary la... more ABSTRACT The paper considers the evolution of turbulent kinetic energy in a turbulent boundary layer perturbed by suction. The results show that the boundary layer equilibrium is altered in a non-linear manner due to suppression of the structures near the wall. The behavior, however, suggests that the wavelength of alteration of the equilibrium of the layer is unaffected by a change in Reynolds number and suction rate.
Thermophysics and Aeromechanics, 2007
Hot-wire measurements have been undertaken in a turbulent boundary layer which is subjected to an... more Hot-wire measurements have been undertaken in a turbulent boundary layer which is subjected to an impulse in form of a short roughness strip with the aim of examining its influence on the structure of the turbulent boundary layer. The results indicate that, while the energy containing motion is shifted from low wave number to high wave number near the wall due to the interfering of the roughness strip with the near-wall structure, the reverse is the case in the outer region. While the anisotropy at small scale changes appreciably, there is no discernable change at the large scale when distance from the wall is increased as reflected in the collapses of spectra shear correlation coefficient at the low wave number. It further shows that the roughness strip alters the flow dynamics of the boundary layer as shown in the changes in the mixing length distribution.
Volume 9: 6th FSI, AE and FIV and N Symposium, 2006
ABSTRACT The influence of the jet-to-cross-flow velocity ratio, R, on vortex shedding from a cyli... more ABSTRACT The influence of the jet-to-cross-flow velocity ratio, R, on vortex shedding from a cylindrical stack of aspect ratio AR = 9 was investigated using hot-wire anemometry. The cross-flow Reynolds number was ReD = 2.3×104 and R was varied from 0 to 3. The stack was partially immersed in a flat-plate boundary layer, where the boundary layer thickness-to-height ratio at the location of the stack was δ/H = 0.5. In the downwash flow regime, when R < 0.7, a single Strouhal number (e.g., St = 0.167 at R = 0) was measured along the entire stack height. In the crosswind-dominated flow regime, when 0.7 ≤ R < 1.5, a higher Strouhal number was obtained (e.g., St = 0.185 at R = 1.0). In the transitional and jet-dominated flow regimes, a jump in Strouhal number (e.g., from St = 0.176 to 0.193 at R = 2.0), occurred within the flat-plate boundary layer. The power spectra showed that the shape and strength of the vortex shedding peak changed along the stack height. In general, the peak was more broad-banded near the base of the stack, became sharper and more distinct within the middle of the combined stack and jet wakes, and then reduced in strength in the jet wake and jet regions. In the transitional and jet-dominated flow regimes, the jump in Strouhal number was seen as a gradual change in dominance between two closely spaced peaks, with both peaks co-existing near the edge of the boundary layer.
Latvian Journal of Physics and Technical Sciences, 2008
Studies of the flow conditions of natural gases in pipelines have led to the development of compl... more Studies of the flow conditions of natural gases in pipelines have led to the development of complex equations for relating the volume transmitted through a gas pipeline to the various factors involved, thus deciding the optimum pressures and pipeline dimensions to be used. From equations of this type, various combinations of pipe diameter and wall thickness for a desired rate
International Journal of Energy and Environmental Engineering, 2012
In this study, the wind speed characteristics and energy potential in three selected locations in... more In this study, the wind speed characteristics and energy potential in three selected locations in the southeastern part of Nigeria were investigated using wind speed data that span between 24 and 37 years and measured at a height of 10 m. It was shown that the annual mean wind speed at a height of 10 m for Enugu, Owerri and Onitsha are 5.42, 3.36 and 3.59 m/s, respectively, while the annual mean power densities are 96.98, 23.23 and 28.34 W/m 2 , respectively. It was further shown that the mean annual value of the most probable wind speed are 5.47, 3.72 and 3.50 m/s for Enugu, Owerri and Onitsha, respectively, while the respective annual value of the wind speed carrying maximum energy are 6.48, 4.33 and 3.90 m/s. The performance of selected commercial wind turbine models (with rated power between 50 and 1,000 kW) designed for electricity generation and a windmill (rated power, 0.36 kW) for water pumping located in these sites was examined. The annual energy output and capacity factor for these turbines, as well as the water produced by the windmill, were determined. The minimum required design parameters for a wind turbine to be a viable option for electricity generation in each location are also suggested.
International Journal of Photoenergy, 2014
Computer simulation of buildings and solar energy systems are being used increasingly in energy a... more Computer simulation of buildings and solar energy systems are being used increasingly in energy assessments and design. This paper evaluates the typical meteorological year (TMY) for Sokoto, northwest region, Nigeria, using 23-year hourly weather data including global solar radiation, dew point temperature, mean temperature, maximum temperature, minimum temperature, relative humidity, and wind speed. Filkenstein-Schafer statistical method was utilized for the creation of a TMY for the site. The persistence of mean dry bulb temperature and daily global horizontal radiation on the five candidate months were evaluated. TMY predictions were compared with the 23-year long-term average values and are found to have close agreement and can be used in building energy simulation for comparative energy efficiency study.
Energy Conversion and Management, 2014
ABSTRACT Due to advances in renewable energy technologies and increase in oil price, hybrid renew... more ABSTRACT Due to advances in renewable energy technologies and increase in oil price, hybrid renewable energy systems are becoming increasingly attractive for power generation applications in remote areas. This paper presents an economic analysis of the feasibility of utilizing a hybrid energy system consisting of solar, wind and diesel generators for application in remote areas of southern Ghana using levelized cost of electricity (LCOE) and net present cost of the system. The annual daily average solar global radiation at the selected site is 5.4 kW h/m2/day and the annual mean wind speed is 5.11 m/s. The National Renewable Energy Laboratory’s Hybrid Optimization Model for Electric Renewable (HOMER) software was employed to carry out the present study. Both wind data and the actual load data have been used in the simulation model. It was found that a PV array of 80 kW, a 100 kW wind turbine, two generators with combined capacity of 100 kW, a 60 kW converter/inverter and a 60 Surrette 4KS25P battery produced a mix of 791.1 MW h of electricity annually. The cost of electricity for this hybrid system is found to be $0.281/kW h. Sensitivity analysis on the effect of changes in wind speed, solar global radiation and diesel price on the optimal energy was investigated and the impact of solar PV price on the LCOE for a selected hybrid energy system was also presented.
Wind Energy, 2012
ABSTRACT The performance characteristics and the near wake of a model wind turbine were investiga... more ABSTRACT The performance characteristics and the near wake of a model wind turbine were investigated experimentally. The model tested is a three‐bladed horizontal axis type wind turbine with an upstream rotor of 0.90 m diameter. The performance measurements were conducted at various yaw angles, a freestream speed of about 10 m s −1, and the tip speed ratio was varied from 0.5 to 12. The time‐averaged streamwise velocity field in the near wake of the turbine was measured at different tip speed ratios and downstream locations. As expected, it was found that power and thrust coefficients decrease with increasing yaw angle. The power loss is about 3% when the yaw angle is less than 10° and increases to more than 30% when the yaw angle is greater than 30°. The velocity distribution in the near wake was found to be strongly influenced by the tip speed ratio and the yaw angle. At the optimum tip speed ratio, the axial velocity was almost uniform within the midsection of the rotor wake, whereas two strong peaks are observed for high tip speed ratios when the yaw angle is 0°. As the yaw angle increases, the wake width was found to be reduced and skewed towards the yawed direction. With increasing downstream distance, the wake velocity field was observed to depend on the tip speed ratio and more pronounced at high tip speed ratio. Copyright © 2011 John Wiley & Sons, Ltd.
Renewable Energy, 2011
The wake interference effect on the performance of a downstream wind turbine was investigated exp... more The wake interference effect on the performance of a downstream wind turbine was investigated experimentally. Two similar model turbines with the same rotor diameter were used. The effects on the performance of the downstream turbine of the distance of separation between the turbines and the amount of power extracted from the upstream turbine were studied. The effects of these parameters on the total power output from the turbines were also estimated. The reduction in the maximum power coefficient of the downstream turbine is strongly dependent on the distance between the turbines and the operating condition of the upstream turbine. Depending on the distance of separation and blade pitch angle, the loss in power from the downstream turbine varies from about 20 to 46% compared to the power output from an unobstructed single turbine operating at its designed conditions. By operating the upstream turbine slightly outside this optimum setting or yawing the upstream turbine, the power output from the downstream turbine was significantly improved. This study shows that the total power output could be increased by installing an upstream turbine which extracts less power than the following turbines. By operating the upstream turbine in yawed condition, the gain in total power output from the two turbines could be increased by about 12%.
Renewable Energy, 2011
ABSTRACT The wind speed distribution and wind energy potential are investigated in three selected... more ABSTRACT The wind speed distribution and wind energy potential are investigated in three selected locations in Oyo state using wind speed data that span between 12 and 20 years measured at 10 m height. In addition, the performance of selected small to medium size wind turbines in these sites were examined. The annual energy output and capacity factor for these turbines were determined. It was found that the monthly mean wind speeds in Oyo state ranges from 2.85 m/s to 5.20 m/s. While the monthly mean power density varies between 27.08 W/m2 and 164.48 W/m2, while the annual mean power density is in the range of 67.28 W/m2 and 106.60 W/m2. Based on annual energy output, wind turbines with cut-in wind speed of about 2.5 m/s and moderate rated wind speeds will be best suited for all the sites.
Journal of Physics: Conference Series, 2011
The effect of jet velocity relative to the crossflow velocity on the higher-order moments of velo... more The effect of jet velocity relative to the crossflow velocity on the higher-order moments of velocity fluctuations characteristics in the wake of stack is reported in this study. The cross-flow Reynolds number was Re D = 2.3×10 4 , and the jet-to-cross-flow velocity ratio was varied from R = 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-stack-height ratio of δ/H = 0.5 at the location of the stack. The skewness factor, flatness factor and triple correlations are found to be influenced by the flow regime. The deviation of skewness and flatness factors from the Gaussian fluctuation values of zero and 3 are more pronounced outside the wake centre region due to the presence of the separated shear layers and vortex structures. The high values of the skewness and flatness factors for all values of velocity ratio within the vicinity of the stack free end are related to the tip vortex structures near the stack free end which decrease in strength as the value of R increases. In addition, the separated shear layers from both sides of the stack contribute to the high values observed away from the wake centreline.
Journal of Fluids and Structures, 2007
The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake and Ka´rma´n vortex ... more The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake and Ka´rma´n vortex shedding for a cylindrical stack of aspect ratio AR ¼ 9 was investigated in a low-speed wind tunnel using thermal anemometry. The cross-flow Reynolds number was Re D ¼ 2.3 Â 10 4 , the jet Reynolds number ranged from Re d ¼ 7.6 Â 10 3 to 4.7 Â 10 4 , and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-stack-height ratio of d/H ¼ 0.5 at the location of the stack. From the behaviour of the turbulent wake and the vortex shedding, the flow around the stack could be classified into three regimes depending on the value of R, which were the downwash (Ro0.7), cross-wind-dominated (0.7pRo1.5), and jet-dominated (RX1.5) flow regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields, as well as the variation of the Strouhal number and the power spectrum along the stack height. r
Journal of Fluids and Structures, 2010
The time-averaged velocity and streamwise vorticity fields within the wake of a stack were invest... more The time-averaged velocity and streamwise vorticity fields within the wake of a stack were investigated in a low-speed wind tunnel using a seven-hole pressure probe. The experiments were conducted at a Reynolds number, based on the stack external diameter, of Re D ¼ 2.3 Â 10 4 . The stack, of aspect ratio AR ¼ 9, was mounted normal to a ground plane and was partially immersed in a flat-plate turbulent boundary layer, where the ratio of the boundary layer thickness to the stack height was d/HE0.5. The jet-to-cross-flow velocity ratio was varied from R ¼ 0 to 3, which covered the downwash, crosswind-dominated and jet-dominated flow regimes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip vortex pair located close to the free end of the stack, and the base vortex pair located close to the ground plane within the flat-plate boundary layer, were similar to those found in the wake of a finite circular cylinder, and were associated with the upwash and downwash flow fields within the stack wake, respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair had the same orientation as the base vortex pair and was associated with the jet rise. The peak vorticity and strength of the streamwise vortex structures were functions of the jet-to-cross-flow velocity ratio. For the tip vortex structures, their peak vorticity and strength reduced as the jet-to-cross-flow velocity ratio increased. r
Journal of Fluids and Structures, 2006
The turbulent wake of a finite circular cylinder mounted normal to a wall and partially immersed ... more The turbulent wake of a finite circular cylinder mounted normal to a wall and partially immersed in a turbulent boundary layer was studied experimentally using two-component thermal anemometry in a low-speed wind tunnel. Four circular cylinders of aspect ratios AR=9, 7, 5, and 3 were tested at a Reynolds number of ReD=6×104. The cylinders were either completely or partially immersed in the wall boundary layer, where the boundary layer thickness relative to the cylinder diameter was δ/D=3.0. A similar turbulent wake structure (mean velocity, turbulence intensity, and Reynolds shear stress distributions) was found for cylinders of AR=9, 7, and 5, while a distinctly different turbulent wake structure was found for the cylinder of AR=3. This was consistent with the results of a previous study that focused on the time-averaged streamwise vortex structures in the wake.