Mark Tachie - Academia.edu (original) (raw)
Papers by Mark Tachie
Proceedings of the 39th IAHR World Congress
ABSTRACT Flow characteristics near and over spillways are important for ecological, as well as de... more ABSTRACT Flow characteristics near and over spillways are important for ecological, as well as design, aspects. Spillways may either interfere with fish movements or offer a safe route for downstream passage. Hydrodynamics and movement behaviour of the European eel and Iberian barbel are investigated for standard WES ogee spillways with upstream face inclinations of θ = 90º, 45º and 30º. Detailed velocity measurements (PIV and ADV) at the upstream end and over the spillway in the streamwise-wall-normal plane were used to characterize flow and link fish behaviour with local hydrodynamic variables. A distinct recirculation pattern was found upstream of the 90º spillway, which was not observed in the other two spillways. This recirculation area seemed to have a strong impact on fish behaviour. European eel were predominantly thigmotactic, exhibiting a more structure–oriented behaviour than the Iberian barbel. Geometry-related differences were found for the European eel, which exhibited the highest rates of passage success in experiments conducted with upstream inclinations of θ = 45º and 30º, and the greatest times of passage and resident times when tested under spillway designs of θ = 90º. Interspecific variations on behaviour were also evident. European eel had a higher passage success when compared to Iberian barbel which spent more time in the test section and took longer to pass the spillway. Most barbel exhibited a positive rheotaxis entering the observation zone and moved downstream tail first, whereas the majority of the eels moved downstream and passed the spillway headfirst. Results indicate that the design of spillways and associated hydrodynamics strongly impact downstream movements of these two species which have distinct biomechanical capabilities and behaviour. Results may have direct application for spillway design to improve survival rates for these and others fish species, as well as other aquatic biota.
AIAA Journal, 2009
are discussed. Significant differences are observed in the reconstructed Reynolds stress profiles... more are discussed. Significant differences are observed in the reconstructed Reynolds stress profiles at the center of the separated shear layer and those close to the reattachment point. The results also indicate that contribution of the energetic structures to the Reynolds stresses is higher at the upstream section of the ribs than in the separated layer. Thiswasattributedtoamoreuniformenergydistributionamongtheproperorthogonaldecompositionmodesinthe separated shear layer than in the upstream section. The distributions of the mean velocity, mixing length, and eddy viscosityatselectedlocationswerealsoanalyzed.Themixing-lengthprofilesintheinnerregionoftheseparatedshear layer do not follow the well-documented linear profile reported for simple near-wall turbulent flows.
38th Fluid Dynamics Conference and Exhibit, 2008
Journal of Fluids Engineering-transactions of The Asme, 1999
The present study deals with the noninvasive measurement of concentration in the intermediate sha... more The present study deals with the noninvasive measurement of concentration in the intermediate shallow turbulent wake region using a video-imaging technique. The flow depths considered in the present study are small compared to the width of the channel and the generated wakes are categorized as shallow. On the basis of the observed behavior, the waves are classified as deep-shallow wakes and shallow-shallow wakes. The topology of the dye concentration distribution in the near and intermediate wake region indicates that the vortex structure tends to be preserved when the flow depth is relatively high and the dominant eddy structures are similar to that noticed in conventional two-dimensional wakes. In shallow-shallow wakes, the conventional Karman vortex street appears to be annihilated or intermittent. The lateral concentration distribution at several axial stations covering the first thirty body widths are considered for analysis. The instantaneous concentrations are observed to be several times higher than the corresponding mean values. Attempts are also made to determine the paths traversed by the vortex cores and the vortex core convection velocity. The axial variation of the wake half-width with depth of flow is also examined. A model is developed to predict the spread of the wake with downstream distance from the test body. A friction length scale is introduced in the model to account for the influence of depth and bed friction on the development of the wake.
Experimental Thermal and Fluid Science, Jan 31, 2008
The paper presents measurements performed over a smooth surface, a transitionally rough surface g... more The paper presents measurements performed over a smooth surface, a transitionally rough surface generated by wire mesh and a fully rough surface that comprised transverse square ribs in a channel. The flow was seeded using fluorescent particles and the high quality vectors obtained using particle image velocimetry (PIV) technique were used to compute the mean velocity, turbulent statistics up to the fourth order moments as well as the production and dissipation terms in the transport equation for the turbulent kinetic energy. By using ...
38th Fluid Dynamics Conference and Exhibit, 2008
River Research and Applications
ABSTRACT Flow characteristics associated with spillways are important to restore ecological conne... more ABSTRACT Flow characteristics associated with spillways are important to restore ecological connectivity because spillways can either constrain or offer safe routes for downstream passage of fish. We studied the hydrodynamics of flow and downstream movement behaviour of the catadromous European eel (Anguilla anguilla) and the potamodromous Iberian barbel (Luciobarbus bocagei) in spillways with upstream face inclinations of θ = 90° (standard) 45° and 30° (modified). The standard spillway was tested for two water depths (H = 32 and 42 cm). Modified spillways facilitated downstream passage and reduced delay times of passage of the European eel. Upstream of the 90° spillway, distinct recirculation areas were observed, and associated turbulence strongly hampered downstream passage of fish. Both species were found to avoid turbulence, but barbel displayed stronger avoidance for areas of rapid changes in flow velocity when comparing to eels. Overall, eels were faster in passing the spillway and had a higher downstream passage success (80%) than barbel (32%). Eels were predominantly thigmotactic in contrast to barbel, which showed limited contact with structures. The results suggest that modified spillways may enhance passage survival.
IUTAM Bookseries, 2010
This paper reports on particle image velocimetry (PIV) measurements in turbulent flows over trans... more This paper reports on particle image velocimetry (PIV) measurements in turbulent flows over transverse triangular ribs attached to the bottom and top walls of a converging channel preceded by an upstream parallel section. The ribs were arranged perpendicular and then at an angle of 45 ı to the side walls of the channel in a non-staggered configuration. The mean velocities and turbulent statistics obtained at various spanwise locations in both the parallel and converging sections of the channel are used to document the salient effects of rib roughness, pressure gradient, rib inclination and spanwise location of the flow field.
Volume 1: Symposia, Parts A, B and C, 2009
ABSTRACT
37th AIAA Fluid Dynamics Conference and Exhibit, 2007
This paper reports an experimental study of turbulent wake of a two-dimensional rectangular cylin... more This paper reports an experimental study of turbulent wake of a two-dimensional rectangular cylinder in a 2500 mm long, 186 mm wide and 197 mm deep re-circulating open channel. The water level upstream of the cylinder was maintained at 100 mm whereas the aspect and blockage ratios defined, respectively, as the cylinder's length to thickness ratio and cylinder thickness to water depth ratio were 9 and 0.12. The cylinder was mounted across the channel at three different vertical locations: relatively close to the plane wall, close to the free surface, and relatively ...
39th AIAA Fluid Dynamics Conference, 2009
39th AIAA Fluid Dynamics Conference, 2009
This paper reports on experiments conducted to study the structure of turbulent flows over a hydr... more This paper reports on experiments conducted to study the structure of turbulent flows over a hydraulically smooth surface and a transitionally rough surface produced using a wire mesh. A high resolution particle image velocimetry (PIV) technique was employed to conduct the velocity measurements. The smooth wall measurements were performed at two different Reynolds numbers while the wire mesh data were obtained for a single Reynolds number. From the PIV data, profiles of the mean velocity, turbulent intensities and Reynolds shear stress as well as two-point ...
39th AIAA Fluid Dynamics Conference, 2009
39th AIAA Fluid Dynamics Conference, 2009
38th Fluid Dynamics Conference and Exhibit, 2008
This paper reports an experimental study of turbulent flow past a rectangular cylinder and a stre... more This paper reports an experimental study of turbulent flow past a rectangular cylinder and a streamlined cylinder in an open channel at incidence. The water depth in the open channel upstream of the cylinder was maintained at 140 mm. Each cylinder type was mounted vertically at the channel mid-span at four angles of incidence (θ = 0°, 7.5°, 15°, and 30°). For each angle of incidence, the particle image velocimetry technique was used to conduct detailed velocity measurements at various streamwise-spanwise planes around and downstream of the cylinder. From ...
38th Fluid Dynamics Conference and Exhibit, 2008
This paper reports a study of turbulent wake of two-dimensional rectangular cylinders in an open ... more This paper reports a study of turbulent wake of two-dimensional rectangular cylinders in an open channel. The water depth upstream of the cylinders was maintained at 100 mm. Three cylinders having aspect ratios (defined as the ratio of the cylinder's length to thickness) of 1, 2 and 4 were mounted vertically at mid-span of the open channel. For each aspect ratio, the cylinders were oriented through four angles of incidence (0°, 15°, 30° and 45°). A particle image velocimetry technique was used to conduct detailed velocity measurements at various streamwise- ...
Volume 1: Symposia, Parts A and B, 2007
This paper reports experimental study of three-dimensional turbulent wall jet over smooth and rou... more This paper reports experimental study of three-dimensional turbulent wall jet over smooth and rough surfaces. The wall jet was created using a square nozzle of size 6 mm and flow into an open channel. The experiments were performed at a Reynolds number based on the nozzle size and jet exit velocity of 4800. A particle image velocimetry was used to conduct detailed measurements over the smooth and rough surfaces at various streamwise-transverse and streamwise-spanwise planes. From these measurements, mean velocities ...
Volume 1: Symposia, Parts A and B, 2007
A particle image velocimetry is used to study the characteristics of separated and reattached tur... more A particle image velocimetry is used to study the characteristics of separated and reattached turbulent flow over two-dimensional transverse blocks of square, rectangular and semi-circular cross-sections fixed to the bottom wall of an open channel. The ratio of upstream boundary layer thickness to block height is considerably higher than in prior studies. The results show that the mean and turbulent statistics in the recirculation region and downstream of reattachment are significantly different from the upstream boundary layer. ...
Volume 1: Symposia, Parts A, B and C, 2009
The paper reports on an experimental investigation of turbulent flow through model two-dimensiona... more The paper reports on an experimental investigation of turbulent flow through model two-dimensional porous media. The porous media was bounded on one side by a solid plane wall and on the other side by a zone of clear fluid. The model porous media comprised of square arrays of circular acrylic rods that were inserted into precision holes drilled onto pairs of removable plates. The removable plates were then inserted into groves made in the side walls of the test channel. The rods fill about 59% of the channel height. Different ...
Proceedings of the 39th IAHR World Congress
ABSTRACT Flow characteristics near and over spillways are important for ecological, as well as de... more ABSTRACT Flow characteristics near and over spillways are important for ecological, as well as design, aspects. Spillways may either interfere with fish movements or offer a safe route for downstream passage. Hydrodynamics and movement behaviour of the European eel and Iberian barbel are investigated for standard WES ogee spillways with upstream face inclinations of θ = 90º, 45º and 30º. Detailed velocity measurements (PIV and ADV) at the upstream end and over the spillway in the streamwise-wall-normal plane were used to characterize flow and link fish behaviour with local hydrodynamic variables. A distinct recirculation pattern was found upstream of the 90º spillway, which was not observed in the other two spillways. This recirculation area seemed to have a strong impact on fish behaviour. European eel were predominantly thigmotactic, exhibiting a more structure–oriented behaviour than the Iberian barbel. Geometry-related differences were found for the European eel, which exhibited the highest rates of passage success in experiments conducted with upstream inclinations of θ = 45º and 30º, and the greatest times of passage and resident times when tested under spillway designs of θ = 90º. Interspecific variations on behaviour were also evident. European eel had a higher passage success when compared to Iberian barbel which spent more time in the test section and took longer to pass the spillway. Most barbel exhibited a positive rheotaxis entering the observation zone and moved downstream tail first, whereas the majority of the eels moved downstream and passed the spillway headfirst. Results indicate that the design of spillways and associated hydrodynamics strongly impact downstream movements of these two species which have distinct biomechanical capabilities and behaviour. Results may have direct application for spillway design to improve survival rates for these and others fish species, as well as other aquatic biota.
AIAA Journal, 2009
are discussed. Significant differences are observed in the reconstructed Reynolds stress profiles... more are discussed. Significant differences are observed in the reconstructed Reynolds stress profiles at the center of the separated shear layer and those close to the reattachment point. The results also indicate that contribution of the energetic structures to the Reynolds stresses is higher at the upstream section of the ribs than in the separated layer. Thiswasattributedtoamoreuniformenergydistributionamongtheproperorthogonaldecompositionmodesinthe separated shear layer than in the upstream section. The distributions of the mean velocity, mixing length, and eddy viscosityatselectedlocationswerealsoanalyzed.Themixing-lengthprofilesintheinnerregionoftheseparatedshear layer do not follow the well-documented linear profile reported for simple near-wall turbulent flows.
38th Fluid Dynamics Conference and Exhibit, 2008
Journal of Fluids Engineering-transactions of The Asme, 1999
The present study deals with the noninvasive measurement of concentration in the intermediate sha... more The present study deals with the noninvasive measurement of concentration in the intermediate shallow turbulent wake region using a video-imaging technique. The flow depths considered in the present study are small compared to the width of the channel and the generated wakes are categorized as shallow. On the basis of the observed behavior, the waves are classified as deep-shallow wakes and shallow-shallow wakes. The topology of the dye concentration distribution in the near and intermediate wake region indicates that the vortex structure tends to be preserved when the flow depth is relatively high and the dominant eddy structures are similar to that noticed in conventional two-dimensional wakes. In shallow-shallow wakes, the conventional Karman vortex street appears to be annihilated or intermittent. The lateral concentration distribution at several axial stations covering the first thirty body widths are considered for analysis. The instantaneous concentrations are observed to be several times higher than the corresponding mean values. Attempts are also made to determine the paths traversed by the vortex cores and the vortex core convection velocity. The axial variation of the wake half-width with depth of flow is also examined. A model is developed to predict the spread of the wake with downstream distance from the test body. A friction length scale is introduced in the model to account for the influence of depth and bed friction on the development of the wake.
Experimental Thermal and Fluid Science, Jan 31, 2008
The paper presents measurements performed over a smooth surface, a transitionally rough surface g... more The paper presents measurements performed over a smooth surface, a transitionally rough surface generated by wire mesh and a fully rough surface that comprised transverse square ribs in a channel. The flow was seeded using fluorescent particles and the high quality vectors obtained using particle image velocimetry (PIV) technique were used to compute the mean velocity, turbulent statistics up to the fourth order moments as well as the production and dissipation terms in the transport equation for the turbulent kinetic energy. By using ...
38th Fluid Dynamics Conference and Exhibit, 2008
River Research and Applications
ABSTRACT Flow characteristics associated with spillways are important to restore ecological conne... more ABSTRACT Flow characteristics associated with spillways are important to restore ecological connectivity because spillways can either constrain or offer safe routes for downstream passage of fish. We studied the hydrodynamics of flow and downstream movement behaviour of the catadromous European eel (Anguilla anguilla) and the potamodromous Iberian barbel (Luciobarbus bocagei) in spillways with upstream face inclinations of θ = 90° (standard) 45° and 30° (modified). The standard spillway was tested for two water depths (H = 32 and 42 cm). Modified spillways facilitated downstream passage and reduced delay times of passage of the European eel. Upstream of the 90° spillway, distinct recirculation areas were observed, and associated turbulence strongly hampered downstream passage of fish. Both species were found to avoid turbulence, but barbel displayed stronger avoidance for areas of rapid changes in flow velocity when comparing to eels. Overall, eels were faster in passing the spillway and had a higher downstream passage success (80%) than barbel (32%). Eels were predominantly thigmotactic in contrast to barbel, which showed limited contact with structures. The results suggest that modified spillways may enhance passage survival.
IUTAM Bookseries, 2010
This paper reports on particle image velocimetry (PIV) measurements in turbulent flows over trans... more This paper reports on particle image velocimetry (PIV) measurements in turbulent flows over transverse triangular ribs attached to the bottom and top walls of a converging channel preceded by an upstream parallel section. The ribs were arranged perpendicular and then at an angle of 45 ı to the side walls of the channel in a non-staggered configuration. The mean velocities and turbulent statistics obtained at various spanwise locations in both the parallel and converging sections of the channel are used to document the salient effects of rib roughness, pressure gradient, rib inclination and spanwise location of the flow field.
Volume 1: Symposia, Parts A, B and C, 2009
ABSTRACT
37th AIAA Fluid Dynamics Conference and Exhibit, 2007
This paper reports an experimental study of turbulent wake of a two-dimensional rectangular cylin... more This paper reports an experimental study of turbulent wake of a two-dimensional rectangular cylinder in a 2500 mm long, 186 mm wide and 197 mm deep re-circulating open channel. The water level upstream of the cylinder was maintained at 100 mm whereas the aspect and blockage ratios defined, respectively, as the cylinder's length to thickness ratio and cylinder thickness to water depth ratio were 9 and 0.12. The cylinder was mounted across the channel at three different vertical locations: relatively close to the plane wall, close to the free surface, and relatively ...
39th AIAA Fluid Dynamics Conference, 2009
39th AIAA Fluid Dynamics Conference, 2009
This paper reports on experiments conducted to study the structure of turbulent flows over a hydr... more This paper reports on experiments conducted to study the structure of turbulent flows over a hydraulically smooth surface and a transitionally rough surface produced using a wire mesh. A high resolution particle image velocimetry (PIV) technique was employed to conduct the velocity measurements. The smooth wall measurements were performed at two different Reynolds numbers while the wire mesh data were obtained for a single Reynolds number. From the PIV data, profiles of the mean velocity, turbulent intensities and Reynolds shear stress as well as two-point ...
39th AIAA Fluid Dynamics Conference, 2009
39th AIAA Fluid Dynamics Conference, 2009
38th Fluid Dynamics Conference and Exhibit, 2008
This paper reports an experimental study of turbulent flow past a rectangular cylinder and a stre... more This paper reports an experimental study of turbulent flow past a rectangular cylinder and a streamlined cylinder in an open channel at incidence. The water depth in the open channel upstream of the cylinder was maintained at 140 mm. Each cylinder type was mounted vertically at the channel mid-span at four angles of incidence (θ = 0°, 7.5°, 15°, and 30°). For each angle of incidence, the particle image velocimetry technique was used to conduct detailed velocity measurements at various streamwise-spanwise planes around and downstream of the cylinder. From ...
38th Fluid Dynamics Conference and Exhibit, 2008
This paper reports a study of turbulent wake of two-dimensional rectangular cylinders in an open ... more This paper reports a study of turbulent wake of two-dimensional rectangular cylinders in an open channel. The water depth upstream of the cylinders was maintained at 100 mm. Three cylinders having aspect ratios (defined as the ratio of the cylinder's length to thickness) of 1, 2 and 4 were mounted vertically at mid-span of the open channel. For each aspect ratio, the cylinders were oriented through four angles of incidence (0°, 15°, 30° and 45°). A particle image velocimetry technique was used to conduct detailed velocity measurements at various streamwise- ...
Volume 1: Symposia, Parts A and B, 2007
This paper reports experimental study of three-dimensional turbulent wall jet over smooth and rou... more This paper reports experimental study of three-dimensional turbulent wall jet over smooth and rough surfaces. The wall jet was created using a square nozzle of size 6 mm and flow into an open channel. The experiments were performed at a Reynolds number based on the nozzle size and jet exit velocity of 4800. A particle image velocimetry was used to conduct detailed measurements over the smooth and rough surfaces at various streamwise-transverse and streamwise-spanwise planes. From these measurements, mean velocities ...
Volume 1: Symposia, Parts A and B, 2007
A particle image velocimetry is used to study the characteristics of separated and reattached tur... more A particle image velocimetry is used to study the characteristics of separated and reattached turbulent flow over two-dimensional transverse blocks of square, rectangular and semi-circular cross-sections fixed to the bottom wall of an open channel. The ratio of upstream boundary layer thickness to block height is considerably higher than in prior studies. The results show that the mean and turbulent statistics in the recirculation region and downstream of reattachment are significantly different from the upstream boundary layer. ...
Volume 1: Symposia, Parts A, B and C, 2009
The paper reports on an experimental investigation of turbulent flow through model two-dimensiona... more The paper reports on an experimental investigation of turbulent flow through model two-dimensional porous media. The porous media was bounded on one side by a solid plane wall and on the other side by a zone of clear fluid. The model porous media comprised of square arrays of circular acrylic rods that were inserted into precision holes drilled onto pairs of removable plates. The removable plates were then inserted into groves made in the side walls of the test channel. The rods fill about 59% of the channel height. Different ...