Martin Wosnik | University of New Hampshire (original) (raw)

Papers by Martin Wosnik

Abstract: Experiments were performed with a large laboratory-scale high solidity cross-flow turbi... more Abstract: Experiments were performed with a large laboratory-scale high solidity cross-flow turbine to investigate Reynolds number effects on performance and wake characteristics and to establish scale thresholds for physical and numerical modeling of individual devices and arrays. It was demonstrated that the performance of the cross-flow turbine becomes essentially Re-independent at a Reynolds number based on the rotor diameter ReD ≈ 106 or an approximate average Reynolds number based on the blade chord length Rec ≈ 2 × 105. A simple model that calculates the peak torque coefficient from static foil data and cross-flow turbine kinematics was shown to be a reasonable predictor for Reynolds number dependence of an actual cross-flow turbine operating under dynamic conditions. Mean velocity and turbulence measurements in the near-wake showed subtle differences over the range of Re investigated. However, when transport terms for the streamwise momentum and mean kinetic energy were calc...

Volume 1B, Symposia: Fluid Measurement and Instrumentation; Fluid Dynamics of Wind Energy; Renewable and Sustainable Energy Conversion; Energy and Process Engineering; Microfluidics and Nanofluidics; Development and Applications in Computational Fluid Dynamics; DNS/LES and Hybrid RANS/LES Methods

A research wind turbine of one meter diameter was designed for the UNH Flow Physics Facility (FPF... more A research wind turbine of one meter diameter was designed for the UNH Flow Physics Facility (FPF), a very large flow physics quality turbulent boundary layer wind tunnel (W 6m, H 2.7m, L 72m), which provides excellent spatial and temporal resolution, low flow blockage and allows measurements of turbine wakes far downstream due its long fetch. The initial turbine design was carried out as an aero-servo model of the NREL 5MW reference turbine, with subsequent modifications to both the hub to accommodate blade mounting and pitch-adjustment, and increases in model blade chord to achieve sufficiently high Reynolds numbers. A trade-off study of turbine design parameters in scale space was conducted. Several candidate airfoil profiles were evaluated numerically with the goal to reach Reynolds-number independence in turbine performance in the target operating range. The model turbine will achieve Reynolds numbers based on blade chord, an important consideration for airfoil performance and ...

Our aim in this paper is to present a brief overview of the scaled hydrokinetic turbine model tes... more Our aim in this paper is to present a brief overview of the scaled hydrokinetic turbine model testing activities in the United States using test turbines specifically designed by the US Department of Energy for its Marine and Hydrokinetic Research and Development program. These test turbines include: (1) a three-bladed horizontal axis turbine (the Sandia turbine) that was designed to demonstrate small scale verification and validation turbine design assessment; and (2) reference tidal and river turbines that were designed to develop baseline levelized cost of energy estimates. These scaled model turbine tests are generating performance and flow field data sets that will be fully documented and disseminated to the public. These data sets will enable MHK developers and researchers to validate their hydrokinetic turbine design and analysis models. In this paper, we present experimental results for two test turbines, including the scaled-model tests of the Sandia horizontal-axis turbine...

Bulletin of the American Physical Society, 2016

Facility (FPF) at UNH has test section dimensions W6.0m, H2.7m, L=72m. It can achieve high Reynol... more Facility (FPF) at UNH has test section dimensions W6.0m, H2.7m, L=72m. It can achieve high Reynolds number boundary layers, enabling turbulent boundary layer, wind energy and wind engineering research with exceptional spatial and temporal instrument resolution. We examined the FPFs ability to experimentally simulate different types of the atmospheric boundary layer (ABL): the stable, unstable, and neutral ABL. The neutral ABL is characterized by a zero potential temperature gradient, which is readily achieved in the FPF by operating when air and floor temperatures are close to equal. The stable and unstable ABLs have positive and negative vertical temperature gradients, respectively, which are more difficult to simulate without direct control of air or test section floor temperature. The test section floor is a 10 inch thick concrete cement slab and has significant thermal mass. When combined with the diurnal temperature variation of the ambient air, it is possible to achieve vertical temperature gradients in the test section, and produce weakly stable or weakly unstable boundary layer. Achievable Richardson numbers and Obukhov lengths are estimated. The different boundary layer profiles were measured, and compared to theoretical atmospheric models.

The Center for Ocean Renewable Energy (CORE) at the University of New Hampshire (UNH) operates a ... more The Center for Ocean Renewable Energy (CORE) at the University of New Hampshire (UNH) operates a sheltered, intermediate scale (“nursery”) tidal energy test site suited for Marine Hydrokinetic (MHK) turbines up to 4 m (13 ft) in diameter at General Sullivan Bridge in Great Bay Estuary, NH. The UNH-CORE Tidal Energy Test Site is located in a constricted area, and has the fastest tidal current velocities in the estuary with maximum currents at over 5 knots (2.6 m/s), and typically greater than 4 knots (2.1 m/s). The test site has a nominal depth of 10 m, a flat bottom, easy access from two local UNH marine facilities and nearby marinas, and hence it is a costeffective site for the testing of tidal energy conversion devices. An 11 m x 3 m test platform has been used for MHK turbines up to 1.5 m diameter since 2008, and a larger 20 m x 10 m test platform with a modular turbine deployment system was designed to accommodate larger turbines up to 4 m in diameter. A 4 m diameter axial turbi...

Bulletin of the American Physical Society, 2014

Bulletin of the American Physical Society, 2015

Submitted for the DFD15 Meeting of The American Physical Society Design of Bi-Directional Hydrofo... more Submitted for the DFD15 Meeting of The American Physical Society Design of Bi-Directional Hydrofoils for Tidal Current Turbines IVAYLO NEDYALKOV, MARTIN WOSNIK, University of New Hampshire — Tidal Current Turbines operate in flows which reverse direction. Bi-directional hydrofoils have rotational symmetry and allow such turbines to operate without the need for pitch or yaw control, decreasing the initial and maintenance costs. A numerical test-bed was developed to automate the simulations of hydrofoils in OpenFOAM and was utilized to simulate the flow over eleven classes of hydrofoils comprising a total of 700 foil shapes at different angles of attack. For promising candidate foil shapes physical models of 75 mm chord and 150 mm span were fabricated and tested in the University of New Hampshire High-Speed Cavitation Tunnel (HiCaT). The experimental results were compared to the simulations for model validation. The numerical test-bed successfully generated simulations for a wide rang...

This is an experimental investigation of the lift and drag characteristics of a new hydrofoil sha... more This is an experimental investigation of the lift and drag characteristics of a new hydrofoil shape that is optimized for low drag under partially cavitating conditions. Comparisons were made with a NACA 0015 cross-section. Each hydrofoil was mounted and tested in the Saint Anthony Falls Laboratory High Speed Cavitation Tunnel. Lift and drag were measured at three different velocities in the range 8-12 m/s over a range of angle of attack and cavitation number. Cavity length and fluctuations in length were also measured using photographic and video observation. Of significant interest was the large increase in lift under partially cavitating conditions. Lift to drag data also show a similar trend. It was also found that cavity length oscillations differ from that on a NACA 0015 hydrofoil with different spectral characteristics. Design aspects and comparisons between predicted and measured data are also described.

Supercavitating vehicles need to be supplied with an artificial cavity through ventilation until ... more Supercavitating vehicles need to be supplied with an artificial cavity through ventilation until they accelerate to conditions at which a natural supercavity can be sustained. A study has been carried out in the high-speed water tunnel at St. Anthony Falls Laboratory to investigate some aspects of the flow physics of such a supercavitating vehicle. Digital strobe photography images were taken to qualitatively describe the cavity shape and wake details. In addition, the amount of ventilation gas required to sustain an artificial cavity at different velocities was investigated. It was found that the strut shape critically affects air demand through cavity-strut wake interaction. The wake of ventilated cavities was then characterized quantitatively using Particle Image Velocimetry (PIV). Since two-camera, filtered PIV was prohibitively costly due to the large amount of fluorescent particles required to seed the tunnel, a new grayscale technique was developed to measure the void fractio...

Minimizing wake losses in wind or marine hydrokinetic (MHK) turbine arrays is a crucial design co... more Minimizing wake losses in wind or marine hydrokinetic (MHK) turbine arrays is a crucial design consideration, as it has a large impact on overall energy production. To understand and mitigate these losses, interactions between turbine wakes must be accurately predicted, with near-wakes being especially important for cross-flow (or vertical-axis) turbines, given their affinity for close-spaced operation. As numerical models become more accurate, validation efforts will need to take into account scale discrepancies between the numerical and physical models and their real-world applications. One such important scaling parameter is the Reynolds number, and it remains unclear what level of confidence can be placed in models validated away from full-scale Reynolds numbers. In other words, what is the minimum acceptable scale mismatch for experimental validation at which models can be said to be “accurate enough?” To address this uncertainty, we investigated—experimentally and numerically—...

Marine hydrokinetic (MHK) energy conversion devices are subject to a wide range of turbulent scal... more Marine hydrokinetic (MHK) energy conversion devices are subject to a wide range of turbulent scales, either due to upstream bathymetry, obstacles and waves, or from wakes of upstream devices in array configurations. The commonly used, robust Acoustic Doppler Current Profilers (ADCP) are well suited for long term flow measurements in the marine environment, but are limited to low sampling rates due to their operational principle. The resulting temporal and spatial resolution is insufficient to measure all turbulence scales of interest to the device, e.g., ``blade-scale turbulence.'' The present study systematically characterizes the spatial and temporal resolution of ADCP and Acoustic Doppler Velocimetry (ADV). Simulations were used to quantitatively investigate the flow scales that each of the instruments can resolve in low and high turbulence intensity flows. For comparison, measurements were conducted at the UNH Tidal Energy Test Site in Great Bay Estuary at General Sulliv...

Abstract: Experiments were performed with a large laboratory-scale high solidity cross-flow turbi... more Abstract: Experiments were performed with a large laboratory-scale high solidity cross-flow turbine to investigate Reynolds number effects on performance and wake characteristics and to establish scale thresholds for physical and numerical modeling of individual devices and arrays. It was demonstrated that the performance of the cross-flow turbine becomes essentially Re-independent at a Reynolds number based on the rotor diameter ReD ≈ 106 or an approximate average Reynolds number based on the blade chord length Rec ≈ 2 × 105. A simple model that calculates the peak torque coefficient from static foil data and cross-flow turbine kinematics was shown to be a reasonable predictor for Reynolds number dependence of an actual cross-flow turbine operating under dynamic conditions. Mean velocity and turbulence measurements in the near-wake showed subtle differences over the range of Re investigated. However, when transport terms for the streamwise momentum and mean kinetic energy were calc...

Volume 1B, Symposia: Fluid Measurement and Instrumentation; Fluid Dynamics of Wind Energy; Renewable and Sustainable Energy Conversion; Energy and Process Engineering; Microfluidics and Nanofluidics; Development and Applications in Computational Fluid Dynamics; DNS/LES and Hybrid RANS/LES Methods

A research wind turbine of one meter diameter was designed for the UNH Flow Physics Facility (FPF... more A research wind turbine of one meter diameter was designed for the UNH Flow Physics Facility (FPF), a very large flow physics quality turbulent boundary layer wind tunnel (W 6m, H 2.7m, L 72m), which provides excellent spatial and temporal resolution, low flow blockage and allows measurements of turbine wakes far downstream due its long fetch. The initial turbine design was carried out as an aero-servo model of the NREL 5MW reference turbine, with subsequent modifications to both the hub to accommodate blade mounting and pitch-adjustment, and increases in model blade chord to achieve sufficiently high Reynolds numbers. A trade-off study of turbine design parameters in scale space was conducted. Several candidate airfoil profiles were evaluated numerically with the goal to reach Reynolds-number independence in turbine performance in the target operating range. The model turbine will achieve Reynolds numbers based on blade chord, an important consideration for airfoil performance and ...

Our aim in this paper is to present a brief overview of the scaled hydrokinetic turbine model tes... more Our aim in this paper is to present a brief overview of the scaled hydrokinetic turbine model testing activities in the United States using test turbines specifically designed by the US Department of Energy for its Marine and Hydrokinetic Research and Development program. These test turbines include: (1) a three-bladed horizontal axis turbine (the Sandia turbine) that was designed to demonstrate small scale verification and validation turbine design assessment; and (2) reference tidal and river turbines that were designed to develop baseline levelized cost of energy estimates. These scaled model turbine tests are generating performance and flow field data sets that will be fully documented and disseminated to the public. These data sets will enable MHK developers and researchers to validate their hydrokinetic turbine design and analysis models. In this paper, we present experimental results for two test turbines, including the scaled-model tests of the Sandia horizontal-axis turbine...

Bulletin of the American Physical Society, 2016

Facility (FPF) at UNH has test section dimensions W6.0m, H2.7m, L=72m. It can achieve high Reynol... more Facility (FPF) at UNH has test section dimensions W6.0m, H2.7m, L=72m. It can achieve high Reynolds number boundary layers, enabling turbulent boundary layer, wind energy and wind engineering research with exceptional spatial and temporal instrument resolution. We examined the FPFs ability to experimentally simulate different types of the atmospheric boundary layer (ABL): the stable, unstable, and neutral ABL. The neutral ABL is characterized by a zero potential temperature gradient, which is readily achieved in the FPF by operating when air and floor temperatures are close to equal. The stable and unstable ABLs have positive and negative vertical temperature gradients, respectively, which are more difficult to simulate without direct control of air or test section floor temperature. The test section floor is a 10 inch thick concrete cement slab and has significant thermal mass. When combined with the diurnal temperature variation of the ambient air, it is possible to achieve vertical temperature gradients in the test section, and produce weakly stable or weakly unstable boundary layer. Achievable Richardson numbers and Obukhov lengths are estimated. The different boundary layer profiles were measured, and compared to theoretical atmospheric models.

The Center for Ocean Renewable Energy (CORE) at the University of New Hampshire (UNH) operates a ... more The Center for Ocean Renewable Energy (CORE) at the University of New Hampshire (UNH) operates a sheltered, intermediate scale (“nursery”) tidal energy test site suited for Marine Hydrokinetic (MHK) turbines up to 4 m (13 ft) in diameter at General Sullivan Bridge in Great Bay Estuary, NH. The UNH-CORE Tidal Energy Test Site is located in a constricted area, and has the fastest tidal current velocities in the estuary with maximum currents at over 5 knots (2.6 m/s), and typically greater than 4 knots (2.1 m/s). The test site has a nominal depth of 10 m, a flat bottom, easy access from two local UNH marine facilities and nearby marinas, and hence it is a costeffective site for the testing of tidal energy conversion devices. An 11 m x 3 m test platform has been used for MHK turbines up to 1.5 m diameter since 2008, and a larger 20 m x 10 m test platform with a modular turbine deployment system was designed to accommodate larger turbines up to 4 m in diameter. A 4 m diameter axial turbi...

Bulletin of the American Physical Society, 2014

Bulletin of the American Physical Society, 2015

Submitted for the DFD15 Meeting of The American Physical Society Design of Bi-Directional Hydrofo... more Submitted for the DFD15 Meeting of The American Physical Society Design of Bi-Directional Hydrofoils for Tidal Current Turbines IVAYLO NEDYALKOV, MARTIN WOSNIK, University of New Hampshire — Tidal Current Turbines operate in flows which reverse direction. Bi-directional hydrofoils have rotational symmetry and allow such turbines to operate without the need for pitch or yaw control, decreasing the initial and maintenance costs. A numerical test-bed was developed to automate the simulations of hydrofoils in OpenFOAM and was utilized to simulate the flow over eleven classes of hydrofoils comprising a total of 700 foil shapes at different angles of attack. For promising candidate foil shapes physical models of 75 mm chord and 150 mm span were fabricated and tested in the University of New Hampshire High-Speed Cavitation Tunnel (HiCaT). The experimental results were compared to the simulations for model validation. The numerical test-bed successfully generated simulations for a wide rang...

This is an experimental investigation of the lift and drag characteristics of a new hydrofoil sha... more This is an experimental investigation of the lift and drag characteristics of a new hydrofoil shape that is optimized for low drag under partially cavitating conditions. Comparisons were made with a NACA 0015 cross-section. Each hydrofoil was mounted and tested in the Saint Anthony Falls Laboratory High Speed Cavitation Tunnel. Lift and drag were measured at three different velocities in the range 8-12 m/s over a range of angle of attack and cavitation number. Cavity length and fluctuations in length were also measured using photographic and video observation. Of significant interest was the large increase in lift under partially cavitating conditions. Lift to drag data also show a similar trend. It was also found that cavity length oscillations differ from that on a NACA 0015 hydrofoil with different spectral characteristics. Design aspects and comparisons between predicted and measured data are also described.

Supercavitating vehicles need to be supplied with an artificial cavity through ventilation until ... more Supercavitating vehicles need to be supplied with an artificial cavity through ventilation until they accelerate to conditions at which a natural supercavity can be sustained. A study has been carried out in the high-speed water tunnel at St. Anthony Falls Laboratory to investigate some aspects of the flow physics of such a supercavitating vehicle. Digital strobe photography images were taken to qualitatively describe the cavity shape and wake details. In addition, the amount of ventilation gas required to sustain an artificial cavity at different velocities was investigated. It was found that the strut shape critically affects air demand through cavity-strut wake interaction. The wake of ventilated cavities was then characterized quantitatively using Particle Image Velocimetry (PIV). Since two-camera, filtered PIV was prohibitively costly due to the large amount of fluorescent particles required to seed the tunnel, a new grayscale technique was developed to measure the void fractio...

Minimizing wake losses in wind or marine hydrokinetic (MHK) turbine arrays is a crucial design co... more Minimizing wake losses in wind or marine hydrokinetic (MHK) turbine arrays is a crucial design consideration, as it has a large impact on overall energy production. To understand and mitigate these losses, interactions between turbine wakes must be accurately predicted, with near-wakes being especially important for cross-flow (or vertical-axis) turbines, given their affinity for close-spaced operation. As numerical models become more accurate, validation efforts will need to take into account scale discrepancies between the numerical and physical models and their real-world applications. One such important scaling parameter is the Reynolds number, and it remains unclear what level of confidence can be placed in models validated away from full-scale Reynolds numbers. In other words, what is the minimum acceptable scale mismatch for experimental validation at which models can be said to be “accurate enough?” To address this uncertainty, we investigated—experimentally and numerically—...

Marine hydrokinetic (MHK) energy conversion devices are subject to a wide range of turbulent scal... more Marine hydrokinetic (MHK) energy conversion devices are subject to a wide range of turbulent scales, either due to upstream bathymetry, obstacles and waves, or from wakes of upstream devices in array configurations. The commonly used, robust Acoustic Doppler Current Profilers (ADCP) are well suited for long term flow measurements in the marine environment, but are limited to low sampling rates due to their operational principle. The resulting temporal and spatial resolution is insufficient to measure all turbulence scales of interest to the device, e.g., ``blade-scale turbulence.'' The present study systematically characterizes the spatial and temporal resolution of ADCP and Acoustic Doppler Velocimetry (ADV). Simulations were used to quantitatively investigate the flow scales that each of the instruments can resolve in low and high turbulence intensity flows. For comparison, measurements were conducted at the UNH Tidal Energy Test Site in Great Bay Estuary at General Sulliv...