BD
B.S. Dsouza
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1
Reproducing an offshore Atmospheric boundary layer in an open-jet wind tunnel
PIV and HWA Experimental study
As the need to reduce the carbon footprint of the energy sector grows, wind energy has emerged as a leading renewable source for sustainable power generation. In particular, the offshore sector has gained significant attention due to its higher wind speeds as well as its reduced noise impact. TU Delft's Faculty of Aerospace Engineering has identified accelerating the energy transition towards renewable energy sources as one of its main goals. To achieve this, offshore wind turbines must be tested under realistic Atmospheric Boundary Layer (ABL) conditions.
Wind-tunnel ABL simulations typically use spires, barriers and roughness elements as passive devices. However, this configuration requires a long downstream length for the boundary layer to develop. Therefore, an alternative approach developed by Cowdrey (1967) is used, which employs a non-uniform rod grid to produce a prescribed power-law mean velocity profile. Moreover, unlike spire-based configurations, this method allows for variations in the turbulence levels of the resulting boundary layer through the grid design parameters.
This thesis investigated the capability of Cowdrey's method to reproduce an offshore ABL in a short open-jet test section. Particle Image Velocimetry and Hot-Wire Anemometry were used to measure the mean velocity profile, turbulence intensity, integral length scales and power spectral density. Cowdrey grids were evaluated over a test matrix with four rod diameters, two cross-sectional shapes, two turbulence design settings, two target boundary layer thicknesses at three free-stream velocities.
Within the tested velocity range, the use of Cowdrey grids increased the boundary layer height by up to 26 times compared with the naturally developing layer within the same fetch length. The fitted power-law exponents for most configurations were slightly larger than the design value but remained close to the target value overall. Moreover, most grids exhibited a good agreement with the logarithmic law in the inner layer and within the available downstream distance, attained the characteristic aerodynamic roughness length of an offshore Atmospheric Boundary Layer. The measured turbulence intensities exhibited elevated near-wall levels relative to semi-empirical relations but qualitatively followed the predicted offshore ABL trends. The power spectral density conformed to the von Kármán model across all sampled heights, with noticeable departures only near the top of the outer layer at the furthest downstream station. Lastly, the longitudinal integral length scales tended to be consistently lower than predicted by semi-empirical relations.
The study provided valuable insights into the applicability of Cowdrey’s method in reproducing a scaled offshore ABL. It laid the foundations for further research regarding ABL testing in TU Delft's experimental facilities. Further improvements should focus on bringing the fitted power law closer to the target value and refining the turbulence characteristics to minimize deviations from accepted standards. ...
Wind-tunnel ABL simulations typically use spires, barriers and roughness elements as passive devices. However, this configuration requires a long downstream length for the boundary layer to develop. Therefore, an alternative approach developed by Cowdrey (1967) is used, which employs a non-uniform rod grid to produce a prescribed power-law mean velocity profile. Moreover, unlike spire-based configurations, this method allows for variations in the turbulence levels of the resulting boundary layer through the grid design parameters.
This thesis investigated the capability of Cowdrey's method to reproduce an offshore ABL in a short open-jet test section. Particle Image Velocimetry and Hot-Wire Anemometry were used to measure the mean velocity profile, turbulence intensity, integral length scales and power spectral density. Cowdrey grids were evaluated over a test matrix with four rod diameters, two cross-sectional shapes, two turbulence design settings, two target boundary layer thicknesses at three free-stream velocities.
Within the tested velocity range, the use of Cowdrey grids increased the boundary layer height by up to 26 times compared with the naturally developing layer within the same fetch length. The fitted power-law exponents for most configurations were slightly larger than the design value but remained close to the target value overall. Moreover, most grids exhibited a good agreement with the logarithmic law in the inner layer and within the available downstream distance, attained the characteristic aerodynamic roughness length of an offshore Atmospheric Boundary Layer. The measured turbulence intensities exhibited elevated near-wall levels relative to semi-empirical relations but qualitatively followed the predicted offshore ABL trends. The power spectral density conformed to the von Kármán model across all sampled heights, with noticeable departures only near the top of the outer layer at the furthest downstream station. Lastly, the longitudinal integral length scales tended to be consistently lower than predicted by semi-empirical relations.
The study provided valuable insights into the applicability of Cowdrey’s method in reproducing a scaled offshore ABL. It laid the foundations for further research regarding ABL testing in TU Delft's experimental facilities. Further improvements should focus on bringing the fitted power law closer to the target value and refining the turbulence characteristics to minimize deviations from accepted standards. ...
As the need to reduce the carbon footprint of the energy sector grows, wind energy has emerged as a leading renewable source for sustainable power generation. In particular, the offshore sector has gained significant attention due to its higher wind speeds as well as its reduced noise impact. TU Delft's Faculty of Aerospace Engineering has identified accelerating the energy transition towards renewable energy sources as one of its main goals. To achieve this, offshore wind turbines must be tested under realistic Atmospheric Boundary Layer (ABL) conditions.
Wind-tunnel ABL simulations typically use spires, barriers and roughness elements as passive devices. However, this configuration requires a long downstream length for the boundary layer to develop. Therefore, an alternative approach developed by Cowdrey (1967) is used, which employs a non-uniform rod grid to produce a prescribed power-law mean velocity profile. Moreover, unlike spire-based configurations, this method allows for variations in the turbulence levels of the resulting boundary layer through the grid design parameters.
This thesis investigated the capability of Cowdrey's method to reproduce an offshore ABL in a short open-jet test section. Particle Image Velocimetry and Hot-Wire Anemometry were used to measure the mean velocity profile, turbulence intensity, integral length scales and power spectral density. Cowdrey grids were evaluated over a test matrix with four rod diameters, two cross-sectional shapes, two turbulence design settings, two target boundary layer thicknesses at three free-stream velocities.
Within the tested velocity range, the use of Cowdrey grids increased the boundary layer height by up to 26 times compared with the naturally developing layer within the same fetch length. The fitted power-law exponents for most configurations were slightly larger than the design value but remained close to the target value overall. Moreover, most grids exhibited a good agreement with the logarithmic law in the inner layer and within the available downstream distance, attained the characteristic aerodynamic roughness length of an offshore Atmospheric Boundary Layer. The measured turbulence intensities exhibited elevated near-wall levels relative to semi-empirical relations but qualitatively followed the predicted offshore ABL trends. The power spectral density conformed to the von Kármán model across all sampled heights, with noticeable departures only near the top of the outer layer at the furthest downstream station. Lastly, the longitudinal integral length scales tended to be consistently lower than predicted by semi-empirical relations.
The study provided valuable insights into the applicability of Cowdrey’s method in reproducing a scaled offshore ABL. It laid the foundations for further research regarding ABL testing in TU Delft's experimental facilities. Further improvements should focus on bringing the fitted power law closer to the target value and refining the turbulence characteristics to minimize deviations from accepted standards.
Wind-tunnel ABL simulations typically use spires, barriers and roughness elements as passive devices. However, this configuration requires a long downstream length for the boundary layer to develop. Therefore, an alternative approach developed by Cowdrey (1967) is used, which employs a non-uniform rod grid to produce a prescribed power-law mean velocity profile. Moreover, unlike spire-based configurations, this method allows for variations in the turbulence levels of the resulting boundary layer through the grid design parameters.
This thesis investigated the capability of Cowdrey's method to reproduce an offshore ABL in a short open-jet test section. Particle Image Velocimetry and Hot-Wire Anemometry were used to measure the mean velocity profile, turbulence intensity, integral length scales and power spectral density. Cowdrey grids were evaluated over a test matrix with four rod diameters, two cross-sectional shapes, two turbulence design settings, two target boundary layer thicknesses at three free-stream velocities.
Within the tested velocity range, the use of Cowdrey grids increased the boundary layer height by up to 26 times compared with the naturally developing layer within the same fetch length. The fitted power-law exponents for most configurations were slightly larger than the design value but remained close to the target value overall. Moreover, most grids exhibited a good agreement with the logarithmic law in the inner layer and within the available downstream distance, attained the characteristic aerodynamic roughness length of an offshore Atmospheric Boundary Layer. The measured turbulence intensities exhibited elevated near-wall levels relative to semi-empirical relations but qualitatively followed the predicted offshore ABL trends. The power spectral density conformed to the von Kármán model across all sampled heights, with noticeable departures only near the top of the outer layer at the furthest downstream station. Lastly, the longitudinal integral length scales tended to be consistently lower than predicted by semi-empirical relations.
The study provided valuable insights into the applicability of Cowdrey’s method in reproducing a scaled offshore ABL. It laid the foundations for further research regarding ABL testing in TU Delft's experimental facilities. Further improvements should focus on bringing the fitted power law closer to the target value and refining the turbulence characteristics to minimize deviations from accepted standards.
Curupira
A dual-drone platform for biodiversity surveys in tropical rainforest environments
Bachelor thesis
(2025)
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A. Dima, C.E. Ochola, C.L. Visser, D. Raonic, E. MERGAERT, G.D.F. Schellekens, I.M. Dolman, J.M. Oppelaar, L. Ledeganck, Y. Cavalcante Tavares, S. Hamaza, Anandini Jayanthi, B.S. Dsouza, J.A. Melkert
Rainforests are estimated to shelter between 40% and 75% of Earth’s biodiversity, including countless endemic species that are vital to the ecosystem health. The large uncertainty in these estimates underscores the significant gaps in our knowledge of this biome, with numerous species yet to be discovered. Simultaneously, human-driven habitat destruction is causing species to disappear before they can ever be identified. This combination of limited knowledge and accelerating loss has transformed the effort to document rainforest biodiversity into a pressing ‘race against the clock’. Ongoing developments in drone technologies offer a promising solution for conducting large-scale surveys of rainforest biodiversity. To enable swift, sustainable and minimally invasive collection of high-quality biodiversity data in rainforest environments, Curupira was developed, an innovative system designed to enhance our understanding of species diversity and ecosystem health. Curupira features a coordinated pair of autonomous drones, working in tandem to conduct efficient, in-depth biodiversity surveys in tropical rainforests.
...
Rainforests are estimated to shelter between 40% and 75% of Earth’s biodiversity, including countless endemic species that are vital to the ecosystem health. The large uncertainty in these estimates underscores the significant gaps in our knowledge of this biome, with numerous species yet to be discovered. Simultaneously, human-driven habitat destruction is causing species to disappear before they can ever be identified. This combination of limited knowledge and accelerating loss has transformed the effort to document rainforest biodiversity into a pressing ‘race against the clock’. Ongoing developments in drone technologies offer a promising solution for conducting large-scale surveys of rainforest biodiversity. To enable swift, sustainable and minimally invasive collection of high-quality biodiversity data in rainforest environments, Curupira was developed, an innovative system designed to enhance our understanding of species diversity and ecosystem health. Curupira features a coordinated pair of autonomous drones, working in tandem to conduct efficient, in-depth biodiversity surveys in tropical rainforests.