In this study, the resilience of large cities and their built infrastructure in New Zealand to ex... more In this study, the resilience of large cities and their built infrastructure in New Zealand to extreme winds, is investigated by coupling the outputs of a very high-resolution, 333-m resolution, numerical weather prediction (NWP) model with computational fluid dynamics (CFD) simulations. Following an extreme wind event on 18 September 2020 in Auckland, in which two trucks travelling over the Auckland Harbour bridge tipped over and damaged the bridge structure, a CFD simulation of airflow over the bridge using the Reynolds-averaged Navier–Stokes (RANS) method and NWP wind speed forecasts as the inlet profile is conducted. The 333 m NWP forecasts were validated against four nearby observation sites, showing generally high correlations of greater than 0.8 and low mean bias (±3 m s−1) and RMSE (<3 m s−1) values. The CFD-based estimates of the mean wind speed-up over the bridge showed that the mean wind speed could increase by a factor of 1.15–1.20 in the vicinity of the road where th...
The general flow features observed on yacht sails can be predicted with well-established fluid dy... more The general flow features observed on yacht sails can be predicted with well-established fluid dynamic theory. Headsails are thin wings with a sharp leading edge and thin-airfoil theory can predict the general flow and pressure fields around these sails. However, a closer look shows viscous flow features, such as the leading edge bubble, that cannot be modelled with inviscid flow and, indeed, cannot be predicted accurately with analytical fluid dynamics. Moreover, the available literature lacks of quantitative flow measurements (e.g. particle imaging velocimetry) and high-fidelity numerical simulations (e.g. wall-resolved large eddy simulations) on yacht sails due to the difficulties related to the high Reynolds numbers and the complex sails' geometries. Therefore there is limited knowledge of the viscous flow field near sails. Here we provide a detailed description of the pressure distributions measured in a wind tunnel on model-scale headsails and we describe the expected flow...
The objective of the research in this paper was to maximise the amount of performance enhancing a... more The objective of the research in this paper was to maximise the amount of performance enhancing aerodynamic down-force generated by the 2005/2006 University of Auckland Formula SAE race car. This was done through a combination of physical modelling using a rolling road wind tunnel research facility and by using computational fluid dynamics. Computational fluid dynamic analysis was used for the design of the body and under-tray of the vehicle. Optimal design gave a lift coefficient of -0.9 from the under-tray. Simulations showed that when the exhaust was vented into two diffuser tunnels under the car, the downforce was increased by 35%. Half-scale vehicle modelling using the wind tunnel rolling road facility gave a lift coefficient of -2.4. In its optimal configuration, the aerodynamic load on the front and rear wheels respectively was able to be adjusted between 43% on the front and 57% on the rear to 33% on the front and 67 % on the rear by changing the angle of the foils. The drag...
Since the announcement that the 34 th America’s Cup will be sailed in catamarans powered by multi... more Since the announcement that the 34 th America’s Cup will be sailed in catamarans powered by multi-element wing sails, interest in wing sail technology has increased enormously. Unfortunately, there is very little information available in the open peer-reviewed literature about designing wings for yachts. While there has been a huge amount of research carried out on the design of multi-element wings for aircraft, the flow domain is very different for yachts and aircraft, as well as the performance objectives. Airline wings at cruise operate at Reynolds numbers in excess of 10 million compared with yacht sail Reynolds numbers in the region of 0.2 to 8 million. Whereas aircraft wings at cruise are designed for minimum drag at a required lift force, yacht wings must provide maximum thrust for specific roll/pitching moments, as well as sailing on either tack, and therefore the optimisation problems are very different. This paper reviews the literature on wing sail design for high perform...
A method for optimising finned-tubed heat-exchanger geometries to minimise air-side pressure drop... more A method for optimising finned-tubed heat-exchanger geometries to minimise air-side pressure drop, for given heat removal rates is outlined. The method allows the number of tube rows to be calculated, and from this the pressure drop across the entire heat-exchanger can be estimated. The liquid side is not treated in detail as correlations giving the convective heat transfer coefficient for the flow of fluids in tubes are relatively well established. An example is given from a typical wind-tunnel with which the author has been associated. However, the principles can be applied equally well to similar gas-liquid heat exchanger situations such as those in the large processing industries which are currently developing rapidly in New Zealand.
Following the 33rd America's Cup which featured a trimaran versus a catamaran, and the recent... more Following the 33rd America's Cup which featured a trimaran versus a catamaran, and the recent 34th America's Cup in 2013 featuring AC72 catamarans with multi-element wing sail yachts sailing at unprecedented speeds, interest in wing sail technology has increased substantially. Unfortunately there is currently very little open peer-reviewed literature available with a focus on multi-element wing design for yachts. The limited available literature focuses primarily on the structures of wings and their control, rather than on the aerodynamic design. While there is substantial available literature on the aerodynamic properties of aircraft wings, the differences in the flow domains between aeroplanes and yachts is significant. A yacht sail will operate in a Reynolds number range of 0.2 to 8 million while aircraft operate regularly in excess of 10 million. Furthermore, yachts operate in the turbulent atmospheric boundary layer and require high maximum lift coefficients at many app...
this paper describes methods for testing model wind turbines in wind tunnels based on published d... more this paper describes methods for testing model wind turbines in wind tunnels based on published data and the experience gained by the author through having tested many different wind turbines in wind tunnels at the university of auckland. wind tunnels can be used to determine the performance of small wind turbines at full scale, or larger wind turbines at reduced scale. such experiments need to be done with care as one needs to be aware of issues regarding blockage, the effect of Reynolds number, and being able to control the speed of the turbine so that is power coefficient can be obtained over a suitable range of tip speed ratios. With rotating machinery, it is also important to have a regard to safety, so the models have to be made with care and a stress analysis carried out to ensure that the material properties are not exceeded during the testing. it is found that wind tunnel testing is a useful way of determining experimentally the performance of wind turbines in order to pred...
This paper presents blade root bending moment measurements of a horizontal-axis tidal turbine for... more This paper presents blade root bending moment measurements of a horizontal-axis tidal turbine for planar oscillatory motion, conducted in a stationary water towing tank. By comparing the measurements with quasi-steady reconstructions for both single and multiple frequency oscillatory motion, the bending moment was shown to be sensitive to both frequency and amplitude, as well as to the mean tip-speed ratio. The unsteady loads associated with the separation of the flow and dynamic stall are shown to be of considerably greater importance than those which are already present for attached flow, such as added mass and dynamic inflow. A linear model fit to the unsteady bending moment also indicates that the inertia contribution is relatively small. For cases where attached flow exists over the majority of the load cycle, these reconstruction methods are likely to be sufficient to obtain a reasonable prediction of the root out-of-plane bending moment. However, turbines whose blades are likely to...
When the future wind direction is uncertain, the tactical decisions of a yacht skipper involve a ... more When the future wind direction is uncertain, the tactical decisions of a yacht skipper involve a stochastic routing problem. The objective of this problem is to maximise the probability of reaching the next mark ahead of all the other competitors. This paper describes a system that models this problem. The tidal current at any location is assumed to be predictable, while the wind forecast is based on current observations. Boat performance in different wind conditions is defined by the output of a velocity prediction program, and we assume a known speed loss for tacking and gybing. The resulting computer program can be used during a yacht race to choose the optimum course, or it can be used for design purposes to simulate yacht races between different design candidates. As an example of application, we compare strategies that minimise the average time to sail the leg, as opposed to those that maximise the probability of winning, and show how optimal routing strategies are different for leading and trailing boats. NOMENCLATURE Scalars Distance between two competitors Delay in finishing under strategy versus the perfect strategy Values that a discrete-time stochastic process can assume at the th time step Time to finish under the strategy Time to finish under the perfect strategy Discrete-time stochastic process, e.g. wind direction at the th time step th random variable uniform in (0,1) Matrices , Policy matrix at the cross-section k on the tack , where is starboard or port Transition matrix Set of matrices Strategy, i.e. set of policy matrices Operators (A) Expected value of (A) ℙ(A|B) Probability density function of A conditioned on B Abbreviations BS Boat speed RMP Race modelling program SPP Shortest path problem VMG Velocity made good 1.
In this study, the resilience of large cities and their built infrastructure in New Zealand to ex... more In this study, the resilience of large cities and their built infrastructure in New Zealand to extreme winds, is investigated by coupling the outputs of a very high-resolution, 333-m resolution, numerical weather prediction (NWP) model with computational fluid dynamics (CFD) simulations. Following an extreme wind event on 18 September 2020 in Auckland, in which two trucks travelling over the Auckland Harbour bridge tipped over and damaged the bridge structure, a CFD simulation of airflow over the bridge using the Reynolds-averaged Navier–Stokes (RANS) method and NWP wind speed forecasts as the inlet profile is conducted. The 333 m NWP forecasts were validated against four nearby observation sites, showing generally high correlations of greater than 0.8 and low mean bias (±3 m s−1) and RMSE (<3 m s−1) values. The CFD-based estimates of the mean wind speed-up over the bridge showed that the mean wind speed could increase by a factor of 1.15–1.20 in the vicinity of the road where th...
In this study, the resilience of large cities and their built infrastructure in New Zealand to ex... more In this study, the resilience of large cities and their built infrastructure in New Zealand to extreme winds, is investigated by coupling the outputs of a very high-resolution, 333-m resolution, numerical weather prediction (NWP) model with computational fluid dynamics (CFD) simulations. Following an extreme wind event on 18 September 2020 in Auckland, in which two trucks travelling over the Auckland Harbour bridge tipped over and damaged the bridge structure, a CFD simulation of airflow over the bridge using the Reynolds-averaged Navier–Stokes (RANS) method and NWP wind speed forecasts as the inlet profile is conducted. The 333 m NWP forecasts were validated against four nearby observation sites, showing generally high correlations of greater than 0.8 and low mean bias (±3 m s−1) and RMSE (<3 m s−1) values. The CFD-based estimates of the mean wind speed-up over the bridge showed that the mean wind speed could increase by a factor of 1.15–1.20 in the vicinity of the road where th...
The general flow features observed on yacht sails can be predicted with well-established fluid dy... more The general flow features observed on yacht sails can be predicted with well-established fluid dynamic theory. Headsails are thin wings with a sharp leading edge and thin-airfoil theory can predict the general flow and pressure fields around these sails. However, a closer look shows viscous flow features, such as the leading edge bubble, that cannot be modelled with inviscid flow and, indeed, cannot be predicted accurately with analytical fluid dynamics. Moreover, the available literature lacks of quantitative flow measurements (e.g. particle imaging velocimetry) and high-fidelity numerical simulations (e.g. wall-resolved large eddy simulations) on yacht sails due to the difficulties related to the high Reynolds numbers and the complex sails' geometries. Therefore there is limited knowledge of the viscous flow field near sails. Here we provide a detailed description of the pressure distributions measured in a wind tunnel on model-scale headsails and we describe the expected flow...
The objective of the research in this paper was to maximise the amount of performance enhancing a... more The objective of the research in this paper was to maximise the amount of performance enhancing aerodynamic down-force generated by the 2005/2006 University of Auckland Formula SAE race car. This was done through a combination of physical modelling using a rolling road wind tunnel research facility and by using computational fluid dynamics. Computational fluid dynamic analysis was used for the design of the body and under-tray of the vehicle. Optimal design gave a lift coefficient of -0.9 from the under-tray. Simulations showed that when the exhaust was vented into two diffuser tunnels under the car, the downforce was increased by 35%. Half-scale vehicle modelling using the wind tunnel rolling road facility gave a lift coefficient of -2.4. In its optimal configuration, the aerodynamic load on the front and rear wheels respectively was able to be adjusted between 43% on the front and 57% on the rear to 33% on the front and 67 % on the rear by changing the angle of the foils. The drag...
Since the announcement that the 34 th America’s Cup will be sailed in catamarans powered by multi... more Since the announcement that the 34 th America’s Cup will be sailed in catamarans powered by multi-element wing sails, interest in wing sail technology has increased enormously. Unfortunately, there is very little information available in the open peer-reviewed literature about designing wings for yachts. While there has been a huge amount of research carried out on the design of multi-element wings for aircraft, the flow domain is very different for yachts and aircraft, as well as the performance objectives. Airline wings at cruise operate at Reynolds numbers in excess of 10 million compared with yacht sail Reynolds numbers in the region of 0.2 to 8 million. Whereas aircraft wings at cruise are designed for minimum drag at a required lift force, yacht wings must provide maximum thrust for specific roll/pitching moments, as well as sailing on either tack, and therefore the optimisation problems are very different. This paper reviews the literature on wing sail design for high perform...
A method for optimising finned-tubed heat-exchanger geometries to minimise air-side pressure drop... more A method for optimising finned-tubed heat-exchanger geometries to minimise air-side pressure drop, for given heat removal rates is outlined. The method allows the number of tube rows to be calculated, and from this the pressure drop across the entire heat-exchanger can be estimated. The liquid side is not treated in detail as correlations giving the convective heat transfer coefficient for the flow of fluids in tubes are relatively well established. An example is given from a typical wind-tunnel with which the author has been associated. However, the principles can be applied equally well to similar gas-liquid heat exchanger situations such as those in the large processing industries which are currently developing rapidly in New Zealand.
Following the 33rd America's Cup which featured a trimaran versus a catamaran, and the recent... more Following the 33rd America's Cup which featured a trimaran versus a catamaran, and the recent 34th America's Cup in 2013 featuring AC72 catamarans with multi-element wing sail yachts sailing at unprecedented speeds, interest in wing sail technology has increased substantially. Unfortunately there is currently very little open peer-reviewed literature available with a focus on multi-element wing design for yachts. The limited available literature focuses primarily on the structures of wings and their control, rather than on the aerodynamic design. While there is substantial available literature on the aerodynamic properties of aircraft wings, the differences in the flow domains between aeroplanes and yachts is significant. A yacht sail will operate in a Reynolds number range of 0.2 to 8 million while aircraft operate regularly in excess of 10 million. Furthermore, yachts operate in the turbulent atmospheric boundary layer and require high maximum lift coefficients at many app...
this paper describes methods for testing model wind turbines in wind tunnels based on published d... more this paper describes methods for testing model wind turbines in wind tunnels based on published data and the experience gained by the author through having tested many different wind turbines in wind tunnels at the university of auckland. wind tunnels can be used to determine the performance of small wind turbines at full scale, or larger wind turbines at reduced scale. such experiments need to be done with care as one needs to be aware of issues regarding blockage, the effect of Reynolds number, and being able to control the speed of the turbine so that is power coefficient can be obtained over a suitable range of tip speed ratios. With rotating machinery, it is also important to have a regard to safety, so the models have to be made with care and a stress analysis carried out to ensure that the material properties are not exceeded during the testing. it is found that wind tunnel testing is a useful way of determining experimentally the performance of wind turbines in order to pred...
This paper presents blade root bending moment measurements of a horizontal-axis tidal turbine for... more This paper presents blade root bending moment measurements of a horizontal-axis tidal turbine for planar oscillatory motion, conducted in a stationary water towing tank. By comparing the measurements with quasi-steady reconstructions for both single and multiple frequency oscillatory motion, the bending moment was shown to be sensitive to both frequency and amplitude, as well as to the mean tip-speed ratio. The unsteady loads associated with the separation of the flow and dynamic stall are shown to be of considerably greater importance than those which are already present for attached flow, such as added mass and dynamic inflow. A linear model fit to the unsteady bending moment also indicates that the inertia contribution is relatively small. For cases where attached flow exists over the majority of the load cycle, these reconstruction methods are likely to be sufficient to obtain a reasonable prediction of the root out-of-plane bending moment. However, turbines whose blades are likely to...
When the future wind direction is uncertain, the tactical decisions of a yacht skipper involve a ... more When the future wind direction is uncertain, the tactical decisions of a yacht skipper involve a stochastic routing problem. The objective of this problem is to maximise the probability of reaching the next mark ahead of all the other competitors. This paper describes a system that models this problem. The tidal current at any location is assumed to be predictable, while the wind forecast is based on current observations. Boat performance in different wind conditions is defined by the output of a velocity prediction program, and we assume a known speed loss for tacking and gybing. The resulting computer program can be used during a yacht race to choose the optimum course, or it can be used for design purposes to simulate yacht races between different design candidates. As an example of application, we compare strategies that minimise the average time to sail the leg, as opposed to those that maximise the probability of winning, and show how optimal routing strategies are different for leading and trailing boats. NOMENCLATURE Scalars Distance between two competitors Delay in finishing under strategy versus the perfect strategy Values that a discrete-time stochastic process can assume at the th time step Time to finish under the strategy Time to finish under the perfect strategy Discrete-time stochastic process, e.g. wind direction at the th time step th random variable uniform in (0,1) Matrices , Policy matrix at the cross-section k on the tack , where is starboard or port Transition matrix Set of matrices Strategy, i.e. set of policy matrices Operators (A) Expected value of (A) ℙ(A|B) Probability density function of A conditioned on B Abbreviations BS Boat speed RMP Race modelling program SPP Shortest path problem VMG Velocity made good 1.
In this study, the resilience of large cities and their built infrastructure in New Zealand to ex... more In this study, the resilience of large cities and their built infrastructure in New Zealand to extreme winds, is investigated by coupling the outputs of a very high-resolution, 333-m resolution, numerical weather prediction (NWP) model with computational fluid dynamics (CFD) simulations. Following an extreme wind event on 18 September 2020 in Auckland, in which two trucks travelling over the Auckland Harbour bridge tipped over and damaged the bridge structure, a CFD simulation of airflow over the bridge using the Reynolds-averaged Navier–Stokes (RANS) method and NWP wind speed forecasts as the inlet profile is conducted. The 333 m NWP forecasts were validated against four nearby observation sites, showing generally high correlations of greater than 0.8 and low mean bias (±3 m s−1) and RMSE (<3 m s−1) values. The CFD-based estimates of the mean wind speed-up over the bridge showed that the mean wind speed could increase by a factor of 1.15–1.20 in the vicinity of the road where th...
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Papers by Richard Flay