Aerodynamics research in cycling has underpinned innovative bicycle design, new refined riding positions and optimised rider apparel. There has been a rise in the level of aerodynamics research focused on cycling since the turn of the millennium, enabled by significant increases in computational power and the availability of software/hardware. However, cycling research has not yet fully embraced para-cycling, with limited studies conducted on the aerodynamic performance of hand-cyclists and other para-cyclists. Wind tunnel experiments and computational fluid dynamics simulations were conducted in this research for the analysis of hand-cycling aerodynamics, focused on competitive H1–H4 category hand-cyclists. A quarter-scale representative geometry of a hand-cyclist was used in high-speed wind tunnel experiments. The accuracy of the simulations performed with the three-dimensional Reynolds-averaged Navier–Stokes equations was found to be dependent on the turbulence model choice and near-wall grid resolution. Computational fluid dynamics simulations predicted the magnitude of the drag and lateral forces to an accuracy of 2.5% using the shear stress transport [Formula: see text] turbulence model. This study also presents the impact of wheel diameter and disc wheels on hand-cycling aerodynamics via computational fluid dynamics simulations, providing a deeper understanding of the aerodynamic characteristics unique to the hand-cycling discipline in the sport of competitive cycling. Drag reductions of up to 8.9% were found when utilising 20-inch diameter spoked wheels, opposed to the 26-inch wheels. Variations in wheel diameter between the front and rear wheels were found to have a significant impact on the C D A in part through altering the pitch angle of the hand-cycle.
Pedestrian wind comfort is analyzed for a new shopping street area in Eindhoven city center. Wind nuisance is especially perceived around a tower of 105 m high, at an intersection of two streets. The Dutch wind nuisance standard NEN 8100 combined with CFD (Computational Fluid Dynamics) simulations is used to assess the pedestrian wind comfort. Special care is given to the grid generation and comparison of the CFD simulations with on-site wind speed measurements. The effectiveness of a series of incremental remedial measures is analyzed. A large canopy is shown to be successful in bringing the wind comfort to an acceptable level.
Accurate Computational Fluid Dynamics (CFD) simulations of Atmospheric Boundary Layer (ABL) flow are essential for a wide range of applications, including atmospheric heat and pollutant dispersion. An important requirement is that the imposed inlet boundary conditions should yield vertical profiles that maintain horizontal homogeneity (i.e. no streamwise gradients) in the upstream part of the computational domain for all relevant parameters, including temperature. Many previous studies imposed a uniform temperature profile at the inlet, which has often led to horizontal inhomogeneity of the temperature profile. This study presents a new temperature inlet profile that can yield horizontal homogeneity for neutral and near-neutral ABL conditions when used in combination with the Standard Gradient Diffusion Hypothesis (SGDH) and a temperature wall function. The horizontal homogeneity by this profile is verified by 2D Reynolds-Averaged Navier-Stokes (RANS) CFD simulations performed with the standard k-ε turbulence model and the SGDH. The approach in this paper can be extended to other types of wall functions and other RANS closure schemes for Reynolds stresses and turbulent heat fluxes.
Mixing ventilation flows consisting of interacting jets (as in airplane cabins) can be highly turbulent and unsteady. The aim of this study is to assess the performance of Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) simulations in predicting the isothermal flow resulting from interacting wall jets in a generic enclosure. Three k-e turbulence models are employed: the standard k-e and RNG k-e models with near-wall modelling, and a low-Reynolds number version of the k-e model. Comparison of the simulations with (time-averaged) PIV measurements reveals a good overall prediction of the velocity and turbulent kinetic energy by all models. Local deviations from the experiments can be attributed to the inability of the steady RANS method to capture the unsteady jet interaction.
Vertical axis wind turbines (VAWT) have recently received growing interest for application in urban environments due to their omni-directional capabilities. However, further research is required to optimize their performance. The central shaft is an inseparable part of a VAWT whose effect on turbine performance is currently not known. In this paper the effect of the shaft on the power coefficient (CP) and thrust coefficient (C-T) of a VAWT is studied for different shaft-to-turbine diameter ratios (δ) and normalized surface roughness heights (ks/ds) using unsteady Reynolds-averaged Navier-Stokes (URANS) Computational Fluid Dynamics (CFD) simulations validated with experiments. The turbine power loss is found to increase by 3.5% by changing δ from 4 to 12%. This is due to the higher width of the shaft wake: blades pass through a larger region with lower velocity in the downwind area. The turbine CP is improved by up to 2% for a rough shaft (ks/ds = 0.08) due to a shift in the flow regime over the shaft from sub-critical to critical. The findings of the present study mean that for Reynolds numbers relevant to small VAWTs, roughening the shaft is an effective strategy to partially regain the power loss related to its presence.
Due to growing interest in wind energy harvesting offshore as well as in the urban environment, vertical axis wind turbines (VAWTs) have recently received renewed interest. Their omni-directional capability makes them a very interesting option for use with the frequently varying wind directions typically encountered in the built environment while their scalability and low installation costs make them highly suitable for offshore wind farms. However, they require further performance optimization to become competitive with horizontal axis wind turbines (HAWTs) as they currently have a lower power coefficient (CP). This can be attributed both to the complexity of the flow around VAWTs and the significantly smaller amount of research they have received. The pitch angle is a potential parameter to enhance the performance of VAWTs. The current study investigates the variations in loads and moments on the turbine as well as the experienced angle of attack, shed vorticity and boundary layer events (leading edge and trailing edge separation, laminar-to-turbulent transition) as a function of pitch angle using Computational Fluid Dynamics (CFD) calculations. Pitch angles of −7° to +3° are investigated using Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations while turbulence is modeled with the 4-equation transition SST model. The results show that a 6.6% increase in CP can be achieved using a pitch angle of −2° at a tip speed ratio of 4. Additionally, it is found that a change in pitch angle shifts instantaneous loads and moments between upwind and downwind halves of the turbine. The shift in instantaneous moment during the revolution for various pitch angles suggests that dynamic pitching might be a very promising approach for further performance optimization.
