Blockage Correction and Reynolds Number Dependency of an Alpine Skier: A Comparison Between Two Closed-Section Wind Tunnels

The purpose of this study was to investigate the impact of blockage effect and Reynolds Number dependency by comparing measurements of an alpine skier in standardized positions between two wind tunnels with varying blockage ratios and speed ranges. The results indicated significant blockage effects which need to be corrected for accurate comparison between tunnels, or for generalization to performance in the field. Using an optimized blockage constant, Maskell’s blockage correction method improved the mean absolute error between the two wind tunnels from 7.7% to 2.2%. At lower Reynolds Numbers (<8 × 105, or approximately 25 m/s in this case), skier drag changed significantly with Reynolds Number, indicating the importance of testing at competition specific wind speeds. However, at Reynolds Numbers above 8 × 105, skier drag remained relatively constant for the tested positions. This may be advantageous when testing athletes from high speed sports since testing at slightly lower speeds may not only be safer, but may also allow the athlete to reliably maintain difficult positions during measurements.

Analysis of the Blockage Effect on a Cavitation Tunnel Using CFD Tools

This paper aims to analyze the tests of blockage effect on Cavitation Tunnel propellers from Institute for Technological Research, IPT, using Siemens commercial CFD (Computational Fluid Dynamics) software STAR-CCM+. The tests presented a relation between the propeller load, the tunnels geometry, the cavitation pattern and the blockage effect. This investigation is conducted in three parts. Firstly, a numerical model without the influence of the walls is conducted to investigate several numerical parameters, such as mesh and turbulence model. In the second part, the numerical model is expanded to include different cases of blockage ratio and advance ratio. A steady-state simulation is conducted, without cavitation model. The results are corrected with potential analysis of blockage correction, showing that this correction is satisfactory. In the last part, blockage simulations with cavitation model are conducted and blockage correction with cavitation is verified, resulting, again, in satisfactory results. However, it can be noted that there is a high influence of blockage ratio in the cavitation area, not contemplated in the classical blockage correction.

Experimental and Numerical Aerodynamic Analysis of a Passenger Car: Influence of the Blockage Ratio on Drag Coefficient

Experimental and numerical investigations were performed to determine the pressure distributions and the drag forces on a passenger car model. Experiments were carried out with 1/5th scale model FIAT Linea for 20% and ~ 1% blockage ratios in the Uludag University Wind Tunnel (UURT) and in the Ankara Wind Tunnel (ART), respectively. Computational fluid dynamics (CFD) analysis for 1/5th scale model with 0%, 5%, and 20% blockage ratios was performed to validate various blockage correction methods supplementary to the experimental results. Three-dimensional, incompressible, and steady governing equations were solved by STAR-CCM+ code with realizable k–ε two-layer turbulence model. The calculated drag coefficients were in good agreement with the experimental results within 6%. Pressure coefficients on the model surfaces have shown similar trends in the experimental and numerical studies. Some of the existing blockage correction methods were successfully compared in this study and predicted drag coefficients were within ± 5%. The authors propose the continuity and the Sykes blockage correction methods for passenger car models because they are very simple and practical and they can be used economically for engineering applications.