Computational Fluid Dynamics Study on the Effect of Using an Under-Tray Addition to Motorsport

The aim of this study is to study the effect of deploying an under-tray to a Formula Society of Automotive Engineers (FSAE) racecar for the Washington University FSAE racing team (WashU Racing) through Computational Fluid Dynamics (CFD). The under-tray geometry was developed to cover the bottom of an FSAE racecar by members of the WashU Racing team (a college FSAE team). The under-tray was added to the existing geometry of the Formula racecar; a mesh around it was then generated using the mesh generator in ANSYS and CFD simulations were performed using ANSYS Fluent to determine lift and drag values for the car in the presence of under-tray. Processing of numerical data was done using ANSYS EnSight. The center of pressure of the car was found analytically. All physical quantities obtained with inclusion of under-tray were compared to those obtained for the model of the car without the under-tray. It was found that under-tray slightly increases the lift coefficient and significantly decreases the drag coefficient. The study shows that the inclusion of an under-tray would be a worthwhile addition to the FSAE car

Surface Structure of Liquid Metals and the Effect of Capillary Waves: X-ray Studies on Liquid Indium

We report x-ray reflectivity (XR) and small angle off-specular diffuse scattering (DS) measurements from the surface of liquid Indium close to its melting point of $156^\circ$C. From the XR measurements we extract the surface structure factor convolved with fluctuations in the height of the liquid surface. We present a model to describe DS that takes into account the surface structure factor, thermally excited capillary waves and the experimental resolution. The experimentally determined DS follows this model with no adjustable parameters, allowing the surface structure factor to be deconvolved from the thermally excited height fluctuations. The resulting local electron density profile displays exponentially decaying surface induced layering similar to that previously reported for Ga and Hg. We compare the details of the local electron density profiles of liquid In, which is a nearly free electron metal, and liquid Ga, which is considerably more covalent and shows directional bonding in the melt. The oscillatory density profiles have comparable amplitudes in both metals, but surface layering decays over a length scale of $3.5\pm 0.6$ \AA for In and $5.5\pm 0.4$ \AA for Ga. Upon controlled exposure to oxygen, no oxide monolayer is formed on the liquid In surface, unlike the passivating film formed on liquid Gallium.Comment: 9 pages, 5 figures; submitted to Phys. Rev.