Unsteady aerodynamics of single and tandem wheels

Abstract

The major unsteady aerodynamic forces and major physics of a generic single wheel and tandem wheels are studied for the first time using wind tunnel tests. The wind-tunnel tests are performed in the 2.1 m × 1.5 m wind tunnel at the University of Southampton. The tandem-wheel configuration consists of two in-line wheels that can be tested at different inter-axis distances and various installation angles. A vibration test is performed in situ on the model assembly to validate the unsteady-load measurements. Mean and unsteady aerodynamic loads and on-surface pressures are measured. Particle Image Velocimetry is used to acquire the velocity fields in the wake downstream of the model and surface oil-flow technique is used to identify the flow features on the surface of the wheels. Proper Orthogonal Decomposition is also used to characterise the wake in terms of unsteady fluctuations. The results of the experiments on the tandem wheels show that higher values of inter-axis distance correspond to slightly higher total mean drag coefficients and remarkably lower drag coefficient RMS values. Higher installation angles are associated with higher mean drag coefficients but generally lower fluctuations of the force coefficients. Non-zero mean lift coefficients are found for low inter-axis distance configurations at zero installation angle. The flow on the single wheel and on the front wheel of the tandem wheels is affected by laminar-turbulent transitional features. The vortical structures past the tandem wheels consist of four vortices that detach from the tyre shoulders of the front wheel and interact with the rear wheel. The study and obtained databases contribute to the general understanding of the complex flow and help to improve engineering predication of the gear aerodynamic loads.

A Detailed Numerical Study on Aerodynamic Interactions of Tandem Wheels on a Generic Vehicle

“…Interactions between tandem cylinders have been also investigated in two-dimensional studies [32][33][34][35][36], showing that bodies trailing a leading body experience a drag reduction. Though Spagnolo et al [37,38] documented the vortex interaction caused by the laminarturbulent transition of the leading wheel for a landing gear with extremely small wheel spacing, the wheels were exposed to the external flow and not entirely representative of automotive flows. Hence, a brief comparison of vortex structures was conducted for tandem Fackrell wheels for a single wheel spacing of 0.5 d [39].…”

Interaction Noise from Tandem Landing Gear Wheels with Hub and Rim Cavities

“…9 The downstream cylinder was demonstrated to be the dominant noise source, which is characterised with tonal noise at the shedding frequency. For a typical landing gear, the separation distance of the tandem wheels is between 1.1D and 1.5D, 10 and in such a range, the shear layer from the upstream cylinder is expected to reattach on the downstream cylinder, 11,12,13,14 and no regular shedding can be observed. Additionally, wheels can be considered as circular cylinders of short aspect ratios, the flow field surrounding which is more complex compared to the large aspect ratio circular cylinders.…”

“…Thus, the tandem landing gear wheels noise is expected to be more broadband. Spagnolo et al experimentally 10 and numerically 15 studied the aerodynamic loads of a tandem wheel case, with three separation distances, i.e. 1.1D, 1.3D and 1.5D.…”