Study of the flow between the train underbody and the ballast track

The purpose of this work is to study the flow between the underbody of a high speed train and the ground, which consists of both ballast and sleepers. The flow is approximated by a turbulent Couette flow. An analytical solution of the turbulent Couette flow is proposed. Comparisons of the analytical results against wind tunnel and on track tests experiments and results of other classical models for turbulent Couette flows are made in order to validate the obtained solution. The analytical velocity profile is also compared with the corresponding one calculated with the commercial code Fluent for an idealized two-dimensional configuration. Another objective of this work is to obtain an equivalent roughness of the track made of sleepers and ballast. The results obtained enable stationary RANS simulations to be undertaken by substituting the track made of sleepers and ballast with an equivalent rough plate. This steady state analysis is not possible if the sleepers are retained. Taking into account the energy conservation, and comparing with the analytical solution, the equivalent roughness of the ballast track is obtained. The influence of the following parameters on the obtained values of the equivalent surface roughness is analyzed: height of the gap, Reynolds number and roughness of the upper wall. (C) 2011 Elsevier Ltd. All rights reserved.