Slipstream

Abstract: In this paper, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are used to extract the most dominant flow structures of a simulated flow in the wake of a high-speed train ...

Abstract: The results of an experimental study of the diffraction of shock waves on plane-walled convex corners are given for a Mach number range from 1·0 to 5·0. The behaviour of the disturbances produced in the region perturbed by the corner are discussed. It is shown that the position of the slipstream and tail of the Prandtl-Meyer fan, and the velocities of the contact surface and second shock become independent of corner angle for angles greater than 75°. Comparisons with theoretical predictions of Jones, Martin & Thornhill (1951) and Parks (1952) are included. In most cases fair agreement is obtained.

Abstract: This paper describes the results of experimental work to determine the structure of the slipstream and wake of a high speed train. The experiments were carried out using a 1/25th scale model of a four-coach train on a moving model rig (MMR). Flow velocities were measured using a rake of single hot films positioned close to the model side or roof. Tests were carried out at different model speeds, with and without the simulation of a crosswind. Velocity time histories for each configuration were obtained from ensemble averages of the results of a number of runs. A small number of particle imaging velocimetry (PIV) experiments were also carried out, and a wavelet analysis revealed details of the unsteady flow structure around the vehicle. It was shown that the flowfield around the vehicle could be divided into a number of different regions of distinct flow characteristics: an upstream region, a nose region, a boundary layer region, a near wake region and a far wake region. If the results were suitabl...

Abstract: The slipstream of high-speed trains is investigated in a wind tunnel through velocity flow mapping in the wake and streamwise measurements with dynamic pressure probes. The flow mapping is used to explain the familiar slipstream characteristics of high-speed trains, specifically the largest slipstream velocities in the near wake. Further, the transient nature of the wake is explored through frequency and probability distribution analysis. The development of a wind tunnel methodology for slipstream assessment is presented and applied, comparing the output to full-scale results available in the literature. The influence of the modelling ballast and rail or a flat ground configuration on the wake structure and corresponding slipstream results are also presented.

Abstract: The production of vorticity or circulation production in shock wave diffraction over sharp convex corners has been numerically simulated and quantified. The corner angle is varied from 5° to 180°. Total vorticity is represented by the circulation, which is evaluated by integrating the velocity along a path enclosing the perturbed region behind a diffracting shock wave. The increase of circulation in unit time, or the rate of circulation production, depends on the shock strength and wall angle if the effects of viscosity and heat conductivity are neglected. The rate of vorticity production is determined by using a solution-adaptive code, which solves the Euler equations. It is shown that the rate of vorticity production is independent of the computational mesh and numerical scheme by comparing solutions from two different codes. It is found that larger wall angles always enhance the vorticity production. The vorticity production increases sharply when the corner angle is varied from 15° to 45°. However, for corner angles over 90°, the rate of vorticity production hardly increases and reaches to a constant value. Strong shock waves produce vorticity faster in general, except when the slipstream originating from the shallow corner attaches to the downstream wall. It is found that the vorticity produced by the slipstream represents a large proportion of the total vorticity. The slipstream is therefore a more important source of vorticity than baroclinic effects in shock diffraction.