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The flow around high speed trains

Global energy consumption due to friction and wear in the mining industry

The aerodynamic characteristics of train/vehicles under cross winds depend on not only the shapes of the vehicles but also those of infrastructures. Accordingly three kinds of wind tunnel tests were made to evaluate the aerodynamic characteristics of typical configurations of the vehicles on typical configurations of infrastructures such as bridges and embankments. The main results obtained from the wind tunnel tests are summarized below. 1. The aerodynamic side force coefficient of the vehicle increases more as the thickness of the bridge girder becomes larger. It also increases more as the roof of the vehicle becomes edgier. 2. The aerodynamic characteristics of the vehicle on the embankment depend on the distribution of the boundary layer on the ground. The aerodynamic side force coefficient of the vehicle on a high embankment is larger than that on a low embankment.

Aerodynamic Characteristics of Train/Vehicles under Cross Winds

Flow structures around a high-speed train extracted using Proper Orthogonal Decomposition and Dynamic Mode Decomposition

We investigate a hierarchy of eddy-viscosity terms in proper orthogonal decomposition (POD) Galerkin models to account for a large fraction of unresolved fluctuation energy. These Galerkin methods are applied to large eddy simulation (LES) data for a flow around a vehicle-like bluff body called an Ahmed body. This flow has three challenges for any reduced-order model: a high Reynolds number, coherent structures with broadband frequency dynamics, and meta-stable asymmetric base flow states. The Galerkin models are found to be most accurate with modal eddy viscosities as proposed by Rempfer & Fasel (J. Fluid Mech., vol. 260, 1994a, pp. 351–375; J. Fluid Mech. vol. 275, 1994b, pp. 257–283). Robustness of the model solution with respect to initial conditions, eddy-viscosity values and model order is achieved only for state-dependent eddy viscosities as proposed by Noack, Morzynski & Tadmor (Reduced-Order Modelling for Flow Control, CISM Courses and Lectures, vol. 528, 2011). Only the POD system with state-dependent modal eddy viscosities can address all challenges of the flow characteristics. All parameters are analytically derived from the Navier–Stokes-based balance equations with the available data. We arrive at simple general guidelines for robust and accurate POD models which can be expected to hold for a large class of turbulent flows.

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On the need for a nonlinear subscale turbulence term in POD models as exemplified for a high-Reynolds-number flow over an Ahmed body

LES study of the influence of the nose shape and yaw angles on flow structures around trains

Theoretical analysis of heat transfer in laminar pulsating flow

Theoretical analysis of heat transfer in a laminar pulsating flow

Detached-eddy simulation of the slipstream of an operational freight train

High-speed trains push air to the front, sides and over the top to form a train slipstream. The extension of the slipstream to the side, top and wake flow depends on train speed, train shape, ambient conditions and the environment in which the train operates. In this paper, the slipstream and wake flow of a 1/20th scale model of a simplified five-coach ICE2-shape train running in two different environments; in open air and when passing a platform, were obtained using large-eddy simulation (LES). The flow Reynolds number was taken to be 300,000; based on the speed and height of the train. The effect of the platform height on the train slipstream was investigated by performing simulations on a platform of different heights: 20, 60, 90 cm. To investigate the effect of mesh resolution on the results, two different computations were performed for the case of the flow around the train running in the open air using a different number of mesh nodes; a fine mesh consisting of 18,000,000 nodes and a coarse mesh con...

Hassan Hemida

Papers

LES study of the influence of the nose shape and yaw angles on flow structures around trains

Theoretical analysis of heat transfer in laminar pulsating flow

Theoretical analysis of heat transfer in a laminar pulsating flow

Detached-eddy simulation of the slipstream of an operational freight train

The calculation of train slipstreams using large-eddy simulation: