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Research Papers: Flows in Complex Systems

# Transient Simulation of the Aerodynamic Response of a Double-Deck Bus in Gusty Winds

[+] Author and Article Information
Hassan Hemida

Division of Fluid Dynamics, Department of Applied Mechanics, Chalmers University of Technology, SE-41296 Gothenburg, Swedenhemida@chalmers.se

Siniša Krajnović

Division of Fluid Dynamics, Department of Applied Mechanics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden

J. Fluids Eng 131(3), 031101 (Feb 04, 2009) (10 pages) doi:10.1115/1.3054288 History: Received May 19, 2008; Revised October 20, 2008; Published February 04, 2009

## Abstract

The purpose of the research reported in this paper was to investigate the aerodynamic response of a double-deck bus in gusty winds using a detached-eddy simulation (DES). The bus was subjected to three different scenarios of wind gusts: gust in a wind tunnel, gust in a natural wind, and gust behind the exit of a tunnel. The proposed scenarios of gusts are in the time domain and take into account the dynamic behavior of natural winds. The Reynolds number of the flow, based on the time-averaged speed of the side wind and a reference length of $0.1 m$, was $1.3×106$. Detailed transient responses of the aerodynamic coefficients and flow structures were investigated. Good agreement was found between the DES results and the available experimental data. A comparison between the influence of the different gust scenarios on the aerodynamic coefficients shows that the gust behind the exit from a tunnel has a stronger influence on the aerodynamics than the other gust scenarios. Moreover, the influence of the gusts on the time history of aerodynamic coefficients is found to be limited to the period of the gust.

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## Figures

Figure 1

The shape of the bus model: (a) view from the side and front and (b) view from the bottom of the bus showing the beams, wheels, and axles

Figure 2

Computational domain: (a) cross section of the tunnel and (b) dimensions of the computational domain

Figure 3

The computational mesh: (a) the mesh at the inlet plane, (b) the mesh around the axles, (c) the mesh around the wheels, and (d) the mesh around the beams and the support

Figure 4

Conventional directions for the aerodynamic coefficient with respect to the side wind direction

Figure 5

Comparison of the DES aerodynamic coefficients and the experiment: (a) drag coefficient, (b) lift coefficient, (c) side force coefficient, and (d) yaw moment coefficient

Figure 6

Local pressure coefficient: (a) the line along which the pressure coefficient is drawn showing the starting point and (b) the pressure coefficient against the length of the line

Figure 7

Scenarios for wind gusts: (a) gust for wind tunnel simulation, (b) gust for open air simulation, and (c) gust at the exit of a tunnel

Figure 8

Gust in a wind tunnel. Aerodynamic response during the gust time normalized by the steady side wind velocity: (a) drag coefficient, (b) side force coefficient, and (c) yaw moment coefficient.

Figure 9

Gust in a wind tunnel. Aerodynamic response during the gust time normalized by transient side wind velocity: (a) drag coefficient, (b) side force coefficient, and (c) yaw moment coefficient.

Figure 10

Surface mesh in the computational domain of the open air and exit of tunnel simulations

Figure 11

Open air gust. Aerodynamic response during the gust time normalized by the speed of the bus: (a) drag coefficient, (b) lift coefficient, and (c) yaw moment coefficient.

Figure 12

Gust at the exit of a tunnel. Horizontal plane at the mid height of the bus colored by velocity magnitude.

Figure 13

Gust at the exit of the tunnel. Aerodynamic response of the bus during the gust normalized by the speed of the bus: (a) drag coefficient, (b) lift coefficient, and (c) side force coefficient.

Figure 14

Instantaneous flow structures around the sides of the bus in a tunnel. (a) and (b) show snapshots at different instants. The view is from the rear of the bus.

Figure 15

Instantaneous flow structures on the top and side faces of the bus. (a) and (b) show snapshots at different instants.

Figure 16

Gust at the exit of a tunnel. Aerodynamic moment response of the bus during the gust normalized by the speed of the bus and one unit length: (a) pitching moment coefficient, (b) rolling moment coefficient, and (c) yaw moment coefficient.

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