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Flow Around Automobiles

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The flow around five very different types of automobiles   (Please click on the icons !)   =   veteran car     ==>   sports car     ==>   cabriolet     ==>   bionic car     ==>   racing car     =   approximately two-dimensionally calculated, is displayed here. The pictures were computed with a 2D-Navier-Stokes-Solver:   for turbulent flow corresponding k,ε-turbulence model, velocity 100 km/h in air at 20 C and 1 bars, discretized in 400 × 300 points (at racing car because of the small profiles with 1200 × 900 points), and the boundary conditions:   inflow left, outflow right, no-slip below, slip above.

scale   veteran car
scale   sports car
scale   cabriolet
scale   bionic car
scale   racing car

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space The upper picture lineup shows the streamlines as well as the color-coded stream function Ψ. There are to see strong vorticity regions particularly after veteran car. The under picture lineup illustrates the static pressure in form of isobars and as color-coded pressure distribution from total pressure 1.01783 bar at red , across the atmospheric pressure 1.01325 bar at yellow , up to 1 bar and slightly under it at blew. In all cases the static pressure in stagnation point is alike the total pressure and maximum. Above and after each automobile low-pressure prevails. The narrower the isobars the stronger pressure drop is.

The difference between overpressure in front of automobile and low-pressure behind it marks the drag coefficient CW , which generally will get by a wind tunnel force measurement; below the CW-values are given according manufacturer information. For a BionicCar it should have measured the exciting small CW-value of 0.095. With program   Drag.c   resp. Drag.f   in folder "Tools" was tried to calculate the CW-value by integration of static pressure above the automobile contour. The numerical values 1.54 / 0.60 / 0.72 / 0.67 / 0,01 were calculated for these automobile types with a discretization in 600 × 300, respectively at racing car with 1200 × 900 points. The finer the discretization the smaller CW-values, but the longer computation takes.


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