Integrated Numerical and Experimental Approach to Determine the Cooling Air Mass Flow in Different Vehicle Development Stages

This paper presents an integrated numerical and experimental approach to take best possible advantage of the common development tools at hand (1D, CFD and wind tunnel) to determine the cooling air mass flow at the different vehicle development stages.

1D tools can be used early in development when neither 3D data nor wind tunnel models with detailed underhood flow are available. A problem that has to be resolved is the dependency on input data. In particular, the pressure coefficients on the outer surface (i.e. at the air inlet and outlet region) and the pressure loss data of single components are of great importance since the amount of cooling air flow is directly linked to these variables. The pressure coefficients at the air inlet and outlet are not only a function of vehicle configuration but also of driving velocity and fan operation. Both, static and total pressure coefficient, yield different advantages and disadvantages and can therefore both be used as boundary conditions. For the characteristic pressure losses of single components in the air path, data from a predecessor can be utilized as a first approximation. The negligence of changed flow topology (flow separations or changing approach flow angles) results in a loss in accuracy. Improvements can be achieved if measurements on test benches or virtual testing of single components as well as component assemblies are integrated in the development process as early as possible. Later in development, CFD simulations of the full vehicle with detailed underhood flow and wind tunnel measurements complement the determination of the cooling air mass flow.

An example for such an integrated procedure and some selected results are presented and discussed for the Porsche Carrera.