Porosity Calculator (Porosity coefficient for CFD)

17.06.2015

KULI-System

Necessary modules: KULI advanced + KULI optimize

KULI File, 59 KB

**With this model the porosity coefficients for the air side resistance of a radiator can be calculated. This makes it easier to use the same air side resistance of a radiator in KULI and in CFD.**

In standard underhood CFD calculations the heat exchangers (radiator, charge air cooler, condenser, etc.) are modeled as porous media. If a radiator is available as a KULI file, then this KULI model can be used to obtain the required coefficients which define the resistance of the radiator in the CFD model. In StarCCM+© (from cd-adapco) the resistance is defined in the following way:

delta p / L = alpha * v^2 + beta * v

where delta p is the static air side pressure difference, L is the depth of the radiator, v is the velocity perpendicular to the radiator surface, and alpha and beta are the coefficients that need to be evaluated. The KULI model makes a parameter variation for the velocity, where the lower and upper bounds can be specified as constants (they are predefined with 1 and 10 m/s, which is a reasonable range for most applications). The velocity is converted into a volume flow with the help of the width and height of the radiator. An analysis controller is used to calculate the sum of the deviations between simulated pressure difference at the component and the pressure difference calculated with the approximation formula. The sum of all these deviations is then put into an optimization target which is set to be a minimum. The coefficients alpha and beta serve as optimization parameters. (Usually these coefficients are in a range of up to 1000 or at most 1500, so this can be taken as a range for the optimization parameters.)

The example can easily be modified to include different formulas for porosities as used by other CFD codes.

Usable from release: KULI 10.1Necessary modules: KULI advanced + KULI optimize

KULI File, 59 KB