Screen characterization under fan induced swirl conditions

In this paper, loss coefficients for a fine and a coarse EMC screen placed in a swirling flow are determined. In an axis-symmetric swirl generator test rig the screen performance is measured under well-defined swirling conditions. Based on velocity and pressure measurements, flux tubes are identified and axial and tangential momentum balances are elaborated for small flux tubes. These balances result in directional loss coefficients. Especially the in-plane coefficients can be accurately determined. In contrast, the normal component can more accurately be determined in a basic wind-tunnel set up. Subsequently, the obtained coefficients are used in the FLOTHERM volume resistance model. The numerical results are validated against fan measurements. The effect of the screen on the tangential velocity component is very well predicted by the model.