Screen characterization under fan induced swirl conditions

In this paper, loss coefficients are determined for a fine and a coarse EMC screen placed in a swirling flow. In an axisymmetric swirl generator test rig the screen performance is measured under well-defined swirling conditions. Based on velocity and pressure measurements on one hand and on axial and tangential momentum balances on the other, directional loss coefficients are obtained. It is shown that in this way in-plane coefficients can be accurately determined. In contrast, the normal component can more accurately be determined in a basic wind-tunnel setup. Subsequently, the obtained coefficients are used in a commercial computational fluid dynamics code using a volume resistance model for the screens. Validation of the numerical results against fan measurements shows that using in-plane coefficients is superior to one-dimensional models. Indeed, in the former case the effect of the screen on the tangential velocity component is well predicted by the model, whereas for the latter only the axial velocity components are affected. Finally, a full rack simulation reveals that component temperatures strongly depend on local flow phenomena. Therefore, it can be concluded that fan induced swirl should always be modeled and that screen models should account for in-plane loss coefficients