An Alternative Method to Improve the CFD Predictions for Vehicle Front End Flow 2015-26-0199
In vehicle Front End Flow (FEF) analysis, the basic objective is to predict the mass flow/velocity of air at radiator inlet with constant fan rotation. In general, the Multiple Reference Frame (MRF) model is used to model the fan. The flow velocity distribution at radiator inlet due to fan rotation should be uniform in circumferential direction whereas, it should vary in radial direction depending upon the blade geometry. However, the drawback with MRF model is that, it gives higher velocities near radiator inlet at regions corresponding to the fan blades and lower velocities at other regions, which is not realistic. This issue is more predominant when the vehicle is at low speeds or when radiator is placed at mid or back of the vehicle or the fan is having less number of blades. In order to nullify this uneven velocity distribution at radiator inlet, Mixing Plane (MP) approach was used in addition to the MRF model. Mixing plane approach is used to get circumferential average velocity on a boundary just before fan inlet. This effect will be felt on radiator inlet, so that the velocity at radiator inlet will also be circumferentially averaged.
In the present work, FEF analysis for a light transport vehicle (LTV) was carried out at various operating conditions with Fan rotation modeled by only MRF model and the combination of MRF plus Mixing plane model. The experimental test was also carried out in test track by placing the anemometers in front of radiator inlet to measure the average velocity magnitude. From the testing and simulation results, it is found that combination of MRF and mixing plane model gives more realistic pattern of velocity distribution at radiator inlet.