Studies on Aero-Acoustics Noise Prediction of MAC Unit Using Computational Modelling 2016-01-0218

In an automotive air conditioning, aero-acoustic noise originating from HVAC (Heating Ventilation and Air Conditioning) unit is one of the major concerns for the customer satisfaction. “Fan blower excessive noise” is one among the top issues for all automotive manufacturers. In this paper, a 3D computational analysis is carried out for a passenger car HVAC unit to predict the noise originated from the HVAC unit. HVAC modeling is done using uni graphics and ANSA and the analysis is carried out using the commercial CFD software STAR CCM+. The inputs for the analysis are the airflow at HVAC Inlet, blower speed and the pressure drop characteristics of evaporator, filter and heater core. The computational model is done by considering the blower region as MRF (Moving Reference Frame) and the air flow is considered incompressible. DES (Detached Eddy Simulation) model is used to resolve the eddies generated by the turbulent flow. The pressure is sampled at measurement point which is processed to give the sound pressure level. The result predicted is the sound pressure level in dBA measured at 50 cm away from HVAC outlet in vent mode. Test is carried out to compare the simulation results. Test is carried out by placing the HVAC unit in the anechoic chamber with the inlet air flow of 450 m³/hr, blower rpm of 4100 and the sound pressure levels are measured using a microphone placed in central position in front of HVAC outlet air opening, 50 cm away from the opening and at an height from ground corresponding to the center of the opening. Simulation results correlate well with the test results and the error is within 10%. This methodology can be used to check the HVAC noise during early design stages resulting in optimized design and better customer satisfaction. Successful validation of the model has led to the application of this methodology in the pre-production stage of new programs during the design phase and it helps to reduce the physical testing.