A Simulation Methodology for Rainwater Ingress into Vehicle HVAC Cowl Box with Design Improvement

The main design objectives to be achieved in the design of HVAC cowl box includes minimizing the pressure drop and eliminating the chances of water ingress in HVAC. There are CFD tools available to study the cowl box pressure drop. However, methods available to study rain water ingress in HVAC are expensive in both mesh preparation and computational time. Using SPH (Smooth Particle based Hydrodynamics) based Preonlab tool, an attempt has been made in this work to study the design improvements of HVAC cowl box to eliminate the chances of flooding during raining. ANSYS FLUENT tool used to study the pressure drop of each design. The simulation aims to investigate the pressure drop in the cowl box and the amount of water intrusion into the HVAC module. L₉ orthogonal array (factorial study) conducted to study the factors influencing the cowl box pressure drop. Inlet area, drain area and outlet area are the factors considered. Designs with segregated airflow path (adding inner duct) in the cowl box eliminated the chances of water ingress. However, because the flow path is obstructed, the pressure drop increased. A new methodology is proposed in the design of cowl box with due consideration of air side pressure drop and water ingress. The current methodology offers valuable insights into design.