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

Cowl Box is the first element of HVAC air passage and responsible for keeping rainwater away from blower unit without much impacting the HVAC air flow rate. Rainwater ingress to HVAC system affects passenger comfort. 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 cowl box. There are CFD tools available to study the cowl box pressure drop. However, methods available to study rain water ingress in cowl box 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 objectives of the simulation are to examine the cowl box pressure drop and water ingress quantity into the HVAC module. Designs with ‘inner duct’ in the cowl box reduced the water ingress. However, the pressure drop increased because the flow path is chocked. A new methodology is proposed in the design of cowl box with due consideration of air side pressure drop and water ingress. We conclude that present approach can provide a useful design information.