Numerical Investigation of Cowl Water Drainage in Automotive Design

Motivation Improper drainage of cowl water (accumulated at the base of the windshield) leads to critical issues in automotive design. Early-phase evaluation of drainage efficiency is critical to avoid costly late-stage design revisions and warranty issues. Traditional physical testing methods are often time-intensive, costly and limited in scope. Therefore, leveraging simulation-driven optimization enables proactive prediction of failure modes and accelerates robust design validation. The Problem Inadequate cowl drainage causes: 1. HVAC system degradation due to moisture ingress (mold growth, blower motor failure). The accumulated water can also enter the cabin. 2. Rust and corrosion in the cowl panel, windshield frame, and adjacent electronics due to accumulation of stagnant water Methodology We investigated multiple design strategies to enhance cowl drainage performance. The following approaches were studied by using STAR-CCM+: 1. Multiphase volume of fluid (VOF) Simulation - To track water flow behavior and identify leakage paths under static/dynamic conditions 2. Drain Tube Optimization - Testing variations in diameter, shape (round/oval/rectangular), and location 3. Geometric Modifications - Including baffle redesigns and slope adjustments to prevent water stagnation Results The optimized design demonstrated an improvement in water drainage efficiency relative to the baseline configuration. Other key findings are: 1. Drainage bottlenecks due to insufficient slope or clog-prone drain geometries 2. HVAC leakage paths when water levels exceeded cowl baffle heights 3. Simulation accurately predicted water film behavior thereby helping identify high risk zones for corrosion Conclusion Digital evaluation using STAR-CCM+ enabled early detection of cowl drainage flaws, reducing reliance on physical tests. The VOF approach provided actionable insights into water management, design robustness and cost avoidance (preventing rust, electrical damage, and HVAC repairs). Implementing these findings enhances long-term vehicle reliability.