Flow Visualization Study of an HVAC Module Operated in Water

Centrifugal blowers serve as the primary source of airflow and aero-acoustic noise in automotive HVAC modules. Flow field measurements inside blowers indicate very complex flow patterns. A detailed flow visualization study was conducted on an actual HVAC fan module operated in water under dynamically similar conditions as those in air with the purpose of studying the complex flow patterns in order to improve the aerodynamic performance of the fan/scroll casing and diffuser components. Fan-scroll/diffuser interaction was also studied as function of fan speed.

Conventional and special (shear thickening) dye injection flow visualization techniques were used to study the complex 3-dimensional vortical and unsteady flow patterns that occur in typical HVAC fans. A major advantage of the flow visualization technique using shear-thickening dye is its usefulness in high the Reynolds number flows that are typically encountered inside HVAC modules. An additional advantage of this dye injection technique is that it can be used with different colored dyes to show regions of flow mixing and track unsteady flow features. Using water as the medium for model testing, the scaling laws indicated that a 1 to 1 scale model was sufficient for the proper application of low speed flow visualization techniques.

The experimental testing identified both qualitatively and quantitatively flow structures possibly responsible for noise augmentation and loss of aerodynamic efficiency. Flow visualization was able to indicate the large-scale flow patterns through the blower. It also clearly showed areas of flow separation (which is the major cause of aerodynamic inefficiency and noise production) and recirculation within the blower housing.