Noise Reduction in Over-molded HVAC Module Doors Industrial Sponsor: Goal: Create a component and or system design that will eliminate any acoustic signal audible to automobile passengers. By-Pass Temperature Door Specs. Mfg. Process: Injection Over-molding Door Material: Hard Plastic Seal Material: 35 Grade Sanoprene Outer Dimensions: 27 x 20 x 5 [mm] (length x width x seal thickness) Problem Statement Result: Eliminated acoustic whistling with the experimentally proven Tear-Drop Design. During the initial 5-15% rotation of an HVAC by- pass temperature door from its sealed to unsealed position, a whistling noise is generated from air flowing between gaps created by door’s seal and HVAC housing in panel full cold mode. Existing HVAC Door Module Provided by: BEHR Design Recommendation Why it Works Team Members: Aaron Kleinow (Industrial Advisor), Dr. Giles Brereton (MSU Faculty Advisor), Bethany Danielski, Andrew W. Siefert, and Matt Warner Over-molded By-Pass Temp. Door Airflow to Passengers A-Side B-Side Whistling Is Audible to Automobile Passengers oA-side seal edge receives Tear-Drop Extension. oTotal Added Volume – mm 3. oEasily Manufactured with existing Injection Over- molding with minimal retooling oInexpensive and easily mass produced. Existing Door Waved Design Ribbed Design Benchmark Values V max =28.5 m/s V avg = 10.3 m/s Waved Results V max = 28.8 m/s V avg = 10.4 m/s Ribbed II. Results V max = 21.8 m/s V avg = 8.9 m/s Previous Investigation Initial investigation focused on decreasing the air velocity between the by-pass door and HVAC housing Whistling Still Remained! Stimulated Vortex Generation and Sound Radiation ο Reliable and robust ο Minimal number of parts ο Adaptive to existing platform ο Low Cost ο Service life exceeds 10 years ο Ease of Manufacture ο Available for mass production ο Size must remain within x 50.8 x 19.0, +/- 0.2 [mm] ο Minimal effect on housing ο Eliminate the acoustic whistle oHousing oHigh Flow Velocity oFlow Separation oVortex Drift Velocity (V d ) = 0.8 x FlowVelocity A-Side By- Pass Door Resonance Conditions for Stimulated Vortex Generation and Sound Emission Time for a vortex to reach Housing = L/V d Vortex Shedding Period T=5d/V Time for pressure pulse to reach door= L/c Condition for Resonance is L/V d =5nd/V Total time= L/V d + L/c  L/V d Resonance Occurs when: L=4nd Resonant Sound Waves Whistling Noise Reducing Tear-Drop Design Tear-Drop Design Increased Seal Tip diameter: oChanges the conditions of resonance for Stimulated Generation. oMinimizes boundary layer separation by increasing seal-tip radius oMinimizes vortex formation thus resonant feedback. 1.Air boundary layers encounter: i) Large pressure gradient between the plenum and channel. ii) Door-seal’s small tip diameter. 1B. The turbulent boundary layer separates from the door and forms air vortices and sound. 2. Sound (Pulsed Pressure) is reflected from the housing providing a feedback mechanism to stimulate the formation of air vortices. 3. Feedback increases the intensity of emitted sound creating the acoustic whistle. Experimental Validation Clay Molding oConceptual designs were modeled by molding clay to the existing door platform. oDoors were tested in HVAC under operation conditions producing whistling. oResults were analyzed and the best design was optimized. oTear-Drop Design was validated by tested prototype (not pictured) Clay Molded By-Pass Door Existing Door Platform Clay Molding Existing By-Pass Door HVAC Unit Design Requirements