Noise Reduction in Over-molded HVAC Module DoorsIndustrial 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 ModuleProvided 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

o A-side seal edge receives Tear-Drop Extension.

o Total Added Volume – 441.5 mm3.

o Easily Manufactured with existing Injection Over-molding with minimal retooling

o Inexpensive and easily mass produced.

Existing Door

Waved Design

Ribbed Design

Benchmark Values

Vmax =28.5 m/s

Vavg= 10.3 m/s

Waved Results

Vmax = 28.8 m/s

Vavg= 10.4 m/s

Ribbed II. Results

Vmax = 21.8 m/s

Vavg= 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 robustο Minimal number of parts

ο Adaptive to existing platformο Low Cost

ο Service life exceeds 10 yearsο Ease of Manufacture

ο Available for mass productionο Size must remain within 101.6 x 50.8 x

19.0, +/- 0.2 [mm]

ο Minimal effect on housingο Eliminate the acoustic whistle

oHousing

oHigh Flow Velocity

oFlow Separation

oVortex Drift Velocity (Vd)

= 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/Vd Vortex Shedding Period T=5d/V

Time for pressure pulse to reach door= L/c Condition for Resonance is L/Vd=5nd/V

Total time= L/Vd + L/c L/Vd Resonance Occurs when: L=4nd

Resonant SoundWaves

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

radiusoMinimizes 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

o Conceptual designs were modeled by molding clay to the existing door platform.

o Doors were tested in HVAC under operation conditions producing whistling.

o Results were analyzed and the best design was optimized.

o Tear-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