Pictures

Pictures from Research Projects

Acoustic Treatment System

The acoustic treatment system consists of 20 inch deep boxes constructed from medium density fiberboard, stuffed with fiberglass and sealed with acoustic foam that are attached to the tunnel test section. The flow surface is created using nearly acoustically transparent sheets of heavy gauge screen. Figure 1 presents a schematic of the test section with acoustic treatment boxes attached.
The system has proven to be quite successful when recently used in the measurement of unsteady surface pressure on an airfoil in turbulence. An internal view of the tunnel test section with treatment installed is shown in figure 2.

Acoustic measurements were also performed to validate the improvement in acoustic quality at various flow speeds. The acoustic measurements of Larssen and Devenport (1999) made with the test section in solid wall configuration are compared with similar measurements in the acoustic treatment configuration. The pressure sound levels of both measurements are presented in figure 3 for a flow speed of 30m/s. Considerable attenuation of the ambient sound field occurs between 10 and 500Hz with as much as 50dB of attenuation occurring between 10 and 20Hz. The spectra converge and crossover at 500Hz with the acoustically treated spectrum rising up to 10dB above the solid wall spectrum. The increase in spectral level above 500Hz with the acoustic treatment in place is likely the result of flow interaction with the screen. Currently, plans are underway to improve the flow surface quality, perhaps with pre-stretched Kevlar.

Current and recent research projects being conducted in the Stability Wind Tunnel by faculty from the Center for Renewable Energy and Aerodynamic Testing (CREATe) include:

• Aerodynamics and Aeroacoustics of Wind Turbine Blade Sections
• Aeroacoustics of a Rotor Ingesting Inhomogeneous Turbulence
• Bio-Inspired Trailing Edge Noise Control
• The Wall Pressure Spectrum of Rough Wall Boundary Layers
• The Aeroacoustics of Step Flows at High Reynolds number
• Data Analytics for Large Sensor Systems
• UAV Aeroacoustics
• Facility and Instrumentation research

More information can be found on the CREATe website: http://www.create.centers.vt.edu/