Matthew S. Kuester

Flow Quality Measurements in the Klebanoff-Saric Wind Tunnel

The Klebanoff-Saric Wind Tunnel is a low-speed, closed-return facility with lowdisturbance flow capabilities suitable for boundary-layer stability and transition studies. Previously known as the Arizona State University (ASU) Transition Facility or the ASU Unsteady Wind Tunnel, the tunnel was relocated to Texas A&M University in 2005. During its subsequent reconstruction, several component modifications were introduced, including more advanced acoustic treatments, pneumatic isolation, duct reshaping, and motor-drive alterations, to further enhance flow quality and experimental control. Details regarding the tunnel capabilities, flow quality improvements and tunnel calibration are provided. Freestream turbulence and acoustic measurements are given.

Acoustic Receptivity Measurements Using Modal Decomposition of a Modified Orr–Sommerfeld Equation

Boundary-layer receptivity to acoustic disturbances plays a key role in transition from laminar to turbulent flow. Acoustic disturbances interact with strong streamwise gradients at the leading edge to create Tollmien–Schlichting waves in the boundary layer. Measurement of Tollmien–Schlichting receptivity to downstream-traveling sound is complicated by the presence of Stokes waves in the boundary layer and upstream-traveling acoustic reflections that also generate downstream-traveling Tollmien–Schlichting waves. Active noise control is used to cancel reflections and enables the measurement of boundary-layer receptivity to downstream-traveling sound. Tollmien–Schlichting wave amplitudes are extracted from hot-wire data using biorthogonal decomposition of modified Orr–Sommerfeld equations that include acoustic disturbance solutions. The new method is implemented to measure the acoustic receptivity of a 20:1 modified superellipse leading edge on a flat plate. The data yield acoustic receptivity coefficients ...

Wind Tunnel Testing of Airfoils for Wind Turbine Applications

Accurate wind tunnel measurements of the lift and drag of airfoil sections are critical for the design and performance evaluation of wind turbine blades. As blades continue to increase in size, the demand for highly accurate wind tunnel results at progressively larger Reynolds numbers has also increased. Performing these wind tunnel measurements requires precise experimental control, and three challenges for these measurements are model surface quality, pressure tap effects, and model deflections under aerodynamic loading. These challenges were systematically studied in the Virginia Tech Stability Wind Tunnel using a DU96-W-180 airfoil geometry at a chord Reynolds number (Rec) of 3.0 × 106. Naphthalene sublimation showed turbulent wedges caused by surface imperfections; removing these imperfections increased the lift curve slope by 3%. Pressure tap diameter effects were investigated by placing taps of varying size at the same chord location on the airfoil. These measurements showed a steady pressure bias correlated to tap diameter when making measurements in turbulent boundary layers, and naphthalene visualizations showed a turbulent wedge created by pressure taps at the leading edge. Finally, laser distance sensors were used to measure model deflections/rotations under aerodynamic loading, improving upon the traditional angle of attack measurement. Addressing these challenges has improved the accuracy of lift measurements in the Stability Wind Tunnel and emphasized the need for precise experimental controls when performing these types of wind tunnel measurements.

Distributed-Roughness-Induced Transient Growth in a Flat Plate Boundary Layer

Surface roughness affects boundary layer transition in several ways, including acting as a receptivity mechanism for transient growth. Several experiments have measured transient growth created by discrete roughness elements; however, very few experiments have studied transient growth initiated by distributed surface roughness. In the present work, transient growth created by streamwise-extended patches of randomly distributed, subcritical surface roughness is measured in a Blasius boundary layer. A deterministic roughness surface was manufactured using rapid prototyping, and detailed measurements of the roughness wake were made using hotwire anemometry. The distributed roughness creates disturbances at multiple spanwise wavelengths that undergo transient growth. These experiments lay the ground work for examining the “shielding” effect, wherein the presence of smaller amplitude distributed roughness may decrease the strength of roughness wakes created by larger roughness peaks.

Acoustic Forcing and Control of Reflected Waves in the Klebanoff-Saric Wind Tunnel

The infrastructure of the Klebano {Saric Wind Tunnel is upgraded in anticipation of boundary layer sound receptivity experiments. Five speakers, installed inside the tunnel, create planar, downstream-traveling sound, and multiple microphones measure the sound output in the test section. The change in wind tunnel area downstream of the test section creates a re ected, upstream-traveling wave during acoustic forcing. An active noise control system uses two speakers downstream of the test section to create upstream-traveling waves that destructively interfere with the re ections. Active noise control reduces the re ections up to 42.3 dB at 10 m/s and 33.2 dB at 20 m/s with an average reduction of 28.6 dB at 10 m/s and 23.2 dB at 20 m/s. Active noise control is also used to reduce upstreamtraveling tonal background noise up to 5.6 dB. The adaptive control system allows greater experimental control during sound receptivity experiments.