Constantinos Kandias, doctoral candidate in aerospace engineering, in the hover testing chamber of the Penn State Compressed Air Wind Tunnel.
UNIVERSITY PARK, Pa. – Researchers in the Department of Aerospace Engineering are applying the newly-developed, unique-in-the-nation Compressed Air Wind Tunnel to test the aerodynamics of big systems such as full-size rotorcraft and wind turbine blades. Built in large part from high pressure pipeline sections, this new facility was strategically designed by Mark Miller, Assistant Professor of Aerospace Engineering, to measure the aerodynamic efficiency and aeroacoustic noise of systems that are too big for academic research facilities.
The key factor in the wind tunnel’s design is the ability to pressurize the air inside it up to 500 psi, roughly 34 times ambient atmospheric pressure. With this increased pressure, the density of the air also increases. Applying the principle that aerodynamic flows are the same in situations with the same “Reynolds number” (Re), which is the product of density, flow speed and size of the airfoil all reduced by the viscosity, the same flow will result from a small model in pressurized, high density air as a full-size vehicle at ambient pressure and density. Put another way, every inch of model scale in the tunnel acts like an equivalent 3 feet of length at atmospheric pressure. Therefore, all the performance parameters engineers are interested in can be measured quickly and cost effectively using only small models.
Schematic of the Compressed Air Wind Tunnel, including the larger diameter section that serves dual purposes as a hover testing chamber and as the turbulence management section when operating in wind tunnel mode which cleans up the flow before it enters the test section.
Dr. Miller and his graduate researchers are now using a 10-inch diameter rotor model to predict the aerodynamic flow of multi-rotor vehicles such as large quad-copter drones and the electric urban air taxis being widely developed as part of “Advanced Air Mobility” transportation plans in civil aviation and the USAF’s Agility Prime initiative. These vehicles need to be carefully designed and proven that they are aerodynamically efficient. Further, at slow speeds, particularly during take-off and landing, the airflow can be very unsteady, sensitive to wind gusts and the vehicle’s attempts to accelerate and decelerate. This could lead to some of the aerodynamic surfaces stalling or having other disrupted flow. The Compressed Air Wind Tunnel is unique not only in its size, but also in its ability to precisely measure the flow-field through instrumentation such as particle image velocimetry, and thus analyze the airflow in these unsteady conditions.
Further, aerospace engineering researchers are applying the wind tunnel to examine the aerodynamics of even larger systems: next generation floating offshore wind turbines. In this case, designs that scale the wind turbines to be very large can increase the power they produce, but at the expense of increasing the structural loads and moments on the blades and increasing the wake each creates and the separation needed between turbines. Sponsored by the Penn State Institute of Energy and the Environment, Dr. Miller, together with Desirae Major, doctoral candidate in aerospace engineering, Sven Schmitz, the Boeing/Welliver Professor of Aerospace Engineering, and Mike Yukish and Simon Miller of the Applied Research Lab and affiliate faculty in Aerospace Engineering, are taking an integrated look at the structural loads and aerodynamics of the turbine blades, together with the design of floating foundations providing the turbines with steady footing. Testing in the compressed air wind tunnel is a critical component for understanding how the turbines should be scaled.
“The capability to so accurately measure the aerodynamics of full-scale systems is a fundamental enabler not just for Penn State, but also for the aviation industry,” noted Amy Pritchett, Professor and Head of Aerospace Engineering. “Full-scale tests have historically been limited to the largest wind-tunnels, achievable only by large government labs and executed at great expense. However, only testing a small part of the vehicle or wind turbine doesn’t provide the complete picture needed to guide design. These projects demonstrate the capability to examine the whole system in pursuit of new wind energy capabilities and ultra-efficient aircraft.”
November 17, 2023 – ARP
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