Unsteady Low-Speed Wind Tunnels

A theory based upon linearized governing equations is developed that describes the operation principles and design parameters for low-speed wind tunnels with longitudinal freestream oscillations. Existing measurements made in unsteady wind tunnels are shown to be consistent with the theory and targeted validation experiments performed in a variable-geometry blowdown-type wind tunnel revealed excellent correspondence with the theoretical results. In particular, the tunnel frequency bandwidth is proportional to the mean tunnel freestream velocity and inversely proportional to the test-section length and the square of the exit area to test-section area ratio. The acoustics equations reveal a “Helmholtz damping ratio” that is not only dependent on the tunnel geometry and exit area but also proportional to the freestream Mach number. At appreciable reduced frequencies, dynamic stall on the louver vanes increases pressure losses, thereby reducing the mean flow speeds. Varying the exit area results in louver-van...

[1]  Partha P. Sarkar,et al.  Development of an active gust generation mechanismrnon a wind tunnel for wind engineering and industrial aerodynamics applications , 2006 .

[2]  Reece A. Clothier,et al.  Fixed-wing MAV attitude stability in atmospheric turbulence—Part 2: Investigating biologically-inspired sensors , 2014 .

[3]  D. A. Kennedy,et al.  Harmonic optimization of a periodic flow wind tunnel , 1981 .

[4]  J. Malone,et al.  Dynamic stall characteristics of an oscillating airfoil in a harmonically varying freestream velocity , 1974 .

[5]  Gregg Abate,et al.  Flight Controls and Performance Challenges for MAVs in Complex Environments , 2008 .

[6]  W. Mccroskey,et al.  Unsteady Viscous Flow on Oscillating Airfoils , 1974 .

[7]  Jeffrey P. Bons,et al.  Modification of Transonic Blowdown Wind Tunnel to Produce Oscillating Freestream Mach Number , 2011 .

[8]  Donald L. Kunz,et al.  The effect of varying freestream velocity on dynamic stall characteristics , 1978 .

[9]  J. Miller,et al.  Separation in oscillating laminar boundary-layer flows , 1971, Journal of Fluid Mechanics.

[10]  D. Greenblatt,et al.  Development and Testing of an Unsteady Low-Speed Wind Tunnel , 2015 .

[11]  Kenneth Granlund,et al.  Airfoil longitudinal gust response in separated vs. attached flows , 2014 .

[12]  K. Mohseni,et al.  Lift evaluation of a two-dimensional pitching flat plate , 2013 .

[13]  P. H. Bauer,et al.  Wind Tunnel Generation of Sinusoidal Lateral and Longitudinal Gusts by Circulation of Twin Parallel Airfoils , 1974 .

[14]  G. E. A. Meier,et al.  Forced oscillations of airfoil flows , 1996 .

[15]  Yongsheng Lian,et al.  Résumé of the AIAA FDTC Low Reynolds Number Discussion Group's Canonical Cases , 2010 .

[16]  R. Wickens.  Wind tunnel investigation of dynamic stall of a NACA 0018 Airfoil oscillating in Pitch , 1985 .

[17]  William S. Saric,et al.  The ASU unsteady wind tunnel and fundamental requirements for freestream turbulence measurements , 1988 .

[18]  G. Charnay,et al.  Periodic Flow in a Wind Tunnel Produced by Rotating Shutters , 1976 .

[19]  D. Favier,et al.  Dynamic Stall Due to Fluctuations of Velocity and Incidence , 1982 .

[20]  A. A. Fejer,et al.  Transition phenomena in oscillating boundary-layer flows , 1964, Journal of Fluid Mechanics.

[21]  David Simms,et al.  Unsteady aerodynamics associated with a horizontal-axis wind turbine , 1996 .

[22]  George Alvin Pierce,et al.  Experimental study of dynamic stall in an oscillating airstream , 1973 .

[23]  L. Carr.  Progress in analysis and prediction of dynamic stall , 1988 .

[24]  T. Theodorsen.  General Theory of Aerodynamic Instability and the Mechanism of Flutter , 1934 .

[25]  J Mayo Greenberg,et al.  Airfoil in sinusoidal motion in a pulsating stream , 1947 .

[26]  J. G. Schepers.  IEA Annex XX: Comparison between calculations and measurements on a wind turbine in yaw in the NASA-Ames wind tunnel , 2007 .

[27]  D. Favier,et al.  COMBINED TRANSLATION/PITCH MOTION: A NEW AIRFOIL DYNAMIC STALL SIMULATION , 1988 .

[28]  J. Edwards,et al.  Theoretical, Computational and Experimental Studies of a Flat Plate Undergoing High-Amplitude Pitching Motion , 2011 .

[29]  Rufus Isaacs,et al.  Airfoil Theory for Flows of Variable Velocity , 1945 .

[30]  Hester Bijl,et al.  Simulating dynamic stall in a two‐dimensional vertical‐axis wind turbine: verification and validation with particle image velocimetry data , 2010 .

[31]  F. X. Caradonna,et al.  An Experimental Analysis of Dynamic Stall on an Oscillating Airfoil , 1974 .

[32]  Michael V. Ol,et al.  Unsteady pitching flat plates , 2013, Journal of Fluid Mechanics.

[33]  D. Greenblatt,et al.  Dynamic Stall Control on a Vertical Axis Wind Turbine Using Plasma Actuators , 2014 .

[34]  E. H. Smith.  Autorotating wings: an experimental investigation , 1971, Journal of Fluid Mechanics.

[35]  R. D. Mehta,et al.  Design rules for small low speed wind tunnels , 1979, The Aeronautical Journal (1968).

[36]  D. Favier,et al.  Large-amplitude fluctuations of velocity and incidence of an oscillating airfoil , 1979 .