Abstract
The design and qualification of a longitudinal gust generator in a low-speed, blow-down, open-return wind tunnel was conducted. Flow-impeding louvers were used to rapidly change the blockage ratio at the inlet, effectively reducing test section flow speeds up to \(60\%\) and \(52\%\) for the closed and open test section configurations of the wind tunnel, respectively. The wind tunnel responds more quickly for higher fan speeds, shorter tunnel lengths, and during louver closing motions (deceleration). A mathematical model developed to predict the wind tunnel’s response shows these same trends and agrees with the experimental data to within 0.03 in amplitude ratio and \(4.3^\circ\) in phase lag, for all cases studied. Comparison of the closed to open test section configurations reveals that flow disturbances propagate nearly instantaneously, or in a globally unsteady manner, within the closed configuration, while they convect at speeds similar to that of the mean flow when testing in the open configuration.
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Abbreviations
- a :
-
Speed of sound, m/s
- A :
-
Cross-sectional area, m2
- B :
-
Model analysis coefficients
- c :
-
Wave or propagation speed, m/s
- \(C_{Corr}\) :
-
Model correction factor
- \(C_{FSP}\) :
-
Fan static pressure constant, m/s2
- D :
-
Fan impeller diameter, m
- f :
-
Driving frequency, Hz
- F :
-
Momentum loss term, N
- FSP :
-
Fan static pressure, Pa
- k :
-
Loss coefficient
- L :
-
Wind tunnel length, m
- M :
-
Mach number
- p :
-
Static pressure, kPa
- q :
-
Dynamic pressure, kPa
- Q :
-
Volumetric flow rate, m3/s
- u :
-
Velocity vector, m/s
- t :
-
Time, s
- U :
-
Flow speed, m/s
- x :
-
Streamwise (longitudinal) position, m
- V :
-
Volume, m3/s
- \(\varDelta\) :
-
Difference or change in a primary quantity
- \(\varepsilon\) :
-
Normalized fluctuating velocity
- \(\sigma\) :
-
Model analysis driving amplitude
- \(\theta\) :
-
Louver angular position, deg.
- \(\rho\) :
-
Density, kg/m3
- \(\tau\) :
-
Wind tunnel time constant, s
- \(\overline{\overline{\tau }}\) :
-
Stress tensor, N/m2
- \(\phi\) :
-
Phase shift, deg.
- \(\omega\) :
-
Radial driving frequency, \(\mathrm {rad/s}\)
- \(\varOmega _{fan}\) :
-
Fan speed, RPM
- atm :
-
Atmospheric conditions
- ex :
-
Exit conditions
- fan :
-
Fan conditions
- in :
-
Inlet conditions
- T :
-
Total conditions
- ts :
-
Test section conditions
- \(*\) :
-
Normalized conditions
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Acknowledgements
The authors would like to thank Matt Rhode, Adrian Stang and Severyn Polakiewicz for assistance in designing and constructing the louver system. The authors would like to acknowledge support from the University of Colorado Boulder Research & Innovation Office through the 2017 Innovative Seed Grant Program. Additional support was provided by the NSF Industry-University Cooperative Research Center for Unmanned Aircraft Systems (C-UAS) and by the Air Force Office of Scientific Research under award number FA9550-18-1-0311 (Dr. Gregg Abate). Any opinions, finding, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Air Force or U.S. Government.
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Farnsworth, J., Sinner, D., Gloutak, D. et al. Design and qualification of an unsteady low-speed wind tunnel with an upstream louver system. Exp Fluids 61, 181 (2020). https://doi.org/10.1007/s00348-020-03018-1
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DOI: https://doi.org/10.1007/s00348-020-03018-1