Abstract
The use of sweep-frequency excitation for rapid measurement of time-dependent pressures on wind-tunnel models is examined. Results obtained from two different wind-tunnels covering the Mach number range from 0.2 to 0.85, and a wide range of flow conditions, are compared with measurements made using the slower, traditional method of discrete-frequency excitation. It is concluded that the sweep-frequency excitation method can reduce testing time in certain flow conditions with no significant loss in accuracy.
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Abbreviations
- M :
-
Mach number
- p :
-
broadband rms local static pressure
- q :
-
12ϱu 2 (dynamic pressure)
- R(Cp/δ) :
-
real (in-phase) part of oscillatory Cp/δ
- I(Cp/δ) :
-
imaginary (in-quadrature) part of oscillatory Cp/δ
- x/c :
-
chord station
- α :
-
wing incidence
- δ :
-
canard or wing oscillatory amplitude (plotted in radians unless otherwise stated)
- η :
-
spanwise station
- η c :
-
canard static incidence
- α c :
-
canard effective incidence (α c = 1.89 α + η c −0.6)
- (T):
-
function of time
- γ 2 :
-
coherence function The coherence function between two signals x(f), y(f) is defined as
- \(\gamma _{xy}^2 (f) = \frac{{|G_{xy} (f)|^2 }}{{G_{xx} (f)G_{yy} (f)}}0 \leqslant \gamma _{xy}^2 (f) \leqslant 1\) :
-
where
- G xy (f) :
-
= cross spectral density function between x and y
- G xx (f) :
-
= auto spectral density function of x
- G yy (f) :
-
= auto spectral density function of y
- f :
-
= frequency
References
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Welsh, B.L., Pyne, C.R. The use of sweep-frequency excitation for unsteady pressure measurement. Experiments in Fluids 7, 9–16 (1989). https://doi.org/10.1007/BF00226591
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DOI: https://doi.org/10.1007/BF00226591