This paper presents a method of generating a highly turbulent freestream flow, up to levels of 20% with a relatively uniform mean velocity field. This method was developed as a result of a combined water channel and wind tunnel study. The method for generating these high turbulence levels includes using high-velocity jets issuing into a mainstream cross-flow. A range of turbulence levels can be generated, using this same flow geometry, by adjusting the jet-to-mainstream velocity ratio or the Reynolds number of the flow.List of symbols
b
Grid bar width
-
D
Turbulence generator jet hole diameter
-
Eu (f)
Spectral energy for streamwise velocity fluctuations
-
f
Frequency
-
H
Channel height
-
L
u
Dissipation length scale,
-
m
Exponent for length scale growth
-
M
Grid mesh size
-
n
Exponent for turbulence decay
-
Re
D
Reynolds number based on jet hole diameter
-
Re
T
Turbulent Reynolds numbers,
u
g
/
V
-
S
Lateral spacing between the jet holes
-
T
Integral time scale of turbulence
-
Tu
Streamwise turbulence intensity,
u/U
-
u
RMS velocity in streamwise direction
-
U
Mean local velocity in streamwise direction
-
U
Freestream velocity in streamwise direction
-
v
RMS velocity in normal direction
-
x
Streamwise distance measured from the turbulence generator jets
-
y
Vertical distance from the wall
-
z
Spanwise distance
-
Boundary layer thickness (
U = 0.99
U
)
-
x
Longitudinal integral length scale of turbulence
This project was supported by Wright Laboratory and Allied-Signal. The authors would also like to thank Mr. David Dotson for his help in constructing the turbulence generator and Mr. Don Schmidt for his help in procuring the blower. The first author would also like to thank Professor Sigmar Wittig and the Institut für Thermische Strömungsmaschinen for support while writing this paper
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