A high-frequency combination probe was used to measure dynamic flow quality in the
test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe
measures fluctuating stagnation (total) temperature and pressure, static pressure,
and flow angles in two orthogonal planes. Simultaneous unsteady temperature and
pressure measurements were also made in the settling chamber of the tunnel. The
data show that the stagnation temperature fluctuations remain constant, and the
stagnation pressure fluctuations increase by a factor of two, as the flow accelerates
from the settling chamber to the test section. In the test section, the maximum rms
value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients l
failed to show vortlcity, entropy, or sound as the dominant mode of turbulence in the
tunnel.
At certain tunnel operating conditions, periodic disturbances are seen in the data
taken in the test section. A possible cause for the disturbances is found to be
acoustic coupling of the test section and plenum chamber via the perforated side
walls in the tunnel. The experimental data agree well with the acoustic coupling
theory.
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