Radiated noise and wall pressure measurements in turbulent boundary layers in dilute polymer solutions
Measurements of radiated noise and wall pressure fluctuations in a turbulent boundary layer in water are described. A comparison is made between measurements in pure water and in dilute solutions of high molecular weight polymers. To obtain these measurements, a new experimental geometry was de...
| Summary: | Measurements of radiated noise and wall pressure
fluctuations in a turbulent boundary layer in water are
described. A comparison is made between measurements in
pure water and in dilute solutions of high molecular weight
polymers. To obtain these measurements, a new experimental
geometry was developed.
The principle of the experiment is as follows: A
flat steel plate 205 cm long by 80 cm wide is rolled into a
single-turn spiral, with a radial gap of 4.5 cm between the
two overlapping ends. The spiral is submerged in water and
rotated about its axis, creating a boundary layer on the
inner surface which leaves the interior of the spiral
through the radial gap. The fluid leaving the interior
through the gap is replaced through the two open ends of
the spiral by means of stationary honeycomb filters which
remove residual turbulence and vorticity.
Measurements of the mean velocity profile show that
the turbulent boundary layer on the inside surface of the
spiral resembles that on a flat plate in a uniform free
stream. A Reynolds number based upon plate length of
5 x 10^6 is obtained.
Wall pressure fluctuations under the boundary layer
are measured with piezoelectric transducers mounted flush in
the wall of the spiral. Radiated noise is measured with a stationary transducer located outside of the boundary layer,
near the center of the spiral. It is shown that the polymer
additives cause significant reductions in both the radiated
noise and wall pressure spectra. The reductions are greatest
at high frequencies, or at Strouhal numbers greater than one.
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