Radiated noise and wall pressure measurements in turbulent boundary layers in dilute polymer solutions

[摘要] Measurements of radiated noise and wall pressurefluctuations in a turbulent boundary layer in water aredescribed. A comparison is made between measurements inpure water and in dilute solutions of high molecular weightpolymers. To obtain these measurements, a new experimentalgeometry was developed.The principle of the experiment is as follows: Aflat steel plate 205 cm long by 80 cm wide is rolled into asingle-turn spiral, with a radial gap of 4.5 cm between thetwo overlapping ends. The spiral is submerged in water androtated about its axis, creating a boundary layer on theinner surface which leaves the interior of the spiralthrough the radial gap. The fluid leaving the interiorthrough the gap is replaced through the two open ends ofthe spiral by means of stationary honeycomb filters whichremove residual turbulence and vorticity.Measurements of the mean velocity profile show thatthe turbulent boundary layer on the inside surface of thespiral resembles that on a flat plate in a uniform freestream. A Reynolds number based upon plate length of5 x 10^6 is obtained.Wall pressure fluctuations under the boundary layerare measured with piezoelectric transducers mounted flush inthe 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 polymeradditives cause significant reductions in both the radiatednoise and wall pressure spectra. The reductions are greatestat high frequencies, or at Strouhal numbers greater than one.

[发布机构] University:California Institute of Technology;Department:Engineering and Applied Science

[关键词] Engineering