The Effects of External Excitation on the Reynolds-Averaged Quantities in a Turbulent Wall Jet

  • Y. Katz
  • E. Horev
  • I. Wygnanski
Part of the NATO ASI Series book series (NSSB, volume 268)

Abstract

The effects of external, two-dimensional excitation on the plane turbulent wall jet were investigated experimentally. Measurements of the streamwise component of velocity were made throughout the flow field for a variety of Reynolds numbers, imposed frequencies, and amplitudes. The present data were always compared to the results generated in the absence of external excitation. Although the bulk of the unexcited flow is self-similar, it depends on the momentum flux at the nozzle and on the viscosity and density of the fluid and not on the width of the nozzle, which was commonly used to reduce the data. These similarity scales were used to check the consistency of the skin friction measurements, which are otherwise determined with considerable difficulty. It was shown that external excitation has no appreciable effect on the rate of spread of the jet or on the decay of its maximum velocity. In fact, the mean velocity distribution did not appear to be altered by the external excitation in any obvious manner. The flow near the surface, however (i.e., for 0 < Y+ < 100), was profoundly different from the unforced flow, indicating a reduction in wall stress exceeding at times 30%. The production of turbulent energy near the surface was also reduced, lowering the intensities of the velocity fluctuations. It was also shown that the inviscid, logarithmic portion of the “law of the wall” cannot be valid in either the forced or the unforced flows, because the Reynolds stress decreases rapidly beyond the distance at which the viscous stress becomes vanishingly small. This casts a doubt on the existence of a “constant stress layer” in the wall jet.

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Copyright information

© Springer Science+Business Media New York 1991

Authors and Affiliations

  • Y. Katz
    • 1
  • E. Horev
    • 1
  • I. Wygnanski
    • 1
  1. 1.Department of Aerospace and Mechanical EngineeringThe University of ArizonaTucsonUSA

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