Experimental investigation on destruction of Reynolds stress in a plane jet

Mamoru Takahashi, Koji Iwano, Yasuhiko Sakai, Yasumasa Ito

Flow structures that cause destruction of the Reynolds (shear) stress are investigated by means of simultaneous measurement of the velocity gradient and pressure. Two types of combined probes are used for the simultaneous measurement of the velocity gradient and pressure. One consists of an X-type hot-wire probe and a pressure probe; another consists of two I-type hot-wire probes arranged in parallel with a small vertical separation (double-I) and a pressure probe. The hot-wire probe and the pressure probe are aligned along the streamwise direction for both combined probes. We confirm that the simultaneous measurement of the velocity gradient and pressure in a plane jet is satisfactorily performed using the combined probes, except for the outside of the velocity half-width. In a plane jet, (p′/ρ)(∂u2′/∂x1)¯ does not contribute to the Reynolds stress destruction, so that the total pressure-rate-of-strain correlation is almost equal to (p′/ρ)(∂u1′/∂x2)¯. The flow structures that destruct the Reynolds stress are extracted by the conditional sampling technique. We find two structures, which support the thought experiment conducted by Hinze (Turbulence, 2nd edn, McGraw-Hill College, Pennsylvania, 1975). The structures are concentrated around large-scale vortex structures, which cause strong momentum transfer. The scale of the structures is intermediate: smaller than large-scale motion contributing to the momentum transfer, and larger than small-scale motion contributing to the energy dissipation.

Experiments in Fluids

60

46

46