CONDITIONAL VELOCITY AND REYNOLDS STRESSES IN A PLANE TURBULENT SHEAR LAYER.

The properties of conditional averages in which the conditional event has the form left brace v less than equivalent to u(x,t) less than v plus dv right brace have been studied for isotropic turbulence and for anisotropic turbulence in a plane high Reynolds number shear layer with 2:1 velocity ratio. In isotropic turbulence it is shown that a linear estimate of the form less than u//i(x plus r,t) vertical u(x,t) greater than equals A//i//j(r) u//j(x,t) is the dominant term in a power series expansion of the conditional average. It is a good approximation for probable values of the velocity fluctuation, and it predicts a vortex ring structure. In the shear layer, conditional averages of the velocity component u(x plus r,t) and v(x plus r,t) and the Reynolds stresses uv(x plus r,t), u**2(x plus r,t), v**2(x plus r,t) have been measured given the values of u(x,t) and v(x,t) using two X-wire probes. Comparison of the conditional velocity with its linear estimate shows good agreement.