Experimental analysis of turbulent structure of viscoelastic fluid flow in downstream of two-dimensional orifice

We performed PIV measurements on the turbulent orifice flows of water and of viscoelastic fluid in two orthogonally different planes, namely, x-y and x-z plane: x, y, and z are the streamwise, wall-normal and spanwise directions, respectively. In the orifice flow of the viscoelastic fluid, a 150-ppm cationic surfactant CTAC (cetyltrimethyl ammonium chloride) solution, spanwise Kelvin-Helmholtz vortices emanating from the orifice edge were damped and wall-normal turbulent motions were greatly suppressed. On the other hand, high-speed fluid streaks in the separated shear layer were found to be almost similar to the water flow by the x-z-plane observation, implying the existence of streamwise vortices in the shear layer.