Experimental studies on the onset of turbulence and frictional losses in an oscillatory turbulent pipe flow

Abstract Transition to turbulence and frictional losses in an oscillatory and reversing flow of air in a pipe have been studied experimentally. A hot-wire anemometer was employed to observe temporal axial velocity variations, while a differential pressure transducer was used to measure temporal variations of pressure drops across the pipe. In contrast to previous work, the similarity parameters chosen for the present study are the kinetic Reynolds number Re ω and the dimensionless oscillation amplitude of fluid A o . A correlation equation in terms of these two similarity parameters for the prediction of the onset of turbulence is obtained. The experimental data show that a change from a favorable pressure gradient to an adverse pressure gradient at high kinetic Reynolds numbers and large dimensionless fluid displacements is responsible for the onset of turbulence. Based on the measured data of pressure drops and cross-sectional mean velocities, a correlation equation for the cycle-averaged friction coefficient of a cyclically turbulent oscillatory flow has been obtained in terms of the two similarity parameters.