Research On Resistance And The Transition Characteristics Of Pulsating Flow In Narrow Channels

The flow characteristics of single-phase pulsating flow and acceleration and decelerationflow in rectangular channel were investigated analytically and experimentally in this paper.Experimental research is aimed at layer、turbulent flow resistance characteristics as well as thetransition area of the transition characteristics under the condition of unsteady flow in therectangular channels.The experimental results show that：In the laminar region, the same flow rate, frictionpressure drop of acceleration situation is greater than that of the steady state, and the frictionpressure drop of decelerate situation is less than that of the steady state; In the whole cycle,the pulsating cycle and pulsation amplitude have no effect on the average friction pressuredrop,the same as steady state. In the turbulent region, pulsating cycle and pulsationamplitude have influence on the average coefficient of frictional resistance,and the moreintense pulse, the greater the coefficient of frictional resistanceThe Re-λ curve and flow trace display results prove that: In the pulsating flowaccelerating stage, With the increase of the pulse frequency, the critical turning point positionis forward, and less than the steady state critical transition Reynolds number. But in thedeceleration phase, With the increase of the pulse frequency, the critical turning point positionis backward，and the greater acceleration is, the larger probability of transition occurrencebecome.Velocity distribution of acceleration and deceleration flow were studied throughtheoretical derivation the theoretical derivation results show that the influence factors ofvelocity distribution is channel size, fluid properties, pressure gradient rate, time, and initialvelocity distribution. In the same section average speed, the greater of the pressure gradientrate is, the larger of the center fluid velocity become, and near wall is opposite. According tothe energy gradient method，the transition position where first occurred is not at the center offlat channel, but at a distance of the channel center when y/h Equal0.58.