| Abstract: | Only a few studies have been devoted to the experimental study of the initial stage of the motion of a liquid from the state of rest in a closed delivery conduit 1]. It can be concluded on the basis of the results of these studies that at the beginning of the process the mechanical energy losses are smaller than in quasistationary flow. These studies also suggest that the laminar nature of the flow persists in the nonstationary flow. However, investigations are of an integral nature and therefore in them the flow structure is not determined. In the present study the development of the motion of the liquid in a delivery conduit from the state of rest is investigated. The tangential frictional stresses at the wall of the conduit, measured by the thermal anemometric method, show that the transitional Reynolds number, at which the laminar flow regime changes into turbulent, depends on the acceleration of the flow and far exceeds the critical value for the case of the stationary flow. At maximum acceleration of the flow equal to 11.78 m/sec2 the transition of the laminar regime to the turbulent at the wall of the conduit occurs at Re = 234, 500. The loss coefficients of mechanical energy have been computed from experimental results, which show that the use of the corresponding coefficient of quasistationary turbulent flow in the computation leads to appreciable errors.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 79–85, November–December, 1977. |
