Abstract
Analyses of a two-dimensional curtain jet at equilibrium condition, under the assumption of inviscid and incompressible flow, have been given by Wald amd Strand. However, the jet entrainmet of the curtan jet due to the viscosity of fluid flow reduces essentially the pressure difference across the jet. Theories concerning the effect of mixing of the jet have been developed by Heyes, Murao and others. Heyes attempted to calculate the effect of the entrainment by approximating the curtain velocity distribution to that in a two-dimensional free jet. There are several criticisms in Heyes's analysis: the assumption that the turbulent mixing process of a curved jet is substantially the same as that of a straight free jet is questionable, and the flow energy loss at the impinging region of a jet is neglected. So far, an exact analysis may be very difficult and has not yet been obtained for flow field of a curved and impinging jet. Therefore, the analysis in this paper is based on the present experimental results for the jet flow. Experiment In the experiment, pressure and velocity distribution over the control surface which surround the curtain jet, are measured, and jet momentum fluxes are determined by the integration of velocity distributions. The main results of this experiment are as follows. (1) It is confirmed by measuring the pressure force and momentum flux that the horizontal momentum balance at control surface is satisfied. (2) The sum of the absolute values of the horizontal momentum flux at both sides of the control surface around the impinging region is neary equal to total momentum flux at a slot exit. (3) The velocity distributions across the jet at its exit almost coincide with that of the potential flow by a vortex. Analysis In this paper, the semi-empirical analysis has been performed by applying the horizontal momentum balance at the control surface which surround the curtain jet, and it is constructed by using experimental result (2) and the following assumptions. (1) The jet flow is incompressible and essentially two-dimensional. (2) The jet center line is the circular arc of radius r_0. (3) From mass flow considerations, the streamline passing through the inner edge of jet nozzle intersects the ground, and in this equilibrium case, this streamline is identical with the dividing streamline. (4) The mean velocity distribution is two-dimensional turbulent jet. This semi-empirical analysis is very useful, and it is seen that the theoretical results agree well with experimental results.
