Rocket Applications of the Cavitating Venturi

F THE past few years the Curtiss-Wright Corporation has used the in its rocket test program as an extremely simple and accurate means for controlling flow of incompressible fluids. Although the interesting phenomenon that makes this possible is apparently not new, it has to the best of the writer's knowledge been employed only in rocket applications. Its principle of operation may be expressed thus: As the pressure drop across a conventional is increased, a point is reached at the throat where substantially all of the upstream head is converted into velocity head. The only static head remaining is that of the fluid vapor pressure. If, under these conditions the upstream head is maintained constant, a further increase of the pressure drop obtained by decreasing the downstream pressure cannot result in increased flow. This characteristic of a has been used to advantage in liquid propellant rockets and may find applications in other than the rocket field. Unusual flow characteristics of thick-plate orifices exhibited early in this company's test program led to the evolution of the cavitating Venturi concept and its application to the control of propellant flows. It may be of interest to examine briefly this early experience with thick orifices having sharp entrances. These orifices were chosen because they provided a simple method of adjusting pressure drop within a rocket hydraulic system, and they could be sized at the test site from the information gained from water calibrations. Because these water calibrations were made of the complete rocket motor hydraulic system as a unit, and because of facility limitations, it was necessary to allow the system to discharge to atmospheric pressure. Although this is generally considered bad practice when calibrating, a few check runs indicated this method to be sufficiently accurate and gave no trouble until later in the test program. In time discrepancies