Pressure Distribution and Induced Force Field on a Conical Nozzle due to Impingement of a Normal Jet into the Supersonic Cross-Flow

Abstract : An experimental investigation was undertaken to study the pressure distribution and induced side force on the wall of a conical nozzle due to intrusion of a jet into a supersonic cross flow. The experiment was carried out to simulate the side injection of fuel coolant from the regenerative cooling system into the supersonic exhaust gas discharging through the nozzle of a rocket engine. The motivation was to shed light on an engine anomaly that occurred during the first Titan IV launch, and thereby to reject or to substantiate the hypothesis that two or three ruptured regenerative cooling tubes caused the near-normal injection of liquid fuel (Aerozine-50) into the exhaust gas in the expansion nozzle section. This scenario was the prime reason for one of the engines to gimbal over to its extreme stop position. The flow of nitrogen (700 psi plenum pressure) through a 1/30th subscale converging- diverging nozzle simulated the main exhaust flow. Injection of a liquid (Freon- 11, water) or a gas (nitrogen) from an injection port drilled at the most probable wall location provided the penetrating side jet. Mass flow rate ratios (jet-to-main flow rates), as well as local Mach number, were matched as closely as possible with those reported from actual flight data. The mass flow ratio was varied to assess the sensitivity of the results to the relative momentum of the jet. Later, wires with different aspect ratios were situated in the supersonic stream replacing the impinging jet at the location of injection. This was done to compare the flow field around a solid bluff body with that around an impinging liquid jet.