Flow Visualization in Out-of-Round Rocket Nozzles

Flow fluctuations in or around rocket nozzles can lead to a deformation of their structure. In case of separated nozzle flow, an inward bended nozzle wall shifts the flow separation position downstream, increasing the bending force lever arm. This flow-structure interaction is a self-reinforcing effect, which can potentially lead to heavy structural damages. These disturbances can be produced either by combustion instabilities or ambient pressure fluctuations. Under certain conditions, they may excite the bell nozzle eigenfrequency. As a result, the structure responds and the nozzle ovalizes. For this reason, the investigation of flow-structure interaction in ovalized nozzles under separated flow condition is difficult to realize [1–4].