Abstract: Experimental investigation on the drag of cavity flame holder was conducted by force measurement system. Integrated fuel injector/flame holder cavity module was installed in a constant area ground direct-connect test combustor, which simulated the incoming flow conditions of Ma=1.92, T=509 K, P=86.6 kPa. Various cavities were studied with several depth (D=10, 15, 20 mm), length-to-depth ratios (L/D=4-10) and trailing wall angles θ=18°, 30°, 45°, 60°). Results of cold flow experiment indicate that cavity drag increases with increasing D and L/D, and decreases between θ=18°-45°, followed by increasing between θ=45°-60°, which suggests that there might be a critical θ (between 30°-60°) at which the drag of a cavity are minimal. The drags of cavities under combustion condition, with hydrogen fuel ignited by a spark igniter, were investigated with two groups of fuel injectors on different positions and several fuel equivalence ratios. It is found that the drag of cavity under combustion condition is less than the drag of cold flow, and affected greatly by the fuel injectors position. The drag of cavity decreases with increasing fuel equivalence ratio, and could be converted into the thrust, instead of drag, under combustion mode which is close to real statue of scramjet.

Key words: scramjet, supersonic combustion, flame holder, cavity, drag