Influence of film cooling on nozzle side loads

A thorough experimental analysis of the influence o f a wall film injection pressure ramping on the nozzle flow behavior has been achieved. The study relies upon a cold gas test campaign of a subscale nozzle with wall film which has been exe cuted in the blowdown R2Ch wind tunnel of ONERA at Meudon Center. The nozzle set-up allows the separate feeding of the main nozzle jet and wall film. Bulkheads and jet spreading devices were necessary to well control and homogenize the stagnation pressure inside each cavi ty of the film injection chamber. In steady state conditions the study shows the strong influen ce of the film mass flow rate on the separation shock location. This influence has severe consequences on measured side loads when the film cooling is non symmetrical. In transient conditions the main conclusion is that nozzle side loads can be significantly increased during start-up if a wall film cooling has been started before. Otherwise film cooling transient injection does not induce much side load activity when the nozzle jet is already stabilized. Nevertheless nozz le side loads can be considerably reduced by controlling the wall film injection pressure rampin g speed.