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List of symbols A injCross-sectional area of the nozzle at the coolant injection point (m 2 ) A throat Cross-sectional area of the throat of the nozzle (m 2 ) AR Area ratio (dimensionless) BR Blowing ratio (dimensionless) c p Specific heat (J kg −1 K −1 ) Hz Unit of frequency (cycles per second) hp Horse power (1 hp = 746 W) J Diffusion flux (kg m −2 s −1 ) p Static pressure (N m −2 ) r Radial coordinate (mm) Re Reynolds number (dimensionless) Sc Schmidt number (dimensionless) TuTurbulence intensity (%)Mass fraction of the component (dimensionless) Greek lettersDegree of film cooling effectiveness (dimensionless) ΔT Temperature difference between surface and ambient (K) Subscripts c CoolantAbstract Experimental and numerical investigations are carried out to analyze the effect of coolant injector configuration on overall film cooling performance in a divergent section of a rocket nozzle. Two different injector orientations are investigated: (1) shaped slots with a divergence angle of 15° (semi-divergent injector) (2) fully divergent slot (fully divergent injector). A 2-dimensional, axis-symmetric, multispecies computational model using finite volume formulation has been developed and validated against the experimental data. The experiments provided a consistent set of measurements for cooling effectiveness for different blowing ratios ranging from 3.7 to 6. Results show that the semi divergent configuration leads to higher effectiveness compared to fully divergent slot at all blowing ratios. The spatially averaged effectiveness results show that the difference between the two configurations is significant at higher blowing ratios. The increase in effectiveness was around 2 % at BR = 3.7 whereas it was around 12 % in the case of BR = 6. Numerical results show the presence of secondary flow recirculation zones near the jet exit for both the injectors. An additional recirculation zone present in the case of fully divergent injector caused an increase in mixing of the coolant and mainstream, and a reduction in film cooling performance.

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An experimental and computational investigation of supersonic film cooling was conducted on a subscale model of a rocket engine nozzle. A computational model of a convergent-divergent nozzle was generated, incorporating a secondary injection module for film cooling in the divergent section. Computational fluid dynamics simulations were run on the model and different injection configurations were analyzed. The computational fluid dynamics simulations also analyzed the parameters that influence film cooling effectiveness. Subsequent to the computational fluid dynamics analysis and literature survey an angled injection configuration was found to be more effective, therefore the hardware was fabricated for the same. The fabricated nozzle was later fixed to an Air-Kerosene combustor and numerous sets of experiments were conducted in order to ascertain the effect on film cooling on the nozzle wall. The film coolant employed was gaseous nitrogen. The results showed substantial cooling along the walls and a considerable reduction in heat transfer from the combustion gas to the wall of the nozzle. Finally the computational model was validated using the experimental results. There was fairly good agreement between the predicted nozzle wall temperature and the value obtained through experiments.