Parametric Study of Oblique Shock Waves Influence on the Supersonic Combustion Chamber Working Process

An increase of the supersonic combustion chamber working process has high practical interest [1]. Supersonic combustion chamber (SCC) working process with a high combustion efficiency organization is limited by low residance time of the working fluid in SCC [2]. Wherein the decrease of the gas velocity lead the total pressure drop SCC exit. A huge amount of the working process organization methods is suggested in a valuable literature [3,4], one of them is a special way organized oblique shock waves system. Specified SCC working process organization method allows to optimize path parameters to increase combustion efficiency and decrease total pressure losses.

Rectangular section SCC, including constant section and expanding section, is chosen as the object of study. SCC is 300 mm long, the height of the inner section is 24 mm, the width of the chamber is 40 mm. Length of the first section is 80 mm, extension of the second section is because of upper wall location with 3° angle. Liquid hydrogen delivery is carried out through the point source located on the height of 12 mm from the down wall om distance of 95 mm from the inner section. Wedge-shaped ledges with a height of 1 mm and angle of 30° to the SCC down wall are used as oblique shock wave generators (Generators).

The task is solved as a two-dimensional. SCC flow described with a full system of the Navier-Stokes equations, air compound matched to the model and described as a gas mixture of O₂, N₂ and H₂O, each of which was considered as an ideal gas. Sutherland law used for the gas viscosity descript.

Modeling air parameters on the inner section set the following: Much number M = 2,05, static pressure p = 341 kPa, static temperature T = 1172 K, gas concentrations C_O2 = 0,21, C_N2 = 0,53 and C_H2O = 0,26. Liquid hydrogen delivered along the SCC down wall with a speed of V = 700 m/s with a value of static temperature of T = 300 K. Mass flow rates of modeling air and hydrogen ratio matched to the oxidant excess factor of α = 3.

A series of calculations varying the Generators location is carried out during the parametric study. A calculation of SCC working process without Generators is taken as a basic. Number and location (on the upper and down wall) of Generators is varied during the next calculations. SCC working process efficiency evaluation is made by the following parameters: SCC combustion efficiency and total pressure recovery factor.

The following patterns are found as a results of research. A number of Generators on the SCC length increase leads to increase combustion efficiency and decrease total pressure recovery factor. Generators location on the both walls allows to achieve significant increase of combustion efficiency (from 0,14 to 0,63). Wherein Generators efficiency decreases in overlap and merger of oblique shock waves of the different Generators while total pressure recovery factor continues to decrease.

The results of conducted research shows the different influence of the oblique shock wave generators on the supersonic combustion chamber working process and integral characteristics. Usage of Generators on the SCC upper and down walls on the several sections along the length turns out to be effective for the increase of combustion efficiency. Wherein increase of total pressure losses along the SCC path is found. Recommendations for the supersonic combustion chamber flow path design is given using the calculation results.