Space correlation measurements in a forced shear layer with wall injection

Comprehension of wall-injection flow in a channel in the presence of different geometric discontinuities is necessary as part of the general investigations concerning combustion instabilities of solid propellant rocket motors. In order to characterise the aerodynamic flow field and to evaluate the influence of an obstacle inside a porous channel in such a case, experimental studies were conducted on a 1/40 scale model of the new ARIANE V motor. In fact, the flow is only induced by wall-injection and the presence of an obstacle creates a particular shear layer development in the obstacle wake. Particular attention was given to the unstable dynamic conditions of the shear layer. A thermal seeding of the shear layer was made in order to qualify the heat transfer therein, and especially to emphasise the turbulent structure development. Transverse and longitudinal spatial correlations were measured to characterise turbulence scales in the shear layer. At the origin of the shear layer, the decay of turbulence memory is found to be similar to that observed in a forced flow boundary layer, but the injecting wall modifies the change in structures. The wall flow is found to preserve the turbulent structures in such a way that the turbulence memory predominates in a longitudinal direction.List of Symbols f frequency (Hz) - h channel height (m) - h_v obstacle height (m) - L mean dimension of large structures (m) - P pressure (Pa) - m mass flow rate (kg/s) - r distance between probes in X direction (m) - r^+(–) distance between probes in Y direction (m) - u longitudinal velocity in X direction (m/s) - v transversal velocity in Y direction (m/s) - T temperature (K) - x,y,z axis system (m) - t = T-T_amb (K) - v kinematic viscosity (mVs) - density (kg/m³) - characteristic porous size (urn) - _u longitudinal rms (m/s) - I_u dynamic turbulence intensity _u/u_max - I_T thermal turbulence intensity - M Mach number u/a - Re_w wall Reynolds number v_wh/v - Re_c longitudinal Reynolds number u_ch/v - R_uT thermal dynamic correlation coefficient - St Strouhal number fh/u - X,Y,Z axis system normalised by the channel height h - X_S longitudinal position of the obstacle - X X-X_S - amb ambient reference - c flowing cavity - fav head end - l lateral direction - g longitudinal direction max maximum at a longitudinal position - w wallThe authors thank the CNES for its financial support, and in particular E. Robert and R. Bee.