The present paper reports on the interaction of a hot side jet in a supersonic freestream and compares the effects with results from cold-gas jet investigations. With high-speed schlieren videos, a significant enlargement of the separation area has been ascertained upstream from the hot-gas jet and quantitatively confirmed with wall pressure measurements. The schlieren videos also show a strong oscillation of the separation and bow shock. By using an algorithm that analyzes the similarity of neighboring images, the oscillation frequency of the separation and bow shock has been measured to be 11.3 kHz. As a consequence of the dominant shocks in the area in front of the jet, the hot jet plume is screened off strongly from the freestream, thus resulting in an upstream inclination. Finally, highspeed videos have revealed large-scale structures in the hot-gas jet and their convection velocities have been analyzed. According to the shocks, the large-scale structures oscillate at 11.3 kHz. Jet oscillation is thus excited by the interaction of the hot-gas jet with the freestream and not by resonances from the combustion chamber. Nomenclature A J = jet exit area, m 2 C pdif = differential pressure coefficient, measured with and without jet flow D = diameter of the cylindrical part of model, mm d J = diameter of jet nozzle, mm d W = diameter of wind-tunnel nozzle, mm F = jet exit thrust, N I = jet exit momentum flux, N M J = Mach number of the side jet M 1 = Mach number of the freestream n = number of frames p = local pressure, bar p t = total pressure of the freestream, bar p tC = total pressure of cold-gas jet in the chamber, bar p tH = total pressure of hot-gas jet in the combustion chamber, bar p 1 = static pressure of the freestream, bar Re D = Reynolds number based on the model diameter D T JC = temperature of cold jet, K T JH = temperature of hot jet, K T tC = total temperature of the freestream and cold jet flow, K T 1 = static temperature of the freestream, K U c = convection velocity of jet flow, m s 1 U J = velocity of jet flow, m s 1 U 1 = velocity of freestream, m s 1 x = distance downstream from the model tip, mm z = direction of jet flow, mm = angle of attack, deg t = time between frames, s = angle of separation shock, deg ' = circumferential angle, deg = convection angle, deg = isentropic exponent = density, kg m 3 Subscripts J = jet exit condition JC = cold jet JH = hot jet t = static condition 1 = freestream
