Abstract
The typical afterbody flow of a space launcher is characterized by a strong interaction of the engine’s exhaust jet and the separated shear layer emerging from the main body. This interaction is further complicated by strong changes in the spatial and temporal behavior of the afterbody flow during the atmospheric ascent of a launcher. Theoretically, a dual-bell nozzle not only allows for a gain in payload compared to standard single-bell nozzles, but also it alters the wake flow topology due to the two nozzle modes. To predict the benefits as well as the additional risks, the afterbody flow of a generic space launcher model equipped with a cold-flow dual-bell nozzle is investigated in detail. The flow was analyzed for sub-, trans- and supersonic Mach numbers ranging from 0.3 to 2.9 for a variety of nozzle pressure ratios. Particle image velocimetry measurements and schlieren measurements with high repetition rate were performed to determine the dynamics of the separated shear layer, the nozzle jet and their interaction. It is shown that the reattachment length of the base flow decreases with increasing nozzle pressure ratio. Furthermore, the nozzle pressure ratio at which the dual-bell nozzle switches from sea-level mode to altitude mode is reduced by 15% with high subsonic outer flow and by as much as 65% for an outer flow at a Mach number of 1.6. Even for a constant nozzle pressure ratio, the nozzle flow topology depends on the Mach number of the outer flow.
Highlights
Access to space is of great importance for the security and comfort of our lives
To analyze the effect of nozzle pressure ratio on the flow dynamics and interactions between the nozzle flow and the base flow, schlieren measurements as well as particle image velocimetry (PIV) measurements were performed over a large range of NPR and M
The interaction of the base flow of a generic space launcher model and a cold exhaust jet from a 2D dual-bell nozzle was investigated in this work
Summary
Access to space is of great importance for the security and comfort of our lives. Satellites in various orbits around the Earth are used to navigate, to communicate and to forecast the weather, among other things. One important point in the risk assessment is the transition from the so-called sea-level mode (top in Fig. 1) to the altitude mode (bottom in Fig. 1), in which the flow separation moves from the contour deflection towards the nozzle exit. The nozzle pressure ratio NPR is used to characterize the nozzle flow state: Fig. 3 Usable nozzle pressure range NPR as a function of the Mach number M for the TWM facility together with the performed PIV and schlieren measurements. Double images with a size of 2048 × 1240 pixel (corresponding to 72 × 44 mm2 ) were recorded with 5 kHz. To analyze the effect of nozzle pressure ratio on the flow dynamics and interactions between the nozzle flow and the base flow, schlieren measurements as well as PIV measurements were performed over a large range of NPR and M. 10,000 Schlieren images or 10,000 PIV double images were recorded and evaluated
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