Computational and Experimental Investigation of Transverse Combustion Instabilities

Abstract

Concurrent experiments and computations are used to analyze combustion instabilities in a transverse mode combustion chamber. The experiments employ a shear-coaxial injector element, positioned within a rectangular chamber and driven by high amplitude transverse acoustics modes by unstable injector elements located near the chamber end-walls. The reacting flow portion of the study element is optically accessible and the chamber is extensively instrumented with high-frequency pressure transducers. Different levels of instability are obtained by varying the operation of the driving elements. High-fidelity computational fluid dynamics simulations are used to model this set-up, although only the study element is fully represented and the transverse acoustics modes are generated by vibrating the side walls at the appropriate frequencies. The computational results are compared quantitatively with the high frequency pressure measurements, and qualitatively by using the CH* chemiluminescence signal from the experiment. The combustion response of the first, second and third transverse modes obtained using a dynamic modal decomposition procedure show excellent agreement between the experiments and simulations. The overall approach shows significant promise for screening the combustion response of candidate injector configurations for rocket applications.

Transverse Combustion Instability in a Rectangular Rocket Motor

“…It was found that the limit cycle does not produce shocks; upon grid refinement the pressure gradients in the transverse direction do not increase. This is consistent with the experimental findings of Shipley et al [17], which did not discover the existence of shocks in the experimentally measured instability. For the OOXOXOO case, a contour plot of the temperature field for the ethane injector is given in Fig.…”

“…4. As can be seen on that plot, the maximum flame temperature is 2890 K, with a coflow temperature of 2660 K, which is in good agreement with the numerical results of Shipley et al [17], who report injector, at the outlet of one of the outermost driving injectors, at the center of the nozzle, and at the edge of the nozzle. The power spectrum density of the pressure signals is also shown, with peaks at the 1931 Hz frequency and its harmonics.…”

“…5 to their experimental counterparts shown in Fig. 8 is on page 9 of [17], we see that the present numerically calculated time histories of pressure are smoother than the experimental measurements; it is also observed that the power spectral density away from the first transverse frequency and its harmonics has a lower magnitude. This can be attributed to the fact that the present study is of a 2-D nature, and the smaller 3-D turbulent structures are not represented.…”

“…Time histories of pressure can be found on Fig. 8 is on page 9 of [17]. The frequency of the first transverse mode component of the instability is 2032 Hz.…”

“…Thus, the present study builds on previous analyses [3,12,13]. A particular experimental configuration, the seven-injector rocket engine studied by the Anderson group at Purdue University [15][16][17], is simulated. The Purdue experimental group studied transverse oscillations in a rectangular cross-section combustion chamber.…”