The Investigation Of Shock Train Characteristics Considering Isolator-combustor Interactions

The isolator is the aerodynamic buffer segment between the hypersonic engineinlet and the combustor. When the combustor pressure is high enough, in order tomatch the backpressure, shock train will form in the isolator. When the combustorchamber is too high, the shock train will gradually be pushed upstream until arriveat the entrance of the isolator, then unstart will occur. Therefore, studying thecharacteristics of the shock train in the isolator will be critical for the stabilitymargin of the hypersonic inlet. Some special situations like the variation of thermalstate, the unsteady isolator outlet boundary and the oscillation characteristics causedby combustion may have specific influence on isolator flowfield. To investigate theisolator shock train characteristics in real situation, it should account for theisolator-combustor interactions. So in this research, by both numerical simulationand experiment, the isolator flowfield and shock train characteristics consideringisolator-combustor interactions will be studied.First, simulation is conducted about freestream air inlet to investigate the shocktrain characteristics with non-uniform incoming flow and coupling effects whencombustion is considered. The physical model is introduced, which concludesforebody, isolator, combustor and exhaust nozzle. The simulation method isvalidated. The isolator flowfield transformation at different equivalence ratio of fuelwith asymmetric injection is analyzed, focusing on the shock train form andstructure transformation. Then the shock train characteristics with asymmetric fuelinjection by changing the fuel rates of upper and lower wall fuel injectors arestudied, and the shock train transitions mechanism is briefly analyzed. Finally, theshock train form and structure transitions with symmetric fuel injections at differentequivalence ratios and asymmetric fuel injections at the same equivalence ratios aresummarized and analyzed.Then the isolator flowfield of the direct-connected inlet at decouplingconditions with different types of incoming flows is numerically studied, mainlyincluding the influence of reflected shock, expansion wave and boundary layer.When with no boundary layer, the shock train will keep symmetric and unstartoccurs as the equivalence ratio reaches0.349. While for no boundary layer condition,with the change of shock incident angle, as the equivalence ratio continues toincrease, unstart does not happen, but the shock train position moves little. If theboundary layer is set, with the increase of its thickness, the resistance ability of theshock train will be weaker, leading to the shock train leading edge moving upstream. For asymmetric boundary layer and with shock incident angle2°, at this time it issimilar to the freestream conditions. Changing the incident angle, due to thevariation of the shock train structures and forms, the incident angle and the shocktrain leading edge have no distinct relationship.Next, experiment is carried out to investigate the shock train characteristicswith isolator-combustor interactions. It is briefly stated about the Scramjet groundtest equipment, the signal acquisition, the experimental process. The stability margincharacterized by only one backpressure based on safety boundary is introduced. Byanalyzing the relationship between the shock train leading edge and thebackpressure, the safety boundary is obtained, and a maximum backpressure basedon safety boundary is received. It is concluded that the maximum backpressure havea linear relationship with Mach numbers. At last, the stability margin characterizedby only one backpressure based on safety boundary can be achieved.The stability margin based on pressure distribution area integral considering theisolator-combustor interactions is presented in the final chapter. The relationships ofthe pressure distribution, backpressure, the shock train leading edge withequivalence ratio during the start-unstart and unstart-restart periods are analyzed,And unstart margins indicated by shock train leading edge and backpressure areevaluated. The stability margin based on pressure distribution area integral isintroduced, which have a better linear relationship with equivalence ratio andperforms better. This method will need many sensors. To optimize the number ofsensors, the Genetic Algorithm is introduced to optimize the needing gauging pointsfor stability margin characterization. And finally the optimal reduction scheme isobtained.