Researches On The Flow Process Of The Supersonic-supersonic Ejector

Supersonic-supersonic ejectors have the advantage of reducing the overall systemlength with a potential increasement in performance. However, researches on the flowcharacteristics of supersonic-supersonic ejectors and the interaction and mixing processof the supersonic primary and secondary flows in the confined mixing chamber havebeen rarely conducted. Therefore, the flow field evolution of supersonic-supersonicejectors should be investigated in details. The present research investigates the pressurematching and recovery characteristics of the supersonic-supersonic ejectorsystematically. The development of the mixing layer and the energy exchange betweenthe primary and secondary flows are also analyzed.It is vital for ejector design to determine the sources of losses in ejectorperformance. In this thesis, the entropy production method was applied to identify andquantify the sources of performace losses of the constant area supersonic-supersonicejector. The composition of the losses and their proportions were examined. Bycombining this thermodynamic method with the one-dimensional aerodynamic theory,the optimum condition of the constant area supersonic-supersonic ejector was obtainedand validated.The starting mechanism of supersonic ejector with a second throat is rathercomplex due to the unsteady and nonlinear effects. Especially, the effect of thesecondary flow on the starting performance of the second-throat supersonic ejector isstill unclear. In the present work, the starting pressure of a second-throat supersonicejector with various secondary flow rate has been measured. Based on the results of thepressure measurements, qualitative analysis has been carried out to clarify the flowbehavior and the physical meaning of the performance diagram.Typical flow fields in the former part of the mixing chamber of the constant areasupersonic-supersonic ejector were analyzed. Three limiting conditions have beendefined. A simplified analytical model has been proposed to predict the limitingpressure ratio which agrees well with the experimental data. The pressure matching andpressure recovery performance of the constant area supersonic-supersonic ejector havebeen investigated systematically. The results show that the experimental maximumcompression ratio was much lower that the theoretical value. This discrepancy may becaused by the different flow pattern between the actual flow field and theoreticalassumption. Besides, when increasing the secondary Mach number, the pressurematching performance increases while the pressure recovery performance decreases.The increasing of the primary Mach number will result in slight desent of the pressurematching performance, but almost no change in the pressure recovery performance. Thepressure recovery performance decreases with the increasing of the stagnation pressure ratio of the primary and secondary flows. The striking angle of the primary flow reducesthe pressure matching performace while improving the pressure recovery performace.The starting process of the supersonic secondary flow in variable areasupersonic-supersonic ejectors was analyzed. The effect of the second-throat on thepressure matching and pressure recovery performance of the ejector was investigatedsystematically. The experimental results indicate that the second-throat lowers thepressure matching performance of the ejector while improving the pressure recoveryperformance. Numerical calculations reveal that the aerodynamic throat opening area ofthe secondary flow which is restricted by the contraction of the mixing chamber, willresult in a lower pressure matching performance. However, the Mach number ahead ofthe shock train is reduced by the converging mixing chamber of the variable areasupersonic-supersonic ejector. The pressure loss caused by the shock train decreases,consequently. And the pressure recovery performance of the variable areasupersonic-supersonic ejector is improved.The development of the mixing layer and velocity fields of the mixing layer werestudied via NPLS and supersonic PIV technique, respectively. Turbulent structures andthe growth rate of the mixing layer were analyzed. Results show that when the staticpressure of the primary flow is lower than that of the secondary flow, the growth rate ofthe mixing layer is smaller than the condition when the static pressures are matched.And in the present work, the growth rate of the mixing layer increases with theincreasing of the convective Mach number.An analytical model based on the Euler methodology was proposed to analyze themomentum and energy exchange between the primary and secondary flows. Resultsshow that the unmatched static pressure of the primary and secondary flows, orincreasing the tempreture of the primary flow, will result in an increasing exchange rateof the momentum and kinetic between the primary and secondary flows. Compared toincrease the stagnation pressure ratio of the primary and secondary flow, increasing thetemperature ratio could improve the efficiency of the ejector more effectively.