Numerical And Experimental Investigation Of Fuel Spray In Supersonic Cross Flow

The liquid fuel atomization processes play an important role on scramjet performance. The time for liquid jet atomization in supersonic cross flow is only several milliseconds. Because of the fast gas flow velocity and the dense liquid droplets clouds, it's difficult to observe and measure the atomization processes, the atomization mechanism is still unclear now. Traditional atomization calculation method is Lagrangian particle trace method. This method use semi empirical models to calculate the atomization processes. The problems are: firstly, most of the models are semi empirical model. The empirical constants used in these models were obtained from low speed flow experiments. Whether these models are applicable in supersonic atomization calculation is still unknown. Secondly, the primary atomization model is too simple, because there is little atomization mechanism known for this process. This thesis researched the atomization processes in supersonic cross flow using numerical simulation and experimental methods.This thesis used two distinct methods to numerical simulate the atomization processes, they were interface trace methods and Lagrangian particle trace method. The interface trace methods calculated the liquid breakup interface processes, most of which were applicable for uncompressible flow only. Since the gas flow in this research is compressible and liquid is uncompressible flow, high precision PPM(Piecewise Parabolic Method) method and volume of fraction model were used to calculate the multiphase compressible flow. The primary atomization and secondary atomization processes were simulated using interface trace method. For the primary atomization, the influence of different gas flow velocities and injector diameters were analyzed. The penetration depth was increased and span width kept constant when the gas flow velocity decreased. Both the penetration depth and the span width were increased when the injector diameter increased. For the secondary atomization, liquid drop was pealed more quickly and the breakup liquid patches were smaller when the gas flow velocity increased. When the liquid diameter increased, it was much more difficult to breakup during the same duration of time.The primary atomization model Blob model and second atomization model such as TAB model, K-H wave model and hybrid model were tested in supersonic cross flow conditions, the results were compared with experimental data. Lagragian calculation research includes some aspects as follows: 1 the influence of empirical constants in atomization model; 2 the hybrid atomization model was much more suitable for the supersonic atomization calculation. The breakup time criteria was changed according to experimental data in order to get a good simulation results; 3 The influences of the turbulence intensity, aerodynamic pressure ratio and evaporation model were researched in breakup process; 4 the three dimensional atomization processes were calculated, both the gas and liquid phase flow field characters were analyzed.For the interface trace method is not fit for small liquid particle simulation, and Lagrangian method is not good for liquid breakup in primary atomization. The interface trace method and Lagrangian method were coupled together to calculate the whole atomization processes in this thesis. The coupled method can take the advantages of the two methods, it is much better for the whole atomization processes simulation compared to each of the individual methods. Schlieren method was adopted to observe the jet atomization phenomena in experiments. The empirical relations of penetration depth were obtained from experimental pictures , which was in good agreement with the numerical results.Level Set method was also used to simulate the liquid drop atomization in uncompressible flow. Several typical secondary atomization phenomena were obtained in interface trace calculation. The influence of some nondimentional numbers such as Weber number (Weg),liquid Reynolds number(Rel),gas Reynolds number(Reg)and density ratio(γ)on atomization were analyzed .