Study on Combustion Performance of the Radial Staged Combustion Chamber with Lobed Nozzles

In order to investigate the effect of the radial gradation of the lobed nozzles on the flow field organization,a cold water model experimental platform for a combustion chamber with radial⁃staged 13-point lobed nozzles is built.Compared with a series of combustion OH*luminescence experiments tested by the University of Cincinnati,the four corresponding working conditions of no load,partial load,cruise and take off are selected.The vortex structure,vorticity value,multi-combustion materiel field and combustion characteristics of the flow field in the radial staged combustion chamber of the lobed nozzles under the equivalence ratio,the fuel injection method,the fuel injection ratio and other factors are numerically studied.The results show that under different influencing factors,the varation trend of the hydroxyl flame field of the lobe combustion chamber is basically the same as that of the hydroxyl light emission experiment of the swirl combustion chamber,but the flame field shape is quite different.The local equivalent ratio has a greater influence on the relevant combustion performance of the combustion chamber.Under the conditions of lower equivalence ratio,three-stage air and fuel injection mode,and gradually transferring the fuel flow of the pilot circuit to the external circuit,the temperature field and flame field of the combustion chamber are more evenly distributed,the outlet temperature field quality is better,the combustion efficiency is higher,and the NO_(X) emission is relatively low.These are basically consistent with the cold test results.The cold experimental results illustrate the importance of the influence of the flow field organization on the combustion organization and verify the reliability of the calculation results.

NUMERICAL INVESTIGATION OF AERODYNAMIC AND MIXING CHARACTERISTICS OF SCARFED LOBED MIXER FOR TURBOFAN ENGINE EXHAUST SYSTEM

The flow field and aerodynamic performances for the scarfed lobed forced mixer are studied based on a computational fluid dynamics（CFD） technique. A series of computations are conducted to obtain the effects of the bypass ratio and the scarf angle on the mixing performance for the scarfed lobed mixer. Results show that the scarfed lobed mixer is reduced in the system weight. Meanwhile, aerodynamic performances are slightly improved compared with the normal lobed mixer. Two reasons for causing the mixing enhancement between the core and the bypass flow are as follows： （1） The stream-wise vortices shed from the training edge of the half/full scarfed lobed mixer earlier is enhanced by about 25%. （2） The mixing augmentation is also associated with the increase of the interface length caused by scarfing. The thermal mixing efficiency is enhanced with the increase of the bypass ratio and the scarfing angle. The scarfed lobed mixer design has no negative effects on the pressure loss. The total pressure recovery coefficient reaches above 0. 935 in various bypass ratios and scarfed angles. As the bypass ratio increases, the total pressure recovery coefficient also increases for the scarfed lobed mixer.

Computation and Validation of Parameter Effects on Lobed Mixer-Ejector Performances

Three-dimensional numerical computation of the flow fields and pumping performances for the lobed mixer-ejector are conducted using full Navier-Stokes equations. In the computation, the inlet of the primary flow uses the mass flowrate boundary condition. The inlet of the second flow and the outlet of the mixing flow use the pressure boundary condition. Compared with the relative experimental resuits, it is shown that the present calculation is reasonable. And a series of numerical studies is performed to obtain the effects of area ratio and length-to-diameter ratio of mixing duct on pumping coefficient and thermal mixing efficiency of a lobed mixer-ejector.

High mixing effectiveness lobed nozzles and mixing mechanisms

For a circular lobed nozzle with the exit plane displaced from the center body,adding a central plug at exit or replacing the nozzle with an alternating-lobe nozzle can improve the mixing effectiveness.In this study,numerical investigations of jet mixing in the lobed nozzles with a central plug and alternating-lobe nozzles in pumping operation were conducted.The effects of the central plugs with the wake ranging from attached to separated flow on the mixing were analyzed,along with the mechanism of improving the mixing performance in a"sword"alternating-lobe nozzle.The simulation results reveal that the large-scale mixing rate,which is dominated by streamwise vortices,is related to the intensity of the attainable heat and mass transfer in the streamwise vortices.The effects of the streamwise vortices on the normal vortex ring are virtually a manifestation of the heat and mass transfer/mixing process of the streamwise vortices.The simulation results also show that the central plug with the attached rear-flow performs better in improving the mixing effectiveness and pumping performance;on the contrary,if the rear-flow is separated,more pressure loss will be induced.In particular,a completely separated flow over the rear of the central plug will severely degrade the attainable heat and mass transfer in the streamwise vortices.For the sword alternating-lobe nozzle,wider sword deep troughs help to increase the flux of the secondary stream around the core region and delay the confluence of the primary stream in the region between the deep and shallow troughs.Thus,the mixing is improved in the middle and posterior segments.Compared to the lobed nozzle with a central plug,the improved sword alternating-lobe nozzle can achieve a higher mixing effectiveness with much less pressure loss,which is preferred in situations when the power loss of the engine is restricted.

Convective heat transfer on flat and concave surfaces subjected to an impinging jet form lobed nozzle

A tri-dimensional lobed nozzle is concerned in the jet impingement on a flat target and a concave target in the current study. The jet impingement heat transfer experiments are conducted under two jet Reynolds numbers(Re=10000 and 20000) and four nozzle-to-surface distances(H/d=2, 4, 6 and 8). Simultaneously, to characterize the flow dynamics of lobed jet impingement onto different target surfaces, some computations are conducted under a specific jet Reynolds number. The results show that the lobed jet is capable of achieving an increase of stagnation Nusselt number about 25% in relative to the round jet at small nozzle-tosurface distances. However, at large nozzle-to-surface distances, the lobed jet otherwise weakens the convective heat transfer in the vicinity of jet stagnation, especially under high jet Reynolds number. When compared to the flat target, approximately a20%–30% reduction of stagnation Nusselt number is produced on a concave target, which is attributed to the combined effect of destabilization and confinement due to the concave curvature.

Performance analysis of lobed nozzle ejectors for high altitude simulation of rocket engines

Ejectors are used in high altitude testing of rocket engines to create vacuum for simulat-ing the engine test in vacuum conditions.The performance of an ejector plays a vital role in creating vacuum at the exit of the engine nozzle and the nozzle design exit pressure at the time of ignition.Consequently,the performance of ejectors has to be improved to reduce the consumption of active fluid.In this investigation,the performance of an ejector has been improved by changing the exit shear plane of the nozzle.Conventionally,conical nozzles are used for creating the required momentum.Lobes of 4 no’s,6 no’s and 8 numbers for an equivalent area ratio=5.88 are used to increase the shear area.The influence of shear plane variation in the suction pressure is studied by a detailed CFD analysis.