Designing method of acceleration and deceleration control schedule for variable cycle engine

Studies show that different geometries of a Variable Cycle Engine(VCE)can be adjusted during the transient stage of the engine operation to improve the engine performance.However,this improvement increases the complexity of the acceleration and deceleration control schedule.In order to resolve this problem,the Transient-state Reverse Method(TRM)is established in the present study based on the Steady-state Reverse Method(SRM)and the Virtual Power Extraction Method(VPEM).The state factors in the component-based engine performance models are replaced by variable geometry parameters to establish the TRM for a double bypass VCE.Obtained results are compared with the conventional component-based model from different aspects,including the accuracy and the convergence rate.The TRM is then employed to optimize the control schedule of a VCE.Obtained results show that the accuracy and the convergence rate of the proposed method are consistent with that of the conventional model.On the other hand,it is found that the new-model-optimized control schedules reduce the acceleration and deceleration time by 45%and 54%,respectively.Meanwhile,the surge margin of compressors,fuel–air ratio and the turbine inlet temperature maintained are within the acceptable criteria.It is concluded that the proposed TRM is a powerful method to design the acceleration and deceleration control schedule of the VCE.

Integration of high-fidelity model of forward variable area bypass injector into zero-dimensional variable cycle engine model

Forward Variable Area Bypass Injector(FVABI)is one of key components which contributes to modulate the cycle parameters of Variable Cycle Engine(VCE)under various operation conditions.The modeling method of zero-dimensional FVABI was reviewed and its deficiency was analyzed based on FVABI flow characteristic.In order to improve the accuracy of VCE performance simulation,the high-fidelity modeling method of FVABI was developed based on its working characteristics.Then it was coupled with the zero-dimensional VCE model and the multi-level VCE model was built.The results indicate that the geometric and aerodynamic parameters can affect the interaction between the two airflows and the zero-dimensional FVABI model is too simple to predict the component performance accurately,especially when the FVABI inner bypass is chocked.Based on the performance curves for single bypass mode and the regression model of multi-scale support vector regression for double bypass mode,the high-fidelity model can predict FVABI performance accurately and rapidly.The integration of high-fidelity FVABI model into zerodimensional VCE model can be done by adjusting iterative variables and balance equations.The multi-level model has good convergence and it can predict VCE performance when the FVABI inner bypass is chocked.

Analytical redundancy of variable cycle engine based on variable-weights neural network

In this paper, variable-weights neural network is proposed to construct variable cycle engine’s analytical redundancy, when all control variables and environmental variables are changing simultaneously, also accompanied with the whole engine’s degradation. In another word,variable-weights neural network is proposed to solve a multi-variable, strongly nonlinear, dynamic and time-varying problem. By making weights a function of input, variable-weights neural network’s nonlinear expressive capability is increased dramatically at the same time of decreasing the number of parameters. Results demonstrate that although variable-weights neural network and other algorithms excel in different analytical redundancy tasks, due to the fact that variableweights neural network’s calculation time is less than one fifth of other algorithms, the calculation efficiency of variable-weights neural network is five times more than other algorithms. Variableweights neural network not only provides critical variable-weights thought that could be applied in almost all machine learning methods, but also blazes a new way to apply deep learning methods to aeroengines.

Flow control of double bypass variable cycle engine in modal transition

To study the change mechanism and the control of the variable cycle engine in the process of modal transition,a variable cycle engine model based on component level characteristics is established.The two-dimensional CFD technology is used to simulate the influence of mode selection valve rotation on the engine flow field,which improves the accuracy of the model.Furthermore,the constant flow control plan is proposed in the modal transition process to reduce the engine installed drag.The constant flow control plan adopts the augmentation linear quadratic regulator control method.Simulation results indicate that the control method is able to effectively control the bypass ratio and demand flow of the variable cycle engine,and make the engine transform smoothly,which ensures the stable operation of the engine in modal transition and the constant demand flow of the engine.

Numerical study of steady flow characteristics of a rear variable-area bypass injector with alternating area regulator

The mixing effectiveness of the airflow between the inner and outer bypass inlets of a Rear Variable-Area Bypass Injector(RVABI)is the key to the afterburner performance of variable cycle engines.This paper describes an optimized RVABI design based on an alternating area regulator to improve the velocity/temperature uniformity of the incoming flow at the afterburner.Compared with a classical RVABI,numerical simulations show that the proposed alternating RVABI performs better in terms of thermal mixing efficiency and total pressure loss in different variable cycle engine modes.Both the increasing air contact area between the inner and outer bypass of alternating structure RVABI,and a larger streamwise vortex in the inner bypass inlet due to the proposed alternating lobe structure in the RVABI contribute to the significantly increase of mixing effectiveness.Besides,the alternating regulator induces strong streamwise vortex,which helps to improve the airflow mixing with its vortex-induced velocity.The interaction between the streamwise vortex and azimuthal vortex further promises the velocity/temperature uniformity after the RVABI.With the increase of alternating lobe’s height ratio,the covering area of the streamwise vortex and the azimuthal vortex is enlarged,which further enhances the thermal mixing efficiency of the RVABI.This design gives an insight into the future design and optimization of RVABI.

Investigations of entrainment characteristics and shear-layer vortices evolution in an axisymmetric rear variable area bypass injector

In this study,firstly,for the axisymmetric RVABI,the change-rule of adverse pressure gradient caused by radial velocity during the transition of internal flow mode in variable geometry is summarized,and a Bypass Ratio(BR) iterative algorithm based on the empirical correlation of non-equilibrium pressure is proposed.The algorithm can estimate the nonlinear relationship between area ratio and BR,with an error range falling below 6.5%.Then,we discuss the favorable effect of uniform mixing on the thrust augmentation of mixed exhaust under variable BR conditions.From this point of view,the characteristics of vortices evolution in different shear strength jets are compared,to clarify the effect of variable cycle parameters on jet mixing.As the results suggest,when ■ is as low as 0.22,the K-H disturbance is of high-frequency wavelet property,and it is difficult to induce large-scale spanwise vortices.The macro migrations of fluid elements in span wise vortices and the diffusion effect caused by edge tearing is weak,which is not conducive to the energy exchange between the two streams.However,the low ■ jet will also correspondingly weaken the viscous dissipation effect of vortices.It is concluded that the dissipation level is proportional to the 2.31 power of the ■.

Exploration of acceptable operating range for a compression system in a double bypass engine

The variable cycle engine is distinguished by its highly adjustable compression system,whose aerodynamic characteristic is extremely complex.To explore the regulation range of a double bypass engine compression system,a multi-dimensional analysis method is developed,through which the coupling mechanism between the compressor component and the bypass is examined.The operation zones of the compressor components and the bypass system are proposed,and the operation range of the compression system is obtained by calculating the overlapping part of the operation zones.The results show that in the double bypass mode,there exists a minimum mode selector valve area and a minimum core driven fan stage stall margin that ensures a feasible bypass flow,the two parameters correspond to each other.Under the given fan and core driven fan stage conditions,the maximum value of the inner bypass ratio is restricted by the upper limit of the forward variable area bypass injector and the maximum Mach number in the total bypass,while the minimum value of the inner bypass ratio depends on the lower limit of the forward variable area bypass injector geometry and the system recirculation margin.The single bypass mode is a unique condition of the double bypass mode,as the operation zone of the compressor component degenerates from a two-dimensional surface to a straight line.There are multiple bypass states available in the single bypass mode,while the regulation range of the bypass ratio is jointly restricted by the operation range of the high pressure compressor and the aerodynamic boundary of the forward variable area bypass injector.

Numerical analysis for the matching of the core driven compression system in a double bypass engine

The numerical analysis for the matching of the core driven compression system in a double bypass variable cycle engine was presented in this paper.The system consists of a one-stage-core driven fan stage(CDFS),an inner bypass duct and a five-stage high pressure compressor(HPC),providing two basic operating modes: the single bypass mode and the double bypass mode.Variable vanes are necessary to realize the mode switch of the system.The correct matching in the double bypass mode requires a proper combination of the mass flow,total pressure ratio and blade speed.The work capacity of the system decreases in the double bypass mode and the pressure ratio tends to decrease more for the CDFS and the front stages of the HPC.The overall system efficiency is higher in the double bypass mode.The radial distributions of aerodynamic parameters are similar in different modes.The notable redistribution of mass flow downstream the CDFS in the single bypass mode leads to strong radial flows and additional mixing losses.The absolute flow angles into the inner bypass increase for the inner span and decrease for the outer span when the system is switched from the single bypass mode to the double bypass mode.