Volume 40, Issue 3

The present work aims to analyze the natural and whirl frequencies of a slant-cracked functionally graded rotor-bearing system using finite element analysis for the flexural vibrations. The functionally graded shaft is modelled using two nodded beam elements formulated using the Timoshenko beam theory. The flexibility matrix of a slant-cracked functionally graded shaft element has been derived using fracture mechanics concepts, which is further used to develop the stiffness matrix of a cracked element. Material properties are temperature and position-dependent and graded in a radial direction following power-law gradation. A Python code has been developed to carry out the complete finite element analysis to determine the Eigenvalues and Eigenvectors of a slant-cracked rotor subjected to different thermal gradients. The analysis investigates and further reveals significant effect of the power-law index and thermal gradients on the local flexibility coefficients of slant-cracked element and whirl natural frequencies of the cracked functionally graded rotor system.

This paper presents the experimental results of an annular combustor. A full scale full annular combustion chamber is tested at ground test stand simulating altitude off-design operating conditions. Traversing thermocouple rakes are used to measure temperatures over the entire annulus at combustor exit. The radial temperature profile is found to be a strong function of operating parameters while the circumferential pattern factor is within the design goal. Increase in reference Mach number at these off-design conditions has caused the redial temperature profiles to deviate and increase from the intended profile. These results will be used for benchmarking the computational model. The computational model will be used for detail study of the temperature non-uniformity over the entire flight envelope and also for modification of combustor liner for performance improvement.

Quasi-one-dimensional model is the most effective way to realize the rapid iterative design of the overall scheme and control system of RBCC aircraft and has become a research hotspot. In the current research, the quasi-one-dimensional model of RBCC propulsion system is simplified. The model does not include physical characteristics such as wall heat transfer, boundary layer change, specific heat ratio change and transonic flow singularity, which makes the accuracy of the model low and cannot adapt to flight control in large airspace. A RBCC model with high accuracy and adaptability to wide-speed fly is established in this paper. Firstly, based on the laws of kinetic energy conservation and energy conservation, the thrust model of ejection mode is established. Secondly, the quasi-one-dimensional flow control equation is deduced, and the physical mechanism models of core flow area, transonic flow, pre-combustion shock train, heat release law and mixing efficiency are established. On this basis, the quasi-one-dimensional flow model of RBCC dual-mode ramjet is established. Thirdly, based on the law of momentum conservation, the mathematical model of rocket mode is deduced, and the thrust model of rocket mode is established. Finally, the accuracy of the quasi-one-dimensional model is verified by CFD numerical simulation and direct-connect experiment. Taking a typical RBCC launch vehicle as an example, the wide-speed performance of the RBCC propulsion system is calculated and analyzed.

An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 10 5 . The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery ( C p  = 0.76) and a lower total pressure loss coefficient of ( C L  = 0.12) at a 17° swirl angle.

The scramjet model used in the control system needs to consider both accuracy and real-time requirements. In this paper, a quasi-one dimensional component level model method for scramjet is proposed. Under the premise of meeting the real-time requirement, this modeling method has higher calculation accuracy, and can obtain higher thrust performance without exceeding the limits. In order to improve the calculation accuracy of the scramjet model, the boundary layer correction and the interaction between shock wave and boundary layer are considered in the inlet and isolator modeling process by using reference temperature method. For the scramjet compression components, the inlet and isolator models are simplified based on shock train theory to improve real-time performance. Meanwhile, the combustor model and nozzle model are established and the combustor model is established with the combination of equal area and isothermal based on temperature limitation. Considering the boundary layer correction, the accuracy of the inlet and isolator model is improved by 8.79 and 7.9% respectively. Compared with the equal area combustion mode, the combined combustion mode can get higher thrust. In the C + + simulation environment, the average calculation time of each state point is about 25 ms which meets the real-time requirements.

Relative high pressure in the rotor–stator (RS) cavity helps to improve its seal effectiveness. However, every 1% increase in the cavity flow results in a decrease of the stage power of turbine by about 0.32% and a decrease in the aerodynamic efficiency by about 0.33%. With rim cavity flow, the pressure distribution in the suction side of rotor blade domain and the turbine flow structure show obvious circumferential differences, which are caused by the interactions between the RS cavity flow and the mainstream. The flow characteristic in the false externally-induced ingress in rim clearance is proposed for the first time to reveal the flow mechanism in the effect of RS rim cavity flow on the turbine.

In this paper, an improved aerodynamic performance optimization method for 3-D low Reynolds number (Re) rotor blade is proposed. A conventional optimization procedure of blade is usually divided into three parts, such as the parameterization method, the fitness value evaluation and the optimization algorithm. This work is mainly focused on the first two parts. The parametrization method, Camber-FFD, is presented based on the camber parametrization method and the free-form deformation algorithm (FFD). The shape of 3-D blade is parameterized by the incidence angles and the coordinates of the maximum camber points. The fitness value evaluation has been realized with the help of an adaptive topological back propagation multi-layer forward artificial neural network (BP-MLFANN). During the training of BP-MLFANN, the hybrid particle swarm optimization method combined with the modified very fast simulate annealing algorithm (HPSO-MVFSA) is adopted to determine the neural network topology adaptively. To verify the effectiveness of this aerodynamic optimization method, the aerodynamic performance of a 3-D low-Re blade, such as Blade D900, is optimized, and the results are compared and analyzed based on the experiments and simulations. It is proved that this aerodynamic optimization method is feasible.

The Reynolds-averaged Navier–Stokes (RANS) solver was used to calculate, using a test rig to verify the accuracy. The interaction mechanism between different sealed cooling air and gas ingestion at the rotor-stator cavity and chute rim clearance has been investigated. Several groups of representative sealed cooling air flow were selected to explore the cooling efficiency, flow characteristics, tangential and radial velocity ratios in the cavity and the pressure potential field characteristics of trailing edge. The conclusions are obtained: the sealed cooling air flow rate has a significant marginal effect on the sealing effect. The gas ingestion behavior under the small sealed cooling air flow belongs to the disc cavity intrusion, and the intrusion and outflow regions at the of rim clearance are obviously divided into the intrusion characteristic section and the outflow characteristic section. The ingestion behavior under large sealed cooling air flow belongs to clearance ingestion, and the intrusion flow is limited to the chute rim clearance position, which cannot be further penetrated into the cavity. At this time, the clearance area and the cavity area become independent, and the gas ingestion characteristics depend more on the internal flow of the clearance and the vortex structure formed.

Aero-engine on-board steady state model is an important part of many advanced engine control algorithms. In order to build a high accuracy and real-time steady-state onboard model in a large envelope, an ICPSM (improved compact propulsion system model) based on batch normalize neural network is proposed in this paper. Compared with piecewise linearization model and support vector machine model, conventional CPSM which is mainly composed of baseline model and nonlinear sub model has the advantages of high real-time performance and small data storage. However, as the similarity conversion error increases with the distance from the design point, the cumulative error of the conventional baseline model also increases, which makes the model unable to maintain high accuracy in the full envelope. Thus, a high accuracy baseline model in full envelope based on batch normalize neural network is proposed in this paper. The simulation result shows that compared with the conventional compact propulsion system model, the percentage error of parameters of the improved compact propulsion system model based on the batch neural network is reduced by two times, the single step operation time is reduced by 18%, and the data storage of the onboard model is reduced as well.

Based on studies of the flow structure in a short cylindrical vortex chamber, the dependence of the flow rate coefficient on its geometric parameters is proposed. It is shown that the liquid flow form in the chamber’s axial vortex the pressure on which surface is corresponds to the pressure of the outflow cavity. These results are used to measure pressure in high-temperature cavities, using a sleeve with a diameter equal to or slightly larger than the diameter of the axial vortex. The sleeve is installed in the vortex chamber, and connects the pressure on its surface to the pressure sensor. The possibility of using a vortex chamber as a damper of pressure fluctuations has been substantiated. The design of the vortex damper and its tests results are presented; these show the possibility of increasing the stabilization time of the outlet pressure more than three-fold. Variants of regulating devices with a vortex chamber, functioning without changing the flow cross-sections, are proposed and the results of their tests are presented. This is achieved either by introducing an obstacle into the chamber cavity or by displacing the axis of the outlet nozzle position.

The experimental system of pulse detonation engine (PDE) is set up to investigate the influence of equivalence ratios on detonation noise characteristics. The research results show that as the equivalence ratio increasing, the amplitudes of detonation noise in all angles and locations increase, and the t B also increases simultaneously, while the t A increases first and then decreases. The equivalence ratio also has a great influence on the intensity of the detonation noise signal in the frequency band of 10–100 Hz, which increases firstly and then decreases with the increase of the equivalence ratio, and the maximum value is obtained at equivalence ratio of 1.1. The results are of great significance to study the mechanism of detonation noise and promote the process of the engineering application.

Numerical calculation of infrared emission from hot plume is of great significance for flight monitoring and detections. In this paper, the SNB (statistical narrow band) model established with parameters derived from the high-resolution spectral database HITEMP 2010 is used to perform the hot plume infrared signature simulations. Accuracy of the model is examined by the exact LBL (line by line) method, which proves the model’s reliability to predict radiative properties of combustion gases. In the application part, the SNB model is used to analyze infrared signatures of aircraft plumes cruising at different flight altitudes. The results show that cruising at a higher-altitude will obviously reduce the plume infrared emission. Besides, the plume infrared emissive energy mainly concentrates in a special wavenumber interval and can be strongly absorbed by atmosphere.