Vibration Attenuation Mechanism of the Rotor System with Anisotropic Support Stiffness

Using the one-dimensional finite element method, the dynamic behaviour of a double-disk rotor system with anisotropic supports is studied in this paper. First, the natural frequencies, whirl state and unbalance response of the rotor system are analysed. Then, the vibration attenuation mechanism of the rotor system under the effect of bearing damping and accelerating rotor is discussed in detail. The research results show that stiffness anisotropy makes natural frequency lines of the rotor system tend to diverge from each other. The damping in bearings not only decreases the amplitude of forward and backward whirls but also reduces the spin speed range of backward whirl. The whirl orbit of the rotor system approximates a straight line at the spin speeds near the critical point of the backward and forward whirls. For the unbalance response of the rotor system with anisotropic supports, the forward natural frequency dominates in the direction of the strong stiffness axis, while the unbalance response in the direction of the weak stiffness axis is mainly affected by the backward natural frequency. Increasing the run-up acceleration can decrease the amplitude of backward and forward whirls, but it cannot reduce the spin speed range of backward whirl

Numerical and Experimental Study on the Multiobjective Optimization of a Two-Disk Flexible Rotor System

With the ever-increasing requirement for the thrust to weight ratio, the rotational speed of modern aeroengine is increasingly improved; thus most of the aeroengine rotor is flexible. Some dynamic problems, such as excessive vibration, appear due to the increase of the rotation speed of the aeroengine. The aim of this study is to reduce the vibration level of the flexible rotor system through optimum design. A laboratory scale two-disk flexible rotor system representing a typical aeroengine rotor system is designed. A combinational optimization strategy coupling the rotordynamics calculation software ANSYS and the multidisciplinary optimization software ISIGHT is proposed to optimize the rotor system. The positions of the disks are selected as the design variables. Constraints are imposed on critical speeds. The disks’ amplitudes and bearings’ transmitted forces are chosen as the optimization objectives. Using this strategy, the optimal positions of the two disks are obtained. The numerical optimization results are verified by the experiments based on the test rig. The results show a significant vibration level reduction after optimization

Numerical studies on supersonic spray combustion in high-temperature shear flows in a scramjet combustor

Numerical simulation is applied to detail the combustion characteristics of n-decane sprays in highly compressible vortices formed in a supersonic mixing layer. The multi-phase reacting flow is modeled, in which the shear flow is solved Eulerianly by means of direct numerical simulation, and the motions of individual sub-grid point-mass fuel droplets are tracked Lagrangianly. Spray combustion behaviors are studied under different ambient pressures. Results indicate that ignition kernels are formed at high-strain vortex braids, where the scalar dissipation rates are high. The flame kernels are then strongly strained, associated with the rotation of the shearing vortex, and propagate to envelop the local vortex. It is observed that the flammable mixtures entrained in the vortex are burned from the edge to the core of the vortex until the reactants are completely consumed. As the ambient pressure increases, the high-temperature region expands so that the behaviors of spray flames are strongly changed. An overall analysis of the combustion field indicates that the time-averaged temperature increases, and the fluctuating pressure decreases, resulting in a more stable spray combustion under higher pressures, primarily due to the acceleration of the chemical reaction

Flexible rotor optimization design with considering the uncertainty of unbalance distribution

A flexible rotor optimization design considering the uncertainty of the unbalance is carried out in this paper. Assuming that the magnitude and phase of unbalance obey normal distribution and uniform distribution respectively, the uncertainty can be quantitatively described. The classical 6 Sigma method is used to perform uncertain optimization design of the rotor system considering this uncertainty. The theoretical results are verified by experiments in which 36 sets of unbalance are artificially distributed to the rotor to simulate the uncertainty. In experiment, the amplitude response of the two disks and the acceleration response of the two bearings are decreased by 14%, 21.5%, 37.2% and 46% respectively in terms of standard deviation. It can be concluded that the optimization design considering the uncertainty can reduce the fluctuation of the response and improving the robustness of the results

Analysis of Dynamic Operating Characteristics of a Pulse Detonation Turbine Engine

In order to obtain the dynamic operating characteristics of a pulse detonation turbine engine (PDTE), a transient model is established considering the shaft dynamics and the volumetric effect of the components in the PDTE. The accuracy of the model is verified with the experimental data from a pulse detonation prototype engine. The deviations between the calculated data and the experimental results are no more than 7.61%. The numerical results show that the operating state of the PDTE will change gradually with the increase of the fuel flow rate or the firing frequency. The quasi-steady state calculations show that there are maximum values for the rotor speed, thrust, and specific thrust when the fuel flow rate is increased from 0.0056 kg/s to 0.0129 kg/s at firing frequency of 10 Hz. The rotor speed, thrust, and specific thrust will suddenly decrease due to the over rich of fuel in the PDC with the increasing of the fuel flow rate. The specific fuel consumption has a minimize value during this process. When the firing frequency is increased from 7 Hz to 18 Hz at a fixed fuel flow rate, the performance parameters such as the thrust, specific thrust, and specific fuel consumption have a similar variation trend. The extremum values of the performance parameters are obtained at firing frequency of 12 Hz. For the dynamic operating process of the PDTE, parameters such as the rotor speed or pressure ratio of the compressor are increased in a cyclic oscillation way when the fuel flow rate or the firing frequency is changed

Analysis of Dynamic Operating Characteristics of a Pulse Detonation Turbine Engine

In order to obtain the dynamic operating characteristics of a pulse detonation turbine engine (PDTE), a transient model is established considering the shaft dynamics and the volumetric effect of the components in the PDTE. The accuracy of the model is verified with the experimental data from a pulse detonation prototype engine. The deviations between the calculated data and the experimental results are no more than 7.61%. The numerical results show that the operating state of the PDTE will change gradually with the increase of the fuel flow rate or the firing frequency. The quasi-steady state calculations show that there are maximum values for the rotor speed, thrust, and specific thrust when the fuel flow rate is increased from 0.0056 kg/s to 0.0129 kg/s at firing frequency of 10 Hz. The rotor speed, thrust, and specific thrust will suddenly decrease due to the over rich of fuel in the PDC with the increasing of the fuel flow rate. The specific fuel consumption has a minimize value during this process. When the firing frequency is increased from 7 Hz to 18 Hz at a fixed fuel flow rate, the performance parameters such as the thrust, specific thrust, and specific fuel consumption have a similar variation trend. The extremum values of the performance parameters are obtained at firing frequency of 12 Hz. For the dynamic operating process of the PDTE, parameters such as the rotor speed or pressure ratio of the compressor are increased in a cyclic oscillation way when the fuel flow rate or the firing frequency is changed