Anping Hou

Flow Control of Annular Compressor Cascade by Synthetic Jets

An experimental investigation conducted in a stationary annular cascade wind tunneldemonstrated that unsteady flow control using synthetic jets (zero mass flux) could effec-tively reduce flow separation in the axial compressor cascade. The synthetic jets drivenby speaker were introduced through the casing radially into the flow-field just adjacent tothe leading edge of the compressor cascade. The experimental results revealed that theaerodynamic performance of the compressor cascade could be improved amazingly bysynthetic jets and the maximum relative reduction of loss coefficient was up to 27.5%. Theoptimal analysis of the excitation frequency, excitation location was investigated at dif-ferent incidences. In order to obtain detailed information on flow-field structure, thedigital particle image velocimetry (DPIV) technique was adopted. The experimental re-sults indicated that the intensity of wake vortices became much weaker and streamlinesbecame smoother and more uniform with synthetic jets.

Numerical and Test Investigation on an Aircraft Inlet Distortion

Abstract Subscale wind tunnel test of an aircraft vehicle is performed at different Mach number, mass-flow and angle of attack. CFD model, corrected by test results, is also presented to predict inlet performance and total pressure distortion. The result shows total pressure recovery decreases and distortion level rises when Mach number increases from subsonic to supersonic speed, AOA is negative and mass-flow value is too large or too small. Compared linear interpolation based on test result of discrete probes, numerical simulation has advantages in showing inlet flow field predicting actual surface distortion level in AIP plane. Swirl distortion is induced by vortex near the fuselage and adjustable ramp and can strengthen total pressure distortion in AIP at negative AOA. And appropriate suction mass-flow coefficient (1.7% to 3%) is beneficial for inlet performance and total pressure distortion control.

Analysis on Flutter Characteristics of Transonic Compressor Blade Row by a Fluid-Structure Coupled Method

A time domain numerical approach is carried out to enhance the understanding of three dimensional blade row aeroelastic characteristics under the parallel computation. The vibration energy of unsteady aerodynamic force on the entire blade row is investigated using numerical solution of 3-D Navier-Stokes equations, coupled with structure finite element models for the blades to identify modal shapes and the structural deformations simultaneously. Interactions between fluid and structure are dealt with in a coupled manner, based on the interface information exchange until convergence in each time step. With this approach good agreement between the numerical results and the experimental data is observed. The flutter mechanism is analyzed according to deformation of the blades. The effect of inter-blade phase angle (IBPA) is included in the analysis by releasing the hypothesis of constant phase angle between adjacent blades in the traveling wave model. The results illustrate fully three dimensional unsteady nonlinear behaviors, such as limit-cycle oscillation. It is shown that all blades flutter at the same mode and frequency, but not at the same amplitude and IBPA. The analysis of the influence of different tip clearance gaps on the flutter characteristics of the blade row is also performed.© 2012 ASME

Investigation on stall inception of axial compressor under inlet rotating distortion

This paper applies a numerical approach to improve the understanding of reaction to various inflow conditions for the compressor system and the mechanism of stall inception under rotating inflow distortions. Full annulus, unsteady, three-dimensional computational fluid dynamics has been used to simulate an axial low-speed compressor operating under rotating distorted inflow conditions. The development of the flow through the rotor is then explained in terms of the redistribution of the flow field and the process of stall inception. The results suggest that the increased flow incidence close to the tip region under co-rotating inflow distortion plays an important role on the stall inception process. The presence of a strong modal wave is observed under co-rotating inflow distortions. This leads to a significant impact on the loss of stall margin, as compared with other distorted inflow conditions. There is a significant peak in the flow coefficient at stall for co-rotating inlet distortion. It can be interpreted as a resonant behavior of the compressor under a strong interaction between the flow field and inlet distortion. It indicates that the stall inception is triggered by the perturbation of the rotating distorted inflow through the long length scale disturbances.

Effects of Nonuniform Tip Clearance on Fan Performance and Flow Field

Nonuniform tip clearance, caused by the deformation of the casing (casing ovalization), exists in all fans to some extent. However, description of the flow behavior with this kind of nonuniform clearance is seldom given in the open literature. In this paper, both steady and unsteady calculations are performed to study the influence of the nonuniform clearance on fan performance and flow field. The investigation method is based on three dimensional RANS equations, carried out by the ANSYS CFX fluid solver. A new factor τ, which is in the range of 0 to 1, is defined to represent the nonuniformity of the tip clearance. A series of numerical models with different tip clearance nonuniformities τ are investigated. In addition, the original, uniform tip clearance is also performed serving as a reference. The results indicate that the fan performance is mainly affected by two factors: the clearance nonuniformity τ and the average clearance level. There is a clear decreasing trend of the fan performance with increasing nonuniformity and average tip clearance level. The maximum clearance can contribute to the reduction of stall margin. Furthermore, the effects of nonuniform clearance on tip leakage vortex and aerodynamic force are also discussed in detail. The deformation of the casing can affect the pressure fluctuation and thus increase the amplitude of the aerodynamic force.Copyright

Investigation on the Effect of Asymmetric Vane Spacing on the Reduction of Rotor Blade Vibration

A transient method to analyze blade forced response under stator-rotor wake influence is proposed in dealing with asymmetric aerodynamic load. The vibration response of the blades is calculated in the fluid-structure coupled manner for the asymmetric vane spacing. Four different types of modification are adopted in the investigation. The reduction effect on the vibration stress due to the asymmetric vane spacing is examined by comparing the response characteristics of frequency and amplitude. Though the asymmetric vane spacing does not much affect the performance of the turbine, the results show that the proper asymmetric vane spacing can decrease the levels of the excitation force at specific frequencies to control the downstream blade forced response. The stress amplitude at the vane passing frequency is decreased by 51% in the most desirable modification in the study. After investigating the vibration characteristics of the blades under the wake excitation from upstream, the mechanism of the vibration reduction due to the asymmetric vane spacing is analyzed.Copyright

Flow Field and Vibration Behavior of the Rotor due to Mistuning IGV in a Transonic Compressor

A fluid-structure coupled approach is utilized to study the influence of mistuning IGV blade on rotor flow field and blade vibration behavior of a transonic compressor. Interaction between fluid and structure are dealt with in a coupled manner, based on the interface exchange of information between the aerodynamic and structural model. The computation fluid mesh is updated at every time step with an improved algebraic method. The unsteady flow field of IGV/rotor with one mistuned IGV blade is studied using full-annulus, 3D CFD model. Then a reduced half-annulus CFD model with one mistuned IGV blade coupled with rotor FEA model is used to identify model shapes, frequencies, vibration stress and the structural deformations. The results show that the mistuning IGV cause the performance map of rotor shift towards the lower flow rate from the rotor with normal IGV. A significant low-frequency and its multiple pressure fluctuation appear in mistuning IGV wake, the fundamental frequency of IGV wake is closely related with the number of mistuning blade. Compared with normal IGV model, the vibration characteristics of rotor blade changed, blade vibration frequency is the same as the main frequency of mistuning IGV wake.Copyright

Investigation on Blade Flutter in Transonic Compressor With a Coupled Numerical Approach

A fluid-solid coupled approach for investigating blade flutter in a compressor under the parallel computation of aeroelasticity is presented. The unsteady flow field of rotor is studied by a CFD model of the entire compressor flowpath, coupled with a finite element model for the blades to identify modal shapes, natural frequencies, vibratory stress and the structural deformations. Interactions between fluid and structure are dealt with in a coupled manner, based on the interface exchange of information between the aerodynamic and structural model. The coupled computational results are presented and compared with experimental data. Blade variations and the way of these variations is related to vibratory stress amplitude are investigated. Transient responses of blade stress are provided to determine whether flutter occurs. This coupled method successfully predicts the flutter of a transonic rotor over range of operating conditions. The nonlinear behaviors of flow field, blade vibrations, and inter-blade phase angle are discussed.Copyright

A Diagnostic and Design Approach of Axial Compressor Based on Local Dynamics

The vortex separate flow that exists on the wall surfaces of blade, shroud, and hub is a major source of the performance loss for the modern axial fans/compressors. To-date the principal diagnostic and redesign approaches to reducing the vortex separate loss have been based on the principal parameters such as pressure, velocity, or Mach number. The original vortex separate flow may be decreased, but a new vortex separate flow which emanates from an else area may be produced, thus the whole course of designing a high performance axial compressor becomes more slowly. This paper presents a novel diagnostic approach based on Local Dynamics, which probes into physical sources of dynamic process and is quite different from principal methods, and a design scheme incorporating new restraint conditions, which depends less on the empirical formulas or models. As examples, one transonic fan rotor is diagnosed, and another low-speed compressor is diagnose and inverse-designed. The examples show that the new approach can enhance the load capability of the axial compressor and provide the high efficiency in a relatively wide working range.Copyright

Control of Unsteady Separated Flows Inside Axial Compressors by Synthetic Jets

By means of planar cascade wind tunnel experiments and relevant numerical simulations, synthetic jets have been used to control boundary layer unsteady separation from the suction side of a compressor airfoil. The reliability of the numerical simulations was validated by experimental results, and optimal analyses of various excitation parameters were carried out by means of numerical simulations. The excitation effects reached the best when the unsteady excitation frequency is equal to (or close to) the characteristic frequency of trailing edged vortex shedding, when the excitation was forced at the separation point and when the excitation direction was vertical to the profile. Generally, the larger the excitation amplitude, the better the excitation effects. The studies showed that this kind of unsteady excitation could regulate boundary layer evolution and development, promote the merging of small vortexes and enhance time-averaged aerodynamic performances in wide incidence, in which the loss coefficient decreases from 0.297 to 0.232 ( =-21.9%), and the static pressure ratio increases from 1.058 to 1.103 ( =77.6%). Based on these optimal analyses, the discrepancy between the experimental and simulation results could be explained, and an improved experiment scheme was thereby put forward. ω δ p δ