A Theoretical Model for Flow Instability Inception in Transonic Fan/Compressors

2013 ◽  
Author(s):  
Xiaofeng Sun ◽  
Xiaohua Liu ◽  
Dakun Sun
Keyword(s):  
Theoretical Model ◽  
Flow Field ◽  
High Speed ◽  
Cfd Simulation ◽  
Flow Instability ◽  
Computational Cost ◽  
Mean Flow ◽  
Transonic Compressor ◽  
Onset Point ◽  
Transonic Fan

This paper applies a theoretical model, which has been developed recently, to calculate the flow instability inception of axial transonic fan/compressors system. After the mean flow field is computed by steady CFD simulation, a body force approach, which is a function of flow field data, is taken to represent the effects of discrete blades on the flow field and duplicate the physical sources of flow turning and loss. Further by applying appropriate boundary conditions and spectral collocation method, a group of homogeneous equations will yield from which the stability equation can be derived. The singular value decomposition method is adopted over a series of fine grids in frequency domain to solve the resultant eigenvalue problem, and the onset point of flow instability can be judged by the imaginary part of the resultant eigenvalue. The present investigation is to validate the feasibility of calculating the stall onset point for single stage transonic compressor. It is shown that this model is capable of predicting instability inception point of transonic flow with reasonable accuracy, and it is sustainable in terms of computational cost for industrial application. It is shown that this model can provide an unambiguous judgment on stall inception without numerous requirements of empirical relations of loss and deviation angle. It provides a possibility to check over-predicted stall margin during the design phase of new high speed fan/compressors. In addition, the effect of flow compressibility on the stall onset point calculation for transonic rotor is studied.

Calculation of Flow Instability Inception in High Speed Axial Compressors

2014 ◽  
Author(s):  
Xiaohua Liu ◽  
Yanpei Zhou ◽  
Xiaofeng Sun ◽  
Dakun Sun
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Body Force ◽  
Present Model ◽  
Flow Instability ◽  
Tip Clearance ◽  
Force Model ◽  
Fine Grid ◽  
Stall Margin ◽  
Onset Point

This paper applies a theoretical model developed recently to calculate the flow instability inception point in axial high speed compressors system. After the mean flow field is computed by steady CFD simulation, a body force approach, which is a function of flow field data and comprises of one inviscid part and the other viscid part, is taken to duplicate the physical sources of flow turning and loss. Further by applying appropriate boundary conditions and spectral collocation method, a group of homogeneous equations will yield from which the stability equation can be derived. The singular value decomposition method is adopted over a series of fine grid points in frequency domain, and the onset point of flow instability can be judged by the imaginary part of the resultant eigenvalue. The first assessment is to check the applicability of the present model on calculating the stall margin of one single stage transonic compressors at 85% rotational speed. The reasonable prediction accuracy validates that this model can provide an unambiguous judgment on stall inception without numerous requirements of empirical relations of loss and deviation angle. It could possibly be employed to check over-computed stall margin during the design phase of new high speed fan/compressors. The following validation case is conducted to study the nontrivial role of tip clearance in rotating stall, and a parameter study is performed to investigate the effects of end wall body force coefficient on stall onset point calculation. It is verified that the present model could qualitatively predict the reduced stall margin by assuming a simplified body force model which represents the response of a large tip clearance on the unsteady flow field.

Calculation of Flow Instability Inception in High Speed Axial Compressors Based on an Eigenvalue Theory

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Xiaohua Liu ◽  
Yanpei Zhou ◽  
Xiaofeng Sun ◽  
Dakun Sun
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Body Force ◽  
Present Model ◽  
Flow Instability ◽  
Tip Clearance ◽  
Force Model ◽  
Fine Grid ◽  
Stall Margin ◽  
Onset Point

This paper applies a theoretical model developed recently to calculate the flow instability inception point in axial high speed compressors system with tip clearance. After the mean flow field is computed by 3D steady computational fluid dynamics (CFD) simulation, a body force approach, which is a function of flow field data and comprises of one inviscid part and the other viscid part, is taken to duplicate the physical sources of flow turning and loss. Further by applying appropriate boundary conditions and spectral collocation method, a group of homogeneous equations will yield from which the stability equation can be derived. The singular value decomposition (SVD) method is adopted over a series of fine grid points in frequency domain, and the onset point of flow instability can be judged by the imaginary part of the resultant eigenvalue. The first assessment is to check the applicability of the present model on calculating the stall margin of one single stage transonic compressors at 85% rotational speed. The reasonable prediction accuracy validates that this model can provide an unambiguous judgment on stall inception without numerous requirements of empirical relations of loss and deviation angle. It could possibly be employed to check overcomputed stall margin during the design phase of new high speed compressors. The following validation case is conducted to study the nontrivial role of tip clearance in rotating stall, and a parameter study is performed to investigate the effects of end wall body force coefficient on stall onset point calculation. It is verified that the present model could qualitatively predict the reduced stall margin by assuming a simplified body force model which represents the response of a large tip clearance on the unsteady flow field.

Experimental Investigation During Stall and Surge in a Transonic Fan Stage and Rotor-Only Configuration

2006 ◽  
Author(s):  
A. J. Gannon ◽  
G. V. Hobson ◽  
R. P. Shreeve ◽  
I. J. Villescas
Keyword(s):  
High Speed ◽  
Fast Response ◽  
Pressure Measurements ◽  
Post Processing ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
The Difference ◽  
Data Signal ◽  
Transonic Fan ◽  
Casing Pressure

High-speed pressure measurements of a transonic compressor rotor-stator stage and rotor-only configuration during stall and surge are presented. Rotational speed data showed the difference between the rotor-only case and rotor-stator stage. The rotor-only case stalled and remained stalled until the control throttle was opened. In the rotor-stator stage the compressor surged entering a cyclical stalling and then un-stalling pattern. An array of pressure probes was mounted in the case wall over the rotor for both configurations of the machine. The fast response probes were sampled at 196 608 Hz as the rotor was driven into stall. Inspection of the raw data signal allowed the size and speed of the stall cell during its growth to be investigated. Post-processing of the simultaneous signals of the casing pressure showed the development of the stall cell from the point of inception and allowed the structure of the stall cell to be viewed.

A Theory on the Onset of Acoustic Resonance in a Multistage Compressor

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Xiaohua Liu ◽  
Tobias Willeke ◽  
Florian Herbst ◽  
Jun Yang ◽  
Joerg Seume
Keyword(s):  
Rotor Blade ◽  
High Speed ◽  
Flow Instability ◽  
Computational Simulation ◽  
Computational Cost ◽  
Acoustic Resonance ◽  
Excitation Source ◽  
Acoustic Excitation ◽  
Tip Leakage Flow ◽  
Suction Surface

A novel theoretical model of the internal flow field in multistage axial compressors based on an eigenvalue approach is developed, in order to predict the onset of acoustic resonance in aircraft engines. Using an example high-speed four-stage compressor, it is shown that one of the resultant frequencies is in excellent agreement with the experimental data in terms of acoustic resonance. On the basis of the computed natural frequency of the whole compression system and the measured spanwise distribution of static pressure, the location of the acoustic excitation source can be found in the third stage. Unsteady flow simulations of the full annulus of this stage reveal two criteria for acoustic excitation at the rotor-blade tip, reversed flow near the suction surface and flow impingement on the pressure surface. Additionally, a fast Fourier transform of the unsteady pressure field at the upper rotor-blade span verifies the existence of the computed unstable frequency of the oscillating tip leakage flow. Using this novel theory, which combines a theoretical calculation of flow-instability frequency of the global system with the computational simulation of a single stage, the onset mechanism and location of the excitation source of acoustic resonance in multistage turbomachinery can be explained at acceptable computational cost.

Characteristics of Tip Clearance Flow Instability in a Transonic Compressor

2010 ◽  
Author(s):  
Chunill Hah ◽  
Melanie Voges ◽  
Martin Mueller ◽  
Heinz-Peter Schiffer
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Flow Instability ◽  
Tip Clearance ◽  
Piv Measurements ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Tip Clearance Vortex

In the present study, unsteady flow phenomena due to tip clearance flow instability in a modern transonic axial compressor rotor are studied in detail. First, unsteady flow characteristics due the oscillating tip clearance vortex measured with the particle image velocimetry (PIV) and casing-mounted unsteady pressure transducers are analyzed and compared to numerical results with a large eddy simulation (LES). Then, measured characteristic frequencies of the unsteady flow near stall operation are investigated. The overall purpose of the study is to advance the current understanding of the unsteady flow field near the blade tip in an axial transonic compressor rotor near the stall operating condition. Flow interaction between the tip leakage vortex and the passage shock is inherently unsteady in a transonic compressor. The currently applied PIV measurements indicate that the flow near the tip region is unsteady even at the design condition. This self-induced unsteadiness increases significantly as the compressor operates toward the stall condition. PIV data show that the tip clearance vortex oscillates substantially near stall. The calculated unsteady characteristics from LES agree well with the PIV measurements. Calculated unsteady flow fields show that the formation of the tip clearance vortex is intermittent and the concept of vortex breakdown from steady flow analysis does not seem to apply in the current flow field. Fluid with low momentum near the pressure side of the blade close to the leading edge periodically spills over into the adjacent blade passage. The spectral analysis of measured end wall and blade surface pressure shows that there are two dominant frequencies near stall. One frequency is about 40–60% of the rotor rotation and the other dominant frequency is about 40–60% of the blade passing frequency (BPF). The first frequency represents the movement of a large blockage over several consecutive blade passages against the rotor rotation. The second frequency represents traditional tip flow instability, which has been widely observed in subsonic compressors. The LES simulations show that the second frequency is due to movement of the instability vortex.

Numerical Simulation of the Flow in a Large-Scale Thrust Bearing

2010 ◽  
Author(s):  
Hong-Jie Wang ◽  
Ru-Zhi Gong ◽  
De-Ping Lu ◽  
Zhong-De Wu ◽  
Feng-Chen Li
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Large Scale ◽  
Thrust Bearing ◽  
Cfd Simulation ◽  
Internal Flow ◽  
Heat Radiation ◽  
Heavy Load ◽  
Cfd Method ◽  
Water Turbines

Thrust bearing is a key component of large-scale water turbine. It closely relates to the efficiency of large-scale water turbines, and even determines whether the large-scale turbine can operate normally. With the development of the capacitance of water turbines, thrust bearing will develop to the direction of high speed and heavy load. The structure, strength, lubrication and the characteristic of heat radiation of large-scale thrust bearing were often researched in the past. To study the flow condition of the large-scale thrust bearing and analyze the load characteristics, CFD simulation was carried out on the model of thrust bearing. In this study, CFD method was used to simulate the internal flow field of the large-scale thrust bearing. The model researched was a thrust bearing for 1000MW water turbines. The diameter of the thrust bearing was over 5.8 meters, and the maximum thrust load of the bearing can reach to 60MN. The thin gap between the runner and the pad was usually neglected in the published CFD calculations of thrust bearing. But the thin gap was taken into account in this investigation. 1/12 of the model was used as the computational field and periodic boundary was used in the calculation. The standard κ-ε turbulence model was used to simulate the thrust bearing model, and the flow field in the thrust bearing was obtained. The thin gap between the runner and the pad is a wedge. The pressure and velocity distribution in the thrust bearing and thin gap was calculated respectively with conditions of different thin gaps and different rotational speeds of runner. After that, the relationship between carrying capacity and the size of clearance or the speed of the runner through analyzing the data has been obtained from the results of the calculation.

Basic Studies of Flow-Instability Inception in Axial Compressors Using Eigenvalue Method

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Xiaohua Liu ◽  
Dakun Sun ◽  
Xiaofeng Sun
Keyword(s):  
High Speed ◽  
Flow Instability ◽  
Flow Perturbation ◽  
Axial Compressors ◽  
Singular Value Decomposition Method ◽  
Onset Point ◽  
Eigenvalue Method ◽  
Point Calculation ◽  
Basic Studies ◽  
Value Decomposition

This paper applies a theoretical model developed recently to calculate the flow-instability inception of an axial transonic single stage compressor. After several calculation methods are compared, the singular value decomposition method is adopted to solve the resultant eigenvalue problem in which the involved matrix is rather large due to multistage configuration. The onset point of flow instability is judged by the imaginary part of the resultant eigenvalue. The effect of flow compressibility on the stall onset point calculation for the transonic rotor is studied. It is shown that the compressibility of flow perturbation plays a major role in computing high speed compressor flow stability.

scholarly journals An Investigation of Acoustic Attenuation Performance of Silencers with Mean Flow Based on Three-Dimensional Numerical Simulation

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Wei Fan ◽  
Li-Xin Guo
Keyword(s):  
Flow Field ◽  
Flow Velocity ◽  
Cfd Simulation ◽  
Data Transfer ◽  
Transmission Loss ◽  
Three Dimensional ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
3D Fem ◽  
Expansion Chamber

Transmission loss (TL) is often used to evaluate the acoustic attenuation performance of a silencer. In this work, a three-dimensional (3D) finite element method (FEM) is employed to calculate the TL of some representative silencers, namely, circular expansion chamber silencer and straight-through perforated pipe silencer. In order to account for the effect of mean flow that exists inside the silencer, the 3D FEM is used in conjunction with the Computational Fluid Dynamics (CFD) simulation of the flow field. More concretely, the 3D mean flow field is computed by firstly using CFD, and then the obtained mean flow data are imported to an acoustic solution undertaken using FEM. The data transfer between the two steps is accomplished by mesh mapping. The results presented demonstrate good agreement between present TL predictions and previously published experimental and numerical works. Also, the details of the flow inside the silencers may be studied. Furthermore, the effect of mean flow velocity on acoustic attenuation performance of the silencers is investigated. It is concluded that for the studied silencers, in general, increasing flow velocity increases the TL and decreases the resonance peaks.

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