scholarly journals Measurement of Flow Pattern Within a Rotating Stall Cell in an Axial Compressor

2006 ◽  
Author(s):  
J. Lepicovsky ◽  
E. P. Braunscheidel
Keyword(s):  
Flow Direction ◽  
Flow Behavior ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Pressure Probe ◽  
Ensemble Averaging ◽  
Flow Angle ◽  
High Frequency Response ◽  
Actual Flow ◽  
Design Speed

Effective active control of rotating stall in axial compressors requires detailed understanding of flow instabilities associated with this compressor regime. Newly designed miniature high frequency response total and static pressure probes as well as commercial thermoanemometric probes are suitable tools for this task. However, during the rotating stall cycle the probes are subjected to flow direction changes that are far larger than the range of probe incidence acceptance, and therefore probe data without a proper correction would misrepresent unsteady variations of flow parameters. A methodology, based on ensemble averaging, is proposed to circumvent this problem. In this approach the ensemble averaged signals acquired for various probe setting angles are segmented, and only the sections for probe setting angles close to the actual flow angle are used for signal recombination. The methodology was verified by excellent agreement between velocity distributions obtained from pressure probe data, and data measured with thermoanemometric probes. Vector plots of unsteady flow behavior during the rotating stall regime indicate reversed flow within the rotating stall cell that spreads over to adjacent rotor blade channels. Results of this study confirmed that the NASA Low Speed Axial Compressor (LSAC) while in a rotating stall regime at rotor design speed exhibits one stall cell that rotates at a speed equal to 50.6% of the rotor shaft speed.

Investigation of the Surge Behavior of a Multi-Stage Axial Compressor With a Multi-Sensor Probe

2011 ◽  
Author(s):  
P. Waniczek ◽  
P. Jeschke ◽  
H. Schoenenborn ◽  
T. Metzler
Keyword(s):  
Flow Field ◽  
Velocity Vector ◽  
Reverse Flow ◽  
Axial Compressor ◽  
Leading Edge ◽  
Field Structure ◽  
Pressure Probe ◽  
High Time Resolution ◽  
Trailing Edge ◽  
Flow Angle

The surge behavior of the first rotor of an eight-stage aero engine high pressure compressor has been investigated experimentally. For that purpose, a new multi-hole pressure probe was developed and adapted to the axial compressor test rig. Due to the high time resolution measurements (more than 45000 measuring points per surge cycle) it is possible to investigate the dynamic flow field of a surge cycle in a time-accurate manner. The results especially show the complex flow field structure at the surge inception. At the rotor leading edge the flow shows perturbations with high amplitudes and initiates the surge event, whereas the flow at the rotor trailing edge is less influenced. The inflow vector turns around the leading edge of the blade relatively slowly. During that turn around three different characteristic flow conditions have been identified. These are ‘zero rotor turning’, ‘turbine-like flow’ and ‘no flow’. ‘No flow’ means, that the absolute velocity vector reaches a flow angle where it consists of a pure tangential velocity component. That is the point where the reverse flow phase is initiated. A 180° shift of the flow direction at the rotor trailing edge is the consequence. After a quasi-steady reverse flow the acceleration of the flow starts. In total, this paper gives new and fundamental insights into the unsteady flow field phenomena during various surge cycles. Especially the transient velocity vector imparts a good idea of the flow field structure of a surging compressor.

scholarly journals Flow angle measurement of a yawed turbine and comparison to models

2017 ◽  
Author(s):  
Tyler Gallant ◽  
David A. Johnson
Keyword(s):  
Wind Turbine ◽  
Flow Direction ◽  
Angle Of Attack ◽  
Experimental Results ◽  
Pressure Probe ◽  
Flow Profile ◽  
Local Flow ◽  
Flow Angle ◽  
Angle Measurements ◽  
Probe Measurements

Abstract. The torque generated by a wind turbine blade is dependent on several parameters, one of which is the angle of attack. Several models for predicting the angle of attack in yawed conditions have been proposed in the literature, but there is a lack of experimental data to use for direct validation. To address this problem, experiments were conducted under controlled conditions at the University of Waterloo Wind Generation Research Facility using a 3.4 m diameter test turbine. A five-hole pressure probe was installed in a modular 3D printed blade and was used to measure the angle of attack, α, as a function of several parameters. Local flow angle measurements for all azimuthal angles were obtained at radial positions of r / R = 0.55 and 0.72 at tip speed ratios (λ) of 5.0, 3.6, and 3.1. The yaw offset of the turbine was varied from −15° to +15°. Span-wise flow angle measurements are presented for the r / R = 0.55 cases, and show the variation in radial flow direction throughout yawed rotation. Experimental results were compared directly to angle of attack values calculated using a model proposed by Morote in 2015. Modeled values were found to be in close agreement with the experimental results. The angle of attack was shown to vary cyclically in the yawed case while remaining mostly constant when aligned with the flow, as expected. These five-hole probe measurements were also used to characterise the upstream flow profile. Wind speeds determined using the five-hole probe measurements are presented and are in agreement with measurements obtained in the wind facility during testing. The quality of results indicates the potential of the developed instrument for wind turbine measurements.

A Three-Dimensional Unsteady Through-Flow Model for Rotating Stall in Axial Compressors

2020 ◽  
Author(s):  
Jin Guo ◽  
Jun Hu ◽  
Xuegao Wang ◽  
Rong Xu
Keyword(s):  
Flow Model ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Design Stage ◽  
Preliminary Evaluation ◽  
Source Terms ◽  
Axial Compressors ◽  
Through Flow

Abstract Rotating stall is a natural limit to the stable operating range of compressors due to the inverse pressure gradient of viscous gas. Effective prediction of compressor stall boundary is an important guarantee for the successful development of aeroengine. In this paper, a three-dimensional unsteady through-flow model based on body force theory is developed to reflect the dynamic stall process of multistage axial compressors with acceptable computational costs. The influence of blade geometric parameters is fully considered in blade force source terms. The source terms are related to the attack angle and Mach number of the blade inlet using the deviation angle and loss model in the through-flow theory. Meanwhile, the temporal lag response of the source terms to the upstream flow conditions is taken into account. Therefore, it can be utilized for predicting the off-design performance and rotating stall characteristics of multistage axial compressors. The developed model is validated on a two-stage low-speed axial compressor. The calculated performance line and stall cell speed are in agreement with the experimental results. The unsteady flow behavior of the compressor during stall is presented by the model. The results indicate that the developed model has the potential to be applied to the preliminary evaluation of compressor stability in design stage.

Spatial Correlation Based Stall Inception Analysis

2007 ◽  
Author(s):  
Joshua D. Cameron ◽  
Scott C. Morris
Keyword(s):  
Spatial Correlation ◽  
High Speed ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Fourier Decomposition ◽  
Stall Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Wide Range ◽  
Response Pressure

Investigations of stall inception and compressor pre-stall behavior have used a variety of techniques to make inferences about the mechanisms of rotating stall inception. Many of these techniques utilized data from arrays of circumferentially spaced hot-wires or high frequency response pressure transducers. This paper presents results from the application of several typical analysis techniques to the interpretation of unsteady casing pressure measurements recorded during two representative stall event in a high-speed axial compressor stage. Results from visual pressure trace inspection, spatial Fourier decomposition, wavelet filtering, and traveling wave energy techniques are presented and compared. The effects of measurement and analysis parameters are also briefly discussed. A new analysis technique based on windowed two-point spatial correlation between adjacent stall inception sensors is described. The method was found to provide both spatial and temporal information about rotating features in the compressor flow and is insensitive to low pass filtering and parameter selection over a wide range of values. It was also found to be valuable for analysis of both pre-stall and stall inception behavior.

scholarly journals Rotating Stall Measurements in the Vaneless Diffuser of a Radial Flow Compressor

1982 ◽  
Author(s):  
P. M. Ligrani ◽  
R. Van Den Braembussche ◽  
M. Roustan
Keyword(s):  
Flow Behavior ◽  
Reynolds Numbers ◽  
Rotating Stall ◽  
Hot Wire ◽  
Vaneless Diffuser ◽  
Inlet Flow ◽  
Flow Angle ◽  
Measurement Results ◽  
Flow Compressor ◽  
Hot Film

Results from an experimental study of flow behavior at the inlet of a vaneless diffuser of a centrifugal compressor are presented. Hot-film measurements and measurement results from a crossed hot-wire probe are discussed for operating points having inlet flow coefficients ranging from 0.006 to 0.019 at different Reynolds numbers. Instantaneous, time-averaged, and phase-averaged absolute velocity and flow angle at the diffuser inlet are deduced from the hot-wire signals after correction for mean density variations. These results show how flow behavior varies in stable, rotating stall and surge regimes of compressor operation. The critical flow angle at the onset of rotating stall shows agreement with other measurements confirming the importance of diffuser inlet width and diffuser inlet flow angle on the onset of rotating stall in vaneless diffusers.

scholarly journals Numerical Study on Rotating Stall in Finite Pitch Cascades

1994 ◽  
Author(s):  
Toshio Nishizawa ◽  
Hiroyuki Takata
Keyword(s):  
Numerical Study ◽  
Flow Behavior ◽  
Vortex Method ◽  
Rotating Stall ◽  
Axial Distance ◽  
Flow Angle ◽  
Guide Vanes ◽  
Stall Inception ◽  
Stall Cells ◽  
Inception Point

Flow behavior of rotating stall in finite pitch cascades is discussed through numerical analyses by means of a vortex method, which is particularly developed to solve unsteady flows through stalled cascades. It is shown that stall vortex and unstall vortex are, shed from each stalled blade periodically, and the behavior of these vortices has considerable effects on various properties of rotating stall, such as magnitude of flow fluctuation, propagation velocity, the number of stall cells, and so on. When a rotating stall is initiated and developed in an isolated cascade at smaller inlet flow angles around the stall inception point, a plural number of stall cells tend to propagate on the growing process, although only one stall cell survives eventually in a fully developed rotating stall. At larger flow angles, a single stall cell splits into two separate cells as it propagates. These processes are found for the first time through the analyses of finite pitch cascades. With the inlet guide vanes upstream, a plural number of stall cells can grow in a fully developed rotating stall, and the number of stall cells depends on the exit flow angle of the guide vanes and the axial distance between the two cascades. The numerical results agree well with experiments.

scholarly journals A High-Frequency-Response Pressure Probe for the Measurement of Unsteady Flow Between Two Rotors in a Hydrodynamic Turbomachine

1996 ◽  
Author(s):  
C. Achtelik ◽  
J. Eikelmann
Keyword(s):  
Unsteady Flow ◽  
Frequency Response ◽  
High Frequency ◽  
Torque Converter ◽  
Pressure Probe ◽  
Ensemble Averaging ◽  
Probe Diameter ◽  
High Frequency Response ◽  
Single Sensor ◽  
Response Pressure

A new, specially-developed high-frequency-response pressure probe was used to measure the unsteady flow in the interaction region between the pump and the turbine in a hydrodynamic torque converter. In order to reduce the probe diameter, a single-hole, single-sensor cylindrical probe (⌀=1.33mm) was developed, to replace the standard multi-hole probe. The smaller the probe the higher the accuracy in unsteady flow. Therefore this is an improvement over three-hole probe. Three-hole probe measurements were simulated by recording data in three different angular positions. The time variable velocity vectors were determined using the probe’s calibration coefficients and the knowledge of the rotor positions (measured by angle-encoders) for every measurement value. During the data processing, a double ensemble averaging was carried out, taking into account the positions of the pump and the turbine.

scholarly journals Flow responses alteration by geometrical effects of tubercles on plates under the maximal angle of attack

2020 ◽  
pp. 095440622097543
Author(s):  
KS Mu ◽  
ABH Kueh ◽  
PN Shek ◽  
MR Mohd Haniffah ◽  
BC Tan
Keyword(s):  
Flow Direction ◽  
Flow Behavior ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Control Case ◽  
Reattachment Length ◽  
Flow Recirculation ◽  
Pressure Profiles ◽  
Maximal Angle ◽  
Geometrical Effects

Plates with leading-edge tubercles experience beneficially more gradual aerodynamics stalling when entering the post-stall regime. Little is known, however, about the corresponding aquatic flow responses when these tubercles-furnished plates are subjected to the maximal angle of attack, with the flow direction perpendicular to their planar area. Hence, this study presents numerically, by means of the flow behavior solver ANSYS, the flow responses alteration in terms of the geometrical effects of tubercles on plates through changes in amplitudes (5 mm, 10 mm, 15 mm) and wavelengths (50 mm, 100 mm, 150 mm) under the maximal angle of attack in comparison to a control case, i.e., without tubercles. Additional to the commonly examined flow velocity and pressure, characteristics such as wake (area, reattachment length, flow recirculation intensity) and newly defined downstream vortical parameters (area, perimeter, and Feret diameters) for the vortex region have been proposed and assessed. It is found that the drag increases with the tubercle wavelength but corresponds inversely with the tubercle amplitude. By correlating with the best beneficial velocity and pressure profiles, it has been characterized that the optimally performing plate is the one that generates the greatest flow recirculation intensity, wake area, and reattachment length, corresponding to the capability to produce also the highest vortical area, perimeter, and major Feret diameter. Compared to the control case, all plates with tubercles alter beneficially these flow behaviors. In conclusion, plates with tubercles contribute favorably to the flow behaviors under the maximal angle of attack compared to the control case while the newly proposed downstream parameters could serve capably as alternatives in corroborating the flow physics description in future studies.

INVESTIGATION ON MODE CHARACTERISTICS OF ROTATING INSTABILITY AND ROTATING STALL IN AN AXIAL COMPRESSOR

2021 ◽  
pp. 1-24
Author(s):  
Zeyuan Yang ◽  
Yadong Wu ◽  
Hua Ouyang
Keyword(s):  
Axial Compressor ◽  
Calibration Method ◽  
Acoustic Mode ◽  
Rotating Stall ◽  
Frequency Spectra ◽  
Compressor Rotor ◽  
Mode Decomposition ◽  
Aerodynamic Instability ◽  
Rotating Instability ◽  
Mode Order

Abstract Rotating instability (RI) and rotating stall (RS) are two types of aerodynamic instability in axial compressors. The former features the side-by-side peaks below the blade passing frequency (BPF) in frequency spectra, and the latter represents one or more stall cells rotating in the compressor. This paper presents an experimental on the nearfield pressure and farfield acoustic characteristics of RI phenomenon in a low-speed axial compressor rotor, which endures both RI and RS at several working conditions. In order to obtain the high-order modes of RI and other aerodynamic instability, a total of 9 or 20 Kulites are circumferentially mounted on the casing wall to measure the nearfield pressure fluctuation using a mode order calibration method. Meantime in the farfield 16 microphones are planted to measure the acoustic mode order using the compressive sensing method. Through calibration the experiments acquire the mode orders generated by RI and the interaction between RI and BPF, which is higher than the number of transducers. As for RS, the mode decomposition shows a mode order of 1, indicating one single stall cell rotating in the compressor. This experiment also shows that amplitude of RI modes is decreased when RS occurs, but RS modes and RI modes will both be enhanced if the flow rate is further reduced. This experiment reveals that RI experiences three stages of “strengthen-weaken-strengthen”, and hence RI may not be regarded only as “prestall” disturbance.

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