Unsteady Secondary Flow in an Annular Compressor Cascade

2013 ◽  
Author(s):  
Georg Hermle ◽  
Martin Lawerenz
Keyword(s):  
Secondary Flow ◽  
Cross Correlation ◽  
Incidence Angle ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Blade Tip ◽  
Rotating Instability ◽  
Blade Tip Clearance

Subject of the experimental investigations presented is the analysis of secondary flow in an annular compressor cascade. Focus lies on the so-called rotating instability. The investigations concentrate on the unsteady pressure field in the area of the blade tip clearance in order to get deeper understanding of the phenomenon of rotating instability. Therefore, transducers were mounted along the leading edges around the circumference of the cascade. This arrangement allows the determination of the coherence and the phasing between the transducers by the cross correlation via Fourier and wavelet transform. The results show the influence of the Mach number and the incidence angle on the onset of the phenomenon. Furthermore, a relation between the characteristic frequencies of the rotating instability to certain modal types can be stated. Moreover, the wavelet cross power spectrum suggests that the phenomenon is not continuously present within the spectra but shows an unsteady appearance.

Experimental Investigations Into Pressure Field in Tip Clearance of Shrouded Rotor Blades

2002 ◽  
Author(s):  
Krzysztof Kosowski ◽  
Marian Piwowarski
Keyword(s):  
Pressure Distribution ◽  
Pressure Pulsation ◽  
Pressure Field ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Pressure Pulsations ◽  
Blade Tip ◽  
Shrouded Rotor ◽  
Blade Tip Clearance

The experimental investigations into the pressure field in the shroud clearance were performed on a one-stage air model turbine of impulse type. Measurements of pressure distribution were carried out for different rotor eccentricities, different values of axial gap and of rotor-stator misalignment, different rotor speeds and different turbine load. The experimental investigations proved that: a) the pressure in the blade tip clearance is not stationary but it pulsates, b) the effect of nozzle trailing edge can be observed in the blade shroud clearance, c) for a given turbine output, the rotor-stator eccentricity and rotor-stator misalignment appear the most important parameters influencing the pressure distribution in the shroud clearance. Aiming to investigate the pressure pulsation transmission through the leakage flow in the blade shroud clearances, pulsations of different amplitudes and frequencies were excited in the turbine inlet duct and corresponding changes of pressure were measured along the shroud width, followed by appropriate harmonic analysis. The investigations were performed for forced pulsations with frequencies ranging from 1Hz to 8 Hz. In all the examined cases, the frequency of pressure pulsations remained unchanged, while the amplitude of the pulsation decreased gradually along the tip clearance. The frequency of these pressure pulsations in the tip clearance was equal to the frequency of the pressure pulsation at the turbine stage inlet and to the frequency of pressure pulsation at the turbine flow passage’s exit.

scholarly journals Validation Studies of Linear Oscillating Compressor Cascade and Use of Influence Coefficient Method

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
H. M. Phan ◽  
L. He
Keyword(s):  
Boundary Layer ◽  
Tip Clearance ◽  
Influence Coefficient ◽  
Far Field ◽  
Compressor Cascade ◽  
Linear Cascade ◽  
Influence Coefficient Method ◽  
Blade Tip ◽  
Coefficient Method ◽  
Blade Tip Clearance

Abstract Advanced predictions of blade flutter have been continually pursued. It is noted however that validation cases of unsteady CFD methods against experimental cases with detailed 3D unsteady pressures are still rather lacking. The main objectives of the present work are two-folds. First, validate and understand the characteristics of blade tip clearance, as well as a bubble-type flow separation for an unsteady CFD solver against a 3D oscillating cascade experiment. And second, examine the applicability of the influence coefficient method (ICM) as widely used in an oscillating linear cascade setup. In the first part, the capability of a widely used commercial solver (CFX) for unsteady flows induced by a 3D oscillating compressor cascade is examined. The present computations have shown consistently a destabilizing effect of increasing blade tip clearance, in agreement with the experiment. More remarkably, the computational analyses reveal a distinctive interplay between the inlet endwall boundary layer and the tip clearance in relation to the aerodynamic damping. Different inlet endwall boundary layer thicknesses are shown to lead to qualitatively different aeroelastic stability characteristics in relation to tip clearance. The aero-damping variation with the tip clearance under the influence of the inlet endwall boundary layer seems to correlate closely to a balancing act between the passage vortex and the tip leakage vortex. The tip clearance aeroelastic behavior seems also in line with a simple quasi-steady analysis. On the other hand, the mid-chord laminar bubble separation on suction surface, though with a clear signature in the local aero-damping, has negligible effects on the overall stability. The second part aims to examine computationally the applicability of the influence coefficient method in a linear cascade setup. The comparison between the cascade-based ICM data and a baseline “tuned cascade” shows that the differences in the sensitivity to the far-field treatment can be significant, depending on inter-blade phase angles. On the other hand, non-linearity effects closely relevant to the basic linear assumption of the ICM are shown to only have a small influence. The present results suggest that extra caution should be exercised when comparing a CFD-based tuned cascade model with a finite cascade-based ICM model, at conditions close to acoustic resonance. The resultant discrepancies may well arise from the inherently different far-field sensitivities between the two models, rather than those typical numerical and physical modeling aspects of interest (e.g., meshing, spatial and temporal discretization errors as well as turbulence modeling).

scholarly journals Validation Studies of Linear Oscillating Compressor Cascade and Use of Influence Coefficient Method

2019 ◽  
Author(s):  
H. M. Phan ◽  
L. He
Keyword(s):  
Boundary Layer ◽  
Tip Clearance ◽  
Influence Coefficient ◽  
Far Field ◽  
Compressor Cascade ◽  
Linear Cascade ◽  
Influence Coefficient Method ◽  
Blade Tip ◽  
Coefficient Method ◽  
Blade Tip Clearance

Abstract Advanced predictions of blade flutter have been continually pursued. It is noted however that validation cases of unsteady CFD methods against experimental cases with detailed 3D unsteady pressures are still rather lacking. The main objectives of the present work are two-folds. Firstly, validate and understand the characteristics of blade tip clearance, as well as a bubble-type flow separation for an unsteady CFD solver against a 3D oscillating cascade experiment. And secondly, examine the applicability of the Influence Coefficient Method (ICM) as widely used in an oscillating linear cascade setup. In the first part, the capability of a widely used commercial solver (CFX) for unsteady flows induced by a 3D oscillating compressor cascade is examined. The present computations have shown consistently a destabilizing effect of increasing blade tip clearance, in agreement with the experiment. More remarkably, the computational analyses reveal a distinctive interplay between the inlet endwall boundary layer and the tip clearance in relation to the aerodynamic damping. Different inlet endwall boundary layer thicknesses are shown to lead to qualitatively different aeroelastic stability characteristics in relation to tip clearance. The aero-damping variation with the tip-clearance under the influence of the inlet endwall boundary layer seems to correlate closely to a balancing act between the passage vortex and the tip-leakage vortex. The tip clearance aeroelastic behaviour seems also in line with a simple quasi-steady analysis. On the other hand, the mid-chord laminar bubble separation on suction surface, though with a clear signature in the local aero-damping, has negligible effects on the overall stability. The second part aims to examine computationally the applicability of the influence coefficient method in a linear cascade setup. The comparison between the cascade based ICM data and a baseline ‘tuned cascade’ shows that the differences in the sensitivity to the far-field treatment can be significant, depending on interblade phase angles. On the other hand, non-linearity effects closely relevant to the basic linear assumption of the ICM are shown to only have a small influence. The present results suggest that extra caution should be exercised when comparing a CFD-based tuned cascade model with a finite cascade-based ICM model, at conditions close to acoustic resonance. The resultant discrepancies may well arise from the inherently different far-field sensitivities between the two models, rather than those typical numerical and physical modelling aspects of interest (e.g. meshing, spatial and temporal discretization errors as well as turbulence modelling).

J051052 tudy on the Tip Leakage Flow in Linear Compressor Cascade : Effects of Blade Tip Clearance and Tip Velocity)

2011 ◽  
Vol 2011 (0) ◽  
pp. _J051052-1-_J051052-4
Author(s):  
Kazunari MATSUDA ◽  
Kenichi FUNAZAKI ◽  
Hideo TANIGUCHI ◽  
Hiromasa KATO ◽  
Masafumi KUMAGAI ◽  
...  
Keyword(s):  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Cascade Effects ◽  
Linear Compressor Cascade ◽  
Tip Velocity ◽  
Blade Tip Clearance

Investigation of rotating instability characteristics in an axial compressor with different tip clearances

2021 ◽  
pp. 095441002199362
Author(s):  
Yadong Wu ◽  
Tao Li ◽  
Shengzhi Lai ◽  
Jie Tian ◽  
Hua Ouyang
Keyword(s):  
Flow Field ◽  
Strong Stability ◽  
Tip Clearance ◽  
Dynamic Mode Decomposition ◽  
Field Energy ◽  
Dynamic Mode ◽  
Mode Decomposition ◽  
Blade Tip ◽  
Rotating Instability ◽  
Blade Tip Clearance

It is believed that the rotating instability phenomenon originating in the compressor tip region is due to leakage flow, which is closely associated with the blade tip clearance. In this work, we have studied the correlation between the dynamic characteristics of blade tip flow and the size of tip clearance for a single-stage low-speed compressor rotor, so as to unveil the mechanism of rotating instability. The full-passage numerical simulations were carried out to obtain the variations in frequency, circumferential mode, and spatial flow field associated with rotating instability. The results of spatial mode decomposition with open clearance show the number of predominate instability modes identified are 25 and 30, respectively. By diminishing the blade tip clearance, all these unstable modes greatly diminished. The formation and propagation of the tip leakage vortex were described in detail to show the development of rotating instability. Two flow field reduced-order methods, proper orthogonal decomposition and dynamic mode decomposition, were used to analyze the flow field, energy proportion, and stability of related modes under different tip clearances. The results show that the first several modes with strong stability account for a large proportion of energy and make a major contribution to flow unsteadiness. The energy proportion and stability of rotating instability decrease as the tip clearance becomes smaller. The blade-passing frequency and its multiples emerge as the main components of the flow field.

Dual-Laser Probe Measurement of Blade-Tip Clearance

1999 ◽  
Vol 121 (3) ◽  
pp. 481-485 ◽  
Author(s):  
H. S. Dhadwal ◽  
A. P. Kurkov
Keyword(s):  
Operating Conditions ◽  
Tip Clearance ◽  
Laser Probe ◽  
Included Angle ◽  
Blade Tip ◽  
Optic Systems ◽  
Tip Radius ◽  
Dual Laser ◽  
Blade Tip Clearance

This paper describes two dual-laser probe integrated fiber optic systems for measuring blade tip clearance in rotating turbomachinery. The probes are nearly flush with the casing inner lining, resulting in minimal flow disturbance. The two probes are closely spaced in a circumferential plane and are slanted at an angle relative to each other so that the blade tip traverse time of the space between the two laser beams varies with the tip radius, allowing determination of the tip clearance at the rotor operating conditions. The tip clearance can be obtained for all the blades in a rotor with a single system, provided there are no synchronous vibrations present at a particular operating condition. These probes were installed in two holders; one provided an included angle between the probes of 20 deg, and the other provided an included angle of 40 deg. The two configurations were calibrated in a vacuum spin rig facility that is capable of reproducing realistic blade tip speeds.

scholarly journals Dual-Laser Probe Measurement of Blade-Tip Clearance

1998 ◽  
Author(s):  
Harbans S. Dhadwal ◽  
Anatole P. Kurkov
Keyword(s):  
Operating Conditions ◽  
Tip Clearance ◽  
Laser Probe ◽  
Included Angle ◽  
Blade Tip ◽  
Optic Systems ◽  
Tip Radius ◽  
Dual Laser ◽  
Blade Tip Clearance

This paper describes two dual-laser probe integrated fiber optic systems for measuring blade tip clearance in rotating turbomachinery. The probes are nearly flush with the casing inner lining resulting in minimal flow disturbance. The two probes are closely spaced in a circumferential plane and are slanted at an angle relative to each other so that the blade tip traverse time of the space between the two laser beams varies with the tip radius allowing determination of the tip clearance at the rotor operating conditions. The tip clearance can be obtained for all the blades in a rotor with a single system, provided there are no synchronous vibrations present at a particular operating condition. These probes were installed in two holders; one provided an included angle between the probes of 20 degrees, and the other provided an included angle of 40 degrees. The two configurations were calibrated in a vacuum spin rig facility that is capable of reproducing realistic blade tip speeds.

scholarly journals Creep-Based Reliability Evaluation of Turbine Blade-Tip Clearance with Novel Neural Network Regression

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3552 ◽  
Author(s):  
Chun-Yi Zhang ◽  
Jing-Shan Wei ◽  
Ze Wang ◽  
Zhe-Shan Yuan ◽  
Cheng-Wei Fei ◽  
...  
Keyword(s):  
Neural Network ◽  
High Pressure ◽  
Reliability Analysis ◽  
Response Surface ◽  
Response Surface Method ◽  
Tip Clearance ◽  
Strong Nonlinearity ◽  
Surface Method ◽  
Blade Tip ◽  
Blade Tip Clearance

To reveal the effect of high-temperature creep on the blade-tip radial running clearance of aeroengine high-pressure turbines, a distributed collaborative generalized regression extremum neural network is proposed by absorbing the heuristic thoughts of distributed collaborative response surface method and the generalized extremum neural network, in order to improve the reliability analysis of blade-tip clearance with creep behavior in terms of modeling precision and simulation efficiency. In this method, the generalized extremum neural network was used to handle the transients by simplifying the response process as one extremum and to address the strong nonlinearity by means of its nonlinear mapping ability. The distributed collaborative response surface method was applied to handle multi-object multi-discipline analysis, by decomposing one “big” model with hyperparameters and high nonlinearity into a series of “small” sub-models with few parameters and low nonlinearity. Based on the developed method, the blade-tip clearance reliability analysis of an aeroengine high-pressure turbine was performed subject to the creep behaviors of structural materials, by considering the randomness of influencing parameters such as gas temperature, rotational speed, material parameters, convective heat transfer coefficient, and so forth. It was found that the reliability degree of the clearance is 0.9909 when the allowable value is 2.2 mm, and the creep deformation of the clearance presents a normal distribution with a mean of 1.9829 mm and a standard deviation of 0.07539 mm. Based on a comparison of the methods, it is demonstrated that the proposed method requires a computing time of 1.201 s and has a computational accuracy of 99.929% over 104 simulations, which are improvements of 70.5% and 1.23%, respectively, relative to the distributed collaborative response surface method. Meanwhile, the high efficiency and high precision of the presented approach become more obvious with the increasing simulations. The efforts of this study provide a promising approach to improve the dynamic reliability analysis of complex structures.

Turbine Blade Tip Clearance Measurement Instrumentation

2007 ◽  
Author(s):  
Eric B. Holmquist ◽  
Peter L. Jalbert
Keyword(s):  
Control System ◽  
Real Time ◽  
Tip Clearance ◽  
Engine Control ◽  
Operating Characteristics ◽  
Static Structure ◽  
Engine Operation ◽  
Area Of Interest ◽  
Blade Tip ◽  
Blade Tip Clearance

New and future gas turbine engines are being required to provide greater thrust with improved efficiency, while simultaneously reducing life cycle operating costs. Improved component capabilities enable active control methods to provide better control of engine operation with reduced margin. One area of interest is a means to assess the relative position of rotating machinery in real-time, in particular hot section turbo machinery. To this end, Hamilton Sundstrand is working to develop a real-time means to monitor blade position relative to the engine static structure. This approach may yield other engine operating characteristics useful in assessing component health, specifically measuring blade tip clearance, time-of-arrival, and other parameters. UTC is leveraging its many years of experience with engine control systems to develop a microwave-based sensing device, applicable to both military and commercial engines. The presentation will discuss a hot section engine demonstration of a blade position monitoring system and the control system implications posed by a microwave-based solution. Considerations necessary to implement such a system and the challenges associated with integrating a microwave-based sensor system into an engine control system are discussed.

scholarly journals Influence of Large Relative Tip Clearances for a Micro Radial Fan and Design Guidelines for Increased Efficiency

2020 ◽  
Author(s):  
Patrick H. Wagner ◽  
Jan Van herle ◽  
Lili Gu ◽  
Jürg Schiffmann
Keyword(s):  
Pressure Rise ◽  
Leading Edge ◽  
High Sensitivity ◽  
Design Guidelines ◽  
Tip Clearance ◽  
Small Scale ◽  
Blade Tip ◽  
Dynamics Simulations ◽  
Experimental Findings ◽  
Blade Tip Clearance

Abstract The blade tip clearance loss was studied experimentally and numerically for a micro radial fan with a tip diameter of 19.2mm. Its relative blade tip clearance, i.e., the clearance divided by the blade height of 1.82 mm, was adjusted with different shims. The fan characteristics were experimentally determined for an operation at the nominal rotational speed of 168 krpm with hot air (200 °C). The total-to-total pressure rise and efficiency increased from 49 mbar to 68 mbar and from 53% to 64%, respectively, by reducing the relative tip clearance from 7.7% to the design value of 2.2%. Single and full passage computational fluid dynamics simulations correlate well with these experimental findings. The widely-used Pfleiderer loss correlation with an empirical coefficient of 2.8 fits the numerical simulation and the experiments within +2 efficiency points. The high sensitivity to the tip clearance loss is a result of the design specific speed of 0.80, the highly-backward curved blades (17°), and possibly the low Reynolds number (1 × 105). The authors suggest three main measures to mitigate the blade tip clearance losses for small-scale fans: (1) utilization of high-precision surfaced-grooved gas-bearings to lower the blade tip clearance, (2) a mid-loaded blade design, and (3) an unloaded fan leading edge to reduce the blade tip clearance vortex in the fan passage.

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