scholarly journals Calculation of Tip Clearance Effects in a Transonic Compressor Rotor

1998 ◽  
Vol 120 (1) ◽  
pp. 131-140 ◽  
Author(s):  
R. V. Chima
Keyword(s):  
Tip Clearance ◽  
Tip Vortex ◽  
Vena Contracta ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Laser Anemometer ◽  
Flow Through ◽  
Gap Height ◽  
Operating Points ◽  
Clearance Model

The flow through the tip clearance region of a transonic compressor rotor (NASA rotor 37) was computed and compared to aerodynamic probe and laser anemometer data. Tip clearance effects were modeled both by gridding the clearance gap and by using a simple periodicity model across the ungridded gap. The simple model was run with both the full gap height, and with half the gap height to simulate a vena-contracta effect. Comparisons between computed and measured performance maps and downstream profiles were used to validate the models and to assess the effects of gap height on the simple clearance model. Recommendations were made concerning the use of the simple clearance model. Detailed comparisons were made between the gridded clearance gap solution and the laser anemometer data near the tip at two operating points. The computed results agreed fairly well with the data but overpredicted the extent of the casing separation and underpredicted the wake decay rate. The computations were then used to describe the interaction of the tip vortex, the passage shock, and the casing boundary layer.

scholarly journals Calculation of Tip Clearance Effects in a Transonic Compressor Rotor

1996 ◽  
Author(s):  
Rodrick V. Chima
Keyword(s):  
Tip Clearance ◽  
Tip Vortex ◽  
Vena Contracta ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Laser Anemometer ◽  
Flow Through ◽  
Gap Height ◽  
Operating Points ◽  
Clearance Model

The flow through the tip clearance region of a transonic compressor rotor (NASA rotor 37) was computed and compared to aerodynamic probe and laser anemometer data. Tip clearance effects were modeled both by gridding the clearance gap and by using a simple periodicity model across the ungridded gap. The simple model was run with both the full gap height, and with half the gap height to simulate a vena-contracta effect. Comparisons between computed and measured performance maps and downstream profiles were used to validate the models and to assess the effects of gap height on the simple clearance model. Recommendations were made concerning the use of the simple clearance model. Detailed comparisons were made between the gridded clearance gap solution and the laser anemometer data near the tip at two operating points. The computed results agreed fairly well with the data but overpredicted the extent of the casing separation and underpredicted the wake decay rate. The computations were then used to describe the interaction of the tip vortex, the passage shock, and the casing boundary layer.

Investigation of Tip Clearance Modeling Techniques for a Transonic Compressor Rotor

2009 ◽  
Author(s):  
Sean T. Barrows ◽  
Ravishankar Balasubramian ◽  
Jen-Ping Chen
Keyword(s):  
Pressure Ratio ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Vena Contracta ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Radial Depth ◽  
Modeling Techniques ◽  
Final Approach ◽  
Viable Approach

Computational fluid dynamics (CFD) codes are becoming an integral part of the design and analysis process involved with creating and improving upon new engine designs. This necessitates the investigation and development of accurate modeling techniques for flow simulations with a quick turn around time of typically 48 hours. The present paper is focused on increasing the fidelity of compressor rotor simulations by examining three rotor tip clearance modeling techniques. The first approach models the tip clearance region as a loss-less, periodic, un-gridded region as first proposed by Kirtley et al. The second approach is a modification of this technique to study the vena-contracta effects. The tip clearance region remains un-gridded, but, the physical radial depth of tip clearance is gradually reduced to the smallest constriction typically seen in the tip clearance because of flow phenomena such as the shroud and blade-tip boundary layers. The final approach is a completely gridded tip clearance region of full depth to verify the vena-contracta approach as well as to determine if any increase in fidelity is achieved through this computationally costly procedure. These three tip clearance modeling approaches are applied to the NASA transonic compressor rotor, Rotor-35, in a rotor only configuration and the predicted operational ranges are compared to available LDV data. Span-wise performance characteristics such as total pressure ratio and total temperature ratio are compared at a near peak efficiency and at a near-stall operating point. Tip-vortex resolution and predictions are also examined. The merits and demerits of the three approaches are discussed and recommendations are made for a viable approach in terms of accuracy and computational resources.

Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor

1999 ◽  
Vol 121 (4) ◽  
pp. 751-762 ◽  
Author(s):  
G. A. Gerolymos ◽  
I. Vallet
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Main Flow ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Computational Method ◽  
Tip Vortex ◽  
Computational Results ◽  
Transonic Compressor ◽  
Compressor Rotor

The purpose of this paper is to investigate tip-clearance and secondary flows numerically in a transonic compressor rotor. The computational method used is based on the numerical integration of the Favre-Reynolds-averaged three-dimensional compressible Navier–Stokes equations, using the Launder–Sharma near-wall k–ε turbulence closure. In order to describe the flowfield through the tip and its interaction with the main flow accurately, a fine O-grid is used to discretize the tip-clearance gap. A patched O-grid is used to discretize locally the mixing-layer region created between the jetlike flow through the gap and the main flow. An H–O–H grid is used for the computation of the main flow. In order to substantiate the validity of the results, comparisons with experimental measurements are presented for the NASA_37 rotor near peak efficiency using three grids (of 106, 2 X 106, and 3 X 106 points, with 21, 31, and 41 radial stations within the gap, respectively). The Launder–Sharma k–ε model underestimates the hub corner stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap, and the mixing downstream of the rotor. The computational results indicate the presence of an important leakage-interaction region where the leakage-vortex after crossing the passage shock-wave mixes with the pressure-side secondary flows. A second trailing-edge tip vortex is also clearly visible.

Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor

1998 ◽  
Author(s):  
G. A. Gerolymos ◽  
I. Vallet
Keyword(s):  
Stokes Equations ◽  
Mixing Layer ◽  
Main Flow ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Computational Method ◽  
Tip Vortex ◽  
Computational Results ◽  
Transonic Compressor ◽  
Compressor Rotor

The purpose of this paper is to numerically investigate tip-clearance and secondary flows in a transonic compressor rotor. The computational method used is based on the numerical integration of the Favre-Reynolds-averaged 3-D compressible Navier-Stokes equations, using the Launder-Sharma near-wall k-ε turbulence closure. In order to accurately describe the flowfield through the tip and its interaction with the main flow, a fine O-grid is used to discretize the tip-clearance-gap. A patched O-grid is used to discretize locally the mixing-layer region created between the jet-like flow through the gap and the main flow. An H-O-H grid is used for the computation of the main flow. In order to substantiate the validity of the results comparisons with experimental measurements are presented for the NASA_37 rotor near peak efficiency using 3 grids (of 106, 2 × 106, and 3 × 106 points, with 21, 31, and 41 radial stations within the gap respectively). The Launder-Sharma k-ε model underestimates the hub corner stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap and the mixing downstream of the rotor. The computational results indicate the presence of an important leakage-interaction-region where the leakage-vortex after crossing the passage shock-wave mixes with the pressure-side secondary flows. A second trailing-edge-tip-vortex is also clearly visible.

Flow Field Unsteadiness in the Tip Region of a Transonic Compressor Rotor

1997 ◽  
Vol 119 (1) ◽  
pp. 122-128 ◽  
Author(s):  
S. L. Puterbaugh ◽  
W. W. Copenhaver
Keyword(s):  
Flow Field ◽  
High Performance ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vortex Interaction ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Operating Points

An experimental investigation concerning tip flow field unsteadiness was performed for a high-performance, state-of-the-art transonic compressor rotor. Casing-mounted high frequency response pressure transducers were used to indicate both the ensemble averaged and time varying flow structure present in the tip region of the rotor at four different operating points at design speed. The ensemble averaged information revealed the shock structure as it evolved from a dual shock system at open throttle to an attached shock at peak efficiency to a detached orientation at near stall. Steady three-dimensional Navier Stokes analysis reveals the dominant flow structures in the tip region in support of the ensemble averaged measurements. A tip leakage vortex is evident at all operating points as regions of low static pressure and appears in the same location as the vortex found in the numerical solution. An unsteadiness parameter was calculated to quantify the unsteadiness in the tip cascade plane. In general, regions of peak unsteadiness appear near shocks and in the area interpreted as the shock-tip leakage vortex interaction. Local peaks of unsteadiness appear in mid-passage downstream of the shock-vortex interaction. Flow field features not evident in the ensemble averaged data are examined via a Navier-Stokes solution obtained at the near stall operating point.

Pre-Stall Instability Distribution Over a Transonic Compressor Rotor

2008 ◽  
Author(s):  
A. J. Gannon ◽  
G. V. Hobson
Keyword(s):  
Steady State ◽  
Low Frequency ◽  
Tip Vortex ◽  
Stable Steady State ◽  
Complex Flow ◽  
Suction Surface ◽  
Steady State Condition ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Area Of Interest

An investigation of the behavior of a transonic compressor rotor when operating close to stall is presented. The specific area of interest is the behavior and location of low-frequency instabilities when operating close to stall. When running close to stall compressors begin to exhibit non-periodic flow between the blade passages even when appearing to be operating in a stable steady-state condition. These frequencies are not geometrically fixed to the rotor and typically appear at 0.3–0.8 of the rotor speed. The presence of these low-frequency instabilities are known and detection are reasonably commonplace, however attempts to quantify the location and strength of these instabilities as stall is approached have proved difficult. In the test rotor probes were positioned in the case-wall upstream, downstream and over the rotor blade tips. Simultaneous data from all the probes was taken at successive steady-state settings each operating closer to stall. The simultaneous data is presented to show the development and distribution of the instabilities over the rotor as stall was approached. Initially the instabilities appeared within the rotor row and extended downstream. At operation closer to stall they protruded upstream and downstream. The greatest amplitude of the instabilities was within the blade row in the complex flow region that contained the tip-vortex interacting with the shock and the shock impinging on the blade suction surface. In the current rotor the data shows that the instabilities were present during steady-state operation when stall was approached even when stall was not imminent. In addition they do not behave in a linear manner as stall was approached.

Numerical Investigations of the Coupled Flow Through a Subsonic Compressor Rotor and Axial Skewed Slot

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Xingen Lu ◽  
Wuli Chu ◽  
Junqiang Zhu ◽  
Yangfeng Zhang
Keyword(s):  
Axial Flow ◽  
Tip Clearance ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Casing Treatment ◽  
Axial Flow Compressor ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Flow Through ◽  
Flow Compressor

In order to advance the understanding of the fundamental mechanisms of axial skewed slot casing treatment and their effects on the subsonic axial-flow compressor flow field, the coupled unsteady flow through a subsonic compressor rotor and the axial skewed slot was simulated with a state-of-the-art multiblock flow solver. The computational results were first compared with available measured data, that showed the numerical procedure calculates the overall effect of the axial skewed slot correctly. Then, the numerically obtained flow fields were interrogated to identify the physical mechanism responsible for improvement in stall margin of a modern subsonic axial-flow compressor rotor due to the discrete skewed slots. It was found that the axial skewed slot casing treatment can increase the stall margin of subsonic compressor by repositioning of the tip clearance flow trajectory further toward the trailing of the blade passage and retarding the movement of the incoming∕tip clearance flow interface toward the rotor leading edge plane.

A Physical Model for the Tip Vortex Loss: Experimental Validation and Scaling Method

2012 ◽  
Author(s):  
Sascha Karstadt ◽  
Peter F. Pelz
Keyword(s):  
Measurement Data ◽  
Suction Side ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Tip Leakage Flow ◽  
Rotating Blades ◽  
Fluid Systems ◽  
Spiral Vortex ◽  
Flow Through

Losses through secondary flows occur in every turbomachine. Between the rotating blades and the casing of a turbomachine there is a secondary flow through the tip clearance caused by the pressure difference between the pressure and the suction side of the blade. This tip leakage flow is not involved in the work done by the rotating blades hence it reduces the aerodynamic efficiency. The flow through the tip clearance rolls up to a spiral vortex on the suction side of the blade and induces drag. Size and circulation of this vortex, according to the Helmholtz vortex theorem, depend on the bound vortex and the width of the tip clearance. Examinations of this structure lead to an idea of describing the tip vortex loss with analytical methods. Therefore an analytical approach is made regarding mainly the circulation at the blade tips. The method is discussed critically in the context of known loss models. It is shown to be a good summary of earlier methods. Since no explicit geometry data of the turbomachine is needed, it is much easier to use. The most important aspect is the excellent agreement with measurements performed at the Chair of Fluid Systems Technology. In total eleven different fan configurations are measured and analyzed in regard to their tip clearance losses. The measurements are performed at a test rig located at the laboratory of the Chair of Fluid Systems Technology at Technische Universität Darmstadt. Additionally further published measurement data is used to validate the method.

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