Periodic Unsteadiness of Compressor Tip Clearance Vortex

2004 ◽  
Author(s):  
Jinwoo Bae ◽  
Kenneth S. Breuer ◽  
Choon S. Tan
Keyword(s):  
Tip Clearance ◽  
Mixing Enhancement ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Reduced Frequency ◽  
Instability Theory ◽  
Forced Responses ◽  
Linear Compressor Cascade ◽  
Tip Clearance Vortex ◽  
Flow Blockage

Natural and forced responses of the tip clearance vortex are measured in a linear compressor cascade to characterize periodic unsteadiness of the tip clearance vortex. There exists a natural frequency at which the tip clearance vortex is the most receptive to external forcing, thus resulting in mixing enhancement and flow blockage reduction. A physical explanation of the source of the observed periodic unsteadiness is suggested based on the trailing vortex instability theory. Observations of the time scale for the unsteadiness from different compressor geometries and flow conditions are shown to scale with a reduced frequency based on convective time through the blade passage.

Experimental Investigation Into the Effects of the Steady Wake-Tip Clearance Vortex Interaction in a Compressor Cascade

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Andreas Krug ◽  
Peter Busse ◽  
Konrad Vogeler
Keyword(s):  
Flow Field ◽  
Experimental Studies ◽  
Axial Compressor ◽  
Field Measurements ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Unsteady Interaction ◽  
Linear Compressor Cascade ◽  
Tip Clearance Vortex ◽  
The Impact

An important aspect of the aerodynamic flow field in the tip region of axial compressor rotors is the unsteady interaction between the tip clearance vortex (TCV) and the incoming stator wakes. In order to gain an improved understanding of the mechanics involved, systematic studies need to be performed. As a first step toward the characterization of the dynamic effects caused by the relative movement of the blade rows, the impact of a stationary wake-induced inlet disturbance on a linear compressor cascade with tip clearance will be analyzed. The wakes were generated by a fixed grid of cylindrical bars with variable pitch being placed at discrete pitchwise positions. This paper focuses on experimental studies conducted at the newly designed low-speed cascade wind tunnel in Dresden. The general tunnel configuration and details on the specific cascade setup will be presented. Steady state flow field measurements were carried out using five-hole probe traverses up- and downstream of the cascade and accompanied by static wall pressure readings. 2D-particle image velocimetry (PIV) measurements complemented these results by visualizing the blade-to-blade flow field. Hence, the structure of the evolving secondary flow system is evaluated and compared for all tested configurations.

Effects of the Steady Wake-Tip Clearance Vortex Interaction in a Compressor Cascade: Part I — Experimental Investigations

2014 ◽  
Author(s):  
Andreas Krug ◽  
Peter Busse ◽  
Konrad Vogeler
Keyword(s):  
Flow Field ◽  
Experimental Studies ◽  
Axial Compressor ◽  
Field Measurements ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Linear Compressor Cascade ◽  
Tip Clearance Vortex ◽  
The Impact

An important aspect of the aerodynamic flow field in the tip region of axial compressor rotors is the unsteady interaction between the tip clearance vortex and the incoming stator wakes. In order to gain an improved understanding of the mechanics involved, systematic studies need to be performed. As a first step towards the characterisation of the dynamic effects caused by the relative movement of the blade rows, the impact of a stationary wake-induced inlet disturbance on a linear compressor cascade with tip clearance will be analysed. The wakes were generated by a fixed grid of cylindrical bars with variable pitch being placed at discrete pitchwise positions. Part I of this two-part paper focuses on experimental studies conducted at the newly designed low-speed cascade wind tunnel in Dresden. The general tunnel configuration and details on the specific cascade setup will be presented. Steady state flow field measurements were carried out using five-hole probe traverses up- and downstream of the cascade and accompanied by static wall pressure readings. 2D-PIV measurements complemented these results by visualizing the blade-to-blade flow field. Hence, the structure of the evolving secondary flow system is evaluated and compared for all tested configurations.

Breakdown of the Tip Clearance Vortex in a Rotor Equivalent Cascade and in a Single-Stage Low-Speed Compressor

2008 ◽  
Author(s):  
Henner Schrapp ◽  
Udo Stark ◽  
Horst Saathoff
Keyword(s):  
Stability Limit ◽  
Single Stage ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Piv Measurements ◽  
Design Point ◽  
Low Speed ◽  
Linear Compressor Cascade ◽  
Tip Clearance Vortex

The paper describes experimental investigations of the tip clearance vortex in a linear compressor cascade with a tip clearance to one side and a compressor with a rotor tip section represented by the cascade. The aim is to show experimentally that breakdown of the tip clearance vortex can take place in subsonic compressors. As a first step, the flow in the linear compressor cascade has been investigated at different flow angles from the design point up to the stability limit of the cascade. In a second step the flow in the tip region of the rotor in a low-speed single-stage compressor has been investigated from the design point up to the stall limit of the compressor. The analysis of PIV measurements reveal a low momentum fluid area in the passage both in the cascade and the compressor when approaching the stall limit. This area is separated from the main flow by an interface that is characterized by high standard deviations of the velocities. The location of this interface correlates well with the positions at which the analysis of the unsteady pressure signals obtained with several flush mounted high-response pressure transducers reveals a bump of increased amplitude at a certain nondimensional frequency. The results in the compressor are for the most part identical to those obtained in the cascade. When approaching stall a distinct bump shows up in the casing wall pressure spectra at a nondimensional frequency comparable to the nondimensional frequency found in the cascade. At the same time an area of very low momentum fluid accumulates in the vicinity of the original vortex axis, as can be shown by PIV measurements in the rotor of the compressor. Additionally it can be shown, that the blockage that is due to the broken down tip clearance vortex leads to a rotating phenomenon, comparable to the phenomenon of ‘rotating instabilities’.

scholarly journals Tip Leakage Flow in Linear Compressor Cascade

1993 ◽  
Author(s):  
S. Kang ◽  
C. Hirsch
Keyword(s):  
Design Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Linear Compressor ◽  
Tip Leakage ◽  
Flow Mixing ◽  
Internal Loss ◽  
Linear Compressor Cascade

Tip leakage flow in a linear compressor cascade of NACA 65-1810 profiles is investigated, for tip clearance levels of 1.0, 2.0 and 3.25 percent of chord at design and off-design flow conditions. Data, velocity and pressures, are collected from three transverse sections inside tip clearance and sixteen sections within flow passage. Tip separation vortex influence is identified from the data. Leakage flow mixing is clearly present inside the clearance and has a significant influence on the internal loss.

scholarly journals Numerical Simulation of 3D Viscous Flow in a Linear Compressor Cascade With Tip Clearance

1994 ◽  
Author(s):  
Shun Kang ◽  
Charles Hirsch
Keyword(s):  
Viscous Flow ◽  
Flow Structure ◽  
Leading Edge ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Linear Compressor ◽  
Linear Compressor Cascade

A Navier-Stokes solver is applied to investigate the 3D viscous flow in a low speed linear compressor cascade with tip clearance at design and off-design conditions with two different meshes. The algebraic turbulence model of Baldwin-Lomax is used for closure. Relative motion between the blades and wall is simulated for one flow coefficient. Comparisons with experimental data, including flow structure, static and total pressures, velocity profiles, secondary flows and vorticity, are presented for the stationary wall case. It is shown that the code predicts well the flow structure observed in experiments and shows the details of the tip leakage flow and the leading edge horseshoe vortex.

Effects of the Steady Wake-Tip Clearance Vortex Interaction in a Compressor Cascade: Part II — Numerical Investigations

2014 ◽  
Author(s):  
Peter Busse ◽  
Andreas Krug ◽  
Konrad Vogeler
Keyword(s):  
Steady State ◽  
Flow Field ◽  
Initial Conditions ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Vortex Interaction ◽  
Compressor Cascade ◽  
Flow Phenomena ◽  
Tip Clearance Vortex ◽  
The Impact

An important aspect of the aerodynamic flow field in the tip region of axial compressor rotors is the unsteady interaction between the tip clearance vortex and the incoming stator wakes. In order to gain an improved understanding of the mechanics involved, systematic studies need to be performed. As a first step towards the characterisation of the dynamic effects caused by the relative movement of the blade rows, the impact of a stationary wake-induced inlet disturbance on a linear compressor cascade with tip clearance will be analyzed. The wakes were generated by a fixed grid of cylindrical bars with variable pitch being placed at discrete pitchwise positions. Part II of this two-part paper focuses on the numerical studies conducted with the scientific flow solver TRACE. Selected measurements, which are discussed in detail in the first part of this paper, are compared with steady state RANS simulation data to determine the validity of the computational model. For this purpose, the flow field obtained in the passage (PIV), at the cascade exit (five-hole probes) and the endwall pressure distributions were used. The presented numerical results show potentials and limitations of the steady state CFD for the prediction of the investigated flow phenomena. The computations provide the initial conditions for future unsteady calculations, and enable a separate depiction of potential effects of steady and unsteady wake-tip clearance vortex interaction.

Unsteady behaviour of the tip clearance vortex in a rotor equivalent compressor cascade

2009 ◽  
Vol 223 (6) ◽  
pp. 635-643 ◽  
Author(s):  
H Schrapp ◽  
U Stark ◽  
H Saathoff
Keyword(s):  
Vortex Breakdown ◽  
Axial Flow ◽  
Stability Limit ◽  
Single Stage ◽  
Tip Clearance ◽  
Measuring System ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Experimental Proof ◽  
Tip Clearance Vortex

From earlier experimental investigations in a single-stage axial-flow pump and different numerical calculations of the flow in single-stage axial-flow compressors, it is known that vortex breakdown of the tip clearance vortex can take place in turbomachines, although an experimental proof for subsonic compressors is lacking. Vortex breakdown, if existent, is a source of high instability in the sensitive tip region of axial-flow pumps and compressors and will also play an important role in the stall inception process. Therefore, the flow in a linear compressor cascade with a 3 per cent tip clearance to one side has been investigated at different flow angles from the design point up to the stability limit of the cascade. The cascade resembles the tip section of a single-stage, axial-flow, low-speed compressor that is also in use at the Technical University of Braunschweig. The measuring techniques used were (a) a commercial particle image velocimetry (PIV) system and (b) a pressure measuring system with several flush mounted high-response pressure transducers at selected locations where the vortex was expected. As the cascade approaches its stall limit, the analysis of the pressure signals in the frequency domain revealed a bump of increased amplitude at a certain non-dimensional frequency for some of the measuring positions. The measuring positions that exhibited the bump correlated very well with a paraboloid-shaped region of high standard deviation enveloping an area of very low momentum fluid. It is shown that the frequency of the striking bump corresponds to the rotational frequency of the vortex calculated from the PIV measurements.

Experiment on Linear Compressor Cascade With 3-D Blade Oscillation

2003 ◽  
Author(s):  
H. Yang ◽  
L. He
Keyword(s):  
Steady Flow ◽  
Three Dimensional ◽  
Diffusion Profile ◽  
Tip Clearance ◽  
Influence Coefficient ◽  
Pressure Amplitude ◽  
Compressor Cascade ◽  
Pressure Transducers ◽  
Influence Coefficient Method ◽  
Linear Compressor Cascade

An experiment has been carried out to enhance the understanding of 3D blade aeroelastic mechanisms and to produce test data of realistic configurations for validation of advanced 3D aeromechanical methods. A low speed rig with a compressor cascade consisting of seven prismatic blades of controlled diffusion profile has been commissioned. The middle blade is mechanically driven to oscillate in a 3D bending/flapping mode. At a nominal steady flow condition unsteady pressure measurements were performed at six spanwise sections for three different reduced frequencies and two different tip-clearance gaps. Off-board pressure transducers were utilized in conjunction with a transfer-function method to correct tubing distortion errors. The linearity of aerodynamic response is confirmed by the tests with different blade oscillation amplitudes, which enables the tuned cascade results to be constructed by using the Influence Coefficient Method. The measured results illustrate fully three-dimensional unsteady behaviour. Strong spanwise unsteady interaction leads to a non-proportional distribution of pressure amplitude at different spanwise locations. The tests with different tip-clearance gaps (1–2% span) show that the near tip region is destabilised as the tip gap is increased. This may be attributed to the local unloading of the corresponding steady flow. The destabilised region is seen to extend to approximately 20% of the blade span. The total aerodynamic damping at the least stable inter-blade phase angle has been reduced by 27%, when the tip gap is increased from nearly zero to 2% span.

An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

2021 ◽  
pp. 1-20
Author(s):  
Liesbeth Konrath ◽  
Dieter Peitsch ◽  
Alexander Heinrich
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Complex Flow ◽  
Flow Topology ◽  
Linear Compressor ◽  
Near Surface ◽  
Oil Flow ◽  
Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0deg to 5deg for both blades indicates at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down.

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