Effects of Rotation on the Flow Structure in a Compressor Cascade

2022 ◽  
pp. 1-24
Author(s):  
Jordi Ventosa-Molina ◽  
Björn Koppe ◽  
Martin Lange ◽  
Ronald Mailach ◽  
Jochen Fröhlich
Keyword(s):  
Flow Structure ◽  
Coriolis Force ◽  
Suction Side ◽  
Transition To Turbulence ◽  
Compressor Cascade ◽  
Tip Leakage ◽  
Large Eddy ◽  
Flow Features ◽  
Effects Of Rotation ◽  
Comparison Of The Results

Abstract In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration, one with the Coriolis force removed, without any other change. This setup allows very clean assessment of the influence of rotation. The turbulence-resolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region the Tip Leakage Vortex is enlarged and destabilised. Inside the tip gap the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly.

Effects of Rotation on the Flow Structure in a Compressor Cascade

2021 ◽  
Author(s):  
Jordi Ventosa-Molina ◽  
Björn Koppe ◽  
Martin Lange ◽  
Ronald Mailach ◽  
Jochen Fröhlich
Keyword(s):  
Flow Structure ◽  
Coriolis Force ◽  
Suction Side ◽  
Transition To Turbulence ◽  
Compressor Cascade ◽  
Tip Leakage ◽  
Large Eddy ◽  
Flow Features ◽  
Effects Of Rotation ◽  
Comparison Of The Results

Abstract In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration, one with the Coriolis force removed, without any other change. This setup allows very clean assessment of the influence of rotation. The turbulence-resolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region the Tip Leakage Vortex is enlarged and destabilised. Inside the tip gap the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly.

scholarly journals Aerodynamic investigation of a linear cascade with tip gap using large-eddy simulation

2021 ◽  
Vol 5 ◽  
pp. 39-49
Author(s):  
Koch Régis ◽  
Sanjosé Marlène ◽  
Moreau Stéphane
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Suction Side ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Large Eddy

The flow in a linear compressor cascade with tip gap is simulated using a wall-resolved compressible Large-Eddy Simulation. The cascade is based on the Virginia Tech Low Speed Cascade Wind Tunnel. The Reynolds number based on the chord is 3.88 x 10⁵ and the Mach number is 0.07. The gap considered in this study is 4.0 mm (2.9% of axial chord). An aerodynamic analysis of the tip-leakage flow allow us identifying the main mechanisms responsible for the development and the convection of the tip-leakage vortex downstream of the cascade. A region of high turbulence and vorticity levels is located along an ellipse that borders the top of the tip-leakage vortex. The influence of the airfoil suction side boundary layer development on the tip-leakage vortex is highlighted by tripping the flow. A tripped boundary layer induces a stronger and larger tip-leakage vortex that tends to move further away from the airfoil suction side and from the endwall compared with an untripped flow. The boundary layer turbulent state influences the tip-leakage flow development.

Large-eddy simulations of tip leakage and secondary flows in an axial compressor cascade using a near-wall turbulence model

2009 ◽  
Vol 223 (6) ◽  
pp. 645-655 ◽  
Author(s):  
D Borello ◽  
G Delibra ◽  
K Hanjalić ◽  
F Rispoli
Keyword(s):  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Wall Region ◽  
Compressor Cascade ◽  
Tip Leakage ◽  
Computational Mesh ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Near Wall

This paper reports on the application of unsteady Reynolds averaged Navier—Stokes (U-RANS) and hybrid large-eddy simulation (LES)/Reynolds averaged Navier—Stokes (RANS) methods to predict flows in compressor cascades using an affordable computational mesh. Both approaches use the ζ— f elliptic relaxation eddy-viscosity model, which for U-RANS prevails throughout the flow, whereas for the hybrid the U-RANS is active only in the near-wall region, coupled with the dynamic LES in the rest of the flow. In this ‘seamless’ coupling the dissipation rate in the k-equation is multiplied by a grid-detection function in terms of the ratio of the RANS and LES length scales. The potential of both approaches was tested in several benchmark flows showing satisfactory agreement with the available experimental results. The flow pattern through the tip clearance in a low-speed linear cascade shows close similarity with experimental evidence, indicating that both approaches can reproduce qualitatively the tip leakage and tip separation vortices with a relatively coarse computational mesh. The hybrid method, however, showed to be superior in capturing the evolution of vortical structures and related unsteadiness in the hub and wake regions.

Experimental Characterization of the Evolution of Global Flow Structure in the Passage of an Axial Compressor

2021 ◽  
Author(s):  
Ayush Saraswat ◽  
Subhra Shankha Koley ◽  
Joseph Katz
Keyword(s):  
Flow Structure ◽  
Rotor Blade ◽  
Incidence Angle ◽  
Substantial Reduction ◽  
Axial Compressor ◽  
Suction Side ◽  
Rotor Wake ◽  
Tip Leakage ◽  
Blade Tip

Abstract Ongoing experiments conducted in a one-and-half stages axial compressor installed in the JHU refractive index-matched facility investigate the evolution of flow structure across blade rows. After previously focusing only on the rotor tip region, the present stereo-PIV (SPIV) measurements are performed in a series of axial planes covering an entire passage across the machine, including upstream of the IGV, IGV-rotor gap, rotor-stator gap, and downstream of the stator. The measurements are performed at flow rates corresponding to pre-stall condition and best efficiency point (BEP). Data are acquired for various rotor-blade orientations relative to the IGV and stator blades. The results show that at BEP, the wakes of IGV and rotor are much more distinct and the wake signatures of one row persists downstream of the next, e.g., the flow downstream of the stator is strongly affected by the rotor orientation. In contrast, under pre-stall conditions, the rotor orientation has minimal effect on the flow structure downstream of the stator. However, the wakes of the stator blades, where the axial momentum is low, are now wider. For both conditions, the flow downstream of the rotor is characterized by two regions of axial momentum deficit in addition to the rotor wake. A deficit on the pressure side of the rotor wake tip is associated with the tip leakage vortex (TLV) of the previous rotor blade, and is much broader at pre-stall condition. A deficit on the suction side of the rotor wake near the hub appears to be associated with the hub vortex generated by the neighboring blade, and is broader at BEP. At pre-stall, while the axial momentum upstream of the rotor decreases over the entire tip region, it is particularly evident near the rotor blade tip, where the instantaneous axial velocity becomes intermittently negative. Downstream of the rotor, there is a substantial reduction in mean axial momentum in the upper half of the passage, concurrently with an increase in the circumferential velocity. Consequently, the incidence angle upstream of the stator increases in certain regions by up to 30 degrees. These observations suggest that while the onset of the stall originates from the rotor tip flow, one must examine its impact on the flow structure in the stator passage as well.

The Influence of Suction-Side Winglet on Tip Leakage Flow in Compressor Cascade

2011 ◽  
Author(s):  
Jingjun Zhong ◽  
Shaobing Han ◽  
Peng Sun
Keyword(s):  
Numerical Study ◽  
Flow Behavior ◽  
Velocity Ratio ◽  
Suction Side ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Cascade Flow ◽  
Highly Loaded

The effect of tip winglet on the aerodynamic performance of compressor cascade are mainly determined by the location of the tip winglet, the tip winglet geometry, the size of tip clearance, and the aerodynamic parameters of the cascade. In this paper, an extensive numerical study which includes three aspects has been carried out to investigate the effects of these influencing factors in a highly-loaded compressor cascade in order to give the guidance for the application of tip winglet to control the tip leakage in modern highly-loaded compressor. Firstly, the numerical method is validated by comparing the numerical results with available measured data. Results show that the numerical procedure is valid and accurate. Then, the cascade flow fields are interrogate to identify the physical mechanism of how suction-side winglet improve the cascade flow behavior. It is found that a significant tip leakage mass flow rate and aerodynamic loss reduction is possible by using proper tip winglet located near the suction side corner of the blade tip. Finally, an optimum width of the suction-side tip winglet is obtained by comparing the compressor performance with different clearances and incidences. The use of the suction-side winglet can reduce the pressure difference between the pressure and the suction sides of the blade and tip leakage velocity ratio. And the winglet also can compact the tip leakage vortex structure, which is benefit to decrease the loss of the tip secondary flow mixing with the primary flow.

Effect of Various Trench Designs on Axial Compressor Blade Tip Aerodynamics

2019 ◽  
Author(s):  
Ashwin Ashok ◽  
Patur Ananth Vijay Sidhartha ◽  
Shine Sivadasan
Keyword(s):  
Axial Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Tip Leakage Vortex ◽  
Stall Margin ◽  
Casing Treatment ◽  
Tip Leakage

Abstract Tip clearance of axial compressor blades allows leakage of the flow, generates significant losses and reduces the compressor efficiency. The present paper aims to discuss the axial compressor tip aerodynamics for various configurations of tip gap with trench. The various configurations are obtained by varying the clearance, trench depth, step geometry and casing contouring. In this paper the axial compressor aerodynamics for various configurations of tip gap with trench have been studied. The leakage flow structure, vorticity features and entropy generations are analyzed using RANS based CFD. The linear compressor cascade comprises of NACA 651810 blade with clearance height varied from 0.5% to 2% blade span. Trail of the tip leakage vortex and the horseshoe vortex on the blade suction side are clearly seen for the geometries with and without casing treatments near the stalling point. Since the trench side walls are similar to forward/backing steps, a step vortex is observed near the leading edge as well as trailing edge of the blade and is not seen for the geometry without the casing treatment. Even though the size of the tip leakage vortex seams to be reduces by providing a trench to the casing wall over the blade, the presence of additional vortices like the step vortex leads to comparatively higher flow losses. An increase in overall total pressure loss due to the application of casing treatment is observed. However an increase in stall margin for the geometries with casing is noted.

Numerical Investigation of Tip Clearance Flow in an Axial Compressor Cascade

2014 ◽  
Vol 599-601 ◽  
pp. 368-371
Author(s):  
Zhi Hui Xu ◽  
He Bin Lv ◽  
Ru Bin Zhao
Keyword(s):  
Computational Simulation ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow ◽  
Blade Tip

Using blade tip winglet to control the tip leakage flow has been concerned in the field of turbomachinery. Computational simulation was conducted to investigate the phenomenological features of tip clearance flow. The simulation results show that suction-side winglet can reduce leakage flow intensity. The tip winglet can also decrease tip leakage mass flow and weaken tip leakage flow mixing with the mainstream and therefore reduce the total pressure loss at the blade tip.

An Integrated Particle-Tracking Impact/Adhesion Model for the Prediction of Fouling in a Subsonic Compressor

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
D. Borello ◽  
F. Rispoli ◽  
P. Venturini
Keyword(s):  
Leading Edge ◽  
Suction Side ◽  
Navier Stokes ◽  
Compressor Cascade ◽  
Deposit Formation ◽  
Stagnation Region ◽  
Vortical Structures ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Linear Compressor Cascade

The present paper reports on the analysis of the motion of adhesive particles and deposit formation in a 3D linear compressor cascade in order to investigate the fouling in turbomachinery flows. The unsteady flow field is provided by a prior hybrid large-eddy simulation (LES)/Reynolds-averaged Navier-Stokes (RANS) computation. The particles are individually tracked and the deposit formation is evaluated on the basis of the well-established Thornton and Ning model. Although the study is limited to three regions of the blade, where the most relevant turbulent phenomena occurs, the prediction of fouling shows good agreement with real situations. Deposits form near the casing and the hub, in the zones where there are strong vortical structures originated by the tip leakage and hub vortices. On the blade, the deposit analysis is focused on three main regions: (a) along the stagnation region on the leading edge; (b) on the suction side, where the particles are conveyed by the hub vortex towards blade surfaces; and (c) on the pressure side, where a clean zone forms between leading edge and the blade surface, as can be seen in real compressors.

Experimental Study of Tip-Gap Turbulent Flow Structure

2006 ◽  
Author(s):  
Genglin Tang ◽  
Roger L. Simpson ◽  
Qing Tian
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Flow Structure ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Normal Velocity ◽  
Compressor Cascade ◽  
Custom Made ◽  
Turbulent Flow Structure

Experimental results are presented from a study of the tip-gap turbulent flow structure in a low-speed linear compressor cascade wind tunnel at Virginia Tech by utilizing surface oil flow visualization, endwall pressure measurements, and instantaneous velocity measurements with a custom-made 3-orthogonal-velocity-component fiber-optic laser-Doppler velocimetry (LDV) system. Tip gap flows are pressure-driven and highly skewed three-dimensional turbulent flows. The crossflow velocity normal to the blade chord is nearly uniform in the mid tip gap and changes substantially from the pressure to suction side due to the local tip pressure loading while the TKE does not vary much across the mid tip gap. The tip gap flow correlations of streamwise and wall normal velocity fluctuations decrease significantly from the leading edge to the trailing edge of the blade due to flow skewing.

scholarly journals Large-Eddy Simulation of Low-Pressure Turbine Cascade with Unsteady Wakes

Aerospace ◽  
2021 ◽  
Vol 8 (7) ◽  
pp. 184
Author(s):  
Zachary Robison ◽  
Andreas Gross
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Three Dimensional ◽  
Suction Side ◽  
Low Pressure ◽  
Flow Fields ◽  
Mean Flow ◽  
Reaction Stage ◽  
Low Pressure Turbine ◽  
Large Eddy

To better understand the wake effects at low Reynolds numbers, large-eddy simulations of a 50% reaction low-pressure turbine stage and a linear cascade with two different bar wake generators were carried out for a chord Reynolds number of 50,000. For the chosen front-loaded high-lift airfoil, the endwall structures are stronger than for more traditional mid-loaded moderate-lift airfoils. By comparing the 50% reaction stage results with the bar wake generator results, insight is gained into the effect of the three-dimensional wake components on the downstream flow field.For the cases with bar wake generator, the endwall boundary layer is growing faster because of the relative motion of the endwall with respect to the freestream. The half-width of the wake is approximately matched for the larger one of the two considered bar wake generators. To improve the quality of the phase-averaged flow fields, the proper orthogonal decomposition was employed as a filter to remove the low-energy unsteady flow field content. Both the mean flow and filtered phase-averaged flow fields were analyzed in detail. Visualizations of the phase-averaged flow field reveal a periodic suppression of the laminar suction side separation from the downstream airfoil even for the smaller bar wake generator. The passage vortex is entirely suppressed for the 50% reaction stage and for the larger bar wake generator. Furthermore, the phase-averaged data for the 50% reaction stage reveal a new longitudinal flow structure that is traced back to near-wall wake vorticity. This flow structure is missing for the bar wake generator cases.

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