Influence of Boundary Layer Skew on the Tip Leakage Vortex of an Axial Compressor Stator

2021 ◽  
pp. 1-19
Author(s):  
Björn Koppe ◽  
Martin Lange ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Major Influence ◽  
Wall Region ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Flow Phenomena ◽  
Gap Height ◽  
End Wall

Abstract For an axial compressor stator with tip gap the boundary layer in the hub end-wall region has a significant influence on the development and progression of the tip leakage vortex. Herein the so-called boundary layer skew, which develops through relative motion of the hub, is of particular interest. Therefore, experimental and numerical investigations of a single axial compressor stator row with varying tip gap height (tip gap height/chord length = 2.0%|5.4%|6.7%) have been conducted. Comparing cases with rotating or stationary hub end-wall segments upstream of the examined vanes allowed to determine the effect of skewed and un-skewed inflow boundary layer. The steady state flow fields up- and downstream of the stator row were measured using five-hole pressure probes. For validation and to improve the understanding of the existing flow phenomena 3D-RANS CFD simulations using a commercial flow solver were carried out. Furthermore, analog cases with no tip gap were examined and considered in the comparisons to extend the knowledge on this boundary layer characteristic. The results show that the boundary layer skew has a major influence on the trajectory and size of the tip leakage vortex for the cases with tip clearance. The effect of reduction of the produced losses decreases with increasing tip gap height.

Influence of Boundary Layer Skew on the Tip Leakage Vortex of an Axial Compressor Stator

2020 ◽  
Author(s):  
Björn Koppe ◽  
Martin Lange ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Major Influence ◽  
Wall Region ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Flow Phenomena ◽  
Gap Height ◽  
End Wall

Abstract For an axial compressor stator with tip gap the boundary layer in the hub end-wall region has a significant influence on the development and progression of the tip leakage vortex. Herein the so-called boundary layer skew, which develops through relative motion of the hub, is of particular interest. Therefore, experimental and numerical investigations of a single axial compressor stator row with varying tip gap height (tip gap height/chord length = 2.0%|5.4%|6.7%) have been conducted. Comparing cases with rotating or stationary hub end-wall segments upstream of the examined vanes allowed to determine the effect of skewed and un-skewed inflow boundary layer. The steady state flow fields up- and downstream of the stator row were measured using five-hole pressure probes. For validation and to improve the understanding of the existing flow phenomena 3D-RANS CFD simulations using a commercial flow solver were carried out. Furthermore, analog cases with no tip gap were examined and considered in the comparisons to extend the knowledge on this boundary layer characteristic. The results show that the boundary layer skew has a major influence on the trajectory and size of the tip leakage vortex for the cases with tip clearance. The effect of reduction of the produced losses decreases with increasing tip gap height.

An Axial Compressor End-Wall Boundary Layer Calculation Method

1979 ◽  
Vol 101 (2) ◽  
pp. 233-245 ◽  
Author(s):  
J. De Ruyck ◽  
C. Hirsch ◽  
P. Kool
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Velocity Profile ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Wall Region ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
End Wall

An axial compressor end-wall boundary layer theory which requires the introduction of three-dimensional velocity profile models is described. The method is based on pitch-averaged boundary layer equations and contains blade force-defect terms for which a new expression in function of transverse momentum thickness is introduced. In presence of tip clearance a component of the defect force proportional to the clearance over blade height ratio is also introduced. In this way two constants enter the model. It is also shown that all three-dimensional velocity profile models present inherent limitations with regard to the range of boundary layer momentum thicknesses they are able to represent. Therefore a new heuristic velocity profile model is introduced, giving higher flexibility. The end-wall boundary layer calculation allows a correction of the efficiency due to end-wall losses as well as calculation of blockage. The two constants entering the model are calibrated and compared with experimental data allowing a good prediction of overall efficiency including clearance effects and aspect ratio. Besides, the method allows a prediction of radial distribution of velocities and flow angles including the end-wall region and examples are shown compared to experimental data.

Vortex Dynamics and Mechanisms for Viscous Losses in the Tip-Clearance Flow

2005 ◽  
Author(s):  
Donghyun You ◽  
Meng Wang ◽  
Parviz Moin ◽  
Rajat Mittal
Keyword(s):  
Tip Clearance ◽  
Wall Region ◽  
Mean Flow ◽  
Mean Velocity ◽  
Tip Leakage Vortex ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Viscous Losses ◽  
Clearance Flow ◽  
End Wall

The tip-clearance flow in axial turbomachines is studied using large-eddy simulation with particular emphasis on understanding the underlying mechanisms for viscous losses in the end-wall region and the unsteady characteristics of the tip-leakage vortical structures. Systematic and detailed analysis of the mean flow field and turbulence statistics has been made in a linear cascade with a moving end-wall. The tip-leakage jet and tip-leakage vortex are found to produce significant mean velocity gradients, leading to the production of vorticity and turbulent kinetic energy. These are the major causes for viscous losses in the cascade end-wall region. An analysis of the energy spectra and space-time correlations of the velocity fluctuations suggests that the tip-leakage vortex is subject to a pitchwise low frequency wandering motion.

Effects of Tip Clearance on the Stall Inception Process in an Axial Compressor Rotor

2013 ◽  
Author(s):  
Kazutoyo Yamada ◽  
Hiroaki Kikuta ◽  
Masato Furukawa ◽  
Satoshi Gunjishima ◽  
Yasunori Hara
Keyword(s):  
Vortex Breakdown ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Flow Phenomena ◽  
Casing Pressure

The paper presents experimental and numerical studies on the effects of tip clearance on the stall inception process in a low-speed axial compressor rotor with a large tip clearance. It has been revealed that in the small tip clearance case, shortly after the spike disturbance which results from the leading-edge separation near the rotor tip appears, the tornado-like vortex is generated by the separation, and soon the compressor falls into stall. In the large tip clearance case, the experiment showed that the performance characteristic differs from that in the small tip clearance case at near-stall conditions. This implies that the stall inception process differs with the tip clearance size. The flow phenomenon in the stall inception leading to such difference has been investigated in this study. Pressure and velocity fields which were ensemble-averaged and phase-locked by the periodic multi-sampling technique were measured on the casing wall and downstream of the rotor, respectively. In addition, to capture the unsteady flow phenomena inside the rotor, “Instantaneous Casing Pressure Field Measurement” was carried out: instantaneous casing pressure fields in one rotor passage region were measured by 30 high response pressure transducers mounted on the casing wall. In order to investigate further details of near-stall flow field for the large tip clearance, DES (Detached Eddy Simulation) has been conducted using a computational mesh with 120 million points. The results are compared with those from previous studies for the small tip clearance. As expected, the measurement results show notable differences in the near-stall flow field between the two tip clearance cases. The results from the casing pressure measurement show that high pressure fluctuation appears on the pressure side near the rotor leading-edge in the large tip clearance case. In the result of the velocity field measurement downstream of the rotor, high turbulence intensity is found near the casing in the large tip clearance case. The numerical results reveal that the vortex breakdown occurs in the tip leakage vortex and induces the oscillation of the tip leakage vortex with its unsteady nature. The flow phenomena confirmed in the experimental results are clearly explained by considering the breakdown of the tip leakage vortex. The vortex breakdown gives rise to not only large blockage but also the rotating disturbance through the interaction of the fluctuating tip leakage vortex with the pressure surface of the adjacent blade, and governs the stall inception process.

Characteristics of the Tip Leakage Vortex in a Low-Speed Axial Compressor With Different Rotor Tip Gaps

2012 ◽  
Author(s):  
Zhibo Zhang ◽  
Xianjun Yu ◽  
Baojie Liu
Keyword(s):  
Axial Compressor ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Tip Clearance ◽  
Test Facility ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

The detailed evolutionary processes of the tip leakage flow/vortex inside the rotor passage are still not very clear for the difficulties of investigating of them by both experimental and numerical methods. In this paper, the flow fields near the rotor tip region inside the blade passage with two tip gaps, 0.5% and 1.5% blade height respectively, were measured by using stereoscopic particle image velocimetry (SPIV) in a large-scale low speed axial compressor test facility. The measurements are conducted at four different operating conditions, including the design, middle, maximum static pressure rise and near stall conditions. In order to analyze the variations of the characteristics of the tip leakage vortex (TLV), the trajectory, concentration, size, streamwise velocity, and the blockage parameters are extracted from the ensemble-averaged results and compared at different compressor operating conditions and tip gaps. The results show that the formation of the TLV is delayed with large tip clearance, however, its trajectory moves much faster in an approximately linear way from the blade suction side to pressure side. In the tested compressor, the size of the tip gap has little effects on the scale of the TLV in the spanwise direction, on the contrary, its effects on the pitch-wise direction is very prominent. Breakdown of the TLV were both found at the near-stall condition with different tip gaps. The location of the initiation of the TLV breakdown moves downstream from the 60% chord to 70% chord as the tip gap increases. After the TLV breakdown occurs, the flow blockage near the rotor tip region increases abruptly. The peak value of the blockage effects caused by the TLV breakdown is doubled with the tip gap size increasing from 0.5% to 1.5% blade span.

Numerical Investigation of Relation Between Unsteady Behavior of Tip Leakage Vortex and Rotating Disturbance in a Transonic Axial Compressor Rotor

2008 ◽  
Author(s):  
K. Yamada ◽  
K. Funazaki ◽  
H. Sasaki
Keyword(s):  
Vortex Breakdown ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Tip Leakage Vortex ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Transonic Axial Compressor ◽  
Rotating Instability

The purpose of this study is to have a better understanding of the unsteady behavior of tip clearance flow at near-stall condition from a multi-passage simulation and to clarify the relation between such unsteadiness and rotating disturbance. This study is motivated by the following concern. A single passage simulation has revealed the occurrence of the tip leakage vortex breakdown at near-stall condition in a transonic axial compressor rotor, leading to the unsteadiness of the tip clearance flow field in the rotor passage. These unsteady flow phenomena were similar to those in the rotating instability, which is classified in one of the rotating disturbances. In other words it is possible that the tip leakage vortex breakdown produces a rotating disturbance such as the rotating instability. Three-dimensional unsteady RANS calculation was conducted to simulate the rotating disturbance in a transonic axial compressor rotor (NASA Rotor 37). The four-passage simulation was performed so as to capture a short length scale disturbance like the rotating instability and the spike-type stall inception. The simulation demonstrated that the unsteadiness of tip leakage vortex, which was derived from the vortex breakdown at near-stall condition, invoked the rotating disturbance in the rotor, which is similar to the rotating instability.

Effects of Tip Clearance Size on Flowfield in a Low-Speed Axial Compressor Rotor

2014 ◽  
Vol 543-547 ◽  
pp. 158-163 ◽  
Author(s):  
Zhen Zhen Duan ◽  
Yang Wei Liu ◽  
Li Peng Lu
Keyword(s):  
Flow Condition ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Primary Role ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Overall Performance ◽  
Corner Vortex

The simulations of a low-speed axial compressor rotor with two tip clearance sizes, 0.5% chord and 1.5% chord, were performed in the study. Overall performance and detailed flow fields at near stall condition are analyzed. The results show that the rotor stall occurs at higher mass flow condition with large tip clearance. For the small tip clearance the tip leakage vortex and the corner vortex both contribute significantly to the rotor stall, and the interaction between the vortices promotes the stall generation. While for the large tip clearance the tip leakage vortex plays a primary role, and the vortices interaction is ignorable.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low-Speed Turbine Blade Cascade With Moving End Wall

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage ◽  
End Wall

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110deg and blade chord of 1.0m. Data were obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0×105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle image velocimetry was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip end-wall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the undertip flow near the end wall due to the moving wall is observed and the effect on the tip leakage vortex examined.

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.

An Axial Compressor End-Wall Boundary Layer Theory

1971 ◽  
Vol 93 (2) ◽  
pp. 300-314 ◽  
Author(s):  
G. L. Mellor ◽  
G. M. Wood
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Axial Compressor ◽  
Jump Condition ◽  
Present Theory ◽  
Boundary Layer Theory ◽  
Tip Clearance ◽  
Main Stream ◽  
Wall Boundary ◽  
End Wall

The essential ingredient missing in existing prediction methods for the performance of multistage axial compressors is that which would account for the effect of end-wall boundary layers. It is, in fact, believed that end-wall boundary layers play a major role in compressor performance and the absence of an adequate theory represents a handicap to turbomachinery designers that might be likened to the handicap that designers of wings, for example, would face if Prandtl had not introduced the idea of a boundary layer. In this paper a new theory is developed which retains all elements of classical boundary layer theory; for example, we discuss variables such as momentum thickness and wall shear stress. However, the present theory introduces new concepts such as axial and tangential defect force thickness, a rotor exit-stator inlet “jump condition” and the importance of these concepts is demonstrated. Inherent in the derivation is an identification of the role of secondary flow and tip clearance flow. A proper means of matching the boundary layer calculations to conventional main stream calculations is suggested. Independent of empirical parametization it appears that the theory is capable of correctly modeling boundary layer blockage, losses, and end-wall stall. Near stall, the main stream-boundary layer interaction is very strong.

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