Effects of the Inlet Boundary Layer Thickness on the Flow in an Axial Compressor (I) - Hub Corner Stall and Tip Leakage Flow -

A three-dimensional computation was conducted to understand effects of the inlet boundary layer thickness on the internal flow and the loss characteristics in a low-speed axial compressor operating at the design condition (φ = 85%) and near stall condition (φ = 65%). At the design condition, independent of the inlet boundary layer thickness, flows in the axial compressor show similar characteristics such as the pressure distribution, size of hub corner-stall, tip leakage flow trajectory, limiting streamlines on the blade suction surface, etc. But, as the load is increased, for the thick inlet boundary layer at hub and casing, the hub corner stall grows to make a large separation region between the hub and suction surface, and the tip leakage flow is more vortical than that observed in the case with thin inlet boundary layer and has the critical point where the trajectory of the tip leakage flow is suddenly turned to the downstream. For the thin inlet boundary layer, the hub corner stall decays to form the thick boundary layer from hub to midspan on the suction surface owing to the blockage of the tip leakage flow and the tip leakage flow leans to the circumferential direction more than at the design condition. In addition to these, the severe reverse flow, induced by both boundary layers on the blade surface and the tip leakage flow, can be found to act as the blockage of flows near the casing, resulting in a heavy loss. As a result of these differences of the internal flow made by the different inlet boundary layer thickness, the spanwise distribution of the total loss is changed dramatically. At the design condition, total pressure losses for two different boundary layers are almost alike in the core flow region but the larger losses are generated at both hub and tip when the inlet boundary layer is thin. At the near stall condition, however, total loss for thick inlet boundary layer is found to be greater than that for thin inlet boundary layer on most of the span except the region near the hub and casing. In order to analyze effects of inlet boundary layer thickness on total loss in detail, total loss is scrutinized through three major loss categories available in a subsonic axial compressor such as profile loss, tip leakage loss and endwall loss.

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Effects of the Inlet Boundary Layer Thickness on the Rotating Stall in an Axial Compressor

Volume 2: Fora ◽

10.1115/fedsm2006-98271 ◽

2006 ◽

Author(s):

Minsuk Choi ◽

Je Hyun Baek ◽

Seong Hwan Oh ◽

Dock Jong Ki

Keyword(s):

Boundary Layer ◽

Layer Thickness ◽

Boundary Layer Thickness ◽

Axial Compressor ◽

Rotating Stall ◽

High Load ◽

Tip Leakage Flow ◽

Suction Surface ◽

Corner Separation ◽

Tip Leakage

A three-dimensional numerical simulation is conducted to study an effect of the inlet boundary layer thickness on the rotating stall in an axial compressor. The inlet boundary layer thickness has significant effects on the hub-corner-separation in the junction of the hub and suction surface. As the load is increased, the size of the hub-corner-separation is increased dramatically for the thick inlet boundary layer but it is diminished to be indistinguishable from the wake of the blade for the thin inlet boundary layer. The difference induced by different inlet conditions at high load should have affected characteristics of the rotating stall such as the inception process and propagation speed of the stall cells. For two cases of different inlet boundary layers, the numerical simulation is progressed as the flow coefficient is decreased until the rotating stall begins and then effects of the inlet boundary layer thickness on the rotating stall are analyzed by using the axial velocity history and the rotary total pressure distribution. For the thick inlet boundary layer, a pre-stall disturbance arises firstly in the hub-corner-separation and then in the tip leakage flow as the load is increased. For the thin inlet boundary layer, however, an asymmetric disturbance is initially generated in the tip region because of the corner-separation in the junction of the casing and suction surface. The disturbance of the tip leakage flow grows to be a stationary stall cell which is adhered to the blade passage by throttling process in case of the thick inlet boundary layer. When the stationary stall cell reach a critical size, this cell moves along the blade row and becomes a short-length-scale rotating stall. However, the rotating stall is not found at a smaller flow rate for the thin inlet boundary layer because the flow in the tip region is more energetic than that of its counterpart. In addition, it is found that the inlet boundary layer thickness has an effect on the cause of the initial disturbance which collapses the axi-symmetric flow under high load and the internal flow with a thick boundary layer on the casing is susceptible to the rotating stall.

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Study on the Effects of Upstream Flow Conditions and Clearance Sizes to Tip Leakage Flow in a Subsonic Large-Scale Rotor

Volume 2A: Turbomachinery ◽

10.1115/gt2014-26573 ◽

2014 ◽

Author(s):

Chenkai Zhang ◽

Jun Hu ◽

Zhiqiang Wang ◽

Ning Ding ◽

Zhiming Mao ◽

...

Keyword(s):

Boundary Layer ◽

Layer Thickness ◽

Boundary Layer Thickness ◽

Pressure Rise ◽

Operating Conditions ◽

Tip Clearance ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Operating Condition ◽

Tip Leakage

To clearly clarify how it affects the detailed tip clearance flow and flow mechanism by varying the upstream boundary layer thickness and tip clearance size, numerical studies were performed on a subsonic rotor, which is used for low-speed model testing of one rear stage embedded in a modern high-pressure compressor. Firstly, available experimental data were adopted to validate the numerical method. Second, comparisons were made for tip leakage vortex structure, the interface of leakage flow/mainflow, endwall loss, isentropic efficiency and pressure-rise between different operating conditions. Then, effects of different clearance sizes and inlet boundary layer thicknesses were investigated. At last, the self-induced unsteadiness at one near-stall operating condition was studied for different cases. Results show that increasing the tip clearance size has a deleterious effect on rotor efficiency and pressure-rise performance over the whole operating range, while thickening the inflow boundary layer is almost the same except that its pressure-rise performance will be increased at mass flow rate larger than design operating condition. Self-induced unsteadiness occurs at near-stall operating conditions, and its appearance depends largely on tip clearance size, while upstream boundary layer thickness has little effect.

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Unsteady Simulation of an Axial Compressor Stage With Casing and Blade Passive Treatments

Journal of Turbomachinery ◽

10.1115/1.2988156 ◽

2009 ◽

Vol 131 (2) ◽

Cited By ~ 32

Author(s):

Nicolas Gourdain ◽

Francis Leboeuf

Keyword(s):

Boundary Layer ◽

Passive Control ◽

Axial Compressor ◽

Suction Side ◽

Boundary Layer Separation ◽

Leakage Flow ◽

Compressor Stage ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Good Ability

This paper deals with the numerical simulation of technologies to increase the compressor performances. The objective is to extend the stable operating range of an axial compressor stage using passive control devices located in the tip region. First, the behavior of the tip leakage flow is investigated in the compressor without control. The simulation shows an increase in the interaction between the tip leakage flow and the main flow when the mass flow is reduced, a phenomenon responsible for the development of a large flow blockage region at the rotor leading edge. A separation of the rotor suction side boundary layer is also observed at near stall conditions. Then, two approaches are tested in order to control these flows in the tip region. The first one is a casing treatment with nonaxisymmetric slots. The method showed a good ability to control the tip leakage flow but failed to reduce the boundary layer separation on the suction side. However, an increase in the operability was observed but with a penalty for the efficiency. The second approach is a blade treatment that consists of a longitudinal groove built in the tip of each rotor blade. The simulation pointed out that the device is able to control partially all the critical flows with no penalty for the efficiency. Finally, some recommendations for the design of passive treatments are presented.

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Effect of Axial Short Slot Casing Treatment and its Center Deviation on Stability of a Transonic Axial Flow Compressor

Volume 2A: Turbomachinery ◽

10.1115/gt2020-14588 ◽

2020 ◽

Author(s):

Sha Zhang ◽

Wuli Chu ◽

Jibo Yang

Keyword(s):

Boundary Layer ◽

Axial Compressor ◽

Subsequent Development ◽

Stability Margin ◽

Axial Position ◽

Central Position ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Casing Treatment ◽

Tip Leakage

Abstract In order to increase the stability margin of axial compressor with low efficiency losses, this paper studies the influence of axial short slot casing treatment and its axial position on compressor performance. A transonic axial compressor rotor, NASA rotor37, is taken as the research object, and the solid wall case and three axial slot casing treatments with different axial positions are studied by numerical simulation. The results show that the configuration with a center deviation of 0 (CT _C) has the best effect, with a margin improvement of 7.6% and an efficiency reduction of 0.09%; the configuration with an upstream positioned axial slot (CT_L) is the second, with a margin improvement of 5.4% and an efficiency reduction of 0.28%; the configuration with a downstream positioned axial slot (CT_T) is the worst, with a margin improvement of 3.6% and an efficiency reduction of 0.3%. A shift of the slot in downstream direction is not effective because it only affects the extent of boundary layer separation and has little effect on the development of the tip leakage flow. The upstream positioned axial slot with unsatisfactory effect affects the tip leakage flow trajectory and weakens the radial vortex at the blade tip, but it cannot affect the subsequent development of the leakage vortex. The short slot casing treatment in the central position effectively inhibits the development of the vortex. At the same time, it affects the development of the boundary layer to some extent and ensures the lower efficiency reduction while obtaining better stability margin.

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Effects of the Inlet Boundary Layer Thickness on Rotating Stall in an Axial Compressor

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-50886 ◽

2008 ◽

Cited By ~ 1

Author(s):

Minsuk Choi ◽

Seong Hwan Oh ◽

Han Young Ko ◽

Je Hyun Baek

Keyword(s):

Boundary Layer ◽

Layer Thickness ◽

Boundary Layer Thickness ◽

Axial Compressor ◽

Internal Flow ◽

Rotating Stall ◽

Tip Leakage Flow ◽

Suction Surface ◽

Corner Separation ◽

The Difference

A three-dimensional numerical simulation was conducted to study an effect of the inlet boundary layer thickness on the rotating stall in an axial compressor. The inlet boundary layer thickness had significant effects on the hub-corner-separation in the junction of the hub and the suction surface. The hub-corner-separation grew significantly for the thick inlet boundary layer as the load was increased, while it was diminished to be indistinguishable from the rotor wake for the thin inlet boundary layer and a new corner-separation was originated near the casing. The difference in the internal flow at the near stall condition also had a large effect on characteristics of the rotating stall, especially the first asymmetric disturbance and the size of the stall cell. While a pre-stall disturbance arises firstly in the hub-corner-separation for the thick inlet boundary layer, an asymmetric disturbance was initially generated in the tip region because of the corner-separation for the thin inlet boundary layer. This disturbance was transferred to the tip leakage flow and grew to be an attached stall cell. When this attached stall cell reached a critical size, it moved along the blade row and became a short-length-scale rotating stall. The size of the stall cell for the thick inlet boundary layer was larger than that for the thin inlet boundary layer. The difference of the stall cell’s size affected the performance of the single rotor, causing large performance drop for the former case but a continuous performance change for the latter case.

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Effects of Tip Leakage Flow on the Aerodynamic Performance and Stability of an Axial-Flow Transonic Compressor Stage

Energies ◽

10.3390/en14144168 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4168

Author(s):

Botao Zhang ◽

Xiaochen Mao ◽

Xiaoxiong Wu ◽

Bo Liu

Keyword(s):

Boundary Layer ◽

Shock Wave ◽

Axial Flow ◽

Leading Edge ◽

Rotating Stall ◽

Tip Clearance ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Transonic Compressor

To explain the effect of tip leakage flow on the performance of an axial-flow transonic compressor, the compressors with different rotor tip clearances were studied numerically. The results show that as the rotor tip clearance increases, the leakage flow intensity is increased, the shock wave position is moved backward, and the interaction between the tip leakage vortex and shock wave is intensified, while that between the boundary layer and shock wave is weakened. Most of all, the stall mechanisms of the compressors with varying rotor tip clearances are different. The clearance leakage flow is the main cause of the rotating stall under large rotor tip clearance. However, the stall form for the compressor with half of the designed tip clearance is caused by the joint action of the rotor tip stall caused by the leakage flow spillage at the blade leading edge and the whole blade span stall caused by the separation of the boundary layer of the rotor and the stator passage. Within the investigated varied range, when the rotor tip clearance size is half of the design, the compressor performance is improved best, and the peak efficiency and stall margin are increased by 0.2% and 3.5%, respectively.

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Study of the Standard k-ε Model for Tip Leakage Flow in an Axial Compressor Rotor

International Journal of Turbo and Jet Engines ◽

10.1515/tjj-2015-0039 ◽

2016 ◽

Vol 33 (4) ◽

Cited By ~ 7

Author(s):

Yanfei Gao ◽

Yangwei Liu ◽

Luyang Zhong ◽

Jiexuan Hou ◽

Lipeng Lu

Keyword(s):

Flow Field ◽

Large Scale ◽

Turbulent Viscosity ◽

Axial Compressor ◽

Leakage Flow ◽

Reynolds Stresses ◽

Mean Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Compressor Rotor

AbstractThe standard k-ε model (SKE) and the Reynolds stress model (RSM) are employed to predict the tip leakage flow (TLF) in a low-speed large-scale axial compressor rotor. Then, a new research method is adopted to “freeze” the turbulent kinetic energy and dissipation rate of the flow field derived from the RSM, and obtain the turbulent viscosity using the Boussinesq hypothesis. The Reynolds stresses and mean flow field computed on the basis of the frozen viscosity are compared with the results of the SKE and the RSM. The flow field in the tip region based on the frozen viscosity is more similar to the results of the RSM than those of the SKE, although certain differences can be observed. This finding indicates that the non-equilibrium turbulence transport nature plays an important role in predicting the TLF, as well as the turbulence anisotropy.

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A Proposal for Passive Wall Treatment Applied in High Performance Axial Flow Compressors

Volume 2A: Turbomachinery ◽

10.1115/gt2020-15238 ◽

2020 ◽

Author(s):

Rubén Bruno Díaz ◽

Jesuino Takachi Tomita ◽

Cleverson Bringhenti ◽

Francisco Carlos Elizio de Paula ◽

Luiz Henrique Lindquist Whitacker

Keyword(s):

Stokes Equations ◽

Axial Compressor ◽

Axial Flow ◽

Tip Clearance ◽

Leakage Flow ◽

Smooth Wall ◽

Tip Leakage Flow ◽

Viscous Effects ◽

Stall Margin ◽

Tip Leakage

Abstract Numerical simulations were carried out with the purpose of investigating the effect of applying circumferential grooves at axial compressor casing passive wall treatment to enhance the stall margin and change the tip leakage flow. The tip leakage flow is pointed out as one of the main contributors to stall inception in axial compressors. Hence, it is of major importance to treat appropriately the flow in this region. Circumferential grooves have shown a good performance in enhancing the stall margin in previous researches by changing the flow path in the tip clearance region. In this work, a passive wall treatment with four circumferential grooves was applied in the transonic axial compressor NASA Rotor 37. Its effect on the axial compressor performance and the flow in the tip clearance region was analyzed and set against the results attained for the smooth wall case. A 2.63% increase in the operational range of the axial compressor running at 100%N, was achieved, when compared with the original smooth wall casing configuration. The grooves installed at compressor casing, causes an increase in the flow entropy generation due to the high viscous effects in this gap region, between the rotor tip surface and casing with grooves. These viscous effects cause a drop in the turbomachine efficiency. For the grooves configurations used in this work, an efficiency drop of 0.7% was observed, compared with the original smooth wall. All the simulations were performed based on 3D turbulent flow calculations using Reynolds Averaged Navier-Stokes equations, and the flow eddy viscosity was determined using the two-equation SST turbulence model. The details of the grooves geometrical dimensions and its implementation are described in the paper.

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On the Recessed Blade Tip With and Without a Porous Material in an Axial Compressor

Volume 2A: Turbomachinery ◽

10.1115/gt2014-26000 ◽

2014 ◽

Author(s):

Young-Jin Jung ◽

Tae-Gon Kim ◽

Minsuk Choi

Keyword(s):

Porous Material ◽

Axial Compressor ◽

Internal Flow ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Flow Solver ◽

Stall Margin ◽

Tip Leakage ◽

Blade Tip ◽

Strong Vortex

This paper addresses the effect of the recessed blade tip with and without a porous material on the performance of a transonic axial compressor. A commercial flow solver was employed to analyze the performance and the internal flow of the axial compressor with three different tip configurations: reference tip, recessed tip and recessed tip filled with a porous material. It was confirmed that the recessed blade tip is an effective method to increase the stall margin in an axial compressor. It was also found in the present study that the strong vortex formed in the recess cavity on the tip pushed the tip leakage flow backward and weakened the tip leakage flow itself, consequently increasing the stall margin without any penalty of the efficiency in comparison to the reference tip. The recessed blade tip filled with a porous material was suggested with hope to obtain the larger stall margin and the higher efficiency. However, it was found that a porous material in the recess cavity is unfavorable to the performance in both the stall margin and the efficiency. An attempt has been made to explain the effect of the recess cavity with and without a porous material on the flow in an axial compressor.

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