Effects of the Inlet Boundary Layer Thickness on the Flow and Loss Characteristics in an Axial Compressor

2005 ◽  
Author(s):  
Minsuk Choi ◽  
Junyoung Park ◽  
Jehyun Baek
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Axial Compressor ◽  
Internal Flow ◽  
Total Loss ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Tip Leakage

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.

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

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.

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

2008 ◽  
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.

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

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.

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

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.

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

2009 ◽  
Vol 131 (2) ◽  
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.

Numerical Investigation on Slot Casing Treatment in a Transonic Axial Compressor Stage: Part 1 — Casing Treatment Design

2016 ◽  
Author(s):  
Mingmin Zhu ◽  
Xiaoqing Qiang ◽  
Jinfang Teng
Keyword(s):  
Axial Compressor ◽  
Leakage Flow ◽  
Compressor Stage ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Stall Margin ◽  
Rotating Speed ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Stall Margin Improvement

Slot-type casing treatment generally has a great potential of enhancing the operating range for tip-critical compressor rotors, however, with remarkable efficiency drop. Part I of this two-part paper was committed to develop a slot configuration with desired stall margin improvement and minimized efficiency loss. Steady simulation was carried out in a 1.5 transonic axial compressor stage at part design rotating speed. At this rotating speed this compressor stage operated at a subsonic condition and showed a rather narrow operating range, which needed to be improved badly. Flow fields analysis at peak efficiency and near stall point showed that the development of tip leakage vortex and resulting blockage near casing resulted in numerical stall. Three kinds of skewed slots with same rotor exposure and casing porosity were designed according to the tip flow field and some empirical strategies. Among three configurations, arc-curved skewed slot showed minimum peak efficiency drop with considerable stall margin improvement. Then rotor exposure and casing porosity were varied based on the original arc-curved skewed slot, with a special interest in detecting their impact on the compressor stability and overall efficiency. Result showed that smaller rotor exposure and casing porosity leaded to less efficiency drop. But meanwhile, effectiveness of improving compressor stability was weakened. The relation between efficiency drop and stall margin improvement fell on a smooth continuous curve throughout all slots configurations, indicating that the detrimental effect of casing treatment on compressor was inevitable. Flow analysis was carried out for cases of smooth casing and three arc-curved configurations at smooth casing near stall condition. The strength of suction/injection, tip leakage flow behavior and removal of blockage near casing were detailed examined. Larger rotor tip exposure and slots number contributed to stronger injection flow. The loss generated within the mixing process of injection flow with main flow and leakage flow is the largest source of entropy increase. Further loss mechanisms were interpreted at eight axial cuts, which were taken through the blade row and slots to show the increase in entropy near tip region. Entropy distributions manifested that loss generations with smooth casing were primarily ascribed to low-momentum tip leakage flow/vortex and suction surface separation at leading edge. CU0 slot, the arc-curved slots with 50% rotor tip exposure, was capable of suppressing the suction surface separation loss. Meanwhile, accelerated tip leakage flow brought about additional loss near casing and pressure surface. Upstream high entropy flow would be absorbed into the rear portion of slots repeatedly, resulting in further loss.

Numerical study of the unsteady behaviors and rotating stall inception process in a counter-rotating axial compressor

2016 ◽  
Vol 230 (14) ◽  
pp. 2716-2727 ◽  
Author(s):  
Xiaochen Mao ◽  
Bo Liu
Keyword(s):  
Numerical Study ◽  
Axial Compressor ◽  
Leading Edge ◽  
Rotating Stall ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Trailing Edge ◽  
Stall Inception ◽  
Tip Leakage

Unsteady computations of a counter-rotating axial compressor are performed and analyzed to investigate the unsteady behaviors in the compressor and the role of the tip leakage flow together with the rotating stall inception process. The results show that the oscillation on the pressure side is much stronger than that on the suction surface for both rotors, especially near the tip region where the trajectory of the tip leakage vortex (TLV) interacts with the blades most often. There exists a periodical leading edge spillage of the interface in rotor2 due to the unsteadiness of tip leakage flow (TLF) at near-stall condition. The blockage generated by the TLV increases dramatically due to the increasing strength of the TLV and the backflow phenomenon as the mass flow decreased. The appearance of the frequency components of 0.5 blade passing frequency (BPF) and 1.5BPF from 0.64BPF can be viewed as the rotating stall inception warning. The fluctuation strength of oscillation frequencies of 0.5BPF and 1.5BPF decreases rapidly from leading edge to trailing edge in rotor2, which indicates that the unsteady fluctuation of TLF at the leading edge in rotor2 is responsible for the stall inception of the compressor. Additionally, both the leading edge spillage and trailing edge backflow phenomena are observed for spike initiated rotating stall at stall point.

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

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.

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

Energies ◽  
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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