A Numerical Investigation of the Flow Mechanisms in a HPC Front Stage With Axial Slots

2003 ◽  
Author(s):  
I. Wilke ◽  
H.-P. Kau
Keyword(s):  
Rotor Blade ◽  
Flow Stability ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Blade Passage ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Front Stage ◽  
The Impact ◽  
Compressor Efficiency

This paper describes the impact of axial slots on the flow field in a transonic rotor blade row. The presented results are completely based on time-accurate 3-dimensional numerical simulations of a high pressure compressor front stage with and without casing treatment. Two different axial positions of a casing treatment consisting of axial slots were tested for their impact on flow stability and efficiency. The first tested position (configuration 1) was chosen in a conventional way. The slots extend approximately from the leading up to the trailing edge of the rotor blades. As expected, the simulations of the compressor stage with this configuration showed a significant increase in flow stability near surge compared to the solid wall case. However, a non negligible decrease in efficiency is also observed. Analyses of flow interactions between casing treatment and rotor blade rows under transonic conditions lead to the general conclusion that the stabilizing effect of circumferential grooves or axial slots mainly results from their impact on the tip leakage flow and its resulting vortex. A characteristic vortex inside the slots is observed in the simulations with the conventionally positioned casing treatment. This vortex removes fluid out of downstream parts of the blade passage and feeds it back into the main flow further upstream. The resulting impact on the tip leakage flow is responsible for the increased flow stability. However, the interaction between the configuration 1 casing treatment flow and the blade passage flow results in a significant relocation of the blade passage shock in the downstream direction. This explains the observed decrease in compressor efficiency. A second slot position (configuration 2) was tested with the objective to improve compressor efficiency. The casing treatment was shifted upstream, so that only 25% of the blade chord remained under the slots. The simulations carried out demonstrate that this shift positively effects the resulting efficiency, but maintains the increased level of flow stability. A time-accurate analysis of the flow shows clearly that the modified casing treatment stabilizes the tip leakage vortex and reduces the influence on the flow inside the blade passage.

A Numerical Investigation of the Flow Mechanisms in a High Pressure Compressor Front Stage With Axial Slots

2004 ◽  
Vol 126 (3) ◽  
pp. 339-349 ◽  
Author(s):  
Ingo Wilke ◽  
Hans-Peter Kau
Keyword(s):  
Rotor Blade ◽  
Flow Stability ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Blade Passage ◽  
Casing Treatment ◽  
Tip Leakage ◽  
High Pressure Compressor ◽  
Compressor Efficiency ◽  
Pressure Compressor

This paper describes the impact of axial slots on the flow field in a transonic rotor blade row. The presented results are completely based on time-accurate three-dimensional numerical simulations of a high pressure compressor front stage with and without casing treatment. Two different axial positions of a casing treatment consisting of axial slots were tested for their impact on flow stability and efficiency. The first tested position (configuration 1) was chosen in a conventional way. The slots extend approximately from the leading up to the trailing edge of the rotor blades. As expected, the simulations of the compressor stage with this configuration showed a significant increase in flow stability near surge compared to the solid wall case. However, a non-negligible decrease in efficiency is also observed. Analyses of flow interactions between casing treatment and rotor blade rows under transonic conditions lead to the general conclusion that the stabilizing effect of circumferential grooves or axial slots mainly results from their impact on the tip leakage flow and its resulting vortex. A characteristic vortex inside the slots is observed in the simulations with the conventionally positioned casing treatment. This vortex removes fluid out of downstream parts of the blade passage and feeds it back into the main flow further upstream. The resulting impact on the tip leakage flow is responsible for the increased flow stability. However, the interaction between the configuration 1 casing treatment flow and the blade passage flow results in a significant relocation of the blade passage shock in the downstream direction. This fact is a main explanation for the observed decrease in compressor efficiency. A second slot position (configuration 2) was tested with the objective to improve compressor efficiency. The casing treatment was shifted upstream, so that only 25% of the blade chord remained under the slots. The simulations carried out demonstrate that this shift positively affects the resulting efficiency, but maintains the increased level of flow stability. A time-accurate analysis of the flow shows clearly that the modified casing treatment stabilizes the tip leakage vortex and reduces the influence on the flow inside the blade passage.

On the Interactions of a Rotor Blade Tip Flow With Axial Casing Grooves in an Axial Compressor Near the Best Efficiency Point

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
Joseph Katz
Keyword(s):  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Maximum Efficiency ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Angle ◽  
Tip Leakage ◽  
Blade Tip ◽  
The Impact

Experiments in a refractive index-matched axial turbomachine facility show that semicircular skewed axial casing grooves (ACGs) reduce the stall flowrate by 40% but cause a 2.4% decrease in the maximum efficiency. Aiming to elucidate mechanism that might cause the reduced efficiency, stereo-PIV measurements examine the impact of the ACGs on the flow structure and turbulence in the tip region near the best efficiency point (BEP), and compare them to those occurring without grooves and at low flowrates. Results show that the periodic inflow into the groove peaks when the rotor blade pressure side (PS) overlaps with the downstream end of the groove, but diminishes when this end faces the suction side (SS). Entrainment of the PS boundary layer and its vorticity generates a vortical loop at the entrance to the groove, and a “discontinuity” in the tip leakage vortex (TLV) trajectory. During exposure to the SS, the backward tip leakage flow separates at the entrance to the groove, generating a counter-rotating circumferential “corner vortex,” which the TLV entrains into the passage at high flowrates. Interactions among these structures enlarge the TLV and create a broad area with secondary flows and elevated turbulence near the groove's downstream corner. A growing shear layer with weaker turbulence also originates from the upstream corner. The groove also increases the flow angle upstream of the blade tip and varies it periodically. Accordingly, the circulation shed from the blade tip and strength of leakage flow increase near the blade leading edge (LE).

Prediction of Tip Leakage Vortex Dynamics in an Axial Compressor Cascade Using RANS Analyses

2020 ◽  
Author(s):  
Martina Ricci ◽  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Andrea Arnone
Keyword(s):  
Vortex Dynamics ◽  
Eddy Viscosity ◽  
Axial Compressor ◽  
Viscosity Model ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Eddy Viscosity Model ◽  
The Impact

Abstract The tip leakage flow in turbine and compressor blade rows is responsible for a relevant fraction of the total loss. It contributes to unsteadiness, and have an important impact on the operability range of compressor stages. Experimental investigations and, more recently, scale-resolving CFD approaches have helped in clarifying the flow mechanism determining the dynamics of the tip leakage vortex. Due to their continuing fundamental role in design verifications, it is important to establish whether RANS/URANS approaches are able to reproduce the effects of such a flow feature, in order to correctly drive the design of the next generation of turbomachinery. Base studies are needed in order to accomplish this goal. In the present work the tip leakage flow in axial compressor rotor blade cascade have been studied. The cascade was tested experimentally in Virginia Tech Low Speed Cascade Wind Tunnel in both stationary and moving endwall configurations. Numerical analyses were performed using the TRAF code, a state-of-the-art in-house-developed 3D RANS/URANS flow solver. The impact of the numerical framework was investigated selecting different advection schemes including a central scheme with artificial dissipation and a high-resolution upwind strategy. In addition, two turbulence models have been used, the Wilcox linear k–ω model and a non-linear eddy viscosity model (Realizable Quadratic Eddy Viscosity Model), which accounts for turbulence anisotropy. The numerical results are scrutinized using the available measurements. A detailed discussion of the vortex evolution inside the blade passage and downstream of the blade trailing edge is presented in terms of streamwise velocity, streamwise vorticity, and turbulent kinetic energy contours. The purpose is to identify guidelines for obtaining the best representation of the vortex dynamics, with the methodologies usually employed in routine design iterations and, at the same time, evidence their weak aspects that need further modelling efforts.

Extensive Experimental Study of Circumferential Single Groove in an Axial Flow Compressor

2014 ◽  
Author(s):  
Jichao Li ◽  
Feng Lin ◽  
Sichen Wang ◽  
Juan Du ◽  
Chaoqun Nie ◽  
...  
Keyword(s):  
Experimental Study ◽  
Unsteady Flow ◽  
Axial Compressor ◽  
Axial Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Good Tool ◽  
Stall Margin ◽  
Casing Treatment ◽  
Tip Leakage

Circumferential single-groove casing treatment becomes an interesting topic in recent few years, because it is a good tool to explore the interaction between the groove and the flow in blade tip region. The stall margin improvement (SMI) as a function of the axial groove location has been found for some compressors, such a trend cannot be predicted by steady high-fidelity CFD simulations. Recent efforts show that to catch such a trend, multi-passage, unsteady flow simulations are needed as the stalling mechanism itself involves cross-passage flows and unsteady dynamics. This indicates a need to validate unsteady numerical simulation results. In this paper, an extensive experimental study of a total of fifteen single casing grooves in a low-speed axial compressor rotor is presented, the groove location varies from 0.4% to 98.3% of axial tip chord are tested. The unsteady pressure data both at casing and at the blade wake with different groove locations are measured and processed, including the movement of trajectory of tip leakage flow, the evolution of unsteadiness of tip leakage flow (UTLF), the unsteady spectrum signature during the stall process, and the outlet unsteady flow characteristic along the span. These data provide a case study for validation of the unsteady CFD results, and may be helpful for further interpretation on the stalling mechanism affected by circumferential casing grooves.

Numerical analysis of the effects of circumferential groove casing suction in a counter-rotating axial flow compressor

2020 ◽  
pp. 095765092095169
Author(s):  
Tian Liang ◽  
Bo Liu ◽  
Stephen Spence ◽  
Liying Jiao
Keyword(s):  
Axial Flow ◽  
Main Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Circumferential Groove ◽  
Flow Compressor ◽  
The Impact

To extend the current understanding of the circumferential groove casing suction applied to a counter-rotating axial flow compressor, the impact of different axial locations of the circumferential suction groove on the characteristics of the tip leakage flow (TLF) and the corresponding physical mechanisms producing the stability enhancement have been studied based on validated numerical simulations. The results show that the optimal location for the suction groove is at around 20% axial chord, which demonstrated a high potential for reducing additional stall mass flow coefficient with about 8.4% increment in the stall margin. After the casing suction groove was applied, the interface between the incoming main flow and TLF was pushed significantly downstream in the second rotor. The blade loading in the region below the groove, the tip leakage flow angle and the reversed axial momentum flux injected into main flow passage through the tip gap were all reduced, which contributed to the stall margin improvement. Detailed analysis of the tip leakage flow structures showed that the TLF originating from different chord locations played different roles in the stall inception process. It was found to be more effective to improve stall margin and adiabatic efficiency by controlling the front part of the TLF, which was most sensitive.

Tip Leakage Flow and Heat Transfer Characteristics on Rotor Casing and Blade Tip in an Axial Gas Turbine Engine: Steady Analysis

2008 ◽  
Author(s):  
Md Hamidur Rahman ◽  
Sung In Kim ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Rotor Blade ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Heat Transfer Characteristics ◽  
Turbine Engine ◽  
Tip Leakage ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Blade Tip

Steady simulations have been performed to investigate tip leakage flow and heat transfer characteristics on the casing and rotor blade tip in a single stage turbine engine. A turbine stage of stator and rotor was modeled with a pressure ratio of 3.2. The predicted isentropic Mach number and adiabatic wall temperature on the casing showed good agreement with available experimental data. The effects of tip clearance height and rotor rotational speed on the blade tip and casing heat transfer characteristics are mainly considered. It is observed that the tip leakage flow structure is highly dependent on the height of the tip gap as well as speeds of the rotor blade. In all cases, flow separates just around the corner of the pressure side of the blade tip. The region of recirculating flow increases with the increase of the clearance height. Then the flow reattaches on the tip surface near the suction side beyond the flow separation. This flow reattachment enhances surface heat transfer. The leakage flow interaction with the reverse cross flow, induced by relative casing motion, is found to have significant effect on the blade tip and casing heat transfer distribution. Critical region of high heat transfer on the casing exists near the blade tip leading edge and along the pressure side edge at all clearance height. Whereas, at high speed rotation, it tends to move towards the trailing edge due to the change of inflow angle.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

Sign in / Sign up

Export Citation Format

Share Document