Numerical Simulation of Effects of Tip Geometry on the Performance of an Axial Compressor

The purpose of this paper is to investigate numerically the effects of the tip geometry on the performance of an axial compressor rotor. There are three case studies which are compared with the base line tip geometry. 1) baseline (flat tip); 2) Cavity (tip with a cavity); 3) SSQA (suction side squealer tip) and 4) SSQB (modified suction side squealer tip). The case of SSQB is a combination of suction side squealer tip and the cavity tip. From leading edge to 10% chord, the tip has a cavity. From 10% chord to trailing edge, the tip has a suction side squealer. The numerical results of 2) show that the cavity tip leads to lower leakage mass flow and greater loss in tip gap and the rotor passage. The loading near the blade tip is lower than the baseline, thus the tangential force of the blade is lower. It leads to lower pressure rise than the baseline. The performance of the compressor for the tip with cavity is worse than the baseline. The results of 3) show that the higher curvature of the suction side squealer increases the loading of the blade and the tangential blade force. With the suction side squealer tip, the leakage flow experiences two vena contractor thus the mass of the leakage flow is reduced which is benefit for the performance of the compressor. The loss in the tip gap is lower than baseline. The performance is better than the baseline with greater pressure rise of the rotor, smaller leakage mass flow and lower averaged loss. For the case the SSQB, the leakage mass flow is lower than the SSQA and the loss in the tip gap and the rotor passage is greater than SSQA. The performance of the case of the SSQB is worse than the case of SSQA.

Stall Inception and Development Process Due to Tip Leakage Flow in Axial Compressor Rotor Blades Row

Journal of Mechanics ◽

10.1017/jmech.2014.4 ◽

2014 ◽

Vol 30 (3) ◽

pp. 307-313 ◽

Author(s):

R. Taghavi-Zenou ◽

S. Abbasi ◽

S. Eslami

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Axial Compressor ◽

Leading Edge ◽

Rotor Blades ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Compressor Rotor

ABSTRACTThis paper deals with tip leakage flow structure in subsonic axial compressor rotor blades row under different operating conditions. Analyses are based on flow simulation utilizing computational fluid dynamic technique. Three different circumstances at near stall condition are considered in this respect. Tip leakage flow frequency spectrum was studied through surveying instantaneous static pressure signals imposed on blades surfaces. Results at the highest flow rate, close to the stall condition, showed that the tip vortex flow fluctuates with a frequency close to the blade passing frequency. In addition, pressure signals remained unchanged with time. Moreover, equal pressure fluctuations at different passages guaranteed no peripheral disturbances. Tip leakage flow frequency decreased with reduction of the mass flow rate and its structure was changing with time. Spillage of the tip leakage flow from the blade leading edge occurred without any backflow in the trailing edge region. Consequently, various flow structures were observed within every passage between two adjacent blades. Further decrease in the mass flow rate provided conditions where the spilled flow ahead of the blade leading edge together with trailing edge backflow caused spike stall to occur. This latter phenomenon was accompanied by lower frequencies and higher amplitudes of the pressure signals. Further revolution of the rotor blade row caused the spike stall to eventuate to larger stall cells, which may be led to fully developed rotating stall.

Performance and Stability Enhancement of NASA Rotor 37 Applying Abradable Coating

Volume 6: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-68074 ◽

2005 ◽

Author(s):

Behnam H. Beheshti ◽

Bijan Farhanieh ◽

Kaveh Ghorbanian ◽

Joao A. Teixeira ◽

Paul C. Ivey

Keyword(s):

Flow Characteristics ◽

Axial Compressor ◽

Tip Clearance ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Axial Compressors ◽

Compressor Rotor ◽

Abradable Coating ◽

Blade Tip ◽

Stability Enhancement

Improvements in sealing mechanism between the rotating and the stationary parts of a turbomachine can extensively reduce the endwall leakage flow. In this regard, abradable seals are incorporated into compressor and turbine blade-tip region. In a gas turbine, equipped with abradable seals, tip of the rotor blade is designed to cut into the material coating of the casing and to form a close fitted circumferential groove for the movement of the blade tip. As a result, the resistance to the leakage flow in the tip gap region increases due to smaller tip clearances (available without any rub-induced damages). Minimizing the tip clearance size can lead to an increase in performance and stability. This paper presents a numerical investigation of abradable coating as a means to seal the tip leakage flow in NASA Rotor 37, a transonic axial compressor rotor. In order to validate the multi block model used in the tip gap region, various flow characteristics are verified with the experimental data for smooth casing at a design clearance of 0.5% span. To have a better understanding of how an abradable seal affects the passage flow field, smooth casing and abradable coating are studied and results are compared for various models including two different incursion depth and width. Results indicate that the application of abradable coating in transonic axial compressors can efficiently improve the performance and stability.

Experimental and Numerical Investigation of Effect of Center Offset Degree on Compressor Stability With Circumferential Grooved Casing Treatment

Volume 2A: Turbomachinery ◽

10.1115/gt2016-56757 ◽

2016 ◽

Author(s):

HaoGuang Zhang ◽

Feng Tan ◽

YanHui Wu ◽

WuLi Chu ◽

Wei Wang ◽

...

Keyword(s):

Axial Compressor ◽

Leading Edge ◽

Groove Depth ◽

Tip Clearance ◽

Central Difference ◽

Stall Margin ◽

Casing Treatment ◽

Compressor Rotor ◽

Stall Margin Improvement ◽

For compressor blade tip stall, one effective way of extending stable operating range is with the application of circumferential grooved casing treatment and its validity was proved by a lot of experimental and numerical investigations. The emphases of most circumferential grooved investigations are focused on the influence of groove depth and groove number on compressor stability, and there is few investigations dealt with the center offset degree of circumferential grooves casing treatment. Hence, an axial compressor rotor with casing treatment (CT) was investigated with experimental and numerical methods to explore the effect of center offset degree on compressor stability and performance. In the work reported here, The center offset degree is defined as the ratio of the central difference between rotor tip axial chord and CT to the axial chord length of rotor tip. When the center of CT is located within the upstream direction of the center of rotor tip axial chord, the value of center offset degree is positive. The experimental and numerical results show that stall margin improvement gained with CT is reduced as the value of center offset degree varies from 0 to 0.33 or −0.33, and the CT with −0.33 center offset degree achieves the lowest value of stall margin improvement at 53% and 73% design rotational speed. The detailed analysis of the flow-field in compressor tip indicates that there is not positive effect made by grooves on leading edge of rotor blade tip when the value of center offset degree is −0.33. As the mass flow of compressor reduces further, tip clearance leakage flow results in the outlet blockage due to the absence of the positive action of grooves near blade tip tail when the value of center offset degree is 0.33. Blockage does not appear in rotor tip passage owing to utilizing the function of all grooves with CT of 0 center offset degree.

Stall margin improvement in a low-speed axial compressor rotor using a blockage-optimised single circumferential casing groove

Journal of the Global Power and Propulsion Society ◽

10.33737/jgpps/133912 ◽

2021 ◽

Vol 5 ◽

pp. 79-89

Author(s):

Ahmad Fikri Mustaffa ◽

Vasudevan Kanjirakkad

Keyword(s):

Axial Compressor ◽

Pressure Rise ◽

Leading Edge ◽

Tip Leakage Flow ◽

Stall Margin ◽

Low Speed ◽

Tip Leakage ◽

Compressor Rotor ◽

Stall Margin Improvement ◽

Edge Based

The stall margin of tip-critical axial compressors can be improved by using circumferential casing grooves. From previous studies, in the literature, the stall margin improvement due to the casing grooves can be attributed to the reduction of the near casing blockage. The pressure rise across the compressor as the compressor is throttled intensifies the tip leakage flow. This results in a stronger tip leakage vortex that is thought to be the main source of the blockage. In this paper, the near casing blockage due to the tip region aerodynamics in a low-speed axial compressor rotor is numerically studied and quantified using a mass flow-based blockage parameter. The peak blockage location at the last stable operating point for a rotor with smooth casing is found to be at about 10% of the tip chord aft of the tip leading edge. Based on this information, an optimised single casing groove design that minimises the peak blockage is found using a surrogate-based optimisation approach. The implementation of the optimised groove is shown to produce a stall margin improvement of about 5%.

A Computational Study of Tip Desensitization in Axial Flow Turbines: Part 2 — Turbine Rotor Simulations With Modified Tip Shapes

Volume 5: Turbo Expo 2004, Parts A and B ◽

10.1115/gt2004-53919 ◽

2004 ◽

Author(s):

James A. Tallman

Keyword(s):

Mass Flow ◽

Computational Study ◽

Three Dimensional ◽

Axial Flow ◽

Numerical Procedure ◽

Suction Side ◽

Turbine Rotor ◽

Leakage Flow ◽

Side Edge ◽

This study used Computational Fluid Dynamics (CFD) to investigate modified turbine blade tip shapes as a means of reducing the leakage flow and vortex. The subject of this study was the single-stage experimental turbine facility at Penn State University, with scaled three-dimensional geometry representative of a modern high-pressure stage. To validate the numerical procedure, the rotor flowfield was first computed with no modification to the tip, and the results compared with measurements of the flowfield. The flow was then predicted for a variety of different tip shapes: first with coarse grids for screening purposes and then with more refined grids for final verification of preferred tip geometries. Part 2 of this two-part paper focuses on flow-field predictions with modified blade tip geometries, and the corresponding comparisons with the baseline, flat-tip solutions presented in Part 1. Fifteen different tip shapes were computed using the ADPAC CFD Solver and moderately sized grids (720,000 nodes). These modified tip shapes incorporated different combinations of blade tip edge rounding and squealer cavities, both square and rounded, as means of reducing the leakage flow and vortex. Rounding of the suction side edge of the blade tip resulted in a considerable reduction in the size and strength of the leakage vortex, while rounding of the pressure side edge of the blade tip significantly increased the mass flow rate through the gap. Rounded squealer cavities acted to reduce the mass flow through the gap and proved advantageous over traditional, square squealer cavities. The presence of a square squealer cavity without edge rounding showed no aerodynamic advantage over a flat tip. Final computations of two preferred tip shapes were then carried out using more refined grids (7.2 million nodes). The final, refined grid computations reconfirmed a reduction in the leakage flow and vortex, as well as their associated losses.

Effects of Blade Tip Geometries on the Aerodynamic Performance of a Compressor Cascade

Volume 7B: Fluids Engineering Systems and Technologies ◽

10.1115/imece2013-62642 ◽

2013 ◽

Author(s):

Hongwei Ma ◽

Jun Zhang ◽

Wei Wei

Keyword(s):

Pressure Rise ◽

Suction Side ◽

Leakage Flow ◽

Pressure Side ◽

Compressor Cascade ◽

Turning Angle ◽

Blade Loading ◽

Blade Width ◽

Blade Tip ◽

Greater Curvature

This paper presents a numerical simulation of effects of blade tip geometries on the flow field of a compressor cascade. The tip geometries include flat tip (baseline), tip with cavity, tip with pressure side extension and suction side squealer tip. For the tip with cavity and pressure side extension, the mass of the leakage flow is reduced. The loss in the tip gap of the cavity tip is greater than the baseline because of the interaction of the cavity flow and the leakage flow. For the tip with pressure side extension, the loss in the gap is also greater than the baseline. The main reason is that the greater blade width makes the mixing process of the leakage flow in the gap more sufficient than the baseline. For both these two cases, the turning angle of the cascade becomes smaller and the pressure rise of the cascade is lower than the flat tip case. For the suction side squealer tip, the greater curvature of squealer increases the blade loading. The turning angle of the cascade and the pressure rise becomes greater which increases total pressure loss slightly.

Reduction of Tip Clearance Losses in an Axial Turbine by Shaped Design of the Blade Tip Region

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27303 ◽

2007 ◽

Author(s):

K. Kusterer ◽

N. Moritz ◽

D. Bohn ◽

T. Sugimoto ◽

R. Tanaka

Keyword(s):

Numerical Investigation ◽

Mass Flow ◽

Suction Side ◽

Tip Clearance ◽

Leakage Flow ◽

Pressure Side ◽

Aerodynamic Efficiency ◽

Blade Tip ◽

Radial Gap ◽

Tip Clearance Vortex

Secondary flows and leakage flows lead to complex vortex structures in the flow field inside the passages of the vanes and blades in turbo machines. These result in aerodynamic losses and, thus, reduced efficiency. One of the major vortex structures is the tip clearance vortex, which is generated on the airfoil’s suction side due to the leakage flow through the tip clearance, e.g. between rotating blades and casing. This leakage flow is induced by the pressure difference between pressure and suction side. The tip clearance vortex intensity strongly depends on the amount of tip clearance leakage. Thus, the reduction of this leakage mass flow increases the aerodynamic efficiency of a turbo-machine. In gas turbines, two ways are commonly used to influence the tip leakage flow: contouring of the radial gap either at blade tip or endwall, or changing the blade tip geometry by application of squealers or winglets on the blade tip. In this paper, a numerical investigation on the principle physics of a specific blade tip design is presented. On the pressure side the blades are extended in the tip region comparable to winglets (“hook-shaped”). With this change, the structures of the flow entering the gap between blade tip and casing are influenced to achieve a reduction of the mass flow in the radial gap. In this approach, the contour of the blade on the pressure side surface is shaped smoothly so that only a low increase of the local stresses should be expected and the blade is manufactured in one part. Furthermore, the height of the tip clearance is not affected. The new blade tip design is applied to 2nd and 3rd blade of the axial turbine in a test configuration of a KHI industrial gas turbine. Thus, a multi-stage numerical approach has been selected for the numerical investigation. The numerical model includes the flow path, vanes and blades of the 2nd and 3rd stage. The mixing plane technique is used to couple the blocks computed in stationary system of reference and rotating system of reference. The aerodynamic efficiency of the new designed blade tip in the two-stage arrangement is compared to the original design. It shows that a slight increase can be achieved in the static polytropic efficiency of the turbine configuration. The influence of the new design on the flow structures in the tip clearance region of the blades is analysed in detail to explain the mechanisms that cause the efficiency increase.

Modeling of Blade Tip Geometries in an Axial Compressor Stage

Process Industries ◽

10.1115/imece2003-55219 ◽

2003 ◽

Author(s):

Carsten Stockhaus ◽

Werner Volgmann ◽

Horst Stoff

Keyword(s):

Beneficial Effect ◽

Axial Compressor ◽

Suction Side ◽

Tip Clearance ◽

Leakage Flow ◽

Efficiency Gain ◽

Pressure Side ◽

Compressor Stage ◽

Tip Leakage Flow ◽

The purpose of this paper is to investigate numerically the tip leakage flow for different blade tip geometries in an axial compressor stage under design and off-design conditions. Using flat tips, suction and pressure side squealers in combination with knife tips, a comparison of the rotor performance in terms of pressure and efficiency gain is reported. Detailed flow characteristics within the tip clearance gap, interaction of the leakage flow with the main flow and resultant turning effects at the exit of the row have been investigated. The CFD method is based on a commercially available compressible Navier-Stokes solver (STAR-CD), using a turbulent compressible high Reynolds number k-ε model. Accurate numerical comparison of different blade tip geometries is achieved by using the same grid for the various shapes. The blocking strategy with O-grid structure is presented. The numerical results show clearly the beneficial effect of cutting away material from the pressure side. The higher surface curvature of the suction side squealer affects the pressure blade loading and increases the lift in the same way. This effect is increased by increasing the squealer height and results in a lower efficiency gain near the surge line. The best modification of the blade tip shows a maximum reduction of the tip discharge coefficient of 20 %. This leads to an improved total pressure ratio of 0.29% and an improved total polytropic efficiency of 0.40% under design condition. The influences of favourable squealer geometries on stage characteristics are described along an operating line. With a simulation of IGV-setting from Δα = −15° to Δα = +20° different operating points have been investigated in a swirl performance map. The beneficial effect of the suction side squealer found for the rotor row could assign to the stator row and results in an improved static pressure gain. Furthermore, design indications are presented which help to keep the efficiency gain under surge condition as high as possible.

Prediction of Low Speed Compressor Rotor Flowfields With Large Tip Clearances

Volume 6: Turbo Expo 2003, Parts A and B ◽

10.1115/gt2003-38637 ◽

2003 ◽

Cited By ~ 7

Author(s):

Anurag Gupta ◽

S. Arif Khalid ◽

G. Scott McNulty ◽

Lyle Dailey

Keyword(s):

Three Dimensional ◽

Axial Compressor ◽

Pressure Rise ◽

Tip Clearance ◽

Navier Stokes ◽

Leakage Flow ◽

Low Speed ◽

Compressor Rotor ◽

Wide Range ◽

Measured Pressure

Rotor tip modeling fidelity, grid resolution, and near wall modeling have been examined to determine the requirements for an accurate prediction of the effects of large tip clearance in a low-speed axial compressor rotor. The effort, using a Reynolds-Averaged Navier-Stokes (RANS) solver, aimed to obtain the most accurate predictions from a three-dimensional, steady, single blade row simulation. A recently tested, modern low speed rotor, was used as the test geometry; the measured pressure rise characteristic as well as detailed data near stall was used to evaluate the ability of different modeling strategies to capture the correct flow structure. The leakage flow was quantified to show that a wide range of tip blockage could be obtained for different simulations of the same geometry and conditions. The results show that using a square tip and gridding to fully resolve the real tip gap was better able to capture the effects of loading on the leakage flow than either of the approximate models studied. Sufficient clustering near the casing to capture the shear layers was also found to be critical. While wall integration provided the best results in simultaneously improving the prediction of pressure rise characteristics and flow range, higher fidelity wall modeling and a casing y+ of approximately 3 were found to provide similar benefits.

Aerothermal Investigations of Tip Leakage Flow in Axial Flow Turbines—Part II: Effect of Relative Casing Motion

Journal of Turbomachinery ◽

10.1115/1.2952378 ◽

2008 ◽

Vol 131 (1) ◽

Cited By ~ 23

Author(s):

S. K. Krishnababu ◽

W. N. Dawes ◽

H. P. Hodson ◽

G. D. Lock ◽

J. Hannis ◽

...

Keyword(s):

Heat Transfer ◽

Mass Flow ◽

Axial Flow ◽

Suction Side ◽

Leakage Flow ◽

Base Line ◽

Tip Leakage Flow ◽

Suction Surface ◽

Average Heat ◽

Tip Leakage

A numerical study has been performed to investigate the effect of casing motion on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. The relative motion between the blade tip and the casing was simulated by moving the casing in a direction from the suction side to the pressure side of the stationary blade. Base line flat tip geometry and squealer type geometries, namely, double squealer or cavity and suction side squealer, were considered at a clearance gap of 1.6%C. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modeled using the shear stress transport k-ω model. The flow conditions correspond to an exit Reynolds number of 2.3×105. The results were compared to those obtained without the relative casing motion reported in Part I of this paper. In general, the effect of relative casing motion was to decrease the tip leakage mass flow and the average heat transfer to the tip due to the decrease in leakage flow velocity caused by a drop in driving pressure difference. Compared to the computations with stationary casing, in the case of all the three geometries considered, the average heat transfer to the suction surface of the blade was found to be larger in the case of the computations with relative casing motion. At a larger clearance gap of 2.8%C, in case of a flat tip, while the tip leakage mass flow decreased due to relative casing motion, only a smaller change in the average heat transfer to the tip and the suction surface of the blade was noticed.