Investigation on the effects of winglet geometry in a high loading compressor rotor

2021 ◽  
pp. 095765092110170
Author(s):  
Qingjun Zhao ◽  
Weiwei Cui ◽  
Wei Zhao ◽  
Xiaorong Xiang ◽  
Jianzhong Xu
Keyword(s):  
Flow Characteristics ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Low Velocity ◽  
Flow Area ◽  
Significant Deterioration ◽  
Maximum Width ◽  
Stall Margin ◽  
Blade Tip

The tip winglet is employed to improve the flow stability of NASA Rotor 37. Two suction-side winglets with the maximum width of 0.25 and 0.5 times of the width of local blade tip section and two pressure-side winglets with the maximum width of 0.5 and 0.9 times of the width of local blade tip section are designed and evaluated by numerical analysis of 3-D flowfield. The results show a rough leakage channel with two static pressure peaks over blade tip is formed due to the existing of pressure side winglet, and it benefits to reduce the effective through-flow area and massflow rate of leakage flow. The blocking effect on leakage flow weakens in new rotor with suction side winglet and it brings out the dramatical increase of leakage massflow rate and additional losses in tip region of rotor. With the comprehensive effects produced by tip winglet on leakage flow, the low-velocity region concerned on the interaction of leakage flow with passage shock has been reduced obviously in rotor with pressure side winglet and it leads to an over 11% increase of stall margin of transonic rotor with no penalty of efficiency. On the contrary, the suction side winglet contributes to a significant deterioration of tip flow characteristics of rotor with full expanded leakage flow and a smaller stall margin with over 17% decrease.

Attenuation of leakage flow using axially nonuniform tip clearance in high loading transonic compressor rotor

2021 ◽  
pp. 095441002110221
Author(s):  
Weiwei Cui ◽  
Fusong Liu ◽  
Xinglu Wang ◽  
Fei Yao
Keyword(s):  
Suction Side ◽  
Boundary Layer Separation ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Front Part ◽  
Low Velocity ◽  
Stall Margin ◽  
Blade Tip ◽  
Transonic Rotor ◽  
Velocity Region

Several linearly nonuniform clearances have been designed to explore a novel strategy for attenuation of leakage flow in tip region of high loading transonic rotor and the effects of axially nonuniform clearance on detailed tip flow structure and stable operating range of rotor have been discussed as well. The results showed that the tip flow characteristic of rotor is affected mainly by the combined effects of two parts of low-velocity flow, which are produced by interaction of leakage flow with passage shock and boundary layer separation near suction side, respectively. However, the stall margin of rotor and isentropic efficiency near tip region is dominated significantly by the former part, and the local changes of size and shape of tip clearance have a large influence on it. Once the strength of leakage flow decreases due to clearance size variation, the boundary layer separation near suction side of blade tip worsens gradually and increases additional aerodynamic losses in passage. Both the mass flow rate and mixing losses of the tip leakage flow can be reduced due to a smaller size of clearance existing in front part of clearance of rotor with a linearly divergent clearance shape, and the area of low-velocity region near pressure side has reduced accordingly. By contrast, a linearly convergent shape of tip clearance can increase both the area of low-velocity region and the mixing loss of leakage flow as a result of a larger size of clearance existing over the front part of blade tip of rotor. Eventually, a divergent shape of tip clearance with a reasonable minimum size near leading edge of blade tip is preferred for transonic rotor in consideration of the benefit in stall margin improvement with nearly no penalty in efficiency.

Numerical Study of Flow and Heat Transfer on a Blade Tip With Different Leakage Reduction Strategies

2003 ◽  
Author(s):  
Sumanta Acharya ◽  
Huitao Yang ◽  
Chander Prakash ◽  
Ron Bunker
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Flow Rates ◽  
Leakage Reduction ◽  
Flow And Heat Transfer ◽  
Reduction Strategies ◽  
Blade Tip

Numerical calculations are performed to explore different strategies for reducing tip leakage flow and heat transfer on the GE-E3 High-Pressure-Turbine (HPT) rotor blade. The calculations are performed for a single blade with periodic conditions imposed along the two boundaries in the circumferential-pitch direction. Several leakage reduction strategies are considered, all for a tip-clearance of 1.5% of the blade span, a pressure ratio (ratio of inlet total pressure to exit static pressure) of 1.2, and an inlet turbulence level of 6.1%. The first set of leakage reduction strategies explored include different squealer tip configurations: pressure-side squealer, suction-side squealer, mean-camber line squealer, and pressure plus suction side squealers located either along the edges of the blade or moved inwards. The suction-side squealer is shown to have the lowest heat transfer coefficient distribution and the lowest leakage flow rates. Two tip-desensitization strategies are explored. The first strategy involves a pressure-side winglet shaped to be thickest at the location with the largest pressure difference across the blade. The second strategy involves adding inclined ribs on the blade tip with the ribs normal to the local flow direction. While both strategies lead to reduction in the leakage flow and tip heat transfer rates, the ribbed tip exhibits considerably lower heat transfer coefficients. In comparing the two desensitization schemes with the various squealer tip configurations, the suction side squealer still exhibits the lowest heat transfer coefficient and leakage flow rates.

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

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.

Influence of Different Rim Widths and Blowing Ratios on Film Cooling Characteristics for a Blade Tip

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Jin Wang ◽  
Bengt Sundén ◽  
Min Zeng ◽  
Qiu-wang Wang
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Film Cooling ◽  
Three Dimensional ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Blade Tip ◽  
Film Cooling Holes

Three-dimensional simulations of the squealer tip on the GE-E3 blade with eight film cooling holes were carried out. The effect of the rim width and the blowing ratio on the blade tip flow and cooling performance were revealed. Numerical simulations were performed to predict the leakage flow and the tip heat transfer with the k–ɛ model. For the squealer tip, the depth of the cavity is fixed but the rim width varies to form a wide cavity, which can decrease the coolant momentum and the tip leakage flow velocity. This cavity contributes to the improvement of the cooling effect in the tip zone. To investigate the influence on the tip heat transfer by the rim width, numerical simulations were performed as a two-part study: (1) unequal rim width study on the pressure side and the suction side and (2) equal rim width study with rim widths of 0.58%, 1.16%, and 1.74% of the axial chord (0.5 mm, 1 mm, and 1.5 mm, respectively) on both the pressure side rim and the suction side rim. With different rim widths, the effect of different global blowing ratios, i.e., M = 0.5, 1.0 and 1.5, was investigated. It is found that the total heat transfer rate is increasing and the heat transfer rates on the rim surface (RS) rapidly ascend with increasing rim width.

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

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

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 ◽  
Blade Tip

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.

Cooling the Tip of a Turbine Blade Using Pressure Side Holes: Part 2 — Heat Transfer Measurements

2004 ◽  
Author(s):  
J. R. Christophel ◽  
K. A. Thole ◽  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Suction Side ◽  
Coolant Flow ◽  
Total Power ◽  
Leakage Flow ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Blade Tip

The clearance gap between a turbine blade tip and its associated shroud allows leakage flow across the tip gap from the pressure side to the suction side of the blade. Understanding how this leakage flow affects heat transfer is critical in extending blade tip durability in terms of oxidation, erosion, clearance, and overall turbine performance. This paper is the second of a two part series that discusses the augmentation of tip heat transfer as a result of blowing from the pressure side of the tip as well as dirt purge holes placed on the tip. For the experimental investigation, three scaled-up blades were used to form a two-passage linear cascade in a low speed wind tunnel. The rig was designed to simulate different tip gap sizes and coolant flow rates. Heat transfer coefficients were quantified by measuring the total power supplied to a constant heat flux surface placed on the tip of the blade and measuring the tip temperatures. Results indicate that increased blowing leads to increased augmentations in tip heat transfer, particularly at the entrance region to the gap. When combined with adiabatic effectiveness measurements, the coolant from the pressure side holes provides an overall net heat flux reduction to the blade tip but is nearly independent of coolant flow levels.

Numerical investigation of blade tip winglet on flow structure in a high loading transonic rotor

2021 ◽  
pp. 095441002110080
Author(s):  
Qingjun Zhao ◽  
Weiwei Cui ◽  
Xiaorong Xiang ◽  
Qiangren Xu ◽  
Jianzhong Xu
Keyword(s):  
Flow Structure ◽  
Flow Instability ◽  
Rotating Stall ◽  
High Loading ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Blade Tip ◽  
Flow Blockage

The interactions of tip leakage flow with mainstream and shock wave result in larger aerodynamic losses and blockage in high loading compressors and tend to be one of the triggers for flow instability. In order to attenuate the influence of leakage flow and improve the stall margin of highly loaded compressor, the new rotors surrounded by tip winglet are investigated by a numerical method. The tip winglet is designed by extending the flat blade tip section in outer 1.5% span of rotor blade. As the angle between the leakage flow and main flow decreases due to winglet, the losses and flow blockage have been weakened near stall condition, and the stall margin of new rotor with pressure-side winglet has an increase of over 10%. The migration and accumulation of low-energy fluids near the corner of casing endwall are affected significantly by tip winglet. As a result, the pressure-side winglet causes an increase of static pressure near the casing corner of pressure surface. Although the driving pressure difference near the leading edge of blade has increased slightly in the tip region, the strength and massflow rate of leakage flow appear to be decreased. As the leakage flow weakens in the new rotor with pressure-side winglet, its interaction with mainstream and shock has been suppressed obviously, and the delay of rotating stall occurs as well. Moreover, the flowfields of the new rotor with pressure-side winglet have been simulated at 40%, 60%, and 80% design speed. It is shown that the flow blockage and losses in the tip region have also reduced near stall point, and an improvement of overall performance is present in the new rotor with pressure-side winglet. All the changes of tip flow structure caused by winglet benefit to an increase of aerodynamic performance of new rotor at full rotational speed range.

Cooling the Tip of a Turbine Blade Using Pressure Side Holes—Part II: Heat Transfer Measurements

2005 ◽  
Vol 127 (2) ◽  
pp. 278-286 ◽  
Author(s):  
J. R. Christophel ◽  
K. A. Thole ◽  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Net Heat Flux ◽  
Blade Tip

The clearance gap between a turbine blade tip and its associated shroud allows leakage flow across the tip from the pressure side to the suction side of the blade. Understanding how this leakage flow affects heat transfer is critical in extending the durability of a blade tip, which is subjected to effects of oxidation and erosion. This paper is the second of a two-part series that discusses the augmentation of tip heat transfer coefficients as a result of blowing from film-cooling holes placed along the pressure side of a blade and from dirt purge holes placed on the tip. For the experimental investigation, three scaled-up blades were used to form a two-passage, linear cascade in a low-speed wind tunnel. The rig was designed to simulate different tip gap sizes and film-coolant flow rates. Heat transfer coefficients were quantified by using a constant heat flux surface placed along the blade tip. Results indicate that increased film-coolant injection leads to increased augmentation levels of tip heat transfer coefficients, particularly at the entrance region to the gap. Despite increased heat transfer coefficients, an overall net heat flux reduction to the blade tip results from pressure-side cooling because of the increased adiabatic effectiveness levels. The area-averaged results of the net heat flux reduction for the tip indicate that there is (i) little dependence on coolant flows and (ii) more cooling benefit for a small tip gap relative to that of a large tip gap.

Preliminary Investigation on the Effect of the Modification of the Sweep Angle at the Blade Tip of Forward Swept Axial Fans

2017 ◽  
Author(s):  
Massimo Masi ◽  
Andrea Lazzaretto
Keyword(s):  
Preliminary Investigation ◽  
Suction Side ◽  
The Other ◽  
Axial Fan ◽  
Sweep Angle ◽  
End Effects ◽  
Flow Rates ◽  
Stall Margin ◽  
Other Hand ◽  
Blade Tip

The flow path close to the suction side of fan rotor blades mostly affects the overall drag of the blading. The blade lift is affected as well because of the separation of the low energy boundary layer that drives the blade into stall at low fan flow rates. Forward sweep allows to position the airfoil sections of blades featuring a positive circulation gradient along the span so that they “accompany” the near-wall flow trajectories at the blade suction side. So, rotor efficiency and stall margin of the fan can be improved. On the other hand, blade end effects play a relevant role in high hub-to-tip and low aspect ratio rotors and may compromise the effectiveness of forward sweep. Nevertheless, some authors in the literature stated the beneficial contribution of changing the sweep angle at the ends of the blade both at design and off-design conditions. The paper studies the end effects on constant-swirl design rotors by means of CFD simulations focusing on the distribution of blade sweep in the near-tip region. In particular, the performance and efficiency calculated for a forward swept tube-axial fan featuring a hub-to-tip ratio equal to 0.4 are compared with those estimated for the corresponding unswept fan at equal duty point. Several modifications of the sweep distribution in the blade tip region are considered in the swept fan to quantify their effect on performance, efficiency and stall margin. Results show that the addition of up to 6 degrees of local forward sweep at the blade tip to the unswept blading does not affect fan pressure at design operation. On the other hand, this local increase of the sweep angle allows for a very notable increase of the peak pressure and efficiency at flow rates close to stall inception.

Sign in / Sign up

Export Citation Format

Share Document