Near Tip Loss Control with a Winglet Baffle Cavity Tip in a Turbine Cascade

2021 ◽  
Author(s):  
Li Li ◽  
Jiang Dengyu ◽  
Chao Zhou ◽  
Luo Hualing ◽  
Hou Weitao ◽  
...  
Keyword(s):  
Mass Flow ◽  
Large Scale ◽  
Experimental Studies ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Pressure Side ◽  
Tip Leakage ◽  
Flow Mixing ◽  
Geometry Feature ◽  
Blade Tip

Abstract The aerodynamic performance of a winglet baffle cavity tip is investigated at different inlet incidences from -12.5° to +12.5°. This blade tip shows geometry feature with a pressure side winglet and a baffle within the tip cavity. The experimental studies were carried out in a large scale linear cascade, and the numerical methods were also used to obtain the detail physics. The baffle on the tip divides the cavity vortex into two main parts, which increases the flow mixing over the tip. As the flow within the vortex exits the tip near the baffle and cavity corner, flow separation occurs over the suction side and reduces local tip leakage mass flow rate significantly. The additional pressure side winglet reduces the contraction coefficient on the pressure side squealer. It is found that the winglet baffle cavity tip can reduce the tip leakage mass flow by 12.1%, and the near tip loss by 4.2%, compared with the squealer tip. As the incidence of incoming flow decreases, the loss near the tip reduces mainly due to a reduction of the passage vortex, which develops from the casing endwall. At the same incidence, the aerodynamic performance of the winglet baffle cavity tip is better than the squealer tip.

The Tip Leakage Flow of an Unshrouded High Pressure Turbine Blade With Tip Cooling

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson
Keyword(s):  
Mass Flow ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Flow Ratio ◽  
Tip Leakage Flow ◽  
Momentum Exchange ◽  
Leakage Loss ◽  
Tip Leakage ◽  
Lower Loss ◽  
Mass Flow Ratio

Experimental, analytical, and numerical methods have been employed to study the aerodynamic performance of four different cooled tips with coolant mass ratios between 0% and 1.2% at three tip gaps of 1%, 1.6%, and 2.2% of the chord. The four cooled tips are two flat tips with different coolant holes, a cooled suction side squealer tip and a cooled cavity tip. Each tip has ten coolant holes with the same diameter. The uncooled cavity tip produces the smallest loss among all uncooled tips. On the cooled flat tip, the coolant is injected normally into the tip gap and mixes directly with flow inside the tip gap. The momentum exchange between the coolant and the flow that enters the tip gap creates significant blockage. As the coolant mass flow ratio increases, the tip leakage loss of the cooled flat tip first decreases and then increases. For the cooled cavity tip, the blockage effect of the coolant is not as big as that on the cooled flat tip. This is because after the coolant exits the coolant holes, it mixes with flow in the cavity first and then mixes with tip flow in the tip gap. The tip leakage loss of the cooled cavity tip increases as the coolant mass flow ratio increase. As a result, at a tip gap of 1.6% of the chord, the cooled cavity tip gives the lowest loss. At the smallest tip gap of 1% of the chord, the cooled flat tip produces less loss than the cooled cavity tip when the coolant mass flow ratios larger than 0.23%. This is because with the same coolant mass flow ratio, a proportionally larger blockage is created at the smallest tip gap. At the largest tip gap of 2.2% of the chord, the cavity tip achieves the best aerodynamic performance. This is because the effect of the coolant is reduced and the benefits of the cavity tip geometry dominate. At a coolant mass flow ratio of 0.55%, the cooled flat tips produce a lower loss than the cavity tip at tip gaps less than 1.3% of the chord. The cooled cavity tip produces the least loss for tip gaps larger than 1.3% of the chord. The cooled suction side squealer has the worst aerodynamic performance for all tip gaps studied.

Aerodynamic Investigation of the Tip Leakage Flow for Blades With Different Tip Squealer Geometries at Transonic Conditions

2009 ◽  
Author(s):  
Toma´sˇ Hofer ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Suction Side ◽  
Loss Coefficient ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Gap Flow ◽  
Tip Gap Flow

Modern high pressure turbines operate at high velocity and high temperature conditions. The gap existing above a turbine rotor blade is responsible for an undesirable tip leakage flow. It is a source of high aerodynamic losses and high heat transfer rates. A better understanding of the tip flow behaviour is needed to provide a more efficient cooling design in this region. The objective of this paper is to investigate the tip leakage flow for a blade with two different squealer tips and film-cooling applied on the pressure side and through tip dust holes in a non-rotating, linear cascade arrangement. The experiments were performed in the VKI Light Piston Compression Tube facility, CT-2. The tip gap flow was investigated by oil flow visualisations and by wall static and total pressure measurements. Two geometries were tested — a full squealer and a partial suction side squealer. The measurements were performed in the blade tip region, including the squealer rim and on the corresponding end-wall for engine representative values of outlet Reynolds and Mach numbers. The main flow structures in the cavity were put in evidence. Positive influence of the coolant on the tip gap flow and on the aerodynamic losses was found for the full squealer tip case: increasing the coolant mass-flow increased the tip gap flow resistance. The flow through the clearance therefore slows down, the tip gap mass-flow and the heat transfer respectively decreases. No such effect of cooling was found in the case of the partial suction side squealer geometry. The absence of a pressure side squealer rim resulted in a totally different tip gap flow topology, indifferent to cooling. The influence of cooling on the overall mass-weighted thermodynamic loss coefficient, which takes into account the different energies of the mainstream and coolant flows was found marginal for both geometries. Finally the overall loss coefficient was found to be higher for the partial suction side squealer tip than for the full squealer tip.

Effects of Tip Gap Size on the Aerodynamic Performance of a Cavity-Winglet Tip in a Turbine Cascade

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Fangpan Zhong ◽  
Chao Zhou
Keyword(s):  
Suction Side ◽  
Aerodynamic Performance ◽  
Gap Size ◽  
Turbine Cascade ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Baseline Case ◽  
Passage Vortex ◽  
Aerodynamic Performances ◽  
Blade Tip

The aerodynamic performance of a cavity-winglet tip is investigated in a high-pressure turbine cascade by experimental and numerical methods. The winglet tip has geometric features of a cavity and a suction side fore-part winglet. A cavity tip is studied as the baseline case. The aerodynamic performances of the two tips are investigated at three tip gaps of 0.8%, 1.7%, and 2.7% chord. At tip gaps of 1.7% and 2.7% chord, the loss near the blade tip is dominated by the tip leakage vortex (TLV) for both tips, and the winglet tip mainly reduces the loss generated by the tip leakage vortex. In the past, it was concerned that at a small tip gap, the winglet tip could introduce extra secondary loss and show little aerodynamic benefits. The winglet tip used in the current study is also found to be able to effectively reduce the loss at the smallest tip gap size of 0.8% chord. This is because at this small tip gap, the tip leakage vortex and the passage vortex (PV) appear simultaneously for the cavity tip. The winglet tip is able to reduce the pitchwise pressure gradient in the blade passage, which tends to suppress the formation of the passage vortex. The effects of the winglet tip on the flow physics and the loss mechanisms are explained in detail.

Axisymmetric Tip Gap Profiling in a Shroudless Axial Turbine

2020 ◽  
Author(s):  
M. Abda ◽  
M. G. Rose
Keyword(s):  
Mass Flow ◽  
Separation Bubble ◽  
Suction Side ◽  
Entropy Generation Rate ◽  
Tip Leakage Flow ◽  
Axial Turbine ◽  
Tip Leakage ◽  
Blade Tip ◽  
Design Value ◽  
Tip Mass

Abstract The inevitable gap between the rotor tips and the casing promotes flow leakage driven by the pressure difference between the pressure side and suction side of the blade. Axisymmetric tip gap profiling was applied at the blade tip and the casing endwall to reduce the tip leakage maintaining the same gap clearance. The investigation was held on a shroudless single stage axial turbine designed in ETH Zurich University named LISA D. The numerical calculation showed that axisymmetric tip gap profiling reduced the tip leakage flow and improved the efficiency by 0.65% and 0.1% respectively. However, the stage mass flow increased and as a result so did the rotor capacity. When the stage mass flow was reduced to the design value to maintain the design capacity, the effect of the axisymmetric tip gap profiling further improved, due to a reduction in the entropy generation rate of the tip leakage and passage vortices. The tip mass flow reduced by 2.39% and the efficiency improved significantly by 0.6%. It was observed that the tip profiling increased the size of the separation bubble in the PS/tip junction, which increased blockage effect in the gap. Hence, reduced the leaking flow to the SS, which results in weaker tip leakage vortex and its associated losses.

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.

An Experimental and Numerical Investigation Into the Effects of Squealer Blade Tip Modifications on Aerodynamic Performance

2013 ◽  
Author(s):  
G. A. Ledezma ◽  
J. Allen ◽  
R. S. Bunker
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Turbine Blades ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Tip Clearance ◽  
Total Pressure Loss ◽  
Pressure Side ◽  
Numerical Predictions ◽  
Blade Tip

Gas turbine blades using the so-called squealer tip configuration represent a majority of the high-pressure first stage blades in service. The squealer tip in its most basic format is simply a two-tooth labyrinth seal projecting from the blade tip towards the stationary shroud or casing. As with all blade tip configurations, the geometry is a compromise between aerodynamics, cooling, mechanical stress, durability, and repair. While many proposed blade tip innovations involve more complex geometries, this study seeks to determine if a simpler geometry, other than a flat tip, can provide equivalent aerodynamic performance with a reasonable chance of satisfying all other design factors. Using an annular sector blade cascade, total pressure loss surveys are measured with three blade tip geometries, the standard squealer tip, a single-sided suction side seal strip, and the single-sided strip with a pressure side winglet added. The same cascade is modeled numerically as a periodic passage for each of the geometries tested. Experiment and simulation both utilize all blade tip cooling flow injection locations and nominal magnitudes, as well as a constant tip clearance above the suction side seal strip. Experimental data show that the removal of the pressure side seal strip reduces the area-averaged total pressure loss slightly, while the addition of a winglet returns the performance to the baseline result. Numerical predictions indicate essentially equal performance for all geometries. The numerical results provide insight into the loss mechanisms of both the tip leakage flows and the coolant injection flows. This study, when combined with literature data on heat transfer and cooling, concludes that the simpler single-sided suction seal strip is better overall than the commonly employed squealer tip.

Effects of Winglet Geometry on the Aerodynamic Performance of Tip Leakage Flow in a Turbine Cascade

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson ◽  
Ian Tibbott ◽  
Mark Stokes
Keyword(s):  
Pressure Difference ◽  
Leading Edge ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Driving Pressure ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Side Edge

Experimental and numerical methods were used to investigate the aerodynamic performance of a winglet tip in a linear cascade. A flat tip and a cavity tip were studied as baseline cases. The flow patterns over the three tips were studied. For the cavity tip and the winglet tip, vortices appear in the cavity and the gutter. These vortices reduce the discharge coefficient of the tip leakage flow. The purpose of using a winglet tip is to reduce the driving pressure difference. The pressure side winglet of the winglet geometry studied in this paper has little effect in reducing the driving pressure difference. It is found that the suction side winglet reduces the driving pressure difference of the tip leakage flow near the leading edge, but increases the driving pressure difference from midchord to the trailing edge. This is also used to explain the findings and discrepancies in other studies. Compared with the flat tip, the cavity tip and the winglet tip achieve a reduction of loss. The effects of the rounding of the pressure side edge of the tips were studied to simulate the effects of deterioration. As the size of the pressure side edge radius increases, the tip leakage mass flow rate and the loss increase. The improvement of the aerodynamic performance by using a winglet remains similar when comparing with a flat tip or a cavity tip with the same pressure side radius.

The Tip Leakage Flow of an Unshrouded High Pressure Turbine Blade With Tip Cooling

2009 ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson
Keyword(s):  
Mass Flow ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Flow Ratio ◽  
Tip Leakage Flow ◽  
Momentum Exchange ◽  
Leakage Loss ◽  
Tip Leakage ◽  
Lower Loss ◽  
Mass Flow Ratio

Experimental, analytical and numerical methods have been employed to study the aerodynamic performance of four different cooled tips with coolant mass ratios between zero and 1.2% at three tip gaps of 1%, 1.6% and 2.2% of the chord. The four cooled tips are two flat tips with different coolant holes, a cooled suction side squealer tip and a cooled cavity tip. Each tip has ten coolant holes with the same diameter. The uncooled cavity tip produces the smallest loss among all uncooled tips. On the cooled flat tip, the coolant is injected normally into the tip gap and mixes directly with flow inside the tip gap. The momentum exchange between the coolant and the flow that enters the tip gap creates significant blockage. As the coolant mass flow ratio increases, the tip leakage loss of the cooled flat tip first decreases and then increases. For the cooled cavity tip, the blockage effect of the coolant is not as big as that on the cooled flat tip. This is because after the coolant exits the coolant holes, it mixes with flow in the cavity first, and then mixes with tip flow in the tip gap. The tip leakage loss of the cooled cavity tip increases as the coolant mass flow ratio increase. As a result, at a tip gap of 1.6% of the chord, the cooled cavity tip gives the lowest loss. At the smallest tip gap of 1% of the chord, the cooled flat tip produces less loss than the cooled cavity tip when the coolant mass flow ratios larger than 0.23%. This is because with the same coolant mass flow ratio, a proportionally larger blockage is created at the smallest tip gap. At the largest tip gap of 2.2% of the chord, the cavity tip achieves the best aerodynamic performance. This is because, the effect of the coolant is reduced and the benefits of the cavity tip geometry dominate. At a coolant mass flow ratio of 0.55%, the cooled flat tips produce a lower loss than the cavity tip at tip gaps less than 1.3% of the chord. The cooled cavity tip produces the least loss for tip gaps larger than 1.3% of the chord. The cooled suction side squealer has the worst aerodynamic performance for all tip gaps studied.

Effects of Winglet Geometry on the Aerodynamic Performance of Tip Leakage FLow in a Turbine Cascade

2012 ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson ◽  
Ian Tibbott ◽  
Mark Stokes
Keyword(s):  
Pressure Difference ◽  
Leading Edge ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Driving Pressure ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Side Edge

Experimental and numerical methods were used to investigate the aerodynamic performance of a winglet tip in a linear cascade. A flat tip and a cavity tip are studied as baseline cases. The flow patterns over the three tips are studied. The flow separates over the pressure side edge. For the cavity tip and the winglet tip, vortices appear in the cavity. These vortices reduce the discharge coefficient of the tip. The purpose of using a winglet tip is to reduce the driving pressure difference. The pressure side winglet of the winglet geometry studied in this paper has little effect in reducing the driving pressure difference. It is found that the suction side winglet reduces the driving pressure difference of the tip leakage flow near the leading edge, but increases the driving pressure difference from midchord to the trailing edge. This is also used to explain the findings and discrepancies in other studies. Compared with the flat tip, the cavity tip and the winglet tip achieve a reduction of the loss to the size of the tip gap. The effects of the rounding of the pressure side edge of the tips were studied to simulate the effects of deterioration. As the size of the pressure side edge radius increase, the tip leakage mass flow rate and the loss increase. The improvement of the aerodynamic performance by using a winglet remains similar when comparing with a flat tip or a cavity tip with the same pressure side radius.

Tip Leakage Flows Near Partial Squealer Rims in an Axial Flow Turbine Stage

2003 ◽  
Author(s):  
Cengiz Camci ◽  
Debashis Dey ◽  
Levent Kavurmacioglu
Keyword(s):  
Total Pressure ◽  
Axial Flow ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Edge Zone ◽  
Tip Leakage ◽  
Partial Length

This paper deals with an experimental investigation of aerodynamic characteristics of full and partial-length squealer rims in a turbine stage. Full and partial-length squealer rims are investigated separately on the pressure side and on the suction side in the “Axial Flow Turbine Research Facility” (AFTRF) of the Pennsylvania State University. The streamwise length of these “partial squealer tips” and their chordwise position are varied to find an optimal aerodynamic tip configuration. The optimal configuration in this cold turbine study is defined as the one that is minimizing the stage exit total pressure defect in the tip vortex dominated zone. A new “channel arrangement” diverting some of the leakage flow into the trailing edge zone is also studied. Current results indicate that the use of “partial squealer rims” in axial flow turbines can positively affect the local aerodynamic field by weakening the tip leakage vortex. Results also show that the suction side partial squealers are aerodynamically superior to the pressure side squealers and the channel arrangement. The suction side partial squealers are capable of reducing the stage exit total pressure defect associated with the tip leakage flow to a significant degree.

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