scholarly journals Effects of Double-Side Labyrinth Seals on Aerodynamic Performance in a Transonic Shrouded Turbine Stage

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Weihang Li ◽  
Shaowen Chen ◽  
Hongyan Liu ◽  
Zhihua Zhou ◽  
Songtao Wang
Keyword(s):  
Labyrinth Seal ◽  
Aerodynamic Performance ◽  
Maximum Efficiency ◽  
Outlet Section ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Labyrinth Seals ◽  
Tip Leakage ◽  
Transonic Turbine

Abstract Labyrinth seals on both rotor casing and blade tip as an effective method to control the leakage flowrate of the shroud and improve aerodynamic performances in a transonic turbine stage are investigated in this study. Compared to the case without the labyrinth seal structure, the cases with three different types of sealing teeth have been shown to reduce significantly the tip leakage flow by computational simulations. The double-side sealing teeth case reduces the leakage flowrate mleakage/mpassage from 3.4% to 1.3% and increases the efficiency by 1.4%, which is the maximum efficiency improvement of all cases. The sealing structures increase the loss inside the shroud while reducing the momentum mixing between shroud leakage flow and mainstream. Therefore, the circumferential distribution of leakage velocity is changed, as well as the distribution of high-loss zones at turbine outlet. Furthermore, the leakage-vortex loss, which is associated with the blockage effect of sealing structure to the tip leakage flow, gains more improvement than the passage-vortex at the rotor outlet section in double-side seal case. In addition, it has also been found that with a larger gap at tip, the double-side seal has better effects of reducing the leakage flow and improving the aerodynamic performance in the transonic turbine stage.

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.

Aerodynamic Interaction Between Incoming Vortex and Tip Leakage Flow in a Turbine Cascade

2018 ◽  
Author(s):  
Kai Zhou ◽  
Chao Zhou
Keyword(s):  
Numerical Study ◽  
Aerodynamic Performance ◽  
Leakage Flow ◽  
Computational Domain ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Swirl Generator ◽  
Swirling Vortex

In turbines, secondary vortices and tip leakage vortices develop and interact with each other. In order to understand the flow physics of vortices interaction, the effects of incoming vortex on the downstream tip leakage flow are investigated in terms of the aerodynamic performance in a turbine cascade. Experimental, numerical and analytical methods are used. In the experiment, a swirl generator was used upstream near the casing to generate the incoming vortex, which interacted with the tip leakage vortex in the turbine cascade. The swirl generator was located at ten different pitchwise locations to simulate the quasi-steady effects. In the numerical study, a Rankine-like vortex was defined at the inlet of the computational domain to simulate the incoming swirling vortex. Incoming vortices with opposite directions were investigated. The vorticity of the positive incoming swirling vortex has a large vector in the same direction as that of the tip leakage vortex. In the case of the positive incoming swirling vortex, the vortex mixes with the tip leakage vortex to form one vortex near the tip as it transports downstream. The vortices interaction reduces the vorticity of the flow near the tip, as well as the loss by making up for the streamwise momentum within the tip leakage vortex core. In contrast, the negative incoming swirling vortex has little effects on the tip leakage vortex and the loss. As the negative incoming swirling vortex transports downstream, it is separated from the tip leakage vortex and forms two vortices. A triple-vortices-interaction kinetic analytical model and one-dimensional mixing model are proposed to explain the mechanism of vortex interaction on the aerodynamic performance.

Tip Clearance Investigation of a Ducted Fan Used in VTOL UAVS: Part 1—Baseline Experiments and Computational Validation

2011 ◽  
Author(s):  
Ali Akturk ◽  
Cengiz Camci
Keyword(s):  
Total Pressure ◽  
Aerodynamic Performance ◽  
Test System ◽  
Tip Clearance ◽  
Computational Techniques ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Ducted Fan ◽  
Rans Simulations

Ducted fans that are popular choices in vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV) offer a higher static thrust/power ratio for a given diameter than open propellers. Although ducted fans provide high performance in many VTOL applications, there are still unresolved problems associated with these systems. Fan rotor tip leakage flow is a significant source of aerodynamic loss for ducted fan VTOL UAVs and adversely affects the general aerodynamic performance of these vehicles. The present study utilized experimental and computational techniques in a 22″ diameter ducted fan test system that has been custom designed and manufactured. Experimental investigation consisted of total pressure measurements using Kiel total pressure probes and real time six-component force and torque measurements. The computational technique used in this study included a 3D Reynolds-Averaged Navier Stokes (RANS) based CFD model of the ducted fan test system. RANS simulations of the flow around rotor blades and duct geometry in the rotating frame of reference provided a comprehensive description of the tip leakage and passage flow. The experimental and computational analysis performed for various tip clearances were utilized in understanding the effect of the tip leakage flow on aerodynamic performance of ducted fans used in VTOL UAVs. The aerodynamic measurements and results of the RANS simulations showed good agreement especially near the tip region.

Effects of Labyrinth Fin Wear on Aerodynamic Performance of Turbine Stages: Part I — Bending Damages

2019 ◽  
Author(s):  
Xin Yan ◽  
Xinbo Dai
Keyword(s):  
Labyrinth Seal ◽  
Flow Fields ◽  
Aerodynamic Performance ◽  
Leakage Flow ◽  
Original Design ◽  
Labyrinth Seals ◽  
Sealing Performance ◽  
Forward Bending ◽  
Design Case ◽  
Isentropic Efficiency

Abstract Labyrinth seals are widely applied in turbo machines because of their geometrical simplicity, convenient installation, reliable operation and excellent sealing performance. However, in realistic operation process, they usually encounter transient conditions (starting-up, shutting down, etc.) and unavoidable vibrations, which may cause wear in the labyrinth fins. After rubbing, the sealing performance of labyrinth seal will be varied in contrast to the original design. Correspondingly, the aerodynamic efficiency of the turbine stage will be affected by the variation of leakage flow in rubbing process. However, in published literature with respect to the labyrinth seal wear, most of the attention has been paid on revealing sealing performance degradation of labyrinth seal itself. Few studies have been concentrated on the influence of labyrinth seal wear on aerodynamic performance of turbine stages. In such background, the present paper utilizes the numerical methods to investigate the effects of labyrinth seal bending damages on aerodynamic performance of turbine stages. Firstly, under several assumptions, the bending geometrical model was established to describe different degrees of bending damages. Secondly, using three-dimensional RANS simulations, the effects of effective clearance variation due to bending on leakage flow and flow fields in turbine stages were investigated. The overall performance of the turbine stages with teeth-bending damages was also compared with the original design case. The influence of the forward bending and backward bending of labyrinth seals were analyzed and compared with each other. The total-total isentropic efficiency of turbine stages, leakage rates, outlet flow angles, reaction degrees and profile static pressure distributions, entropic distributions and flow fields in seals were obtained and compared to the original design case. The results indicate that the leakage rates in the worn labyrinth seal are quite relevant to the effective clearance, especially for the backward bending damages. As the effective clearances in backward bending cases are increased by 0.2–0.6mm, the isentropic efficiency of turbine stages is decreased by about 1–2%. However, for the forward bending damages, the aerodynamic performance and leakage rates in turbine stages are not sensitive to the effective clearance.

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.

The Development of Turbine Exit Flow in a Swan-Necked Inter-Stage Diffuser

2003 ◽  
Author(s):  
R. J. Miller ◽  
R. W. Moss ◽  
R. W. Ainsworth ◽  
N. W. Harvey
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Inlet Flow ◽  
Time Resolved ◽  
Tip Leakage ◽  
Numerical Predictions

This paper describes both the migration and dissipation of flow phenomena downstream of a transonic high-pressure turbine stage. The geometry of the HP stage exit duct considered is a swan-necked diffuser similar to those likely to be used in future engine designs. The paper contains results both from an experimental programme in a turbine test facility and from numerical predictions. Experimental data was acquired using three fast-response aerodynamic probes capable of measuring Mach number, whirl angle, pitch angle, total pressure and static pressure. The probes were used to make time-resolved area traverses at two axial locations downstream of the rotor trailing edge. A 3D time-unsteady viscous Navier-Stokes solver was used for the numerical predictions. The unsteady exit flow from a turbine stage is formed from rotor-dependent phenomena (such as the rotor wake, the rotor trailing edge recompression shock, the tip-leakage flow and the hub secondary flow) and vane-rotor interaction dependant phenomena. This paper describes the time-resolved behaviour and three-dimensional migration paths of both of these phenomena as they convect downstream. It is shown that the inlet flow to a downstream vane is dominated by two corotating vortices, the first caused by the rotor tip-leakage flow and the second by the rotor hub secondary flow. At the inlet plane of the downstream vane the wake is extremely weak and the radial pressure gradient is shown to have caused the majority of the high loss wake fluid to be located between the mid-height of the passage and the casing wall. The structure of the flow indicates that between a high pressure stage and a downstream vane simple two-dimensional blade row interaction does not occur. The results presented in this paper indicate that the presence of an upstream stage is likely to significantly alter the structure of the secondary flow within a downstream vane. The paper also shows that vane-rotor interaction within the upstream stage causes a 10° circumferential variation in the inlet flow angle of the 2nd stage vane.

Multi-Objective Optimization of Turbine Blade Tip With Film Cooling Holes

2021 ◽  
Author(s):  
Shuai Yang ◽  
Min Zhang ◽  
Yan Liu ◽  
Jinguang Yang
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Aerodynamic Performance ◽  
Tip Clearance ◽  
Pareto Optimum ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Multi Objective ◽  
Film Cooling Holes

Abstract Tip leakage flow is inevitable due to the tip clearance over rotor blades in turbines. This phenomenondeteriorates blade aerodynamic performance and induces severe thermal damage to the tip surface.Introduction of cooling jets to the tip can effectively controls the tip leakage flow and improves the tip heat transfer. Therefore, this paper aims to optimize film cooling holes on a flat tip of a subsonic cascade and an topology-optimized tip of a transonic cascade. A design variable is a material parameter defined at each grid node along the blade camber line. This idea is based on the topology optimization method. The objective is to minimize blade energy loss and maximize tip heat transfer intensity. A response surface optimization based on the design of experiment (DOE) analysis is employed, and a multi-objective Genetic Algorithm is used to get Pareto optimum solutions. During the DOE process, a CFD method using injection source terms is integrated for numerical simulations to reduce computational costs. Optimized tip film cooling holes are finally re-constructed. The influence of the newly designed tip cooling holes configuration on blade aero-thermal performance is evaluated via CFD simulations using body-fitted mesh. Results show that compared with the uniform arrangement of cooling film holes along the axial direction, all the optimized film cooling holes can improve both blade aerodynamic performance and tip heat transfer performance.

Impact of Passive Tip-Injection on Tip-Leakage Flow in Axial Low Pressure Turbine Stage

2015 ◽  
Author(s):  
Pouya Ghaffari ◽  
Reinhard Willinger ◽  
Sabine Bauinger ◽  
Andreas Marn
Keyword(s):  
Aerodynamic Resistance ◽  
Low Pressure ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Low Pressure Turbine ◽  
Blade Tip ◽  
Tip Injection ◽  
The Impact

In addition to geometrical modifications of the blade tip for reducing tip-leakage mass flow rate the method of passive tip-injection serves as an aerodynamic resistance towards the tip-leakage flow. The impact of this method has been investigated thoroughly at unshrouded blades in linear cascades. Furthermore combinations of shrouded blades with passive tip-injection have been investigated analytically as well as via numerical simulations for incompressible flow in linear cascades. The objective of this paper is to consider a real uncooled low pressure turbine stage with shrouded blades and to investigate the effect of passive tip-injection on various operational characteristics. CFD calculations have been carried out in a rotational frame taking into consideration compressible flow and serve for evaluating the method of passive tip-injection in the given turbine stage. Experimental data obtained from the machine without tip-injection serve as boundary conditions for the CFD calculations.

A Novel Suction-Side Winglet Design Philosophy for High-Pressure Turbine Rotor Tips

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Chao Zhou ◽  
Fangpan Zhong
Keyword(s):  
Suction Side ◽  
Leakage Flow ◽  
The Novel ◽  
Front Part ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Tip Leakage ◽  
Design Philosophy ◽  
Passage Vortex

Winglet tips are promising candidates for future high-pressure turbine rotors. Many studies found that the design of the suction-side winglet is the key to the aerodynamic performance of a winglet tip, but there is no general agreement on the exact design philosophy. In this paper, a novel suction-side winglet design philosophy in a turbine cascade is introduced. The winglets are obtained based on the near-tip flow field of the datum tip geometry. The suction-side winglet aims to reduce the tip leakage flow particularly in the front part of the blade passage. It is found that on the casing endwall, the pressure increases in the area where the winglet is used. This reduces the tip leakage flow in the front part of the blade passage and the pitchwise pressure gradient on the endwall. As a result, the size of the tip leakage vortex reduces. A surprising observation is that the novel optimized winglet tip design eliminates the passage vortex and results in a further increasing of the efficiency. The tip leakage loss of the novel winglet tip is 18.1% lower than the datum cavity tip, with an increase of tip surface area by only 19.3%. The spanwise deflection of the winglet due to the centrifugal force is small. The tip heat load of the winglet tip is 17.5% higher than that of the cavity tip. Numerical simulation shows that in a turbine stage, this winglet tip increases the turbine stage efficiency by 0.9% mainly by eliminating the loss caused by the passage vortex at a tip gap size of 1.4% chord compared with a cavity tip.

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