Aerodynamic Effects of an Incoming Vortex on Turbines With Different Tip Geometries

2021 ◽  
Vol 143 (8) ◽  
Author(s):  
Kai Zhou ◽  
Chao Zhou
Keyword(s):  
Suction Side ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Loss Mechanism ◽  
Tip Leakage Vortex ◽  
Blade Passage ◽  
Aerodynamic Loss ◽  
Tip Leakage ◽  
Swirl Generator

Abstract Experimental and numerical methods were used to investigate the aerodynamic effects of a near-casing streamwise incoming vortex flow on the tip leakage flow of different tip geometries in an unshrouded high-pressure turbine. A flat tip, a cavity tip, and a suction side winglet tip were investigated with the quasi-steady method first. A swirl generator was used to produce the incoming vortex in a linear cascade. In the flat tip case, the incoming vortex interacts with the tip leakage flow and the two vortices gradually mix together. The tip leakage loss is reduced due to the streamwise momentum supplement within the tip leakage vortex core. For the cavity tip, the tip leakage vortex appears at a location relatively downstream in the blade passage compared with the flat tip and no evident vortex interaction is observed. The incoming vortex causes extra viscous dissipation within the blade passage and increases the aerodynamic loss for the cavity tip. For the winglet tip, the extension of the suction side winglet tends to push the incoming vortex and the tip leakage vortex move and mix together, thus reducing the loss. Then, the effects of periodic unsteady vortex transportations were investigated by conducting unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations. The incoming vortex is stretched as it transports downstream. The unsteady incoming vortex is easier to interact with the tip leakage vortex for the winglet tip. As a result, the winglet tip is the most efficient tip design with unsteady incoming flow among the three tips and achieves a 3.7% reduction of mixed-out loss coefficient compared with the flat tip, larger than 2.8% reduction in the uniform inlet condition. The detailed loss mechanism is discussed in this paper.

Aerodynamic Effects of an Incoming Vortex on Turbines With Different Tip Geometries

2020 ◽  
Author(s):  
Kai Zhou ◽  
Chao Zhou
Keyword(s):  
Suction Side ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Loss Mechanism ◽  
Tip Leakage Vortex ◽  
Blade Passage ◽  
Aerodynamic Loss ◽  
Tip Leakage ◽  
Swirl Generator

Abstract Experimental and numerical methods were used to investigate the aerodynamic effects of a near-casing streamwise incoming vortex flow on the tip leakage flow of different tip geometries in an unshrouded high pressure turbine. A flat tip, a cavity tip and a suction-side winglet tip were investigated with quasi-steady method first. A swirl generator was used to produce the incoming vortex in a linear cascade. In the flat tip case, the incoming vortex interacts with the tip leakage flow and the two vortices gradually mix together. The tip leakage loss is reduced due to the streamwise momentum supplement within the tip leakage vortex core. For the cavity tip, the tip leakage vortex appears at a location relatively downstream in the blade passage compared to the flat tip and no evident vortex interaction is observed. The incoming vortex causes extra viscous dissipation within the blade passage and increases the aerodynamic loss for the cavity tip. For the winglet tip, the extension of the suction side winglet tends to push the incoming vortex and the tip leakage vortex move and mix together, thus reducing the loss. Then the effects of periodic unsteady vortex transportations were investigated by conducting unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations. The incoming vortex is stretched as it transports downstream. The unsteady incoming vortex is easier to interact with the tip leakage vortex for the winglet tip. As a result, the winglet tip is the most efficient tip design with unsteady incoming flow among the three tips, and achieves 3.7% reduction of mixed-out loss coefficient compared to the flat tip, larger than 2.8% reduction in the uniform inlet condition. The detailed loss mechanism is discussed in the paper.

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.

An Investigation on Aerodynamics Loss Mechanism of Squealer Tips of a High Pressure Turbine Blade Using URANS

2016 ◽  
Author(s):  
Jin-sol Jung ◽  
Okey Kwon ◽  
Changmin Son
Keyword(s):  
High Pressure ◽  
Turbine Blade ◽  
Wall Thickness ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Loss Mechanism ◽  
Tip Leakage

The flow leaking over the tip of a high pressure turbine blade generates significant aerodynamic losses as it mixes with the mainstream flow. This study investigates the effect of blade tip geometries on turbine performance with both steady RANS and unsteady URANS analyses. Five different squealer geometries for a high pressure turbine blade have been examined: squealer on pressure side, squealer on suction side, cavity squealer, cavity squealer with pressure side cutback, and cavity squealer with suction side cutback. With the case of the cavity squealer, three different squealer wall thickness are investigated for the wall thickness (w) of 1x, 2x and 4x of the tip gap (G). The unsteady flow analyses using CFX have been conducted to investigate unsteady characteristics of the tip leakage flow and its influence on turbine performances. Through the comparison between URANS analyses, detailed vortex and wake structures are identified and studied at different fidelities. It is found that the over tip leakage flow loss is affected by the tip suction side geometry rather than that of the pressure side geometry. The unsteady results have contributed to resolve the fundamentals of vortex structures and aerodynamic loss mechanisms in a high pressure turbine stage.

Numerical Study of Vortices and Their Interactions in the Passage of Rotor Blade With Tip Gap

2019 ◽  
Author(s):  
Sachin Singh Rawat ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Turbulence Model ◽  
Numerical Study ◽  
Flow Direction ◽  
Three Dimensional ◽  
Suction Side ◽  
Leakage Flow ◽  
Angle Distribution ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage

Abstract A detailed three-dimensional steady-state numerical investigation using ANSYS CFX-18.2 on a high-pressure turbine blade with linear cascade is done for tip leakage flow of an axial gas turbine. Stationary casing with a fixed blade having tip gap is considered for the present study. There is leakage flow from the pressure side to the suction side of the blade which consecutively rolls up in the passage and forms the tip leakage vortex. The formation of vortices and their interaction with each other inside the passage is complex which makes experimental investigation difficult. The effect of tip gap size, off-design incidence angles, outlet Mach number, pitch size and flow path (stagger angle) are several parameters considered during the present study. The strength of tip leakage vortex and the vortex formed inside the gap is maximum. The losses are compared in terms of total pressure loss coefficient. The deviation of the flow direction is measured in terms of yaw angle distribution. Among various turbulence model available in CFX 18.2 the BSL k-ω turbulence model shows the most reliable results with experimental data. The results are compared with the base model without the tip gap. This investigation incites a better design of the blade tip with a precise reduction in losses.

Numerical Investigation on Loss Mechanism and Performance Improvement for a Zero Inlet Swirl Turbine Rotor

2017 ◽  
Author(s):  
Wei Zhao ◽  
Qingjun Zhao ◽  
Xiuming Sui ◽  
Weiwei Luo ◽  
Jianzhong Xu
Keyword(s):  
Suction Side ◽  
Turbine Rotor ◽  
Axial Position ◽  
Leakage Flow ◽  
Blade Profile ◽  
Tip Leakage Flow ◽  
Loss Mechanism ◽  
Tip Leakage ◽  
Stagnation Points ◽  
Inlet Swirl

A zero inlet swirl turbine rotor (ZISTR) is originally presented as the first stage in a multistage vaneless counter-rotating turbine (MVCT), which only consists of 4 rotors without any vanes. The vanes upstream of a ZISTR are removed to reduce the turbine weight and length, as well as the viscous losses and coolants associated with vanes. However, due to the lack of inlet swirl the stagger angles for ZISTR blade profiles are high and the blade deflections are very small, resulting in almost straight cambers and very thin airfoils. The motivation of this paper is to reveal the overall performance and key loss sources of a ZISTR associated with its special blade profile, and provide corresponding optimization approaches for its practical usages. The 3D viscous numerical results show that the wake, the suction side trailing edge shock and the tip leakage flow have substantial influence on the rotor performance. To optimize the performance of a ZISTR, reducing blade solidity is proposed to decrease the viscous and shock losses by increasing the portion of the inviscid mainstream. Leaned blade is also presented to restrict the tip leakage flow by adjusting the axial position of stagnation points on the blade profile, obtaining an increase in efficiency of 0.9%. The off-design performance of the optimized rotor is also presented to show the effect of the blade lean on efficiency at various rotating speeds and back pressures.

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

2016 ◽  
Author(s):  
Chao Zhou ◽  
Fangpan Zhong
Keyword(s):  
Design Method ◽  
Suction Side ◽  
Leakage Flow ◽  
The Novel ◽  
Front Part ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Blade Passage ◽  
Tip Leakage

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 method. In this paper, a novel suction side winglet design method will be 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 winglet tip design eliminates the scraping vortex and results in a further increasing of the efficiency. The tip leakage loss of the novel winglet tip is 23% lower than the datum cavity tip, with an increase of tip surface area by only 20%. The spanwise deflection of the winglet due to the centrifugal force is small. Numerical simulation shows that in a turbine stage, this winglet tip increases the turbine stage efficiency by 0.9% at a tip gap size of 1% span compared with a cavity tip.

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

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Kai Zhou ◽  
Chao Zhou
Keyword(s):  
Numerical Study ◽  
Leakage Flow ◽  
Computational Domain ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Loss Mechanism ◽  
Flow Physics ◽  
Tip Leakage ◽  
Swirl Generator ◽  
Secondary Vortices

In turbines, secondary vortices and tip leakage vortices form in the blade passage and interact with each other. In order to understand the flow physics of this vortices interaction, the effects of incoming vortex on the downstream tip leakage flow are investigated by experimental, numerical, and analytical methods. In the experiment, a swirl generator was used upstream of a linear turbine cascade to generate the incoming vortex, which could interact with the downstream tip leakage vortex (TLV). 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 (SV). The effects of the directions of the incoming vortices were investigated. In the case of a positive incoming SV, which has a large vorticity vector in the same direction as that of the TLV, the vortex mixes with the TLV to form one major vortex near the casing as it transports downstream. This vortices interaction reduces the loss by increasing the streamwise momentum within the TLV core. However, the negative incoming SV has little effects on the TLV and the loss. As the negative incoming SV transports downstream, it travels away from the TLV and two vortices can be identified near the casing. A triple-vortices-interaction kinetic model is used to explain the flow physics of vortex interaction, and a one-dimensional mixing analytical model are proposed to explain the loss mechanism.

Characteristics of Tip-Clearance Flows of a Compressor Cascade and a Propulsion Pump

1997 ◽  
Author(s):  
Y. T. Lee ◽  
M. J. Laurita ◽  
J. Feng ◽  
C. L. Merkle
Keyword(s):  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Blade Passage ◽  
Tip Leakage ◽  
Pump Rotor ◽  
Leakage Flows ◽  
Tip Leakage Flows

Tip-leakage flows for a linear compressor cascade and a one-stage shrouded pump rotor are discussed in this paper. A numerical method solving the Reynolds averaged Navier Stokes equations is used to explore various detail features of the tip-leakage flows. Calculation results for the cascade provide an assessment for predicting flow past a non-rotating blade passage with zero and 2% chord clearances. On the other hand, the pump rotor configuration provides a swirling passage flow with the complication of a trailing-edge separation vortex mixed with the tip-clearance and passage vortices and produces a very complex three-dimensional flow in the rotor wake. The physical aspects of the tip-clearance flows are discussed including suction-side reloading and pressure-side unloading due to a tip clearance and formation and transportation of the tip-leakage vortex. Detailed velocity comparisons in the blade passage and the tip gap region are shown to indicate the difficulty of predicting tip-leakage flow. The pressure at the core of the tip vortex is also examined to evaluate the strength of the tip-leakage vortex. Some computational guidelines for design usage are provided for these tip-leakage flow calculations.

Swirl and Tip Leakage Flow Interaction With Struts in Axial Diffusers

2002 ◽  
Author(s):  
H.-U. Fleige ◽  
W. Riess ◽  
J. Seume
Keyword(s):  
Pressure Recovery ◽  
Scale Model ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Swirl Generator ◽  
Inlet Swirl ◽  
Gas Turbine Exhaust ◽  
Turbine Exhaust

A scale model of a typical gas turbine exhaust diffuser (annular followed by conical) is investigated experimentally and numerically. The turbine exhaust flow is modelled using a radial type swirl generator and a simulated tip leakage flow. Static pressure measurements are carried out on the walls and on the center line of the conical part. Four swirl angles and three strut configurations are investigated. Pressure recovery coefficients are depicted as a function of diffuser length. Velocity and turbulence profiles are measured using ID-LDA in two directions. A CFD analysis of the model is carried out using a commercial Navier-Stokes code and the standard as well as the Chen k-ε turbulence model. Even without struts, inlet swirl higher than 8° is found to adversely influence the pressure recovery of the diffuser. The profiled struts showed not to be able to redirect the flow and for swirl angles higher than 10°, cylindrical struts were found to yield better diffuser performance than profiled struts.

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