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.

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 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 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.

Three-Dimensional Navier-Stokes Analysis of Turbine Rotor and Tip-Leakage Flowfield

1997 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The 3-D viscous flowfield in the rotor passage of a single-stage turbine, including the tip-leakage flow, is computed using a Navier-Stokes procedure. A grid-generation code has been developed to obtain embedded H grids inside the rotor tip gap. The blade tip geometry is accurately modeled without any “pinching”. Chien’s low-Reynolds-number k-ε model is employed for turbulence closure. Both the mean-flow and turbulence transport equations are integrated in time using a four-stage Runge-Kutta scheme. The computational results for the entire turbine rotor flow, particularly the tip-leakage flow and the secondary flows, are interpreted and compared with available data. The predictions for major features of the flowfield are found to be in good agreement with the data. Complicated interactions between the tip-clearance flows and the secondary flows are examined in detail. The effects of endwall rotation on the development and interaction of secondary and tip-leakage vortices are also analyzed.

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.

Effects of the Last Stage Rotor Tip Leakage Flow on the Aerodynamic Performance of the Exhaust Hood for Steam Turbines

2013 ◽  
Author(s):  
Jun Li ◽  
Zhigang Li ◽  
Zhenping Feng
Keyword(s):  
Static Pressure ◽  
Aerodynamic Performance ◽  
Pressure Recovery ◽  
Leakage Flow ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Last Stage ◽  
Recovery Performance

The static pressure recovery coefficient of the exhaust hood has significant impact on the aerodynamic performance of the low pressure cylinder for steam turbines. Numerical investigations on the aerodynamic performance of the exhaust hood and full last stage with consideration of the rotor tip leakage were presented in this paper. Three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions and k–ε turbulent model were utilized to analyze the static pressure recovery performance of the exhaust hood using the commercial CFD software ANSYS-CFX. Effect of the last stage rotor tip leakage flow on the aerodynamic performance of the downstream exhaust hood was conducted by comparison of the computational domains for the exhaust hood and full last stage with and without tip clearance. The numerical results show that the last stage rotor tip leakage jet can suppress the flow separation near the diffuser wall of the exhaust hood and improve its static pressure recovery performance. The detailed flow fields of the exhaust hood with and without consideration of the rotor tip leakage flow were also illustrated and corresponding flow mechanism was discussed.

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.

Tip Clearance Investigation of a Ducted Fan Used in VTOL Unmanned Aerial Vehicles—Part I: Baseline Experiments and Computational Validation

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Ali Akturk ◽  
Cengiz Camci
Keyword(s):  
Unmanned Aerial Vehicles ◽  
Total Pressure ◽  
Aerodynamic Performance ◽  
Test System ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Ducted Fan ◽  
Aerial Vehicles

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 559 mm diameter ducted fan test system that has been custom designed and manufactured. The 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 computational fluid dynamics model of the ducted fan test system. Reynolds-averaged Navier–Stokes simulations of the flow around the 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 the 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.

Impeller-Diffuser Interaction in Centrifugal Compressor

2000 ◽  
Author(s):  
Y. K. P. Shum ◽  
C. S. Tan ◽  
N. A. Cumpsty
Keyword(s):  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Potential Effect ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Beneficial Effects ◽  
Radial Gap

A study has been conducted, using an unsteady three-dimensional Reynolds-averaged Navier-Stokes simulation, to define the effect of impeller-diffuser interaction on the performance of a centrifugal compressor stage. The principal finding from the study was that the most influential aspect of this unsteady interaction was the effect on impeller tip leakage flow. In particular, the unsteadiness due to the upstream potential effect of the diffuser vanes led to larger viscous losses associated with the impeller tip leakage flow. The consequent changes at the impeller exit with increasing interaction were identified as reduced slip, reduced blockage, and increased loss. The first two were beneficial to pressure rise while the third one was detrimental. The magnitudes of the effects were examined using different impeller-diffuser spacings and it was shown that there was an optimal radial gap size for maximum impeller pressure rise. The physical mechanism was also determined: when the diffuser was placed closer to the impeller than the optimum, increased loss overcame the benefits of reduced slip and blockage. The findings provide a rigorous explanation for experimental observations made on centrifugal compressors. The success of a simple flow model in capturing the pressure rise trend indicated that although the changes in loss, blockage and slip were due largely to unsteadiness, the consequent impacts on performance were mainly one-dimensional. The influence of flow unsteadiness on diffuser performance was found to be less important than the upstream effect, by a factor of seven in terms of stage pressure rise in the present geometry. It is thus concluded that the beneficial effects of impeller-diffuser interaction on overall stage performance come mainly from the reduced blockage and reduced slip associated with the unsteady tip leakage flow in the impeller.

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