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flow Range Enhancement by secondary flow Effect in Low Solidity Circular Cascade Diffusers

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Journal of Thermal Science 2014年第4期23卷 391-400页

作者： Daisaku Sakaguchi Min Thaw Tun Kanata Mizokoshi Daiki Kishikawa Nagasaki Japan

High-pressure ratio and wide operating range are highly required for compressors and blowers. The technical issue of the design is achievement of suppression of flow separation at small flow rate without deteriorating the efficiency at design flow rate. A numerical simulation is very effective in design procedure, however, cost of the numerical simulation is generally high during the practical design process, and it is difficult to confn＇m the optimal design which is combined with many parameters. A multi-objective optimization technique is the idea that has been proposed for solving the problem in practical design process. In this study, a Low Solidity circular cascade Diffuser （LSD） in a centrifugal blower is successfully designed by means of multi-objective optimization technique. An optimization code with a meta-model assisted evolutionary algorithm is used with a commercial CFD code ANSYS-CFX. The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified by overall performance test. The detailed flow in the diffuser is also confirmed by means of a Particle Image Velocimeter. secondary flow is clearly captured by PIV and it spreads to the whole area of LSD blade pitch. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow e

关键词： Low solidity circular cascade diffuser Multi-objective optimization secondary flow flow range enhancement

Experimental Investigation of the secondary flow in a Rotating Smooth Channel Subjected to Thermal Boundary Conditions

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Journal of Thermal Science 2020年第6期29卷 1463-1474页

作者： LI Haiwang YOU Haoliang YOU Ruquan TAO Zhi National Key Laboratory of Science and Technology on Aero-Engines Aero-thermodynamics Beihang UniversityBeijing 100191China

In the current study,thermal boundary conditions are considered in a rotating smooth channel with a square cross-section to investigate the secondary flow and compare it to that of the same channel without *** measurement is conducted at three streamwise planes(X=445 mm,525 mm,605 mm).The flow parameters are the Reynolds number(Re=4750,which was based on the average longitudinal or primary velocity U and the hydraulic diameter D of the channel cross-section),the rotation number(Ro=?D/U,where?is the rotational velocity,ranging from 0 to 0.26),and the aspect ratio of the channel cross-section(AR=1,which is calculated by dividing the channel height by the channel width).The leading and trailing walls are heated under a constant heat flux qw=380 W/m^2,and the top and bottom walls are isothermal at room *** work is in a series with our previous work without thermal boundary *** on the experimental data,we obtained a four-vortex *** is a counter-rotating vortex pair near the leading side and the trailing *** the leading and trailing walls are heated,the buoyancy force increases the relative vertical position of the vortex pair near the trailing side from 5%to 12.5%of the hydraulic *** moving upstream along the streamwise direction,the upper vortex near the trailing wall becomes weaker,whereas the lower vortex becomes *** the rotational speed increases,the vortex pair near the trailing side is inhibited by the Coriolis *** heated thermal boundary conditions,the vortex pair near the trailing side reappears due to the effect of buoyancy *** results indicate that the buoyancy force has a substantial effect on the secondary flow regime under thermal boundary conditions.

关键词： flow dynamic rotating smooth channel secondary flow buoyancy force

Controlling secondary flow in high-lift low-pressure turbine using boundary-layer slot suction

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Chinese Journal of Aeronautics 2024年第3期37卷 21-33页

作者： Xiao QU Liunan LI Yingjie ZHANG Xingen LU Junqiang ZHU Yanfeng ZHANG School of Mechanical Engineering Beijing Institute of TechnologyBeijing 100081China Key Laboratory of Light-Duty Gas-Turbine Institute of Engineering ThermophysicsChinese Academy of SciencesBeijing 100190China School of Aeronautics and Astronautics University of Chinese Academy of SciencesBeijing 100190China

The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary *** present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of *** slotted schemes for the boundary layer of the endwall were designed(Plan A and Plan B),and the effects of suction mass flow on secondary flow were *** underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was *** results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum *** A and B significantly reduced the secondary kinetic energy by 44.2%and 36.9%,respectively,compared with the baseline cascade at the suction mass flow ratios of 1%.With an increase in the mass flow ratio of suction,the secondary flow was gradually reduced in both Plans A and *** is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage *** unsteady wakes,the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2%for Plan A,because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.

关键词： Low-pressure turbine secondary flow flow control Boundary-layer suction Incoming wake

Numerical Investigation of Influence of Tip Leakage flow on secondary flow in Transonic Centrifugal Compressor at Design Condition

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Journal of Thermal Science 2015年第2期24卷 117-122页

作者： Masanao Kaneko Hoshio Tsujita Graduate School of Engineering Hosei University3-7-2Kajino-choKoganei-shiTokyo184-8584Japan Department of Mechanical Engineering Faculty of Science and EngineeringHosei University

In a centrifugal compressor, the leakage flow through the tip clearance generates the tip leakage vortex by the in- teraction with the main flow, and consequently makes the flow in the impeller passage more complex by the inte- raction with the passage vortex. In addition, the tip leakage vortex interacts with the shock wave on the suction surface near the blade tip in the transonic centrifugal compressor impeller. Therefore, the detailed examination for the influence of the tip leakage vortex becomes seriously important to improve the aerodynamic performance cs- pccia｜ly for the transonic centrifugal compressor. In this study, the flows in the transonic centrifugal compressor with and without the tip clearance at the design condition were analyzed numerically by using the commercial CFD code. The computed results revealed that the tip leakage vortex induced by the high loading at the blade tip around the leading edge affected the loss generation by the reduction or the suppression of the shock wave on the suction surface of the blade.

关键词： Transonic Centrifugal Compressor Leakage Vortex secondary flow Shock Wave Numerical Analysis

Unsteady wakes-secondary flow interactions in a high-lift low-pressure turbine cascade

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Chinese Journal of Aeronautics 2020年第3期33卷 879-892页

作者： Xiao QU Yanfeng ZHANG Xingen LU Junqiang ZHU Key Laboratory of Light-Duty Gas-Turbine Institute of Engineering ThermophysicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 100190China

Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine(LPT)*** of the measurements were conducted in both the presence and absence of incoming wakes,and numerical analysis was performed to elucidate the flow *** increasing Reynolds number,the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers,leading to a lower blade loading near the leading edge and suppression of the Pressure Side(PS)leg of the horseshoe ***,the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side(SS)separation bubble and increased mixing loss in the free-flow region at high Reynolds *** wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,*** contrast,at the high Reynolds number of 100,000,the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes,and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade.

关键词： Experimental study High-lift Incoming wakes Low-pressure turbine secondary flow

Influences of Incidence Angle on 2D-flow and secondary flow Structure in Ultra-Highly Loaded Turbine Cascade

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Journal of Thermal Science 2014年第1期23卷 13-21页

作者： Hoshio Tsujita Atsumasa Yamamoto Department of Mechanical Engineering Hosei University3-7-2Kajino-choKoganei-shiTokyo Japan

An increase of turbine blade loading can reduce the numbers of blade and stage of gas turbines. However, an increase of blade loading makes the secondary flow much stronger because of the steep pitch-wise pressure gradient in the cascade passage, and consequently deteriorates the turbine efficiency. In this study, the computations were performed for the flow in an ultra-highly loaded turbine cascade with high turning angle in order to clarify the effects of the incidence angle on the two dimensional flow and the secondary flow in the cascade passage, which cause the profile loss and the secondary loss, respectively. The computed results showed good agreement with the experimental surface oil flow visualizations and the blade surface static pressure at mid-span of the blade. The profile loss was strongly increased by the increase of incidence angle especially in the positive range. Moreover, the positive incidences not only strengthened the horseshoe vortex and the passage vortex but also induced a new vortex on the end-wall. Moreover, the newly formed vortex influenced the formation of the pressure side leg of horseshoe vortex.

关键词： Turbine Cascade Incidence Angle Numerical Analysis secondary flow

Relationship between the Intensity of secondary flow and Convection Heat Transfer in a Helically Coiled Circular Tube with Uniform Wall Temperature

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Journal of Thermal Science 2023年第3期32卷 1007-1022页

作者： ZHANG Jinlong ZHAO Chuangyao WANG Liangbi School of Mechanical Engineering Lanzhou Jiaotong UniversityLanzhouGansu 730070China Key Laboratory of Railway Vehicle Thermal Engineering of MOE Lanzhou Jiaotong UniversityLanzhou 730070China School of Building Services Science and Engineering Xi'an University of Architecture and TechnologyXi'an 710055China

Numerical method is used to investigate fully developed laminar flow in helically coiled circular tube in this *** non-dimensional parameter(secondary flow Reynolds number Se)based on absolute vorticity flux along the mainstream is used to indicate the intensity of secondary flow caused by the centrifugal effect in helically coiled circular *** relationship between the intensity of secondary flow and the intensity of laminar convective heat transfer is *** effects of curvature and torsion on the enhancement of heat transfer are also *** results reveal that the absolute vorticity flux along the mainstream can be used to indicate the local or averaged intensity of secondary flow;the non-dimensional parameter of the absolute vortex along the main flow determines the convective heat transfer and friction *** relationships of Nusselt number and friction factor with the Se are *** effect of curvature on Nusselt number is obvious,but the effect of torsion on Nusselt number is less obvious.

关键词： helically coiled circular tube convective heat transfer heat transfer enhancement secondary flow

Development of secondary flow field under rotating condition in a straight channel with square cross-section

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Chinese Journal of Aeronautics 2018年第8期31卷 1703-1715页

作者： Ruquan YOU Kuan WEI Zhi TAO Haiwang LI Guoqiang XU National Key Laboratory of Science and Technology on Aero-Engines Aero-Thermodynamics Beihang University Collaborative Innovation Center for Advanced Aero-Engine Beihang University Aero Engine Academy of China Aero Engine (Group) Corporation of China

The developing secondary flow fields in the entrance section of a rotating straight channel were experimentally investigated using Particle Image Velocimetry（PIV）. The effects of streamwise position, Reynolds number and rotation number on the development of the secondary flow fields were revealed. The results show that the absolute values of vorticity flux of the trailing side roll cells increase with increasing radius of the measured plane and rotation number. When the absolute value of vorticity flux exceeds a critical value, the merging of the trailing side roll cells appears. Moreover, when the number of the trailing side vortex pairs is even, the absolute values of vorticity flux of the leading side vortices increase along streamwise direction. Otherwise, the absolute values decrease along the streamwise direction. By the circulation analysis, this phenomenon was found to have relationship with the merging of the trailing side roll cells, and further concluded that the secondary flow field in a rotating channel has to be treated as a whole. At last,the increase of the Reynolds number was found to be able to induce the merging position moves upstream.

关键词： Circulation analysis Entrance section Field Programmable GataArray (FPGA) Particle Image Velocimetry(PlV) Rotating channel secondary flow

Effect of turbulence-driven secondary flow on particle preferential concentration and clustering in turbulent square duct flows

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Particuology 2021年第2期19卷 70-83页

作者： Yanlin Zhao Yanzhi Wang Jun Yao International Joint Laboratory on Clean Energy Science and Technology Beijing Key Laboratory of Process Fluid Filtration and SeparationCollege of Mechanical and Transportation EngineeringChina University of Petroleum-BeijingBeijing 102249China

In this study,the preferential concentration and clustering of inertial particles in fully developed turbulent square duct flows are studied using large eddy simulations combined with Lagrangian approach,where the Reynolds number is equal to Reτ=600(based on the mean friction velocity and duct full height),and the particle Stokes number ranges from 0.0007 to *** results obtained for duct flows are compared with those for channel flows under the same working ***,the effect of the secondary flow on the particle concentration in duct flows is *** equation of particle motion is governed by the drag force,lift force,added mass force,pressure gradient force,and *** inter-phase interaction that was considered includes one-way and two-way *** simulations of a single phase are verified and in good agreement with the available literature *** the discrete phase,particles in the duct flow are found to be more dispersed in the vertical direction compared with the channel *** near-wall regions,a small fraction of particles tends to accumulate in duct corners,forming stable particle streaks under the effect of the secondary ***,most particles are likely to reside preferentially in the low-speed flow regions and form elongated particle streaks steadily in the middle region of duct or channel *** Voronoi diagram analysis shows that the near-wall secondary flows in the square duct could cause particle clusters to transfer from regions of high to low concentration,and this trend increases with particle *** addition,two-way coupling is found to enhance the near-wall particle accumulation and to promote particles to form more elongated streaks than one-way ***,the mechanism responsible for the particle preferential concentration in turbulent square duct flows is determined.

关键词： secondary flow Preferential concentration Turbulence Particles Square duct