Flow Characteristics of Axial Compressor Tandem Cascades at Large Off-Design Incidence Angles

2013 ◽  
Author(s):  
Tim Schneider ◽  
Dragan Kožulović
Keyword(s):  
Flow Separation ◽  
Flow Characteristics ◽  
Axial Compressor ◽  
Suction Side ◽  
Operating Range ◽  
Current State ◽  
Aerodynamic Interaction ◽  
Mach Numbers ◽  
Side Flow ◽  
Tandem Cascades

In a number of recent and former publications, compressor tandem blade configurations show potential to outperform single blade configurations in terms of turning, loss and operating range at high aerodynamic loading levels. However, very little insight is given into the mechanisms of flow breakdown when comparing tandem blades to single blades at large off-design incidence angles. Single blade cascades tend to fail as a result of either pressure side flow separation for high negative incidence or suction side flow separation for high positive incidence, the latter being mostly accompanied by significant increase of underturning. Tandem blade cascades are expected to show a different behavior due to the aerodynamic interaction in the blade overlapping region. Two different tandem blade configurations are examined together with their respective reference single blades, one being a recently designed and optimized tandem blade for high subsonic inlet Mach numbers, which has also been investigated in cascade wind tunnel testing. The other one is a more generic tandem blade based on NACA65 family, designed for medium inlet Mach numbers using current state-of-the-art understanding of tandem design. The mechanisms of flow breakdown are examined using quasi two-dimensional RANS simulations which are validated with test data for one of the aforementioned tandem configurations. A detailed analysis of the flow structure at heavy off-design conditions gives insight into the characteristics of tandem flow breakdown. In particular, the ability of the tandem configuration to extend the operating range to larger positive incidence is described. The shortcomings of the tandem cascade at large negative incidence are also commented. These and further conclusions can be used to improve tandem blade performance at moderate off-design conditions.

scholarly journals STUDI NUMERIK SEPARASI ALIRAN 3D AKIBAT PENAMBAHAN FFST PADA BIDANG TUMPU AIRFOIL ASIMETRI

Otopro ◽  
2020 ◽  
Vol 16 (1) ◽  
pp. 12
Author(s):  
Ika Nurjannah ◽  
Herman Sasongko ◽  
Heru Mirmanto
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Flow Separation ◽  
Flow Characteristics ◽  
Axial Compressor ◽  
Horseshoe Vortex ◽  
The Body ◽  
3D Flow ◽  
Flow Loss ◽  
Flow Through

3D flow separation is a form of flow loss that cannot be avoided on turbo engines. In the axial compressor, 3D flow separation is due to the interaction between the blade boundary layer and the casing boundary layer or the hub boundary layer. The result of the secondary flow causes blockage of the flow which causes the pressure on the compressor to decrease. Efforts to reduce secondary flow are carried out by adding a FFST to endwall. This research was conducted in a numerical simulation using FLUENT 6.3.26 software. The parameters used in the free stream flow Re = 1.64 x 105 and Turbulence Intensity Tu = 0.3% to assess the comparison of the flow characteristics on the endwall of the British 9C7 / 22.5C50 asymmetric airfoil due to the addition of a FFST and without FFST with variations angle of attack (α) of 00, 80, 120, 140, 160 .The results show that the addition of FFST can increase the turbulent intensity in the area near the wall which turns into momentum, so that it has an impact on the ability of the flow to overcome the adverse pressure in the trailing edge area and further backward (delayed) separation which results in smaller wake. With the addition of the angel of attack, the saddle point position is more directed to the lower side and the attachment line is not induced by the horseshoe vortex, so that the flow is more able to follow the contours of the body, as a result the curling flow is weaker and the wake is narrower and the blockage (energy loss) can be reduced. The most effective energy reduction due to secondary flow through FFST occurs at α = 8 ° at 7.36%.

Development of a Fluidic Actuator for Adaptive Flow Control on a Thick Wind Turbine Airfoil

2014 ◽  
Author(s):  
Sebastian Niether ◽  
Bernhard Bobusch ◽  
David Marten ◽  
Georgios Pechlivanoglou ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Flow Control ◽  
Wind Turbine ◽  
Flow Separation ◽  
Pressure Difference ◽  
Angle Of Attack ◽  
Suction Side ◽  
Turbine Rotor ◽  
Adaptive Flow Control ◽  
Order Of Magnitude ◽  
Side Flow

Wind turbines are exposed to unsteady incident flow conditions such as gusts or tower interference. These cause a change in the blades’ local angle of attack, which often leads to flow separation at the inner rotor sections [1]. Recirculation areas and dynamic stall may occur, which lead to an uneven load distribution along the blade. In this work a fluidic actuator is developed that reduces flow separation. The functional principle is adapted from a fluidic amplifier. High pressure air fed by an external supply flows into the interaction region of the actuator. Two control ports, oriented perpendicular to the inlet, allow for a steering of the actuation flow. One of the control ports is connected to the suction side, the other to the pressure side of the airfoil. Depending on the pressure difference that varies with the angle of attack, the actuation air is directed into one of four outlet channels. These guide the air to different chordwise exit locations on the airfoil’s suction side. The appropriate actuation location adjusts automatically according to the pressure difference between the control ports and therefore incidence. Suction side flow separation is delayed as the boundary layer is enriched with kinetic energy. Experiments were conducted on a DU97-W-300 airfoil [2] at Re = 2.2 · 105. Compared to the baseline, changes in lift with angle of attack were reduced by an order of magnitude. An AeroDyn simulation of a full wind turbine rotor was performed that compares the baseline to a rotor design with adaptive flow control.

scholarly journals Flow behaviors in a Kaplan turbine runner with different tip clearances

2021 ◽  
Vol 13 (5) ◽  
pp. 168781402110158
Author(s):  
Yue Ma ◽  
Bing Qian ◽  
Zhiguo Feng ◽  
Xuan Wang ◽  
Guangtai Shi ◽  
...  
Keyword(s):  
Flow Separation ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Stress Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Kaplan Turbine ◽  
Blade Tip

Tip clearance between the runner blade tip and shroud in a Kaplan turbine is inevitable, and the tip leakage flow (TLF) and tip leakage vortex (TLV) induced by the tip clearance have a considerable effect on the flow behaviors. To reveal the effect of the tip clearance on the flow characteristics, based on the Reynolds time-averaged Navier-Stokes (N-S) equation and the shear stress transfer (SST) k-ω turbulence model, the three-dimensional turbulence flow in a Kaplan turbine is simulated using ANSYS CFX. Meanwhile, the flow laws in the tip clearance are emphatically analyzed and summarized. Results show with the increase of the tip clearance, the negative pressure region in the blade suction side (SS) middle, the SS near the blade tip and the blade tip becomes more and more obvious. In the meantime, the flow behaviors on the blade pressure side (PS) are relatively stable, and the flow separation on the SS near blade tip merges. The larger the tip clearance is, the more obvious the flow separation phenomenon displays. In addition, the TLV is a spatial three-dimensional spiral structure formed by the entrainment effect of the TLF and main flow, and as the tip clearance increases, the TLV becomes more obvious.

Development of a Fluidic Actuator for Adaptive Flow Control on a Thick Wind Turbine Airfoil

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Sebastian Niether ◽  
Bernhard Bobusch ◽  
David Marten ◽  
Georgios Pechlivanoglou ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Flow Separation ◽  
System Integration ◽  
Pressure Difference ◽  
Angle Of Attack ◽  
Suction Side ◽  
Turbine Rotor ◽  
Adaptive Flow Control ◽  
Order Of Magnitude ◽  
Side Flow

Wind turbines are exposed to unsteady incident flow conditions such as gusts or tower interference. These cause a change in the blades' local angle of attack, which often leads to flow separation at the inner rotor sections. Recirculation areas and dynamic stall may occur, which lead to an uneven load distribution along the blade. In this work, a fluidic actuator is developed that reduces flow separation. The functional principle is adapted from a fluidic amplifier. High pressure air fed by an external supply flows into the interaction region of the actuator. Two control ports, oriented perpendicular to the inlet, allow for a steering of the actuation flow. One of the control ports is connected to the suction side, the other to the pressure side of the airfoil. Depending on the pressure difference that varies with the angle of attack, the actuation air is directed into one of four outlet channels. These guide the air to different chordwise exit locations on the airfoil's suction side. The appropriate actuation location adjusts automatically according to the pressure difference between the control ports and therefore incidence. Suction side flow separation is delayed as the boundary layer is enriched with kinetic energy. Experiments were conducted on a DU97-W-300 airfoil at Re = 2.2 × 105. Compared to the baseline, lift variations due to varying angles of attack were reduced by an order of magnitude. A Fast/Aerodyn simulation of a full wind turbine rotor was performed to show the real world load reduction potential. Additionally, system integration is discussed, which includes suggestions on producibility and operational details.

scholarly journals Influence of Tip Clearance on Flow Characteristics of Axial Compressor

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1445
Author(s):  
Moru Song ◽  
Hong Xie ◽  
Bo Yang ◽  
Shuyi Zhang
Keyword(s):  
Flow Field ◽  
Flow Characteristics ◽  
Axial Compressor ◽  
Suction Side ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Tip Clearance Vortex

This paper studies the influence of tip clearance on the flow characteristics related to the performance. Based on full-passage numerical simulation with experimental validation, several clearance models are established and the performance curves are obtained. It is found that there exists an optimum clearance for the stable working range. By analyzing the flow field in tip region, the role of the tip leakage flow is illustrated. In the zero-clearance model, the separation and blockage along the suction side is the main reason for rotating stall. As the tip clearance is increased to the optimum value, the separation is suppressed by the tip leakage flow. However, with the continuing increasing of the tip clearance, the scale and strength of the tip clearance vortex is increased correspondingly. When the tip clearance is larger than the optimum value, the tip clearance vortex gradually dominates the flow field in the tip region, which can increase the unsteadiness in the tip region and trigger forward spillage in stall onset.

Influence of Additional Leading-Edge Surface Roughness on Performances in Highly Loaded Compressor Cascade

2015 ◽  
Vol 32 (2) ◽  
Author(s):  
Shaowen Chen ◽  
Hao Xu ◽  
Shijun Sun ◽  
Longxin Zhang ◽  
Songtao Wang
Keyword(s):  
Surface Roughness ◽  
Flow Characteristics ◽  
Axial Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Local Area ◽  
Compressor Cascade ◽  
Edge Surface ◽  
Aerodynamic Parameters ◽  
Highly Loaded

AbstractExperimental research has been carried out at low speed to investigate the effect of additional leading-edge surface roughness on a highly-loaded axial compressor cascade. A 5-hole aerodynamic probe has been traversed across one pitch to obtain the distribution of total pressure loss coefficient, secondary flow vector, flow angles and other aerodynamic parameters at the exit section. Meanwhile, ink-trace flow visualization has been used to measure the flow fields on the walls of cascades and a detailed topology structure of the flow on the walls has been obtained. Aerodynamic parameters and flow characteristics are compared by arranging different levels of roughness on various parts of the leading edge. The results show that adding surface roughness at the leading edge and on the suction side obviously influences cascade performance. Aggravated 3-D flow separation significantly increases the loss in cascades, and the loss increases till 60% when the level of emery paper is 80 mm. Even there is the potential to improve cascade performance in local area of cascade passage. The influence of the length of surface roughness on cascade performance is not always adverse, and which depends on the position of surface roughness.

Comparison of Test Results Obtained on Plane and Annular, Fixed or Rotating Supersonic Blade Cascades

1975 ◽  
Vol 97 (2) ◽  
pp. 245-253 ◽  
Author(s):  
J. Paulon ◽  
J. Reboux ◽  
R. Sovrano
Keyword(s):  
Flow Separation ◽  
Theoretical Calculations ◽  
Suction Side ◽  
Back Pressure ◽  
Test Results ◽  
Flow Configuration ◽  
Pressure Distributions ◽  
Supersonic Regime ◽  
Annular Cascade ◽  
Side Flow

Results of an experimental research on the comparison of flow patterns in linear and annular, fixed and rotating supersonic blade cascades are presented. The fixed plane cascade and the fixed annular cascade give very similar results at low back pressure and the flow configuration (Schlieren pictures) and the pressure distributions are those given by theoretical calculations. In the rotating cascade the fully started supersonic regime was not obtained. At high back pressure, sidewall flow separation perturbates the flow pattern in the plane cascade. In the annular setups, the flow configuration with suction side flow separation is correctly predicted by the theory.

Mach Number Distribution and Profile Losses for Low-Pressure Turbine Profiles With High Diffusion Factors

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Flow Separation ◽  
Total Pressure ◽  
Suction Side ◽  
Low Pressure ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
High Diffusion ◽  
Mach Numbers

The results of this investigation come from two linear cascades at high diffusion factors (DFs). The measurements presented for each low-pressure turbine (LPT) profile were conducted at midspan under a range of Reynolds- and exit Mach numbers. The exit Mach number was varied in a range covering low subsonic up to values where a transonic flow regime on the suction side of the blade could be expected. This work focuses on two profiles with a diffusion factor in a range of 0.18≤DF≤0.22, where values in this range are considered as a comparable for the two cascades. Profile A is a front-loaded design and has shown no obvious flow separation on the suction side of the blade. Compared to the design A, design B is a more aft-loaded profile which exhibits flow separation on the suction side for all Reynolds numbers investigated. The integral total pressure losses were evaluated by wake traverses downstream of the airfoil. To determine the isentropic Mach numbers and the character of the boundary layer along the suction side of the profile, the static pressure measurements and traverses with a flattened Pitot probe were carried out. A correlation between the position of maximum Mach number on the suction side and the integral total pressure losses has been successfully established. The results show that the optimum location of peak Mach number to minimize integral total pressure losses is significantly dependent on the Reynolds number. However, the correlation presented in this paper, which is based on the data of the integral total pressure losses of an attached boundary layer, is not able to predict the integral total pressure loss or the location of the maximum Mach number on the suction side of the blade when an open separation bubble occurs.

Investigation of Flow Separation Characteristics in a Pump as Turbines Impeller Under the Best Efficiency Point Condition

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Tong Lin ◽  
Xiaojun Li ◽  
Zuchao Zhu ◽  
Renhua Xie ◽  
Yanpi Lin
Keyword(s):  
Flow Separation ◽  
Topological Structure ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Surface Friction ◽  
Suction Side ◽  
Peak Position ◽  
Transient Pressure ◽  
Point Condition

Abstract The impeller, which is the main energy conversion component of a pump as turbine (PAT), is designed for pumping mode, and its internal flow characteristics are quite complicated even at the best efficiency point (BEP) of the turbine mode. This study aims to investigate the flow separation characteristics in a PAT impeller under the BEP condition by numerical method. The hydraulic performance and transient pressure characteristics of PAT predicted numerically were verified through experimentation. The surface friction lines and flow topological structure were applied to diagnose the flow separation at the surface of the blade. The relationship between flow topological structure and vortex in the impeller and static pressure at the blade were analyzed. Analysis results show that the backflow and open flow separation are observed significantly in the leading region and near the shroud of the trailing region of suction side. The passage vortex always appears near the spiral node. The saddle point and spiral node correspond to the peak position of adverse pressure and the lowest position between two peak values of the static pressure of the blade, respectively. The inflow conditions of blade and shape of the trailing edge significantly influence the flow separations in the impeller.

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