scholarly journals Computational Analysis of the Blade Loading on Tip Clearance Effects

2020 ◽  
Vol 6 (4) ◽  
pp. 95
Author(s):  
Limin Wang ◽  
Yadong Liu ◽  
Chengqin Li
Keyword(s):  
Computational Analysis ◽  
Tip Clearance ◽  
Blade Loading

Influences of Tip Leakage Flows Discharged From Main and Splitter Blades on Flow Field in Transonic Centrifugal Compressor Stage

2018 ◽  
Author(s):  
Masanao Kaneko ◽  
Hoshio Tsujita
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Blade Loading ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Transonic Centrifugal Compressor ◽  
Tip Leakage Flows

A transonic centrifugal compressor impeller is generally composed of the main and the splitter blades which are different in chord length. As a result, the tip leakage flows from the main and the splitter blades interact with each other and then complicate the flow field in the compressor. In this study, in order to clarify the individual influences of these leakage flows on the flow field in the transonic centrifugal compressor stage at near-choke to near-stall condition, the flows in the compressor at four conditions prescribed by the presence and the absence of the tip clearances were analyzed numerically. The computed results clarified the following noticeable phenomena. The tip clearance of the main blade induces the tip leakage vortex from the leading edge of the main blade. This vortex decreases the blade loading of the main blade to the negative value by the increase of the flow acceleration along the suction surface of the splitter blade, and consequently induces the tip leakage vortex caused by the negative blade loading of the main blade at any operating points. These phenomena decline the impeller efficiency. On the other hand, the tip clearance of the splitter blade decreases the afore mentioned acceleration by the formation of the tip leakage vortex from the leading edge of the splitter blade and the decrease of the incidence angle for the splitter blade caused by the suction of the flow into the tip clearance. These phenomena reduce the loss generated by the negative blade loading of the main blade and consequently reduce the decline of the impeller efficiency. Moreover, the tip clearances enlarge the flow separation around the diffuser inlet and then decline the diffuser performance independently of the operating points.

Prediction of the Nonuniform Tip Clearance Effect on the Axial Compressor Flow Field

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Young-Seok Kang ◽  
Shin-Hyoung Kang
Keyword(s):  
Flow Field ◽  
Axial Velocity ◽  
Axial Compressor ◽  
High Flow ◽  
Circumferential Direction ◽  
Tip Clearance ◽  
Recirculation Region ◽  
Tip Leakage Flow ◽  
Blade Loading ◽  
Design Effects

It is well-known that nonuniform tip clearance in an axial compressor induces pressure and velocity perturbations along the circumferential direction. This study develops a numerical modeling to predict perturbed flows in an axial compressor with a nonuniform tip clearance and presents a mechanism of the flow redistribution in the axial compressor at design and off-design conditions. The modeling results are compared with CFD results (2006, “Prediction of the Fluid Induced Instability Force of an Axial Compressor,” ASME FEDSM 2006, Miami, FL) not only to validate the present modeling, but also to investigate more detailed flow fields. In an axial compressor, nonuniform tip clearance varies local flow passage area and resultant axial velocity along the circumferential direction. There are small axial velocity differences between maximum and minimum clearances near the design condition, while large pressure differences are investigated according to local locations. However, contribution of the main flow region overrides the tip clearance effect as the flow coefficient deviates from the design condition. Moreover, the flow field redistribution becomes noticeably strong when the off-design effects are incorporated. In case of high flow coefficients, the low relative flow angle near the minimum clearance regions results in a large negative incidence angle and forms a large flow recirculation region and a corresponding large amount of loss occurs near the blade pressure surface. It further promotes strong flow field perturbations at the off-design conditions. The integration of these pressure and blade loading perturbations with a control volume analysis leads to the well-known Alford’s force. Alford’s force is always negative near the design condition; however, it reverses its sign to positive at the high flow coefficients. At the high flow coefficients, tip leakage flow effects lessen, while increased off-design effects amplify blade loading perturbations and a steep increase in Alford’s force. This study enables that nonuniform flow field, and the resultant Alford’s force, which may result in an unstable rotor-dynamic behavior, can be easily evaluated and assessed during the compressor, fan, or blower design process.

Effect of Endwall Motion on Blade Tip Heat Transfer

2003 ◽  
Vol 125 (2) ◽  
pp. 267-273 ◽  
Author(s):  
V. Srinivasan ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Pressure Gradients ◽  
Tip Leakage Flow ◽  
Blade Loading ◽  
Linear Cascade ◽  
Tip Leakage ◽  
Blade Tip ◽  
Wind Tunnel Data

Local mass transfer measurements were conducted on the tip of a turbine blade in a five-blade linear cascade with a blade-centered configuration. The tip clearance levels ranged from 0.6 to 6.9% of blade chord. The effect of relative motion between the casing and the blade tip was simulated using a moving endwall made of neoprene mounted on the top of the wind tunnel. Data were obtained for a single Reynolds number of 2.7×105 based on cascade exit velocity and blade chord. Pressure measurements indicate that the effect of endwall motion on blade loading at a clearance of 0.6% of blade chord is to reduce the pressure gradients driving the tip leakage flow. With the introduction of endwall motion, there is a reduction of about 9% in mass transfer levels at a clearance of 0.6% of chord. This is presumably due to the tip leakage vortex coming closer to the suction side of the blade and ‘blocking the flow,’ leading to reduced tip gap velocities and hence lower mass transfer.

Design and Test of an Aspirated Counter-Rotating Fan

2006 ◽  
Author(s):  
Jack L. Kerrebrock ◽  
Alan H. Epstein ◽  
Ali A. Merchant ◽  
Gerald R. Guenette ◽  
David Parker ◽  
...  
Keyword(s):  
Guide Vane ◽  
Pressure Ratio ◽  
Tip Clearance ◽  
Inlet Guide Vane ◽  
Suction Surface ◽  
Viscous Boundary Layer ◽  
Blade Loading ◽  
Design Speed ◽  
Viscous Boundary ◽  
Shock Loss

The design and test of a two-stage, vaneless, aspirated counter-rotating fan is presented in this paper. The fan nominal design objectives were a pressure ratio of 3:1 and adiabatic efficiency of 87%. A pressure ratio of 2.9 at 89% efficiency was measured in the tests. The configuration consists of a counter-swirl-producing inlet guide vane, followed by a high tip speed (1450 feet/sec) non-aspirated rotor, and a counter-rotating low speed (1150 feet/sec) aspirated rotor. The lower tip speed and lower solidity of the second rotor results in a blade loading above conventional limits, but enables a balance between the shock loss and viscous boundary layer loss, the latter of which can be controlled by aspiration. The aspiration slot on the second rotor suction surface extends from the hub up to 80% span, with a conventional tip clearance, and the bleed flow is discharged at the hub. The fan was tested in a short duration blowdown facility. Particular attention was given to the design of the instrumentation to obtain efficiency measurements within 0.5 percentage points. High response static pressure measurements were taken between the rotors and downstream of the fan to determine the stall behavior. Pressure ratio, mass flow, and efficiency on speedlines from 90% to 102% of the design speed are presented and discussed along with comparison to CFD predictions and design intent. The results presented here complement those presented earlier for two aspirated fan stages with tip shrouds, extending the validated design space for aspirated compressors to include designs with conventional unshrouded rotors and with inward removal of the aspirated flow.

scholarly journals Analysis of Aerodynamically Induced Whirling Forces in Axial Flow Compressors

2000 ◽  
Vol 122 (4) ◽  
pp. 761-768 ◽  
Author(s):  
Z. S. Spakovszky
Keyword(s):  
System Analysis ◽  
Axial Flow ◽  
Tip Clearance ◽  
Design Tools ◽  
Mean Flow ◽  
Blade Loading ◽  
Force Prediction ◽  
Engine Design ◽  
Comparable Magnitude ◽  
Axial Flow Compressors

A new analytical model to predict the aerodynamic forces in axial flow compressors due to asymmetric tip-clearance is introduced. The model captures the effects of tip-clearance induced distortion (i.e., forced shaft whirl), unsteady momentum-induced tangential blade forces, and pressure-induced forces on the spool. Pressure forces are shown to lag the tip-clearance asymmetry, resulting in a tangential (i.e., whirl-inducing) force due to spool pressure. This force can be of comparable magnitude to the classical Alford force. Prediction and elucidation of the Alford force is also presented. In particular, a new parameter denoted as the blade loading indicator is deduced. This parameter depends only on stage geometry and mean flow and determines the direction of whirl tendency due to tangential blade loading forces in both compressors and turbines. All findings are suitable for incorporation into an overall dynamic system analysis and integration into existing engine design tools. [S0889-504X(00)01604-4]

Effect of Tip Clearance on the Aeroelastic Stability of a Wide-Chord Fan Rotor

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Xu Dong ◽  
Yingjie Zhang ◽  
Ziqing Zhang ◽  
Xingen Lu ◽  
Yanfeng Zhang
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Tip Clearance ◽  
Influence Coefficient ◽  
Pressure Amplitude ◽  
Aeroelastic Stability ◽  
Local Flow ◽  
Blade Loading ◽  
Unsteady Pressure ◽  
Aerodynamic Damping

Abstract This research presents a series of simulations that investigate the effects of tip clearance on the aeroelastic stability of a wide-chord high-speed transonic fan rotor. The results show that the stall margin and the total pressure ratio decreases as the tip clearance increases. The effect of tip clearance on the blade loading can extend to 30% span. The phase of the influence coefficient without tip clearance is different from that with clearance, which causes the most unstable aerodynamic damping to shift in the nodal diameter. As the clearance increases from 0.25 mm to 2 mm, the damping decreases. The nonmonotonic behavior found by other researchers was not observed in this study. We conclude that the tip clearance affects the aeroelastic stability in two ways. The first is to change the blade loading so that the amplitude of the unsteady pressure increases or decreases, while the phase hardly changes, resulting in changes in aerodynamic damping. The second is to change the local flow so that the unsteady pressure amplitude and the phase change locally.

Prediction of Asymmetric Tip Clearance Effect on Flow Redistributions in an Axial Compressor

2007 ◽  
Author(s):  
Young-Seok Kang ◽  
Shih-Hyoung Kang
Keyword(s):  
Flow Field ◽  
Axial Compressor ◽  
High Flow ◽  
Main Flow ◽  
Circumferential Direction ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Blade Loading ◽  
Flow Blockage ◽  
Blockage Effect

Asymmetric tip clearance in an axial compressor induces pressure and velocity redistributions along the circumferential direction in an axial compressor. This paper presents the mechanism of the flow redistribution due to the asymmetric tip clearance with a simple numerical modeling. The flow field of a rotor of an axial compressor is predicted when an asymmetric tip clearance occurs along the circumferential direction. The modeling results are supported by CFD results not only to validate the present modeling but also to investigate more detailed flow fields. Asymmetric tip clearance makes local flow area and resultant axial velocity vary along the circumferential direction. This flow redistribution ‘seed’ results in a different flow patterns according to the flow coefficient. Flow field redistribution patterns are largely dependent on the local tip clearance performance at low flow coefficients. However, the contribution of the main flow region becomes dominant while the tip clearance effect becomes weak as the flow coefficient increases. The flow field redistribution pattern becomes noticeably strong if a blockage effect is considered when the flow coefficient increases. The relative flow angle at the small clearance region decreases which result in a negative incidence angle at the high flow coefficient. It causes a recirculation region at the blade pressure surface which results in the flow blockage. It promotes the strength of the flow field redistribution at the rotor outlet. These flow pattern changes take an effect on the blade loading perturbations. The integration of blade loading perturbation from control volume of the circumferential momentum analysis leads to well-known Alford’s force. Alford’s force is always negative when the flow blockage effects are excluded. However when the flow blockage effect is incorporated into the modeling, main flow effects on the flow redistribution is also reflected on the Alford’s force at the high flow coefficient. Alford’s force steeply increases as the flow coefficient increases, because of the tip leakage suppression and strong flow redistribution. The predicted results are well agreed to CFD results by Kang and Kang (2006).

Comparative Study on Tip Clearance Flow Fields in Two Types of Transonic Centrifugal Compressor Impeller With Splitter Blades

2010 ◽  
Author(s):  
Kazutoyo Yamada ◽  
Yusuke Tamagawa ◽  
Hisataka Fukushima ◽  
Masato Furukawa ◽  
Seiichi Ibaraki ◽  
...  
Keyword(s):  
Leading Edge ◽  
Tip Clearance ◽  
Low Velocity ◽  
Blade Loading ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Transonic Centrifugal Compressor ◽  
Compressor Impeller ◽  
Clearance Flow ◽  
Velocity Region

Two types of transonic centrifugal compressor impeller with splitter blades, which are different in blade count, have been investigated in this study. RANS (Reynolds-Averaged Navier-Stokes) simulations were carried out for several operating conditions to clarify differences in aerodynamic performance characteristic and tip clearance flow field between the two compressors. The simulation shows that basically similar flow events happen in both compressors. A low velocity region is generated near the tip at low flow rate conditions, which results from an expansion of the tip leakage vortex. The low velocity region expands as the flow rate is decreased, and interacts with the pressure surface of the splitter blade near the leading edge. This causes a descent of the blade loading near the tip of the leading edge, and an accumulation of high entropy fluid near the casing-suction corner. Moreover, the tip clearance flow spills ahead of the leading edge of the splitter blade at near stall condition, and eventually the spillage happens at the full blade at stall condition. However, the major difference in solidity influences tip clearance flow/blade interaction, which leads to changes in the performance characteristics. In the impeller with low solidity, the tip leakage vortex breaks down with a large blockage effect because of high blade loading at the tip, which decreases the pressure ratio. The impeller with high solidity is subject to the spillage, which results in an early and large-scale stall that decreases the efficiency.

Tip Clearance Effects on Unsteady Behavior of the Tip Leakage Vortex and Stator/Rotor Interaction Tonal Noise

2012 ◽  
Author(s):  
Lei Zhao ◽  
Wei-Yang Qiao ◽  
Zhong-Qiang Mu ◽  
Ping-Ping Chen
Keyword(s):  
Noise Level ◽  
Tip Clearance ◽  
Tonal Noise ◽  
Blade Loading ◽  
Tip Leakage Vortex ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow ◽  
Matching Strategy ◽  
Unsteady Behavior

In turbomachinery the tip leakage vortex is an obvious periodic phenomenon associated with rotor blade, its interaction with stator wake will affect the tonal noise level and aerodynamic performance. This study assesses the effects of tip leakage vortex on the stator/rotor interaction tonal noise and its unsteady behavior by 3D unsteady numerical simulations and the Triple-Plane Pressure matching strategy. The fluctuation of blade loading distribution and the interaction of wake negative jet with tip clearance flow change the structure and position of tip leakage vortex and scrapping vortex periodically. From the time-average results, the incoming wakes reduced the strength of vortices. The result also shows that the tonal noise level of turbine stage is decreased with the enlargement of tip clearance.

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