On the Efficiency Alteration Mechanisms Due to Cavitation in Kaplan Turbines

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Sebastián Leguizamón ◽  
Claire Ségoufin ◽  
Phan Hai-Trieu ◽  
François Avellan
Keyword(s):  
Pressure Coefficient ◽  
Direct Consequence ◽  
Suction Side ◽  
Cavitation Model ◽  
Trailing Edge ◽  
Coefficient Distribution ◽  
Cavitation Region ◽  
Efficiency Increase ◽  
Turbulence Production ◽  
The One

A transport-equation-based homogeneous cavitation model previously assessed and validated against experimental data is used to investigate and explain the efficiency alteration mechanisms in Kaplan turbines. On the one hand, it is shown that the efficiency increase is caused by a decrease in energy dissipation due to a decreased turbulence production driven by a drop in fluid density associated with the cavitation region. This region also entails an increase in torque, caused by the modification of the pressure distribution throughout the blade, which saturates on the suction side. On the other hand, the efficiency drop is shown to be driven by a sharp increase in turbulence production at the trailing edge. An analysis of the pressure coefficient distribution explains such behavior as being a direct consequence of the pressure-altering cavitation region reaching the trailing edge. Finally, even though the efficiency alteration behavior is very sensitive to the dominant cavitation type, it is demonstrated that the governing mechanisms are invariant to it.

scholarly journals Effects of the outlet position of splitter blade on the flow characteristics in low-specific-speed centrifugal pump

2018 ◽  
Vol 10 (7) ◽  
pp. 168781401878952 ◽  
Author(s):  
Jinfeng Zhang ◽  
Guidong Li ◽  
Jieyun Mao ◽  
Shouqi Yuan ◽  
Yefei Qu ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Suction Side ◽  
Trailing Edge ◽  
Pressure Surface ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Good Agreement

To elucidate the influences of the outlet position of splitter blades on the performance of a low-specific-speed centrifugal pump, two different splitter blade schemes were proposed: one located in the middle of the channel and the other having a deviation angle at the trailing edge of splitter blade toward the suction side of the main blade. Experiments on the model pump with different splitter blade schemes were conducted, and numerical simulations on internal flow characteristics in the impellers were studied by means of the shear stress transport k- ω turbulence model. The results suggest that there is a good agreement between the experimental and numerical results. The splitter blade schemes can effectively optimize the structure of the jet-wake pattern and improve the internal flow states in the impeller channel. In addition, the secondary flow and inlet circulation on the pressure surface of main blade, the flow separation on the suction side of splitter blade, the pressure coefficient distributions on blade surface can achieve an evident amelioration when the trailing edge of splitter blade toward the suction side of the main blade is mounted at an appropriate position.

Fan Shaped and Cylindrical Holes Studied in Vane Film Cooling Test Rig

2010 ◽  
Author(s):  
Mats Kinell ◽  
Esa Utriainen ◽  
Jonas Hyle´n ◽  
Jonas Gustavsson ◽  
Andreas Bradley ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Pressure Coefficient ◽  
Suction Side ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Coefficient Distribution ◽  
Shaped Hole

In order to optimize the vane film cooling and thereby increase the efficiency of a gas turbine, different film cooling configurations were experimentally investigated. Dynamic similarity was obtained regarding main flow Reynolds number, airfoil pressure coefficient, adiabatic wall temperature and film cooling ejection ratio. The maximum reached Mach number was 0.52. The geometry of the test section, consisting of one vane and two flow paths, was modified in order to meet the dimensionless pressure coefficient distribution around the airfoil experienced by a full stage airfoil. This would ascertain that scaled but engine realistic pressure gradients would be achieved in the rig test. During the test, the cold airfoil was suddenly imposed to a hot main stream and the evaluation of both the film cooling effectiveness and the heat transfer coefficient distribution on the visiable surface could be done at one single test using time-resolved temperature measurements obtained through IR thermography. A high resolution MWIR camera was used together with a silicon viewing window. The post-processing allowed for corrections regarding emissions and determination of the desired parameters on the vane surface. Results, heat transfer coefficients and film cooling effectiveness, for fan shaped and cylindrical film cooling holes configurations are compared. The results show clear benefit of using shaped holes over cylindrical ditto, especially on the suction side where near hole film effectiveness is enhanced by approximately 25%, but the results also show that this benefit diminishes to nothing in the suction side trailing edge region. The local heat transfer coefficients are generally lower for the shaped hole configurations. Contrary to the film effectiveness the shaped holes configurations show lower heat transfer coefficients also at the suction side trailing edge region, making use of the shaped hole configurations superior to cylindrical ones as the heat flux to the surface is reduced. Numerical predictions using a boundary layer code, TEXSTAN, and CFD, for a smooth wall configuration corresponds well with the measured results.

Turbine Blade Trailing Edge Flow Characteristics at High Subsonic Outlet Mach Number

2003 ◽  
Vol 125 (2) ◽  
pp. 298-309 ◽  
Author(s):  
Claus H. Sieverding ◽  
Hugues Richard ◽  
Jean-Michel Desse
Keyword(s):  
Mach Number ◽  
Pressure Distribution ◽  
Turbine Blade ◽  
Vortex Shedding ◽  
High Speed ◽  
Pressure Coefficient ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Suction Side ◽  
Trailing Edge

The paper presents an experimental investigationof the effect of the trailing edge vortex shedding on the steady and unsteady trailing blade pressure distribution of a turbine blade at high subsonic Mach number M2,is=0.79 and high Reynolds number RE=2.8×106. The vortex formation and shedding process is visualized using a high-speed schlieren camera and a holographic interferometric density measuring technique. The blade is equipped with a rotatable trailing edge cylinder instrumented side-by-side with a pneumatic pressure tap and a fast response pressure sensor for detailed measurements of the trailing edge pressure distribution. The experiments demonstrate that contrary to the isobaric dead air region demonstrated at low subsonic Mach numbers the data reveal the existence of a highly nonuniform trailing edge pressure distribution with a strong pressure minimum at the center of the trailing edge. This finding is significant for the determination of the base pressure coefficient that is in general measured with a single pressure-sensing hole at the trailing edge center. The paper investigates further the effect of the vortex shedding on the blade rear suction side and discusses the superposition of unsteady effects emanating from the trailing edge and from the neighboring blade. The experimental data are a unique source for the validation of unsteady Navier-Stokes codes.

scholarly journals The Correction and Evaluation of Cavitation Model considering the Thermodynamic Effect

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Wei Li ◽  
Yongfei Yang ◽  
Wei-dong Shi ◽  
Xiaofan Zhao ◽  
Weiqiang Li
Keyword(s):  
Experimental Data ◽  
Volume Fraction ◽  
Pressure Coefficient ◽  
Cavitation Model ◽  
Evaporation Coefficient ◽  
Bubble Volume ◽  
Coefficient Distribution ◽  
Catalytic Role ◽  
Thermodynamic Effects ◽  
The Difference

Two cavitation models with thermodynamic effects were established based on the Rayleigh-Plesset equation to predict accurately the cavitation characteristics in the high-temperature fluid. The evaporation and the condensation coefficient of the cavitation model were corrected. The cavitation flow of NACA0015 airfoil was calculated using the modified cavitation model, where the influence of the thermodynamic effects of airfoil cavitation was analyzed. The result showed that the pressure coefficient distribution and the bubble volume fraction simulated have the same tendency of Zwart-Gerber-Belamri model’s result. According to the experimental data, the two models provide more accurate results. At the room temperature, the values of dpv/dT obtained by the two improved models are approximately equal. The difference between the two models’ results increases gradually with the temperature increasing, but it is still small. The simulation results are consistent with the experimental data when the evaporation coefficient is 10 and 1. When the evaporation coefficient is 1, the bubble growth is inhibited, the volume fraction becomes lower, and the cavitation area becomes flat. As the temperature increases, the cavitation area and the bubble volume fraction at airfoil front edge become larger, showing that the temperature plays a “catalytic” role in the cavitation process.

Numerical Investigation on Shock-Induced Separation Structure of Supercritical Airfoil

2013 ◽  
Vol 756-759 ◽  
pp. 4502-4505 ◽  
Author(s):  
Xin Xu ◽  
Da Wei Liu ◽  
De Hua Chen ◽  
Yuan Jing Wang
Keyword(s):  
Stokes Equations ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Trailing Edge ◽  
Navier Stokes Equations ◽  
Supercritical Airfoil ◽  
Coefficient Distribution

The supercritical airfoil has been widely applied to large airplanes for sake of high aerodynamic efficiency. But at transonic speeds, the complicated shock-induced separation on the upper surface of supercritical airfoil will change the aerodynamic characteristics. The transonic flows over a typical supercritical airfoil CH were numerically investigated in this paper, in order to analyses different shock-induced separation structure. The two-dimensional Navier-Stokes equations were solved with structure grids by utilizing the S-A turbulence model. The computation attack angles of CH airfoil varied from 0oto 4o, Mach numbers varied from 0.74 to 0.82 while Reynolds numbers varied from 3×106to 50×106per airfoil chord. It is shown that with the attack angle increases, the separation bubble occurred on the upper surface first, then the trailing-edge separation occurred, the trailing-edge would separate totally at last. The different separation structure would result in different pressure coefficient distribution and boundary layer thickness.

Influence of tip clearance and cavity depth on heat transfer in a cutback squealer tip

2020 ◽  
pp. 095441002096469
Author(s):  
Weijie Wang ◽  
Shaopeng Lu ◽  
Hongmei Jiang ◽  
Qiusheng Deng ◽  
Jinfang Teng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
High Heat ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Cavity Depth ◽  
High Heat Transfer ◽  
Blade Tip ◽  
High Heat Transfer Coefficient

Numerical simulations are conducted to present the aerothermal performance of a turbine blade tip with cutback squealer rim. Two different tip clearance heights (0.5%, 1.0% of the blade span) and three different cavity depths (2.0%, 3.0%, and 6.0% of the blade span) are investigated. The results show that a high heat transfer coefficient (HTC) strip on the cavity floor appears near the suction side. It extends with the increase of tip clearance height and moves towards the suction side with the increase of cavity depth. The cutback region near the trailing edge has a high HTC value due to the flush of over-tip leakage flow. High HTC region shrinks to the trailing edge with the increase of cavity depth since there is more accumulated flow in the cavity for larger cavity depth. For small tip clearance cases, high HTC distribution appears on the pressure side rim. However, high HTC distribution is observed on suction side rim for large tip clearance height. This is mainly caused by the flow separation and reattachment on the squealer rims.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Cavitation Experiments on Turbopump Inducers and Hydrofoils at Alta/Centrospazio: Overview and Future Activities

2005 ◽  
Author(s):  
Angelo Cervone ◽  
Cristina Bramanti ◽  
Emilio Rapposelli ◽  
Luca d’Agostino
Keyword(s):  
Thermal Effects ◽  
Cavity Length ◽  
Rocket Engine ◽  
Pressure Coefficient ◽  
Suction Side ◽  
Test Facility ◽  
Final Part ◽  
Cloud Cavitation ◽  
Naca 0015

The aim of the present paper is to provide some highlights about the most interesting experimental activities carried out during the years 2000–2004 through the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Centrospazio/Alta S.p.A. After a brief description of the facility, the experimental activities carried out on a NACA 0015 hydrofoil for the characterization of the pressure coefficient on the suction side and evaluation the cavity length and oscillations are presented. Then, the results obtained to characterize the performance and the cavitation instabilities on three different axial inducers are showed: in particular, a commercial three-bladed inducer, the four-bladed inducer installed in the LOX turbopump of the Ariane Vulcain MK1 rocket engine and the “FAST2”, a two-bladed one manufactured by Avio S.p.A. using the criteria followed for the VINCI180 LOX inducer. The most interesting results are related to the effects of the temperature on the cavitation instabilities on hydrofoils and inducers. Experiments showed that some instabilities, like the cloud cavitation on hydrofoils and the surge on inducers, are strongly affected by the temperature, while others seem not to be influenced by the thermal effects. In the final part of this paper, some indications of the main experimental activities scheduled for the next future are provided.

To what question is the Badiouan notion of the subject an answer? On the dialectical elaboration of the concept in his early work

2016 ◽  
Vol 43 (1) ◽  
pp. 96-120
Author(s):  
Jan-Jasper Persijn
Keyword(s):  
Direct Consequence ◽  
The Other ◽  
The Political ◽  
Academic World ◽  
Systematic Account ◽  
Political Field ◽  
Political Implications ◽  
The Subject ◽  
The One ◽  
Work Up

Alain Badiou’s elaboration of a subject faithful to an event is commonly known today in the academic world and beyond. However, his first systematic account of the subject ( Théorie du Sujet) was already published in 1982 and did not mention the ‘event’ at all. Therefore, this article aims at tracing back both the structural and the historical conditions that directed Badiou’s elaboration of the subject in the early work up until the publication of L’Être et l’Événément in 1988. On the one hand, it investigates to what extent the (early) Badiouan subject can be considered an exceptional product of the formalist project of the Cahiers pour l’Analyse as instigated by psychoanalytical discourse (Lacan) and a certain Marxist discourse (Althusser) insofar as both were centered upon a theory of the subject. On the other hand, this article examines the radical political implications of this subject insofar as Badiou has directed his philosophical aims towards the political field as a direct consequence of the events of May ’68.

Experimental and Numerical Investigation on the Performance of a Family of Three HP Transonic Turbine Blades

2004 ◽  
Author(s):  
D. Corriveau ◽  
S. A. Sjolander
Keyword(s):  
Flow Velocity ◽  
Turbine Blades ◽  
Suction Side ◽  
Experimental Results ◽  
Base Pressure ◽  
Suction Surface ◽  
Trailing Edge ◽  
Lower Base ◽  
Shock System ◽  
Transonic Turbine

Experimental results concerning the performance of three high-pressure (HP) transonic turbine blades having fore-, aft- and mid-loadings have been presented previously by Corriveau and Sjolander [1]. Results from that study indicated that by shifting the loading towards the rear of the airfoil, improvements in loss performance of the order of 20% could be obtained near the design Mach number. In order to gain a better understanding of the underlying reasons for the improved loss performance of the aft-loaded blade, additional measurements were performed on the three cascades. Furthermore, 2-D numerical simulations of the cascade flow were performed in order to help in the interpretation of the experimental results. Based on the analysis of additional wake traverse data and base pressure measurements combined with the numerical results, it was found that the poorer loss performance of the baseline mid-loaded profile compared to the aft-loaded blade could be traced back to the former’s higher rear suction side curvature. The presence of higher rear suction surface curvature resulted in higher flow velocity in that region. Higher flow velocity at the trailing edge in turn contributed to reducing the base pressure. The lower base pressure at the trailing edge resulted in a stronger trailing edge shock system for the mid-loaded blade. This shock system increased the losses for the mid-loaded baseline profile when compared to the aft-loaded profile.

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