Experimental Investigations of Cavitation Performance Breakdown in an Axial Waterjet Pump

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Huang Chen ◽  
Nick Doeller ◽  
Yuanchao Li ◽  
Joseph Katz
Keyword(s):  
Suction Side ◽  
Rapid Expansion ◽  
Experimental Investigations ◽  
Tip Leakage Flow ◽  
Flow Area ◽  
Cloud Cavitation ◽  
Tip Leakage ◽  
Bernoulli’S Equation ◽  
Pressure Distributions ◽  
Waterjet Pump

Abstract This experimental study examines the mechanisms causing cavitation breakdown in an axial waterjet pump. The database includes performance curves, images of cavitation, measured changes to endwall pressure as the blade passes, as well as velocity and pressure distributions inside the blade passage, the latter estimated using Bernoulli's Equation in the rotor reference frame. They show that cavitation breakdown is associated with a rapid expansion of the attached cavitation on the blade suction side (SS) into the blade overlap region, blocking part of the entrance to this passage, increasing the velocity and reducing the pressure along the pressure side (PS) of the blade. Initially, expansion of the SS cavitation compensates for the reduced PS pressure, resulting in a slight increase in performance. Further reduction of the inlet pressure causes a rapid decrease in performance as the SS pressure remains at the vapor pressure, while the PS pressure keeps on decreasing. In addition, during the breakdown, entrainment of the cloud cavitation by the tip leakage vortex generates the previously observed perpendicular cavitating vortices (PCVs) that extend across the passage and reduce the through-flow area in the tip region. Tests have been repeated after installing circumferential casing grooves aimed at manipulating the tip leakage flow and reduce the formation of PCVs. These grooves indeed reduce the tip region blockage during early phases. However, they have a small effect on the performance degradation by cavitation breakdown, presumably owing to their limited effect on the attached SS cavitation and tip region cloud cavitation.

Numerical Simulation of Tip Clearance Control in Axial Turbine Rotor: Part 2—Passive Control of Five Different Tip Platforms

2008 ◽  
Author(s):  
Wei Li ◽  
Wei-Yang Qiao ◽  
Kai-Fu Xu ◽  
Hua-Ling Luo
Keyword(s):  
Flow Control ◽  
Passive Control ◽  
Suction Side ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow

The tip leakage flow has significant effects on turbine in loss production, aerodynamic efficiency, etc. Then it’s important to minimize these effects for a better performance by adopting corresponding flow control. The active turbine tip clearance flow control with injection from the tip platform is given in Part-1 of this paper. This paper is Part-2 of the two-part papers focusing on the effect of five different passive turbine tip clearance flow control methods on the tip clearance flow physics, which consists of a partial suction side squealer tip (Partial SS Squealer), a double squealer tip (Double Side Squealer), a pressure side tip shelf with inclined squealer tip on a double squealer tip (Improved PS Squealer), a tip platform extension edge in pressure side (PS Extension) and in suction side (SS Extension) respectively. Combined with the turbine rotor and the numerical method mentioned in Part 1, the effects of passive turbine tip clearance flow controls on the tip clearance flow were sequentially simulated. The detailed tip clearance flow fields with different squealer rims were described with the streamline and the velocity vector in various planes parallel to the tip platform or normal to the tip leakage vortex core. Accordingly, the mechanisms of five passive controls were put in evidence; the effects of the passive controls on the turbine efficiency and the tip clearance flow field were highlighted. The results show that the secondary flow loss near the outer casing including the tip leakage flow and the casing boundary layer can be reduced in all the five passive control methods. Comparing the active control with the passive control, the effect brought by the active injection control on the tip leakage flow is evident. The turbine rotor efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine rotor efficiency, and it increased by 0.215%.

Tip Leakage Flows Near Partial Squealer Rims in an Axial Flow Turbine Stage

2003 ◽  
Author(s):  
Cengiz Camci ◽  
Debashis Dey ◽  
Levent Kavurmacioglu
Keyword(s):  
Total Pressure ◽  
Axial Flow ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Edge Zone ◽  
Tip Leakage ◽  
Partial Length

This paper deals with an experimental investigation of aerodynamic characteristics of full and partial-length squealer rims in a turbine stage. Full and partial-length squealer rims are investigated separately on the pressure side and on the suction side in the “Axial Flow Turbine Research Facility” (AFTRF) of the Pennsylvania State University. The streamwise length of these “partial squealer tips” and their chordwise position are varied to find an optimal aerodynamic tip configuration. The optimal configuration in this cold turbine study is defined as the one that is minimizing the stage exit total pressure defect in the tip vortex dominated zone. A new “channel arrangement” diverting some of the leakage flow into the trailing edge zone is also studied. Current results indicate that the use of “partial squealer rims” in axial flow turbines can positively affect the local aerodynamic field by weakening the tip leakage vortex. Results also show that the suction side partial squealers are aerodynamically superior to the pressure side squealers and the channel arrangement. The suction side partial squealers are capable of reducing the stage exit total pressure defect associated with the tip leakage flow to a significant degree.

Method for Non-Dimensional Tip Leakage Flow Characterization in Radial Turbines

2018 ◽  
Author(s):  
José Ramón Serrano ◽  
Roberto Navarro ◽  
Luis Miguel García-Cuevas ◽  
Lukas Benjamin Inhestern
Keyword(s):  
Suction Side ◽  
Tip Clearance ◽  
Navier Stokes ◽  
The Novel ◽  
Tip Leakage Flow ◽  
Navier Stokes Equation ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Wide Range ◽  
Clearance Flow

Tip leakage loss characterization and modeling plays an important role in small size radial turbine research. The momentum of the flow passing through the tip gap is highly related with the tip leakage losses. The ratio of fluid momentum driven by the pressure gradient between suction side and pressure side and the fluid momentum caused by the shroud friction has been widely used to analyze and to compare different sized tip clearances. However, the commonly used number for building this momentum ratio lacks some variables, as the blade tip geometry data and the viscosity of the used fluid. To allow the comparison between different sized turbocharger turbine tip gaps, work has been put into finding a consistent characterization of radial tip clearance flow. Therefore, a non-dimensional number has been derived from the Navier Stokes Equation. This number can be calculated like the original ratio over the chord length. Using the results of wide range CFD data, the novel tip leakage number has been compared with the traditional and widely used ratio. Furthermore, the novel tip leakage number can be separated into three different non-dimensional factors. First, a factor dependent on the radial dimensions of the tip gap has been found. Second, a factor defined by the viscosity, the blade loading, and the tip width has been identified. Finally, a factor that defines the coupling between both flow phenomena. These factors can further be used to filter the tip gap flow, obtained by CFD, with the influence of friction driven and pressure driven momentum flow.

The Tip Leakage Flow of an Unshrouded High Pressure Turbine Blade With Tip Cooling

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson
Keyword(s):  
Mass Flow ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Flow Ratio ◽  
Tip Leakage Flow ◽  
Momentum Exchange ◽  
Leakage Loss ◽  
Tip Leakage ◽  
Lower Loss ◽  
Mass Flow Ratio

Experimental, analytical, and numerical methods have been employed to study the aerodynamic performance of four different cooled tips with coolant mass ratios between 0% and 1.2% at three tip gaps of 1%, 1.6%, and 2.2% of the chord. The four cooled tips are two flat tips with different coolant holes, a cooled suction side squealer tip and a cooled cavity tip. Each tip has ten coolant holes with the same diameter. The uncooled cavity tip produces the smallest loss among all uncooled tips. On the cooled flat tip, the coolant is injected normally into the tip gap and mixes directly with flow inside the tip gap. The momentum exchange between the coolant and the flow that enters the tip gap creates significant blockage. As the coolant mass flow ratio increases, the tip leakage loss of the cooled flat tip first decreases and then increases. For the cooled cavity tip, the blockage effect of the coolant is not as big as that on the cooled flat tip. This is because after the coolant exits the coolant holes, it mixes with flow in the cavity first and then mixes with tip flow in the tip gap. The tip leakage loss of the cooled cavity tip increases as the coolant mass flow ratio increase. As a result, at a tip gap of 1.6% of the chord, the cooled cavity tip gives the lowest loss. At the smallest tip gap of 1% of the chord, the cooled flat tip produces less loss than the cooled cavity tip when the coolant mass flow ratios larger than 0.23%. This is because with the same coolant mass flow ratio, a proportionally larger blockage is created at the smallest tip gap. At the largest tip gap of 2.2% of the chord, the cavity tip achieves the best aerodynamic performance. This is because the effect of the coolant is reduced and the benefits of the cavity tip geometry dominate. At a coolant mass flow ratio of 0.55%, the cooled flat tips produce a lower loss than the cavity tip at tip gaps less than 1.3% of the chord. The cooled cavity tip produces the least loss for tip gaps larger than 1.3% of the chord. The cooled suction side squealer has the worst aerodynamic performance for all tip gaps studied.

The Internal Structure of the Tip Leakage Vortex Within the Rotor of an Axial Waterjet Pump

2010 ◽  
Author(s):  
Rinaldo L. Miorini ◽  
Huixuan Wu ◽  
Joseph Katz
Keyword(s):  
Vortex Sheet ◽  
Test Facility ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Vortex Filaments ◽  
Tip Leakage Vortex ◽  
Blade Passage ◽  
Tip Leakage ◽  
The Core ◽  
Waterjet Pump

The complex flow field in the tip region of a turbomachine rotor, including the tip leakage flow and tip leakage vortex (TLV), has been studied for decades. Yet many associated phenomena are still not understood. This paper provides detailed data on the instantaneous and phase averaged inner structure of the tip flow, and evolution of the TLV. Observations are based on series of high resolution planar particle image velocimetry measurements performed in a transparent waterjet pump fitted into an optical refractive index matched test facility. Velocity distributions and turbulence statistics are obtained in several meridional planes inside the rotor. We observe that the instantaneous TLV structure is composed of several unsteady vortex filaments that propagate into the blade passage. These filaments are first embedded into a vortex sheet generated at the suction side of the blade tip, and then they wrap around each other and roll up into the TLV. These vortices do not have sufficient time to merge into a single compact structure within the blade passage. We also find that the leakage vortex induces flow separation at the casing endwall and entrains the casing boundary layer with its counter-rotating vorticity. As it propagates in the rotor passage, the TLV migrates towards the pressure side of the neighboring blade. Unsteadiness associated with observed vortical structures is also investigated. We notice that, at early stages of the TLV evolution, turbulence is elevated in the vortex sheet, in the flow entrained from the endwall, and near the vortex core. Interestingly, the turbulence observed around the core is not consistent with the local distribution of turbulent kinetic energy production rate. This mismatch indicates that, given a TLV section, production likely occurs at preceding stages of the vortex evolution. Then, the turbulence is convected to the core of the TLV, and we suggest that this transport has substantial component along the vortex. Because we observe that the meandering of vortex filaments dominate the flow in the passage, we decompose the unsteadiness surrounding the TLV core to contributions from interlaced vortices and broadband turbulence. Results of this decomposition show that the two contributions are of the same order of magnitude. The TLV is investigated also beyond the trailing edge of the rotor blade. During these late stages of its evolution, the TLV approaches the pressure side of the neighboring blade and vortex breakdown occurs, causing rapid broadening of the phase average core, with little change in overall circulation. Associated turbulence occupies almost half the width of the blade passage and turbulence production there is also broadly distributed. Proximity of the TLV to the pressure side of the neighboring blade also affects entrainment of flow into the incoming tip region.

scholarly journals Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines

1998 ◽  
Author(s):  
A. A. Ameri ◽  
E. Steinthorsson ◽  
David L. Rigby
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Flow Conditions ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Axial Turbines ◽  
Gap Height ◽  
Stage Efficiency

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E3 first stage turbine, which represents a modern gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.

scholarly journals The Effect of Blade Tip Geometry on the Tip Leakage Flow in Axial Turbine Cascades

1991 ◽  
Author(s):  
F. J. G. Heyes ◽  
H. P. Hodson ◽  
G. M. Dailey
Keyword(s):  
Discharge Coefficient ◽  
Suction Side ◽  
Generation Process ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Overall Performance ◽  
Turbine Cascades ◽  
Made In ◽  
Blade Tip Geometry

The phenomenon of tip leakage has been studied in two linear cascades of turbine blades.The investigation includes an examination of the performance of the cascades with a variety of tip geometries. The effects of using plain tips, suction side squealers and pressure side squealers are reported. Traverses of the exit flow field were made in order to determine the overall performance. A method of calculating the tip discharge coefficients for squealer geometries is put forward. In linking the tip discharge coefficient and cascade losses a procedure for predicting the relative performance of tip geometries is developed. The model is used to examine the results obtained using the different tip treatments and to highlight the important aspects of the loss generation process.

Squealer Tip Leakage Flow Characteristics in Transonic Condition

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Wei Li ◽  
Hongmei Jiang ◽  
Qiang Zhang ◽  
Sang Woo Lee
Keyword(s):  
Flow Characteristics ◽  
Leading Edge ◽  
Flow Region ◽  
Suction Side ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Cavity Depth ◽  
Tip Leakage ◽  
Flow Flux ◽  
Subsonic Region

The over-tip-leakage (OTL) flow characteristics for a typical squealer tip of a high-pressure turbine blade, which consists of subsonic and transonic flow, have been numerically investigated in the present study, in comparison with the corresponding flat tip results. For the squealer tip employed, flow choking behavior still exists above the tip surface, even though the Mach number is lower and the transonic region is smaller than that for the flat tip. Detailed flow structure analysis shows that most of the fluid entering the squealer cavity is from the frontal leading edge region. The fluid migrates along the cavity and is ejected at various locations near the suction side rim. These fluids form a large subsonic flow zone under the supersonic flow passing over the tip gap which reduces the OTL flow flux. The squealer design works even in the presence of choked OTL flow. Comparisons between results from three different cavity depths with and without relative casing motion suggest that the over-tip-leakage flow flux has much dependence upon the cavity depth for the subsonic region, but is less sensitive to the depth for the transonic tip flow region. Such behavior has been confirmed with and without the existence of relative casing motion.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

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