Numerical investigation of the blade tip leakage vortex cavitation in a waterjet pump

2019 ◽  
Vol 187 ◽  
pp. 106170 ◽  
Author(s):  
Qiang Guo ◽  
Xianbei Huang ◽  
Baoyun Qiu
Keyword(s):  
Numerical Investigation ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip ◽  
Waterjet Pump

Three-Dimensional Structure and Turbulence Within the Tip Leakage Vortex of an Axial Waterjet Pump

2011 ◽  
Author(s):  
Rinaldo L. Miorini ◽  
Huixuan Wu ◽  
David Tan ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Strain Rate ◽  
Shear Layer ◽  
Production Rate ◽  
Three Dimensional ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip ◽  
Turbulence Production ◽  
Waterjet Pump

The flow structure and dynamics of turbulence are investigated by means of three-dimensional stereo particle image velocimetry (Stereo-PIV) measurements within the tip leakage vortex (TLV) of an axial waterjet pump rotor. Both the blades and casing of the pump are transparent and their optical refractive indices are matched with that of the pumped fluid, providing unobstructed optical access to the sample area without image distortion. Data are acquired on selected meridional planes in the rotor passage as well as in three-dimensional domains obtained by stacking closely-spaced planes situated within the rotor passage. Presented data have been sampled in one of these 3D regions, at 67% of the blade tip chordlength. All components of velocity and vorticity are calculated, together with the whole strain-rate and Reynolds stress tensors. The entire set of contributors to the turbulence production-rate is also available. The TLV and associated flow structures are completely 3D and change significantly along the blade tip chordwise direction. The vortex originates from the rollup of a multi-layered tip leakage flow, and propagates within the rotor passage towards the neighboring blade. Because of layered backflow rollup, vorticity entrained in the TLV is convected along different paths and re-oriented several times within the vortex. As a result, the TLV consists of a core surrounded by a tube of three-dimensional vorticity that wraps around it helically. Propagation of tip leakage backflow into the passage and subsequent TLV rollup also cause flow separation at the casing endwall with ejection of boundary layer vorticity that is finally entrained into the outer perimeter of the TLV. This complex TLV flow dominates the tip region of the rotor and involves non-uniform distributions of strain-rate and Reynolds stresses resulting in well-defined peaks of turbulence production-rate. For instance, turbulence is produced locally both at the flow contraction point near the region of aforementioned endwall separation and in the shear layer that connects the vortex with the suction side corner of the blade tip. The spatial inhomogeneity of turbulent kinetic energy (TKE) distribution within the TLV, and the mismatch between locations of TKE and production-rate peaks can be explained by analyzing the 3D mean flow advection of turbulence, for example from the region of endwall boundary layer separation towards the outer region of the TLV. In addition to being spatially non-uniform, turbulence is also anisotropic in both the shear layer and periphery of the TLV. Conversely, turbulence is intense and relatively isotropic near the TLV core, as well as monotonically increasing along the vortex centerline. This trend cannot be described solely in terms of local production of turbulence; it must also involve slow turbulence dissipation associated with the meandering of relatively large-size, interlaced vortex filaments in the TLV core region.

Measurements of the Tip Clearance Flow for a High-Reynolds-Number Axial-Flow Rotor

1995 ◽  
Vol 117 (4) ◽  
pp. 522-532 ◽  
Author(s):  
W. C. Zierke ◽  
K. J. Farrell ◽  
W. A. Straka
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Vortex Core ◽  
Rotor Blade ◽  
High Reynolds Number ◽  
Tip Clearance ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip ◽  
High Reynolds

A high-Reynolds-number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region, with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. The flow visualization on the blade surface and within the flow field indicate the existence of a trailing-edge separation vortex, a vortex that migrates radially upward along the trailing edge and then turns in the circumferential direction near the casing, moving in the opposite direction of blade rotation. Flow visualization also helps in establishing the trajectory of the tip leakage vortex core and shows the unsteadiness of the vortex. Detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jetlike profile to a wakelike profile as the tip clearance becomes smaller. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex, a vortex associated with high losses.

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 Numerical investigation of tip leakage vortex cavitation

2019 ◽  
Vol 240 ◽  
pp. 072003
Author(s):  
Ali Maghooli ◽  
Mehrdad Raisee ◽  
Seyed Ahmad Nourbakhsh
Keyword(s):  
Numerical Investigation ◽  
Tip Leakage Vortex ◽  
Tip Leakage

Effects of Tip Gap Size on the Aerodynamic Performance of a Cavity-Winglet Tip in a Turbine Cascade

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Fangpan Zhong ◽  
Chao Zhou
Keyword(s):  
Suction Side ◽  
Aerodynamic Performance ◽  
Gap Size ◽  
Turbine Cascade ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Baseline Case ◽  
Passage Vortex ◽  
Aerodynamic Performances ◽  
Blade Tip

The aerodynamic performance of a cavity-winglet tip is investigated in a high-pressure turbine cascade by experimental and numerical methods. The winglet tip has geometric features of a cavity and a suction side fore-part winglet. A cavity tip is studied as the baseline case. The aerodynamic performances of the two tips are investigated at three tip gaps of 0.8%, 1.7%, and 2.7% chord. At tip gaps of 1.7% and 2.7% chord, the loss near the blade tip is dominated by the tip leakage vortex (TLV) for both tips, and the winglet tip mainly reduces the loss generated by the tip leakage vortex. In the past, it was concerned that at a small tip gap, the winglet tip could introduce extra secondary loss and show little aerodynamic benefits. The winglet tip used in the current study is also found to be able to effectively reduce the loss at the smallest tip gap size of 0.8% chord. This is because at this small tip gap, the tip leakage vortex and the passage vortex (PV) appear simultaneously for the cavity tip. The winglet tip is able to reduce the pitchwise pressure gradient in the blade passage, which tends to suppress the formation of the passage vortex. The effects of the winglet tip on the flow physics and the loss mechanisms are explained in detail.

Numerical investigations on tip leakage flow characteristics and vortex trajectory prediction model in centrifugal compressor

2016 ◽  
Vol 230 (8) ◽  
pp. 757-772 ◽  
Author(s):  
Huijing Zhao ◽  
Zhiheng Wang ◽  
Shubo Ye ◽  
Guang Xi
Keyword(s):  
Prediction Model ◽  
Flow Instability ◽  
Leading Edge ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip

To better understand the characteristics of tip leakage flow and interpret the correlation between flow instability and tip leakage flow, the flow in the tip region of a centrifugal impeller is investigated by using the Reynolds averaged Navier–Stokes solver technique. With the decrease of mass flow rate, both the tip leakage vortex trajectory and the mainflow/tip leakage flow interface are shifted towards upstream. The mainflow/tip leakage flow interface finally reaches the leading edge of main blade at the near-stall condition. A prediction model is proposed to track the tip leakage vortex trajectory. The blade loading at blade tip and the averaged streamwise velocity of main flow within tip clearance height are adopted to determine the tip leakage vortex trajectory in the proposed model. The coefficient k in Chen’s model is found to be not a constant. Actually, it is correlated with h/b (the ratio of blade tip clearance height to blade tip thickness), because h/b will significantly influence the flow structure across the tip clearance. The effectiveness of the proposed prediction model is further demonstrated by tracking the tip leakage vortex trajectories in another three centrifugal impellers characterized with different h/b (s).

Study of Shock/Blade Tip Leakage Vortex/Boundary Layer Interaction in a Transonic Rotor With IDDES Method

2013 ◽  
Author(s):  
Ke Shi ◽  
Song Fu
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Vortex Breakdown ◽  
Leading Edge ◽  
Wave Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Layer Interaction ◽  
Boundary Layer Interaction ◽  
Blade Tip

In the present study, Improved Delayed Detached Eddy Simulation (IDDES) based on k-ω-SST turbulence model is applied to study the unsteady phenomenon in a transonic compressor rotor. Particular emphasis is on the understanding of the complex underlying mechanisms for the flow unsteadiness caused by the interaction of passage shock, blade tip leakage vortex (BTLV) and the blade boundary layer. The sources of the significant unsteadiness of the flow are shown. At the lower span height, where the BTLV is far away, the shock wave ahead of the blade leading edge impinges on the suction surface boundary layer of the adjacent blade, causing the shock wave/boundary layer interaction (SWBLI). Boundary layer thickness grows, while flow separates after the interaction. Predicted by IDDES calculation, this shock-induced separation exists as a separation bubble. The flow reattaches very soon after separation. At the near tip region, the shock wave surface deforms due to the strong interaction between the shock and the BTLV. Oscillation of the shock wave surface near the vortex core infers an unsteady contend between the shock and the vortex. Iso-surfaces of the Q parameter are applied to identify the vortex and its structure. Normally, the vortex breakdown in the rotor passage will lead to stall. However, in the present transonic case, the vortex breakdown was observed even at the near peak efficiency point. While the mass flow rate decreases, the shock waves formed ahead of the rotor blade leading edge were pushed upstream, causing earlier casing wall boundary layer separation. Upstream moving behavior of the shock is considered a new stall process.

Effects of blade rotation on axial turbine tip leakage vortex breakdown and loss

2016 ◽  
Vol 231 (9) ◽  
pp. 1634-1649
Author(s):  
Jie Gao ◽  
Qun Zheng ◽  
Yunning Liu ◽  
Ping Dong
Keyword(s):  
Vortex Breakdown ◽  
Great Influence ◽  
Main Flow ◽  
Leakage Flow ◽  
Centrifugal Forces ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Rotation ◽  
Coriolis And Centrifugal Forces ◽  
Blade Tip

The tip leakage vortex breakdown occurs under a few conditions in modern turbines, which leads to extra vortex breakdown losses, but the mechanisms of vortex breakdown and its influencing factors still remain unclear. This paper is a continuation of the previous effort and focuses on the effect of blade rotation on the leakage vortex dynamics in an unshrouded turbine. The analyses on leakage vortex breakdown characteristics are first shown, and then the isolating effects of relative casing motion and Coriolis and centrifugal forces on leakage vortex breakdown and loss are investigated. Based on these, the overall effects of blade rotation on leakage vortex breakdown characteristics are examined. Results indicate that the scraping effects of the casing endwall have a great influence on the blade tip leakage vortex breakdown and loss. However, the effect of Coriolis and centrifugal forces is relatively small. Although the mismatch of both velocity components of the leakage flow and the main flow becomes slightly small with the casing motion, the blade tip mixing loss per unit leakage flow increases due to the fact that the leakage vortex breaks down in advance.

Sign in / Sign up

Export Citation Format

Share Document