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.

The Behavior of the Casing Boundary Layer With the Presence of Tip Leakage Vortex

2018 ◽  
Author(s):  
Xi Nan ◽  
Feng Lin ◽  
Takehiro Himeno ◽  
Toshinori Watanabe
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Flow Loss ◽  
Produce Flow

Casing boundary layer effectively places a limit on the pressure rise capability achievable by the compressor. The separation of the casing boundary layer not only produce flow loss but also closely related to the compressor rotating stall. The motivation of this paper is to present a viewpoint that the casing boundary layer should be paid attention to in parallel with other flow factors on rotating stall trigger. This paper illustrates the casing boundary layer behavior by displaying its separation phenomena with the presence of tip leakage vortex at different flow conditions. Skin friction lines and the corresponding absolute streamlines are used to demonstrate the three-dimensional flow patterns on and near the casing. The results depict a Saddle, a Node and several tufts of skin friction lines dividing the passage into four zones. The tip leakage vortex is enfolded within one of the zones by the separated flows. All the flows in each blade passage are confined within the passage as long as the compressor is stable. The casing boundary layer of a transonic compressor is also examined in the same way, which results in qualitatively similar zonal flows that enfolds the tip leakage vortex. This research develops a new way to study the casing boundary layer in rotating compressors. The results may provide a first-principle based explanation to stalling mechanisms for compressors that are casing sensitive.

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.

Numerical Simulation of the Shock-Tip Leakage Vortex Interaction in a HPC Front Stage

1999 ◽  
Vol 121 (3) ◽  
pp. 456-468 ◽  
Author(s):  
M. Hoeger ◽  
G. Fritsch ◽  
D. Bauer
Keyword(s):  
Three Dimensional ◽  
Leading Edge ◽  
Navier Stokes ◽  
Stream Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Blade Tip ◽  
Operating Points ◽  
Insight Into

For a single-stage transonic compressor rig at the TU Darmstadt, three-dimensional viscous simulations are compared to L2F measurements and data from the EGV leading edge instrumentation to demonstrate the predictive capability of the Navier–Stokes code TRACE_S. In a second step the separated regions at the blade tip are investigated in detail to gain insight into the mechanisms of tip leakage vortex-shock interaction at operating points close to stall, peak efficiency, and choke. At the casing the simulations reveal a region with axially reversed flow, leading to a rotationally asymmetric displacement of the outermost stream surface and a localized additional pitch-averaged blockage of approximately 2 percent. Loss mechanisms and streamline patterns deduced from the simulation are also discussed. Although the flow is essentially three-dimensional, a simple model for local blockage from tip leakage is demonstrated to significantly improve two-dimensional simulations on S1-surfaces.

Study on Unsteady Tip Leakage Vortex Cloud Cavitation in an Axial Flow Pump Using an Improved Numerical Method

2015 ◽  
Author(s):  
Desheng Zhang ◽  
Weidong Shi
Keyword(s):  
Shear Layer ◽  
Numerical Method ◽  
Three Dimensional ◽  
Axial Flow ◽  
Cloud Cavitation ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Sheet Cavitation ◽  
Axial Flow Pump ◽  
Flow Pump

The aim of the present investigation is to simulate and analyze the formation of three-dimensional tip leakage vortex (TLV) cloud cavitation and the periodic collapse of TLV-induced vortices cavitation. The improved SST k-ω turbulence model and the homogeneous cavitation model were validated by the simulation of unsteady cavitation shedding flow around the NACA66-mod hydrofoil, and then the unsteady TLV cloud cavitation and unstable vortices cavitation in an axial flow pump were predicted by using the improved numerical method. The predicted three-dimensional cavitation structure of TLV and vortices as well as the collapse features show a qualitative agreement with the high speed photography results. Numerical results show that the TLV cavitation cloud in the axial flow pump mainly includes tip clearance cavitation, shear layer cavitation and TLV cavitation, and TLV-induced vortices cavitation occurs in the downstream of blade trailing edge (TE). TLV cavitation cloud is relatively steady before about 80% blade chord with the high vapor volume fraction inside the TLV core. The unsteady TLV cavitation cloud occurs near the TE of blade where the transient cavity shapes of sheet cavitation and TLV cavitation all fluctuate, which results in the decrease of the axial velocity in the tip region. It is found that the unstable vortices cavitation in shear layer in the downstream of TE collapses periodically. The correlation analysis shows that TLV cavitation cloud and vortices cavitation collapse are significantly associated with the interaction between TLV breakdown and boundary layer in the downstream of blade TE.

Flow Field Unsteadiness in the Tip Region of a Transonic Compressor Rotor

1997 ◽  
Vol 119 (1) ◽  
pp. 122-128 ◽  
Author(s):  
S. L. Puterbaugh ◽  
W. W. Copenhaver
Keyword(s):  
Flow Field ◽  
High Performance ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vortex Interaction ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Operating Points

An experimental investigation concerning tip flow field unsteadiness was performed for a high-performance, state-of-the-art transonic compressor rotor. Casing-mounted high frequency response pressure transducers were used to indicate both the ensemble averaged and time varying flow structure present in the tip region of the rotor at four different operating points at design speed. The ensemble averaged information revealed the shock structure as it evolved from a dual shock system at open throttle to an attached shock at peak efficiency to a detached orientation at near stall. Steady three-dimensional Navier Stokes analysis reveals the dominant flow structures in the tip region in support of the ensemble averaged measurements. A tip leakage vortex is evident at all operating points as regions of low static pressure and appears in the same location as the vortex found in the numerical solution. An unsteadiness parameter was calculated to quantify the unsteadiness in the tip cascade plane. In general, regions of peak unsteadiness appear near shocks and in the area interpreted as the shock-tip leakage vortex interaction. Local peaks of unsteadiness appear in mid-passage downstream of the shock-vortex interaction. Flow field features not evident in the ensemble averaged data are examined via a Navier-Stokes solution obtained at the near stall operating point.

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.

Education Committee Best Paper of 1995 Award: Methods of Classical Mechanics Applied to Turbulence Stresses in a Tip Leakage Vortex

1996 ◽  
Vol 118 (4) ◽  
pp. 622-629 ◽  
Author(s):  
J. G. Moore ◽  
S. A. Schorn ◽  
J. Moore
Keyword(s):  
Stress Tensor ◽  
Reynolds Stress ◽  
Classical Mechanics ◽  
Three Dimensional ◽  
Surface Model ◽  
Reynolds Stresses ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Stress Tensors ◽  
Principal Directions

Moore et al. measured the six Reynolds stresses in a tip leakage vortex in a linear turbine cascade. Stress tensor analysis, as used in classical mechanics, has been applied to the measured turbulence stress tensors. Principal directions and principal normal stresses are found. A solid surface model, or three-dimensional glyph, for the Reynolds stress tensor is proposed and used to view the stresses throughout the tip leakage vortex. Modeled Reynolds stresses using the Boussinesq approximation are obtained from the measured mean velocity strain rate tensor. The comparison of the principal directions and the three-dimensional graphic representations of the strain and Reynolds stress tensors aids in the understanding of the turbulence and what is required to model it.

Three-Dimensional Navier-Stokes Analysis of Turbine Rotor and Tip-Leakage Flowfield

1997 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The 3-D viscous flowfield in the rotor passage of a single-stage turbine, including the tip-leakage flow, is computed using a Navier-Stokes procedure. A grid-generation code has been developed to obtain embedded H grids inside the rotor tip gap. The blade tip geometry is accurately modeled without any “pinching”. Chien’s low-Reynolds-number k-ε model is employed for turbulence closure. Both the mean-flow and turbulence transport equations are integrated in time using a four-stage Runge-Kutta scheme. The computational results for the entire turbine rotor flow, particularly the tip-leakage flow and the secondary flows, are interpreted and compared with available data. The predictions for major features of the flowfield are found to be in good agreement with the data. Complicated interactions between the tip-clearance flows and the secondary flows are examined in detail. The effects of endwall rotation on the development and interaction of secondary and tip-leakage vortices are also analyzed.

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.

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