Modification of DDES Based on SST kω Model for Tip Leakage Flow in Turbomachinery

Volume 2C: Turbomachinery ◽

10.1115/gt2020-14851 ◽

2020 ◽

Author(s):

Yanfei Gao ◽

Yangwei Liu

Keyword(s):

Reynolds Number ◽

Flow Model ◽

Turbulence Modeling ◽

Streamwise Vortex ◽

Original Model ◽

Leakage Flow ◽

Mean Flow ◽

Tip Leakage Flow ◽

Modified Model ◽

Tip Leakage

Abstract Both LES and DDES are conducted in a low-Reynolds number tip leakage flow model. The DDES uses the SST kω model and employs the same grid with the LES, but the turbulence field diverges from the LES result. Referring to the comparison between LES and DDES, a modification of the zonal function in the DDES model is proposed, which enhances the dissipation of the modeled turbulence thus promote the transition to fully LES in the tip region when the mesh is fine enough. It can generate much finer vortex structure than the original model, including the primary streamwise vortex, induced vortices and the vortex fragments after breakdown. The modification fixes the underestimation of the vorticity and pressure drop at the formation stage of the tip leakage vortex, and generates more reasonable turbulence field and energy spectra. The modified model is introduced to a real rotor simulation at engineering Reynolds number. Compared with the original model on both mean flow field and turbulence field, the modified model shows favorable agreements with the measurements. The study also gives a practical example of using the tip leakage flow model in turbulence modeling.

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Investigation of Turbulence Characteristics in a Tip Leakage Flow Model Using Large-Eddy Simulation

Volume 2A: Turbomachinery ◽

10.1115/gt2019-90844 ◽

2019 ◽

Author(s):

Yanfei Gao ◽

Yangwei Liu ◽

Lipeng Lu

Keyword(s):

Large Eddy Simulation ◽

Flow Model ◽

Side Wall ◽

Leakage Flow ◽

Mean Flow ◽

Tip Leakage Flow ◽

Turbulence Characteristics ◽

Tip Leakage ◽

Eddy Simulation ◽

Large Eddy

Abstract A simple tip leakage flow (TLF) model which consists of a square duct with a longitudinal slit on the top of a side wall is proposed to reproduce the jet flow/main flow shear mechanism of the tip leakage vortex (TLV) rolling-up in turbomachinery. Large-eddy simulation (LES) is employed to investigate the turbulence characteristics of the flow model under low Reynolds number condition. The geometry and boundary conditions of the flow model are simplified from a compressor rotor and modified to apply to low-Re condition for LES. The vortex structures and turbulence characteristics of the LES results are compared with the measurements of the rotor. It is found that the flow model could reproduce similar flow field and turbulence structures compared with the TLF in the real rotor, thus it can be used to investigate the turbulence in practical flows. Reynolds-Averaged Navier-Stokes (RANS) calculations are also carried out. The mean flow and turbulence behaviors of different cases are analyzed. The budgets of turbulent kinetic energy (k) are analyzed to investigate the turbulence transport nature in the TLF model, indicating that the non-equilibrium transport process of k is significant, especially the pressure and turbulent transport, which is not predicted by RANS.

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Study of the Standard k-ε Model for Tip Leakage Flow in an Axial Compressor Rotor

International Journal of Turbo and Jet Engines ◽

10.1515/tjj-2015-0039 ◽

2016 ◽

Vol 33 (4) ◽

Cited By ~ 7

Author(s):

Yanfei Gao ◽

Yangwei Liu ◽

Luyang Zhong ◽

Jiexuan Hou ◽

Lipeng Lu

Keyword(s):

Flow Field ◽

Large Scale ◽

Turbulent Viscosity ◽

Axial Compressor ◽

Leakage Flow ◽

Reynolds Stresses ◽

Mean Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Compressor Rotor

AbstractThe standard k-ε model (SKE) and the Reynolds stress model (RSM) are employed to predict the tip leakage flow (TLF) in a low-speed large-scale axial compressor rotor. Then, a new research method is adopted to “freeze” the turbulent kinetic energy and dissipation rate of the flow field derived from the RSM, and obtain the turbulent viscosity using the Boussinesq hypothesis. The Reynolds stresses and mean flow field computed on the basis of the frozen viscosity are compared with the results of the SKE and the RSM. The flow field in the tip region based on the frozen viscosity is more similar to the results of the RSM than those of the SKE, although certain differences can be observed. This finding indicates that the non-equilibrium turbulence transport nature plays an important role in predicting the TLF, as well as the turbulence anisotropy.

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Tip Leakage Flow Reduction of a Linear Turbine Cascade Using String-Type DBD Plasma Actuators

Volume 2B: Turbomachinery ◽

10.1115/gt2018-76680 ◽

2018 ◽

Author(s):

Takayuki Matsunuma ◽

Takehiko Segawa

Keyword(s):

Reynolds Number ◽

Plasma Actuators ◽

Leakage Flow ◽

Turbine Cascade ◽

Tip Leakage Flow ◽

Dbd Plasma ◽

Tip Leakage ◽

String Type ◽

Displacement Thickness ◽

Blade Tip

Tip leakage flow through the small gap between the blade tip of a turbine and the casing endwall reduces the aerodynamic performance. String-type dielectric barrier discharge (DBD) plasma actuators made of silicone printed-circuit board were used for the active control of the tip leakage flow of a linear turbine cascade. Sinusoidal voltage excitation with amplitude varying from 4 kV to 6 kV (peak-to-peak voltage: 8 kVp-p to 12 kVp-p) and fixed frequency of 10 kHz was applied to the plasma actuators. The two-dimensional velocity field in the blade passage was estimated by particle image velocimetry (PIV) under the very low Reynolds number conditions of Re = 7.1 × 103 and 1.42 × 104. The tip leakage flow was reduced by the flow control using plasma actuators. The high turbulence intensity region caused by the tip leakage flow was also reduced. For the quantitative comparisons, the displacement thickness of the absolute velocity distributions was examined. By the flow control of the plasma actuators, the displacement thickness at tip-side gradually decreased as the input voltage increased. Although three types of plasma actuators were used, with thin, thick, and flat electrodes and different ratios of discharge area, the differences in their effect were negligible. The reason for these very small differences in effect is the wide spread of the plasma discharge from the encapsulated electrode in the plasma actuator to the exposed electrode of the blade tip. At the relatively high Reynolds number condition of Re = 1.42 × 104, the effect of the plasma actuator was smaller than that at the lower Reynolds number condition of Re = 7.1 × 103.

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

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

10.1115/97-gt-421 ◽

1997 ◽

Cited By ~ 3

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.

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Comparison of Turbine Tip Leakage Flow for Flat Tip and Squealer Tip Geometries at High-Speed Conditions

Journal of Turbomachinery ◽

10.1115/1.2162183 ◽

2004 ◽

Vol 128 (2) ◽

pp. 213-220 ◽

Cited By ~ 82

Author(s):

Nicole L. Key ◽

Tony Arts

Keyword(s):

Reynolds Number ◽

High Speed ◽

Flow Characteristics ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Cascade Arrangement ◽

Oil Flow ◽

Blade Tip ◽

Tip Velocity

The tip leakage flow characteristics for flat and squealer turbine tip geometries are studied in the von Karman Institute Isentropic Light Piston Compression Tube facility, CT-2, at different Reynolds and Mach number conditions for a fixed value of the tip gap in a nonrotating, linear cascade arrangement. To the best knowledge of the authors, these are among the very few high-speed tip flow data for the flat tip and squealer tip geometries. Oil flow visualizations and static pressure measurements on the blade tip, blade surface, and corresponding endwall provide insight to the structure of the two different tip flows. Aerodynamic losses are measured for the different tip arrangements, also. The squealer tip provides a significant decrease in velocity through the tip gap with respect to the flat tip blade. For the flat tip, an increase in Reynolds number causes an increase in tip velocity levels, but the squealer tip is relatively insensitive to changes in Reynolds number.

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Development of a Tip-Leakage Flow—Part 1: The Flow Over a Range of Reynolds Numbers

Journal of Fluids Engineering ◽

10.1115/1.2201616 ◽

2006 ◽

Vol 128 (4) ◽

pp. 751-764 ◽

Cited By ~ 20

Author(s):

Ghanem F. Oweis ◽

David Fry ◽

Chris J. Chesnakas ◽

Stuart D. Jessup ◽

Steven L. Ceccio

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Three Dimensional ◽

Reynolds Numbers ◽

Leakage Flow ◽

Core Size ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Downstream Distance ◽

Secondary Vortices

An extensive experimental investigation was carried out to examine the tip-leakage flow on ducted propulsors. The flow field around three-bladed, ducted rotors operating in uniform inflow was measured in detail with three-dimensional laser Doppler velocimetry and planar particle imaging velocimetry. Two geometrically similar, ducted rotors were tested over a Reynolds number range from 0.7×106 to 9.2×106 in order to determine how the tip-leakage flow varied with Reynolds number. An identification procedure was used to discern and quantify regions of concentrated vorticity in instantaneous flow fields. Multiple vortices were identified in the wake of the blade tip, with the largest vortex being associated with the tip-leakage flow, and the secondary vortices being associated with the trailing edge vortex and other blade-wake vortices. The evolution of identified vortex quantities with downstream distance is examined. It was found that the strength and core size of the vortices are weakly dependent on Reynolds number, but there are indications that they are affected by variations in the inflowing wall boundary layer on the duct. The core size of the tip-leakage vortex does not vary strongly with varying boundary layer thickness on the blades. Instead, its dimension is on the order of the tip clearance. There is significant flow variability for all Reynolds numbers and rotor configurations. Scaled velocity fluctuations near the axis of the primary vortex increase significantly with downstream distance, suggesting the presence of spatially uncorrelated fine scale secondary vortices and the possible existence of three-dimensional vortex-vortex interactions.

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A Simple Leakage Flow Model Including Viscous Effect

Volume 4: Energy Systems Analysis, Thermodynamics and Sustainability; Combustion Science and Engineering; Nanoengineering for Energy, Parts A and B ◽

10.1115/imece2011-63415 ◽

2011 ◽

Author(s):

Yuping Qian ◽

Jian Cui ◽

Chaoqing Chen ◽

Yifang Gong ◽

Qiushi Li

Keyword(s):

Flow Rate ◽

Flow Model ◽

Leakage Flow ◽

Viscous Effect ◽

Tip Leakage Flow ◽

Stall Margin ◽

Factors Affecting ◽

Tip Leakage ◽

Compressor Rotor ◽

Leakage Flow Rate

The tip leakage flow rate can be directly linked to the loss and stall margin. In this paper, key factors affecting the tip leakage flow rate are explained based on a simple leakage flow model including viscous effect. Based on the numerical results, the flow model is verified in a low speed compressor rotor, and finally a simplified one-dimensional tip blockage model is established based on the Khalid’s model, which may be helpful in the design of compressor.

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An Investigation of Tooth Tip Leakages in Gerotor Pumps: Modeling and Experimental Validation

Journal of Verification Validation and Uncertainty Quantification ◽

10.1115/1.4046295 ◽

2020 ◽

Vol 5 (1) ◽

Author(s):

Fnu Rituraj ◽

Andrea Vacca

Keyword(s):

Flow Model ◽

Fuel Injection ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Positive Displacement ◽

Flow Parameters ◽

Gerotor Pumps ◽

Hydrostatic Transmissions ◽

The Impact

Abstract Gerotors are inexpensive positive displacement pumps commonly used in hydrostatic transmissions, fuel injection, and automotive lubrication systems. In these pumps, leakages at the tooth tips of the gears are the major source of volumetric losses that prevents their usage in high pressure applications. However, due to the curvature of typical gear profiles, the flow relations available in the literature do not accurately model this leakage flow. In this paper, a novel tooth tip leakage flow model is developed based on dimensional analysis. Key geometric and flow parameters are identified and a set of computational fluid dynamics (CFD) simulations are conducted on the tooth tip geometry to establish the flow relationship. This relationship is first verified with the analytical formulation derived from Reynolds equation. Then, an experimental setup is designed to reproduce the flow conditions at the tooth tip of gerotors. Experiments are conducted for a range of geometric and flow parameters, and results from the experiments are used to validate the proposed leakage flow model. The tooth tip leakage flow model developed and validated in this work is valuable for pump designers in determining the impact of gear geometry and clearances on volumetric performance of the pump. Moreover, the model can be readily used in any lumped parameter based simulation tool permitting a fast and accurate prediction of the tooth tip leakage flow and hence the volumetric efficiency of the unit.

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