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

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.

Modelling and Validation of Tooth Tip Leakages in Gerotor Pumps

2019 ◽  
Author(s):  
Fnu Rituraj ◽  
Andrea Vacca
Keyword(s):  
Fuel Injection ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Charge Pumps ◽  
Tip Leakage ◽  
Flow Parameters ◽  
Lumped Parameter ◽  
Gerotor Pumps ◽  
Analytical Relations ◽  
The Impact

Abstract Gerotor pumps are commonly used as charge pumps in hydrostatic transmission systems as well as in fuel injection and automotive lubrication systems. For high pressure applications, Gerotors suffer from internal leakages which are one of the main sources of volumetric loss. The curvature of typical gear profiles for Gerotors prevents the usage of simple analytical relations to describe this leakage flow. In this paper, a non-dimensional functional relationship is developed between geometric and flow parameters to model this leakage flow. A set of CFD simulations are conducted on the tooth tip geometry to establish this relationship. Then, an experimental setup is designed to reproduce the flow conditions at tooth tip of Gerotor. Experiments are conducted for a range of geometric and flow parameters and results from experiments are used to validate the proposed non-dimensional model. The tooth tip leakage 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.

Prediction of Tip Leakage Vortex Dynamics in an Axial Compressor Cascade Using RANS Analyses

2020 ◽  
Author(s):  
Martina Ricci ◽  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Andrea Arnone
Keyword(s):  
Vortex Dynamics ◽  
Eddy Viscosity ◽  
Axial Compressor ◽  
Viscosity Model ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Eddy Viscosity Model ◽  
The Impact

Abstract The tip leakage flow in turbine and compressor blade rows is responsible for a relevant fraction of the total loss. It contributes to unsteadiness, and have an important impact on the operability range of compressor stages. Experimental investigations and, more recently, scale-resolving CFD approaches have helped in clarifying the flow mechanism determining the dynamics of the tip leakage vortex. Due to their continuing fundamental role in design verifications, it is important to establish whether RANS/URANS approaches are able to reproduce the effects of such a flow feature, in order to correctly drive the design of the next generation of turbomachinery. Base studies are needed in order to accomplish this goal. In the present work the tip leakage flow in axial compressor rotor blade cascade have been studied. The cascade was tested experimentally in Virginia Tech Low Speed Cascade Wind Tunnel in both stationary and moving endwall configurations. Numerical analyses were performed using the TRAF code, a state-of-the-art in-house-developed 3D RANS/URANS flow solver. The impact of the numerical framework was investigated selecting different advection schemes including a central scheme with artificial dissipation and a high-resolution upwind strategy. In addition, two turbulence models have been used, the Wilcox linear k–ω model and a non-linear eddy viscosity model (Realizable Quadratic Eddy Viscosity Model), which accounts for turbulence anisotropy. The numerical results are scrutinized using the available measurements. A detailed discussion of the vortex evolution inside the blade passage and downstream of the blade trailing edge is presented in terms of streamwise velocity, streamwise vorticity, and turbulent kinetic energy contours. The purpose is to identify guidelines for obtaining the best representation of the vortex dynamics, with the methodologies usually employed in routine design iterations and, at the same time, evidence their weak aspects that need further modelling efforts.

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

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.

Numerical analysis of the effects of circumferential groove casing suction in a counter-rotating axial flow compressor

2020 ◽  
pp. 095765092095169
Author(s):  
Tian Liang ◽  
Bo Liu ◽  
Stephen Spence ◽  
Liying Jiao
Keyword(s):  
Axial Flow ◽  
Main Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Circumferential Groove ◽  
Flow Compressor ◽  
The Impact

To extend the current understanding of the circumferential groove casing suction applied to a counter-rotating axial flow compressor, the impact of different axial locations of the circumferential suction groove on the characteristics of the tip leakage flow (TLF) and the corresponding physical mechanisms producing the stability enhancement have been studied based on validated numerical simulations. The results show that the optimal location for the suction groove is at around 20% axial chord, which demonstrated a high potential for reducing additional stall mass flow coefficient with about 8.4% increment in the stall margin. After the casing suction groove was applied, the interface between the incoming main flow and TLF was pushed significantly downstream in the second rotor. The blade loading in the region below the groove, the tip leakage flow angle and the reversed axial momentum flux injected into main flow passage through the tip gap were all reduced, which contributed to the stall margin improvement. Detailed analysis of the tip leakage flow structures showed that the TLF originating from different chord locations played different roles in the stall inception process. It was found to be more effective to improve stall margin and adiabatic efficiency by controlling the front part of the TLF, which was most sensitive.

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

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.

Impact of Passive Tip-Injection on Tip-Leakage Flow in Axial Low Pressure Turbine Stage

2015 ◽  
Author(s):  
Pouya Ghaffari ◽  
Reinhard Willinger ◽  
Sabine Bauinger ◽  
Andreas Marn
Keyword(s):  
Aerodynamic Resistance ◽  
Low Pressure ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Low Pressure Turbine ◽  
Blade Tip ◽  
Tip Injection ◽  
The Impact

In addition to geometrical modifications of the blade tip for reducing tip-leakage mass flow rate the method of passive tip-injection serves as an aerodynamic resistance towards the tip-leakage flow. The impact of this method has been investigated thoroughly at unshrouded blades in linear cascades. Furthermore combinations of shrouded blades with passive tip-injection have been investigated analytically as well as via numerical simulations for incompressible flow in linear cascades. The objective of this paper is to consider a real uncooled low pressure turbine stage with shrouded blades and to investigate the effect of passive tip-injection on various operational characteristics. CFD calculations have been carried out in a rotational frame taking into consideration compressible flow and serve for evaluating the method of passive tip-injection in the given turbine stage. Experimental data obtained from the machine without tip-injection serve as boundary conditions for the CFD calculations.

A Numerical Investigation of the Flow Mechanisms in a HPC Front Stage With Axial Slots

2003 ◽  
Author(s):  
I. Wilke ◽  
H.-P. Kau
Keyword(s):  
Rotor Blade ◽  
Flow Stability ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Blade Passage ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Front Stage ◽  
The Impact ◽  
Compressor Efficiency

This paper describes the impact of axial slots on the flow field in a transonic rotor blade row. The presented results are completely based on time-accurate 3-dimensional numerical simulations of a high pressure compressor front stage with and without casing treatment. Two different axial positions of a casing treatment consisting of axial slots were tested for their impact on flow stability and efficiency. The first tested position (configuration 1) was chosen in a conventional way. The slots extend approximately from the leading up to the trailing edge of the rotor blades. As expected, the simulations of the compressor stage with this configuration showed a significant increase in flow stability near surge compared to the solid wall case. However, a non negligible decrease in efficiency is also observed. Analyses of flow interactions between casing treatment and rotor blade rows under transonic conditions lead to the general conclusion that the stabilizing effect of circumferential grooves or axial slots mainly results from their impact on the tip leakage flow and its resulting vortex. A characteristic vortex inside the slots is observed in the simulations with the conventionally positioned casing treatment. This vortex removes fluid out of downstream parts of the blade passage and feeds it back into the main flow further upstream. The resulting impact on the tip leakage flow is responsible for the increased flow stability. However, the interaction between the configuration 1 casing treatment flow and the blade passage flow results in a significant relocation of the blade passage shock in the downstream direction. This explains the observed decrease in compressor efficiency. A second slot position (configuration 2) was tested with the objective to improve compressor efficiency. The casing treatment was shifted upstream, so that only 25% of the blade chord remained under the slots. The simulations carried out demonstrate that this shift positively effects the resulting efficiency, but maintains the increased level of flow stability. A time-accurate analysis of the flow shows clearly that the modified casing treatment stabilizes the tip leakage vortex and reduces the influence on the flow inside the blade passage.

A Simple Leakage Flow Model Including Viscous Effect

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.

Numerical investigation of tip clearance size effect on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor

2017 ◽  
Vol 231 (3) ◽  
pp. 474-484 ◽  
Author(s):  
Xiaochen Mao ◽  
Bo Liu
Keyword(s):  
Size Effect ◽  
Axial Compressor ◽  
Size Variation ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Remarkable Effect ◽  
Tip Leakage ◽  
Dual Stage ◽  
The Impact

Based on a validation of the numerical methods with an experiment, numerical simulations are carried out to study the effect of tip clearance size on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor. The predicted results showed that the variation of the tip clearance size in rotor2 has a more significant impact on the overall performance and stall margin of the compressor. In addition, the impact of the tip clearance size effect is mainly on the rotor with the tip clearance size variation. The variation of the tip clearance size in rotor2 almost has no influence on the performance of rotor1, while the performance of rotor2 is increased about 1.37% at near-stall point when the tip clearance size of rotor1 is increased to 1.0 mm from 0.5 mm. At peak efficiency condition, the tip clearance size variation in rotor1 has remarkable influence on the tip leakage vortex intensity, onset point and trajectory in rotor1, but has little influence on those in rotor2. However, the tip clearance size variation in rotor2 has remarkable effect on those in both rotors. Different tip clearance size combination schemes can impact the stall-free characteristic in the counter-rotating axial compressor.

On the Interactions of a Rotor Blade Tip Flow With Axial Casing Grooves in an Axial Compressor Near the Best Efficiency Point

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
Joseph Katz
Keyword(s):  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Maximum Efficiency ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Angle ◽  
Tip Leakage ◽  
Blade Tip ◽  
The Impact

Experiments in a refractive index-matched axial turbomachine facility show that semicircular skewed axial casing grooves (ACGs) reduce the stall flowrate by 40% but cause a 2.4% decrease in the maximum efficiency. Aiming to elucidate mechanism that might cause the reduced efficiency, stereo-PIV measurements examine the impact of the ACGs on the flow structure and turbulence in the tip region near the best efficiency point (BEP), and compare them to those occurring without grooves and at low flowrates. Results show that the periodic inflow into the groove peaks when the rotor blade pressure side (PS) overlaps with the downstream end of the groove, but diminishes when this end faces the suction side (SS). Entrainment of the PS boundary layer and its vorticity generates a vortical loop at the entrance to the groove, and a “discontinuity” in the tip leakage vortex (TLV) trajectory. During exposure to the SS, the backward tip leakage flow separates at the entrance to the groove, generating a counter-rotating circumferential “corner vortex,” which the TLV entrains into the passage at high flowrates. Interactions among these structures enlarge the TLV and create a broad area with secondary flows and elevated turbulence near the groove's downstream corner. A growing shear layer with weaker turbulence also originates from the upstream corner. The groove also increases the flow angle upstream of the blade tip and varies it periodically. Accordingly, the circulation shed from the blade tip and strength of leakage flow increase near the blade leading edge (LE).

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