scholarly journals A Simulation of Secondary Flow in Centrifugal Impeller Channel by a Stationary Three-Dimensional Curved Duct

1992 ◽  
Author(s):  
Shimpei Mizuki ◽  
Hoshio Tsujita
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Flow Patterns ◽  
Centrifugal Impeller ◽  
Meridional Plane ◽  
Blade Surface ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Qualitative Similarity

A duct with three-dimensional curvatures was employed in order to investigate the complex secondary flow patterns similar to those within centrifugal impellers. The curvature within a pair of co-cylindrical surfaces of the duct simulates that within the meridional plane of an impeller, and the curvature within the other pair of co-cylindrical surfaces perpendicular to the above-mentioned surfaces simulates the effect of the Coriolis force within the blade-to-blade surface. The computed and the measured results showed the qualitative similarity of the secondary flow patterns to those within centrifugal impellers except the effects of pressure rise by the centrifugal force generated by the impeller rotation and the tip leakage flow.

scholarly journals Analysis of Flow Within Pump Impeller of Torque Converter

1996 ◽  
Author(s):  
Hoshio Tsujita ◽  
Shimpei Mizuki ◽  
Eiji Ejiri
Keyword(s):  
Coordinate System ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Internal Flow ◽  
Torque Converter ◽  
Flow Patterns ◽  
Speed Ratio ◽  
Meridional Plane ◽  
Pump Impeller ◽  
Simple Method

It is difficult to measure flow patterns within rotating elements of a torque converter due to the complicated construction. Therefore, the numerical calculation is considered to be an effective tool to know the internal flow. Three-dimensional incompressible turbulent flow within a pump impeller of an automotive torque converter was analyzed numerically at three different speed ratios, 0.02, 0.4 and 0.8 under the same inlet boundary condition. The speed ratio was defined as the ratio of rotating speed of the turbine impeller to that of the pump. The governing equations using the k-ε model in the physical component tensor form were solved with a boundary-fitted coordinate system fixed on a rotating impeller. The solution algorithm was the SIMPLE method applied to the curvilinear coordinate system. The computed results were compared with those obtained experimentally by an oil film flow visualization technique for the pressure, suction, core and shell surfaces. Moreover, the results at three different speed ratios were examined in detail in order to clarify the behavior of secondary flow patterns. The computed results showed good agreement with the experimental results and clarified the behavior of the complicated flow patterns. The secondary flow patterns were strongly influenced by the correlation between the intensities of the Corinlis force (COF) and the centrifugal force due to the passage curvature in the meridional plane (CMF).

Role of Tip Leakage in Stall of a Transonic Centrifugal Impeller

2009 ◽  
Author(s):  
Hamid R. Hazby ◽  
Liping Xu
Keyword(s):  
Total Pressure ◽  
Three Dimensional ◽  
Adverse Pressure Gradient ◽  
Operating Conditions ◽  
Centrifugal Impeller ◽  
Stable Operation ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Flow Features ◽  
Blade Tip

The objective of the current paper is to employ numerical simulations to identify flow features, which could lead to the breakdown of stable operation in transonic centrifugal impellers at near-stall operating conditions. Steady state three-dimensional viscous flow calculations are used to investigate the flow inside a transonic impeller representative of state of the art automotive turbocharger technology. The detailed impeller flow field is compared at different operating conditions. It is observed that the interaction of the relative total pressure deficit coming from the main blade tip region and the adverse pressure gradient in the splitter passage results in a breakdown of the flow in the tip region. These low relative total pressure fluids originate from the main blade tip leakage flow and/or the transported boundary layers. Effects due to the splitter wall shear stress and the turbulence model on the flow are also investigated and addressed in the paper.

Impeller-Diffuser Interaction in Centrifugal Compressor

2000 ◽  
Author(s):  
Y. K. P. Shum ◽  
C. S. Tan ◽  
N. A. Cumpsty
Keyword(s):  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Potential Effect ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Beneficial Effects ◽  
Radial Gap

A study has been conducted, using an unsteady three-dimensional Reynolds-averaged Navier-Stokes simulation, to define the effect of impeller-diffuser interaction on the performance of a centrifugal compressor stage. The principal finding from the study was that the most influential aspect of this unsteady interaction was the effect on impeller tip leakage flow. In particular, the unsteadiness due to the upstream potential effect of the diffuser vanes led to larger viscous losses associated with the impeller tip leakage flow. The consequent changes at the impeller exit with increasing interaction were identified as reduced slip, reduced blockage, and increased loss. The first two were beneficial to pressure rise while the third one was detrimental. The magnitudes of the effects were examined using different impeller-diffuser spacings and it was shown that there was an optimal radial gap size for maximum impeller pressure rise. The physical mechanism was also determined: when the diffuser was placed closer to the impeller than the optimum, increased loss overcame the benefits of reduced slip and blockage. The findings provide a rigorous explanation for experimental observations made on centrifugal compressors. The success of a simple flow model in capturing the pressure rise trend indicated that although the changes in loss, blockage and slip were due largely to unsteadiness, the consequent impacts on performance were mainly one-dimensional. The influence of flow unsteadiness on diffuser performance was found to be less important than the upstream effect, by a factor of seven in terms of stage pressure rise in the present geometry. It is thus concluded that the beneficial effects of impeller-diffuser interaction on overall stage performance come mainly from the reduced blockage and reduced slip associated with the unsteady tip leakage flow in the impeller.

Rotor-Tip Flow Fields Near Inception Point of Modal Disturbance in an Axial-Flow Fan

2010 ◽  
Author(s):  
Takahiro Nishioka ◽  
Toshio Kanno ◽  
Hiroshi Hayami
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Flow Fields ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Flow Fan ◽  
Stall Inception ◽  
Tip Leakage

The rotor-tip flow fields in two rotors of a low-speed axial-flow fan were experimentally and numerically investigated to clarify the mechanism behind modal stall inception. A NACA 65 wing section and a controlled diffusion airfoil were applied to the two rotors. At the small stagger-angle setting for both rotors, which is ten degrees smaller than the design value, the modal disturbance is observed near the peak pressure-rise point, and the rotor blades at the tip stall before the modal disturbance is observed. In the modal stall inception, the interface between the incoming flow and the reversed tip-leakage flow does not become parallel to the leading edge plane, although backflow from the trailing edge initiates near the stall condition. The reversed tip-leakage flow does not spill from the leading edge at the stall condition. Moreover, the tip-leakage vortex breakdown does not occur near or at the stall condition. A three-dimensional separation vortex is induced by secondary flow on the suction surface near the stall condition and develops at the stall condition. It is concluded from these results that the rotor-tip flow fields in the modal stall inception differ from those in the spike stall inception and that the three-dimensional separation vortex induced by the secondary flow influences the initiation of modal disturbance.

Impeller–Diffuser Interaction in a Centrifugal Compressor

2000 ◽  
Vol 122 (4) ◽  
pp. 777-786 ◽  
Author(s):  
Y. K. P. Shum ◽  
C. S. Tan ◽  
N. A. Cumpsty
Keyword(s):  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Potential Effect ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Beneficial Effects ◽  
Radial Gap

A study has been conducted, using an unsteady three-dimensional Reynolds-averaged Navier–Stokes simulation, to define the effect of impeller–diffuser interaction on the performance of a centrifugal compressor stage. The principal finding from the study was that the most influential aspect of this unsteady interaction was the effect on impeller tip leakage flow. In particular, the unsteadiness due to the upstream potential effect of the diffuser vanes led to larger viscous losses associated with the impeller tip leakage flow. The consequent changes at the impeller exit with increasing interaction were identified as reduced slip, reduced blockage, and increased loss. The first two were beneficial to pressure rise, while the third was detrimental. The magnitudes of the effects were examined using different impeller–diffuser spacings and it was shown that there was an optimal radial gap size for maximum impeller pressure rise. The physical mechanism was also determined: When the diffuser was placed closer to the impeller than the optimum, increased loss overcame the benefits of reduced slip and blockage. The findings provide a rigorous explanation for experimental observations made on centrifugal compressors. The success of a simple flow model in capturing the pressure rise trend indicated that although the changes in loss, blockage, and slip were due largely to unsteadiness, the consequent impacts on performance were mainly one-dimensional. The influence of flow unsteadiness on diffuser performance was found to be less important than the upstream effect, by a factor of seven in terms of stage pressure rise in the present geometry. It is thus concluded that the beneficial effects of impeller–diffuser interaction on overall stage performance come mainly from the reduced blockage and reduced slip associated with the unsteady tip leakage flow in the impeller. [S0889-504X(00)01704-9]

Flow Structures in the Tip Region for a Transonic Compressor Rotor

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Juan Du ◽  
Feng Lin ◽  
Jingyi Chen ◽  
Chaoqun Nie ◽  
Christoph Biela
Keyword(s):  
Numerical Simulations ◽  
Reference Frame ◽  
Three Dimensional ◽  
Flow Structures ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Three Dimensional Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Tip Leakage Flows

Numerical simulations are carried out to investigate flow structures in the tip region for an axial transonic rotor, with careful comparisons with the experimental results. The calculated performance curve and two-dimensional (2D) flow structures observed at casing, such as the shock wave, the expansion wave around the leading edge, and the tip leakage flow at peak efficiency and near-stall points, are all captured by simulation results, which agree with the experimental data well. An in-depth analysis of three-dimensional flow structures reveals three features: (1) there exists an interface between the incoming main flow and the tip leakage flow, (2) in this rotor the tip leakage flows along the blade chord can be divided into at least two parts according to the blade loading distribution, and (3) each part plays a different role on the stall inception mechanism in the leakage flow dominated region. A model of three-dimensional flow structures of tip leakage flow is thus proposed accordingly. In the second half of this paper, the unsteady features of the tip leakage flows, which emerge at the operating points close to stall, are presented and validated with experiment observations. The numerical results in the rotor relative reference frame are first converted to the casing absolute reference frame before compared with the measurements in experiments. It is found that the main frequency components of simulation at absolute reference frame match well with those measured in the experiments. The mechanism of the unsteadiness and its significance to stability enhancement design are then discussed based on the details of the flow field obtained through numerical simulations.

The Aerothermal Performance of a Cooled Winglet Tip in a High Pressure Turbine Cascade

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson ◽  
Ian Tibbott ◽  
Mark Stokes
Keyword(s):  
Mass Flow ◽  
Heat Load ◽  
Blade Surface ◽  
Flow Ratio ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Cooling Effectiveness ◽  
Tip Leakage ◽  
Coolant Injection

The aerothermal performance of a winglet tip with cooling holes on the tip and on the blade surface near the tip is reported in this paper. The investigation was based on a high pressure turbine cascade. Experimental and numerical methods were used. The effects of the coolant mass flow rate are also studied. Because the coolant injection partially blocks the tip leakage flow, more passage flow is turned by the blade. As a result, the coolant injection on the winglet tip reduces the deviation of the flow downstream of the cascade due to the tip leakage flow. However, the tip leakage loss increases slightly with the coolant mass flow ratio. Both the computational fluid dynamics tools and experiments using the Amonia–Diazo technique were used to determine the cooling effectiveness. On the blade pressure side surface, low cooling effectiveness appears around the holes due to the lack of the coolant from the cooling hole or the lift-off of the coolant from the blade surface when the coolant mass flow is high. The cooling effectiveness on the winglet tip is a combined effect of the coolant ejected from all the holes. On the top of the winglet tip, the average cooling effectiveness increases and the heat load decreases with increasing coolant mass flow. Due to its large area, the cooled winglet tip has a higher heat load than an uncooled flat tip at engine representative coolant mass flow ratio. Nevertheless, the heat flux rate per unit area of the winglet is much lower than that of an uncooled flat tip. The cycle analysis is carried out and the effects of relative tip-to-casing endwall motion are address.

Tip Leakage Flow Characteristics Downstream of an Axial Flow Fan

1996 ◽  
Author(s):  
P. Puddu
Keyword(s):  
Vortex Flow ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Tip Leakage Flow ◽  
Single Wire ◽  
Vortex System ◽  
Tip Leakage ◽  
Stress Components ◽  
Computer Controlled

The three-dimensional viscous flow characteristics and the complex vortex system downstream of the rotor of an industrial exial fan have been determined by an experimental investigation using hot-wire anemometer. Single-wire slanted and straight type probes have been rotated about the probe axis using a computer controlled stepper motor. Measurements have been taken at four planes behind the blade trailing edge. The results show the characteristics of the relative flow as velocity components, secondary flow and kinetic energy defect. Turbulence intensity and Reynolds stress components in the leakage vortex area are also presented. The evolution of the leakage vortex flow during the decay process has also been evaluated in terms of dimension, position and intensity.

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.

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