Effects of tip clearance size on vortical structures and turbulence statistics in tip-leakage flows: A direct numerical simulation study

2021 ◽  
Vol 33 (8) ◽  
pp. 085127
Author(s):  
Wenqiang Shang ◽  
Dong Li ◽  
Kun Luo ◽  
Jianren Fan ◽  
Jianhua Liu
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Simulation Study ◽  
Tip Clearance ◽  
Turbulence Statistics ◽  
Vortical Structures ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Tip Leakage Flows

Influences of Tip Leakage Flows Discharged From Main and Splitter Blades on Flow Field in Transonic Centrifugal Compressor Stage

2018 ◽  
Author(s):  
Masanao Kaneko ◽  
Hoshio Tsujita
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Blade Loading ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Transonic Centrifugal Compressor ◽  
Tip Leakage Flows

A transonic centrifugal compressor impeller is generally composed of the main and the splitter blades which are different in chord length. As a result, the tip leakage flows from the main and the splitter blades interact with each other and then complicate the flow field in the compressor. In this study, in order to clarify the individual influences of these leakage flows on the flow field in the transonic centrifugal compressor stage at near-choke to near-stall condition, the flows in the compressor at four conditions prescribed by the presence and the absence of the tip clearances were analyzed numerically. The computed results clarified the following noticeable phenomena. The tip clearance of the main blade induces the tip leakage vortex from the leading edge of the main blade. This vortex decreases the blade loading of the main blade to the negative value by the increase of the flow acceleration along the suction surface of the splitter blade, and consequently induces the tip leakage vortex caused by the negative blade loading of the main blade at any operating points. These phenomena decline the impeller efficiency. On the other hand, the tip clearance of the splitter blade decreases the afore mentioned acceleration by the formation of the tip leakage vortex from the leading edge of the splitter blade and the decrease of the incidence angle for the splitter blade caused by the suction of the flow into the tip clearance. These phenomena reduce the loss generated by the negative blade loading of the main blade and consequently reduce the decline of the impeller efficiency. Moreover, the tip clearances enlarge the flow separation around the diffuser inlet and then decline the diffuser performance independently of the operating points.

Investigation Into Core Compressor Tip Leakage Modelling Techniques Using a 3D Viscous Solver

2001 ◽  
Author(s):  
Jonathan P. Glanville
Keyword(s):  
Transport Model ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Modelling Techniques ◽  
Flow Through ◽  
Tip Leakage Flows

The leakage flow through the tip clearance gap of an axial compressor has a significant effect on loss production and stall behaviour. Accurate modelling is essential if improved designs are to be developed which control such flows. Studies have been carried out using the DERA TRANSCode 3D Reynolds-Averaged Navier-Stokes code to predict the tip leakage flows in a low speed research compressor. Calculations were carried out using both a simple pinched-tip model and an improved mesh which allowed the true square-tip geometry to be represented. Comparisons between the Baldwin-Lomax algebraic turbulence model and the Spalart-Allmaras one-equation transport model were also made. The results showed that the predictions of both the detailed flows and the loss levels were sensitive to the modelling and that substantial improvements in accuracy were possible.

scholarly journals Shock Formation in Overexpanded Tip Leakage Flow

1992 ◽  
Author(s):  
John Moore ◽  
Kevin M. Elward
Keyword(s):  
Rectangular Channel ◽  
Tip Clearance ◽  
Gas Flows ◽  
Shock Formation ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Hydraulic Analogy ◽  
Tip Leakage Flows ◽  
Turbine Design

Shock formation due to overexpansion of supersonic flow at the inlet to the tip clearance gap of a turbomachine has been studied. The flow was modelled on a water table using a sharp-edged rectangular channel. The flow exhibited an oblique hydraulic jump starting on the channel sidewall near the channel entrance. This flow was analyzed using hydraulic theory. The results suggest a model for the formation of the jump. The hydraulic analogy between free surface water flows and compressible gas flows is used to predict the location and strength of oblique shocks in analogous tip leakage flows. Features of the flow development are found to be similar to those of compressible flow in sharp-edged orifices. Possible implications of the results for high-temperature gas turbine design are considered.

An Experimental and Numerical Study of Tip-Leakage Flows in an Idealized Turbine Tip Gap at High Mach Numbers

2018 ◽  
Author(s):  
Maximilian Passmann ◽  
Stefan aus der Wiesche ◽  
Franz Joos
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Blow Down ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Mach Numbers ◽  
High Mach ◽  
Tip Leakage Flows

This paper presents results of a detailed investigation of turbine tip-leakage flows at high Mach numbers. The experimental work was carried out using a small blow-down wind tunnel. An idealized blade test section was used to study blade tip-clearance effects in transonic conditions. Unshrouded blade tips are considered and different tip gap heights are investigated. A high blade exit Mach number of Me = 2 was selected deliberately. While conventional transonic turbine stages generally operate at lower supersonic exit Mach numbers, the conditions are representative for ORC turbines. Both experimental and numerical results are presented in this contribution. The results indicate, that tip leakage flow under transonic conditions leads to a complex three-dimensional flow field. A strong interaction between tip gap vortex and trailing edge shocks was observed, that also had a profound effect on the base region. While no final statement on losses could be made in the present configuration, the results indicate a weakened shock system.

Characteristics of Tip-Clearance Flows of a Compressor Cascade and a Propulsion Pump

1997 ◽  
Author(s):  
Y. T. Lee ◽  
M. J. Laurita ◽  
J. Feng ◽  
C. L. Merkle
Keyword(s):  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Blade Passage ◽  
Tip Leakage ◽  
Pump Rotor ◽  
Leakage Flows ◽  
Tip Leakage Flows

Tip-leakage flows for a linear compressor cascade and a one-stage shrouded pump rotor are discussed in this paper. A numerical method solving the Reynolds averaged Navier Stokes equations is used to explore various detail features of the tip-leakage flows. Calculation results for the cascade provide an assessment for predicting flow past a non-rotating blade passage with zero and 2% chord clearances. On the other hand, the pump rotor configuration provides a swirling passage flow with the complication of a trailing-edge separation vortex mixed with the tip-clearance and passage vortices and produces a very complex three-dimensional flow in the rotor wake. The physical aspects of the tip-clearance flows are discussed including suction-side reloading and pressure-side unloading due to a tip clearance and formation and transportation of the tip-leakage vortex. Detailed velocity comparisons in the blade passage and the tip gap region are shown to indicate the difficulty of predicting tip-leakage flow. The pressure at the core of the tip vortex is also examined to evaluate the strength of the tip-leakage vortex. Some computational guidelines for design usage are provided for these tip-leakage flow calculations.

scholarly journals Focusing Schlieren Visualization of Transonic Turbine Tip-Leakage Flows

2020 ◽  
Vol 5 (1) ◽  
pp. 1
Author(s):  
Maximilian Passmann ◽  
Stefan aus der Wiesche ◽  
Franz Joos
Keyword(s):  
Suction Side ◽  
Tip Clearance ◽  
Depth Of Focus ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Schlieren System ◽  
Shock System ◽  
Transonic Turbine ◽  
Tip Leakage Flows

This paper presents a focusing schlieren system designed for the investigation of transonic turbine tip-leakage flows. In the first part, the functional principle and the design of the system are presented. Major design considerations and necessary trade-offs are discussed. The key optical properties, e.g., depth of focus, are verified by means of a simple bench test. In the second part, results of an idealized tip-clearance model as well as linear cascade tests at engine representative Reynolds and Mach numbers are presented and discussed. The focusing schlieren system, designed for minimum depth of focus, has been found to be well suited for the investigation of three-dimensional transonic flow fields in turbomachinery applications. The schlieren images show the origin and growth of the tip-leakage vortex on the blade suction side. A complex shock system was observed in the tip region, and the tip-leakage vortex was found to interact with the suction side part of the trailing edge shock system. The results indicate that transonic vortex shedding is suppressed in the tip region at an exit Mach number around M 2 , i s = 0.8.

Shock Formation in Overexpanded Tip Leakage Flow

1993 ◽  
Vol 115 (3) ◽  
pp. 392-399 ◽  
Author(s):  
J. Moore ◽  
K. M. Elward
Keyword(s):  
Rectangular Channel ◽  
Tip Clearance ◽  
Gas Flows ◽  
Shock Formation ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Hydraulic Analogy ◽  
Tip Leakage Flows ◽  
Turbine Design

Shock formation due to overexpansion of supersonic flow at the inlet to the tip clearance gap of a turbomachine has been studied. The flow was modeled on a water table using a sharp-edged rectangular channel. The flow exhibited an oblique hydraulic jump starting on the channel sidewall near the channel entrance. This flow was analyzed using hydraulic theory. The results suggest a model for the formation of the jump. The hydraulic analogy between free surface water flows and compressible gas flows is used to predict the location and strength of oblique shocks in analogous tip leakage flows. Features of the flow development are found to be similar to those of compressible flow in sharp-edged orifices. Possible implications of the results for high-temperature gas turbine design are considered.

Numerical Investigation on the Originating Mechanism of Unsteadiness in Tip Leakage Flow for a Transonic Fan Rotor

2008 ◽  
Author(s):  
Juan Du ◽  
Feng Lin ◽  
Hongwu Zhang ◽  
Jingyi Chen
Keyword(s):  
Computational Model ◽  
Numerical Investigation ◽  
Main Flow ◽  
Tip Clearance ◽  
The Self ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Tip Leakage Flows

Despite the fact that the importance of steady tip leakage flows in rotor efficiency and stability has been long recognized and extensively studied, the unsteadiness of tip leakage flows became an interesting research topic only about 10 years ago. Many issues, such as its onset conditions, its role in compressor instability, etc. need to be further explored. In this paper, we present a numerical investigation on the influences of two important driving “forces”, the incoming main flow and the tip leakage flow, to clarify the originating mechanism of self-induced unsteadiness in transonic compressors. NASA Rotor 67 is chosen as the computational model. It is found that among all the simulated cases, the self-induced unsteadiness exists when the size of the tip clearance equals or larger than design tip clearance of the computational model. The time-dependent flow pattern in the rotor tip region is provided to illustrate that the main unsteady regions are on the blade’s pressure side that happens to be under the alternate influence of tip leakage flow and the incoming main flow. It is found the self-induced unsteady mechanism in the transonic rotor is the same as that in previously studied low-speed rotor. The interaction between shock wave and tip leakage vortex does not initiate the self-induced unsteadiness, but might be the cause of other unsteadiness, such as turbulent unsteadiness. A correlation based on the momentum ratio of tip leakage flow over the main incoming flow at the tip region is used as an indicator for the onset of the self-induced unsteadiness in tip leakage flow.

Blade Lean and Tip Leakage Flows in Highly Loaded Compressor Cascades

2021 ◽  
Vol 30 (4) ◽  
pp. 1388-1405
Author(s):  
Zhiyuan Cao ◽  
Cheng Song ◽  
Xiang Zhang ◽  
Xi Gao ◽  
Bo Liu
Keyword(s):  
Tip Leakage ◽  
Leakage Flows ◽  
Tip Leakage Flows ◽  
Highly Loaded
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