Analytical grid generation and numerical assessment of tip leakage flows in sliding vane rotary machines

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.

Download Full-text

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

Volume 2B: Turbomachinery ◽

10.1115/gt2018-75345 ◽

2018 ◽

Cited By ~ 1

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.

Download Full-text

Aerodynamic Performance of Blade Tip End-Plates Designed for Low-Noise Operation in Axial Flow Fans

Journal of Fluids Engineering ◽

10.1115/1.3026723 ◽

2009 ◽

Vol 131 (8) ◽

Cited By ~ 12

Author(s):

Alessandro Corsini ◽

Franco Rispoli ◽

A. G. Sheard

Keyword(s):

Flow Behavior ◽

Acoustic Emissions ◽

Axial Flow ◽

Low Noise ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Leakage Flows ◽

Blade Tip ◽

Tip Leakage Flows

This study assesses the effectiveness of modified blade-tip configurations in achieving passive noise control in industrial fans. The concepts developed here, which are based on the addition of end-plates at the fan-blade tip, are shown to have a beneficial effect on the fan aeroacoustic signature as a result of the changes they induce in tip-leakage-flow behavior. The aerodynamic merits of the proposed blade-tip concepts are investigated by experimental and computational studies in a fully ducted configuration. The flow mechanisms in the blade-tip region are correlated with the specific end-plate design features, and their role in the creation of overall acoustic emissions is clarified. The tip-leakage flows of the fans are analyzed in terms of vortex structure, chordwise leakage flow, and loading distribution. Rotor losses are also investigated. The modifications to blade-tip geometry are found to have marked effects on the multiple vortex behaviors of leakage flow as a result of changes in the near-wall fluid flow paths on both blade surfaces. The improvements in rotor efficiency are assessed and correlated with the control of tip-leakage flows produced by the modified tip end-plates.

Download Full-text

Broaband Noise Prediction Models And Measurements of Tip Leakage Flows

14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference) ◽

10.2514/6.2008-2845 ◽

2008 ◽

Cited By ~ 2

Author(s):

Julien Grilliat ◽

Marc Jacob ◽

Emmanuel Jondeau ◽

Michel Roger ◽

Roberto Camussi

Keyword(s):

Prediction Models ◽

Noise Prediction ◽

Tip Leakage ◽

Leakage Flows ◽

Tip Leakage Flows

Download Full-text

Blade Tip Shape Optimization for Enhanced Turbine Aerothermal Performance

Volume 3C: Heat Transfer ◽

10.1115/gt2013-94754 ◽

2013 ◽

Cited By ~ 2

Author(s):

C. De Maesschalck ◽

S. Lavagnoli ◽

G. Paniagua

Keyword(s):

Leakage Flow ◽

Optimization Strategy ◽

Flow Conditions ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Leakage Flows ◽

Turbine Efficiency ◽

Gap Flow ◽

Blade Tip ◽

Tip Leakage Flows

In high-speed unshrouded turbines tip leakage flows generate large aerodynamic losses and intense unsteady thermal loads over the rotor blade tip and casing. The stage loading and rotational speeds are steadily increased to achieve higher turbine efficiency, and hence the overtip leakage flow may exceed the transonic regime. However, conventional blade tip geometries are not designed to cope with supersonic tip flow velocities. A great potential lays in the modification and optimization of the blade tip shape as a means to control the tip leakage flow aerodynamics, limit the entropy production in the overtip gap, manage the heat load distribution over the blade tip and improve the turbine efficiency at high stage loading coefficients. The present paper develops an optimization strategy to produce a set of blade tip profiles with enhanced aerothermal performance for a number of tip gap flow conditions. The tip clearance flow was numerically simulated through two-dimensional compressible Reynolds-Averaged Navier-Stokes (RANS) calculations that reproduce an idealized overtip flow along streamlines. A multi-objective optimization tool, based on differential evolution combined with surrogate models (artificial neural networks), was used to obtain optimized 2D tip profiles with reduced aerodynamic losses and minimum heat transfer variations and mean levels over the blade tip and casing. Optimized tip shapes were obtained for relevant tip gap flow conditions in terms of blade thickness to tip gap height ratios (between 5 and 25), and blade pressure loads (from subsonic to supersonic tip leakage flow regimes) imposing fixed inlet conditions. We demonstrated that tip geometries which perform superior in subsonic conditions are not optimal for supersonic tip gap flows. Prime tip profiles exist depending on the tip flow conditions. The numerical study yielded a deeper insight on the physics of tip leakage flows of unshrouded rotors with arbitrary tip shapes, providing the necessary knowledge to guide the design and optimization strategy of a full blade tip surface in a real 3D turbine environment.

Download Full-text

Evaluation of the Interaction Losses in a Transonic Turbine HP Rotor/LP Vane Configuration

Journal of Turbomachinery ◽

10.1115/1.2841012 ◽

1997 ◽

Vol 119 (1) ◽

pp. 68-76 ◽

Cited By ~ 20

Author(s):

I. K. Jennions ◽

J. J. Adamczyk

Keyword(s):

Three Dimensional ◽

Numerical Approach ◽

Secondary Flows ◽

Tip Leakage ◽

Leakage Flows ◽

Trade Offs ◽

Aerodynamic Interaction ◽

Transonic Turbine ◽

Tip Leakage Flows ◽

Made In

Transonic turbine rotors produce shock waves, wakes, tip leakage flows, and other secondary flows that the downstream stators have to ingest. While the physics of wake ingestion and shock interaction have been studied quite extensively, few ideas for reducing the aerodynamic interaction losses have been forthcoming. This paper aims to extend previously reported work performed by GE Aircraft Engines in this area. It reports on both average-passage (steady) and unsteady three-dimensional numerical simulations of a candidate design to shed light on the interaction loss mechanisms and evaluate the design. The results from these simulations are first shown against test data for a baseline configuration to engender confidence in the numerical approach. Simulations with the proposed newly designed rotor are then performed to show the trade-offs that are being made in such designs. The new rotor does improve the overall efficiency of the group and physical explanations are presented based on examining entropy production.

Download Full-text

Performance Evaluation of Pumps in Air and Water

Journal of Engineering for Power ◽

10.1115/1.3609153 ◽

1968 ◽

Vol 90 (2) ◽

pp. 145-148

Author(s):

Glenn M. Wood

Keyword(s):

Reynolds Number ◽

Performance Evaluation ◽

Shaft Speed ◽

Pump Performance ◽

Tip Leakage ◽

Leakage Flows ◽

Significant Difference ◽

Reynolds Number Effects ◽

Tip Leakage Flows ◽

Tip Shroud

To explore the feasibility of establishing pump performance in air, two different designs were tested over the same range of shaft speed and flow rate in both water and air. The larger unit of 3000-gpm capacity was of unshrouded design, whereas the smaller, 195-gpm capacity pump was fabricated with a full tip shroud on the impeller. Although similar trends in performance were observed for each pump tested in air and water, some dissimilarities were observed. In particular, the head rise characteristic curves for both pumps were noticeably higher in air than in water. This is contrary to trends predicted by Reynolds number effects and is apparently due to significant difference in the impeller tip leakage flows when pumping liquid or gas.

Download Full-text

Controlling Leakage Flows Over a Rotor Blade Tip Using Air-Curtain Injection: Part II — Rotor Casing Film Cooling

Volume 5B: Heat Transfer ◽

10.1115/gt2019-90234 ◽

2019 ◽

Cited By ~ 1

Author(s):

Qiang Zhao ◽

Xing Yang ◽

Zhao Liu ◽

Zhenping Feng ◽

Terrence W. Simon

Keyword(s):

Film Cooling ◽

Leading Edge ◽

Cooling Effectiveness ◽

Air Curtain ◽

Film Cooling Effectiveness ◽

Tip Leakage ◽

Leakage Flows ◽

Blade Tip ◽

Tip Injection ◽

Tip Leakage Flows

Abstract In modern gas turbine engines, the rotor casing region experiences high thermal loads due to complex flow structures and aerothermal effects. Thus, casing cooling is one of essential measures to ensure turbine service lifetime and performance. However, studies on heat transfer and cooling over the rotor casing with tip leakage flows are limited in the open literature during the past decades. The present work aims at controlling leakage flows over the blade tip and decreasing heat loads on the rotor casing. A novel approach proposed in a companion paper (GT2019-90232) is adopted in this paper as Part II by introducing an air-curtain injection from the rotor casing through a pair of inclined rows of discrete holes positioned in the range of 30% and 50% axial chord downstream of the blade leading edge in the casing. This air-curtain injection approach is applied to flat and recessed tips with and without tip injection to evaluate its sealing capability on tip leakage flows and film cooling effectiveness on the casing for two injection ratios of 0.7% and 1.0%. In this paper, Reynolds-averaged Navier-Stokes (RANS) simulations with Shear Stress Transport (SST) k-ω turbulence model and γ-Reθ transition model, which are validated with relevant experimental data, are performed to investigate tip leakage flows and film cooling effectiveness on the casing in a single-stage, high-pressure gas turbine engine. Results show that casing injection can reduce tip leakage mass flow effectively by changing the development and migration of tip leakage mass flows, especially when the recessed tip is applied. Adding tip injection would further reduces the tip leakage. The casing injection also provides an excellent cooling effect on the casing across rotor middle chord through trailing edge regions. In the presence of the recessed tip, coolant spreads out well on the rotor tip and the casing surfaces, resulting in better film cooling effectiveness on the casing over rotor tip leading edge. In addition, the tip injection could provide an extra cooling effect in some other regions of the casing.

Download Full-text