Tip Leakage in Small Radial Turbines: Optimum Tip-Gap and Efficiency Loss Correlations

2010 ◽  
Author(s):  
Jasper Kammeyer ◽  
Christoph Natkaniec ◽  
Joerg R. Seume
Keyword(s):  
Internal Combustion Engines ◽  
Operating Conditions ◽  
Test Facility ◽  
Leakage Flow ◽  
Combustion Engines ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Flow Mechanisms ◽  
Radial Turbines

The tip-leakage flow mechanisms in turbocharger turbines used for downsized internal combustion engines and the associated losses are investigated over a range of operating conditions. Experiments are performed on a small, 35 mm diameter turbocharger turbine with varying tip-gap heights in a turbocharger test facility and numerical simulations are presented for extending the parameter range to sizes not covered experimentally. The sensitivity of turbine efficiency to tip-gap is evaluated and correlations for the estimation of tip-leakage related loss of efficiency are developed. An optimum applicable tip-gap size for radial turbines is suggested. The results show that the magnitude of the tip-leakage losses, e.g. in downsizing turbocharger turbines, provides a high potential for their improvement.

Controlling Tip Leakage Flow Over a Shrouded Turbine Rotor Using an Air-Curtain

2009 ◽  
Author(s):  
Eric M. Curtis ◽  
John D. Denton ◽  
John P. Longley ◽  
Budimir Rosic
Keyword(s):  
Axial Direction ◽  
Turbine Rotor ◽  
Test Facility ◽  
Jet Flows ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Air Curtain ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Air Turbine

This paper describes an experimental and computational investigation into the performance of an air-curtain seal used to control the leakage flow over the tip shroud of a turbine rotor. The results show that a seal of this type has the potential to reduce or eliminate shroud leakage whilst having a practical level of clearance between the stationary and moving components. The experimental measurements were undertaken using a single-stage low-speed air turbine equipped with a continuous circumferential nozzle in the casing to deliver an axisymmetric jet into the cavity over the rotor shroud. The jet was angled at 45° to the axial direction so that its momentum opposed the shroud leakage flow. In this arrangement the air-curtain was able to sustain the pressure difference between the inlet and outlet of the rotor blade row without any leakage. The test facility had comprehensive instrumentation for obtaining accurate measurements of turbine efficiency that were corrected for the externally supplied additional flow required for the air-curtain. Measurements were obtained for a range of jet flows and show the change in the turbine efficiency as the jet flow is increased. The measurements have been compared with calculations.

The Effect of the Operating Conditions of the Last Turbine Stage on the Performance of an Axial Exhaust Diffuser

2011 ◽  
Author(s):  
Victor Opilat ◽  
Joerg R. Seume
Keyword(s):  
Gas Turbines ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Pressure Recovery ◽  
Test Facility ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Inlet Flow ◽  
Tip Leakage

The exhaust diffusers studied in this paper are installed behind the last turbine stage of gas turbines, including those used in combined cycle power plants. For the design of efficient diffusers, the effects caused by the last turbine stage need to be taken into account. In the present paper, results are presented to estimate the performance of a diffuser operating under a variation of multiple modelling parameters: tip leakage flow, the swirl, and the rotating blade wakes. To provide a better understanding of the flow parameters, a test facility with a turbine stage simulator is used to model these flow effects and an optical endoscopic planar measurement technique based upon Particle Image Velocimetry (PIV) is applied. The pressure recovery is estimated for various turbine conditions using a variety of relevant parameters. Within a range of conditions, a PIV study is performed to try to understand the typical flow phenomena which influence the performance of axial diffusers. The rise of turbulent energy in the inlet flow positively affects the diffuser performance. A small positive swirl angle in the inlet flow (behind the rotating bladed wheel in experiments) has a stabilizing effect on the diffuser. The tip leakage flow from the last turbine stage can also positively affect the pressure recovery in the diffuser.

Effect of Active Modulation of Through-Casing Coolant Injection on Turbine Efficiency

2017 ◽  
Author(s):  
Brian M. T. Tang ◽  
Marko Bacic ◽  
Peter T. Ireland
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Total Pressure ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Coolant Injection ◽  
Cooling Air

This paper presents a computational investigation into the impact of cooling air injected through the stationary over-tip turbine casing on overall turbine efficiency. The high work axial flow turbine is representative of the high pressure turbine of a civil aviation turbofan engine. The effect of active modulation of the cooling air is assessed, as well as that of the injection locations. The influence of the through-casing coolant injection on the turbine blade over-tip leakage flow and the associated secondary flow features are examined. Transient (unsteady) sliding mesh simulations of a one turbine stage rotor-stator domain are performed using periodic boundary conditions. Cooling air configurations with a constant total pressure air supply, constant mass flow rate and actively controlled total pressure supply are assessed for a single geometric arrangement of cooling holes. The effects of both the mass flow rate of cooling air and the location of its injection relative to the turbine rotor blade are examined. The results show that all of the assessed cooling configurations provided a benefit to turbine row efficiency of between 0.2 and 0.4 percentage points. The passive and constant mass flow rate configurations reduced the over-tip leakage flow, but did so in an inefficient manner, with decreasing efficiency observed with increasing injection mass flow rate beyond 0.6% of the mainstream flow, despite the over-tip leakage mass flow rate continuing to reduce. By contrast, the active total pressure controlled injection provided a more efficient manner of controlling this leakage flow, as it permitted a redistribution of cooling air, allowing it to be applied in the regions close to the suction side of the blade tip which more directly reduced over-tip leakage flow rates and hence improved efficiency. Cooling air injected close to the pressure side of the rotor blade was less effective at controlling the leakage flow, and was associated with increased aerodynamic loss in the passage vortex.

Analysis of tip-leakage flow in an axial fan at varying tip-gap sizes and operating conditions

2019 ◽  
Vol 183 ◽  
pp. 107-129 ◽  
Author(s):  
Seyed Mohsen Alavi Moghadam ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Operating Conditions ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Fan ◽  
Tip Leakage

Characteristics of the Tip Leakage Vortex in a Low-Speed Axial Compressor With Different Rotor Tip Gaps

2012 ◽  
Author(s):  
Zhibo Zhang ◽  
Xianjun Yu ◽  
Baojie Liu
Keyword(s):  
Axial Compressor ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Tip Clearance ◽  
Test Facility ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

The detailed evolutionary processes of the tip leakage flow/vortex inside the rotor passage are still not very clear for the difficulties of investigating of them by both experimental and numerical methods. In this paper, the flow fields near the rotor tip region inside the blade passage with two tip gaps, 0.5% and 1.5% blade height respectively, were measured by using stereoscopic particle image velocimetry (SPIV) in a large-scale low speed axial compressor test facility. The measurements are conducted at four different operating conditions, including the design, middle, maximum static pressure rise and near stall conditions. In order to analyze the variations of the characteristics of the tip leakage vortex (TLV), the trajectory, concentration, size, streamwise velocity, and the blockage parameters are extracted from the ensemble-averaged results and compared at different compressor operating conditions and tip gaps. The results show that the formation of the TLV is delayed with large tip clearance, however, its trajectory moves much faster in an approximately linear way from the blade suction side to pressure side. In the tested compressor, the size of the tip gap has little effects on the scale of the TLV in the spanwise direction, on the contrary, its effects on the pitch-wise direction is very prominent. Breakdown of the TLV were both found at the near-stall condition with different tip gaps. The location of the initiation of the TLV breakdown moves downstream from the 60% chord to 70% chord as the tip gap increases. After the TLV breakdown occurs, the flow blockage near the rotor tip region increases abruptly. The peak value of the blockage effects caused by the TLV breakdown is doubled with the tip gap size increasing from 0.5% to 1.5% blade span.

Blade Tip Shape Optimization for Enhanced Turbine Aerothermal Performance

2013 ◽  
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.

A Study on the Mechanism of Tip Leakage Flow Unsteadiness in an Isolated Compressor Rotor

2006 ◽  
Author(s):  
Hongwu Zhang ◽  
Xiangyang Deng ◽  
Feng Lin ◽  
Jingyi Chen ◽  
Weiguang Huang
Keyword(s):  
Pressure Difference ◽  
Operating Conditions ◽  
Static Balance ◽  
Leakage Flow ◽  
Flow Mechanism ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Aerodynamic Loading ◽  
Compressor Rotor ◽  
Through Flow

A numerical study of unsteady tip leakage flow in an isolated axial compressor rotor is presented, aiming at clarifying the originating flow mechanism of this unsteady phenomenon. First, CFD simulations utilizing a three-dimensional, time-accurate, Reynolds-averaged Navier-Stokes solver demonstrates that the tip leakage flow pattern, which manifests itself as an interacting cross- and through-flow in the tip region, can become periodically oscillatory in a range of operating conditions. A flow mechanism is then clarified to explain this unsteady flow phenomenon at its onset that this periodic flow oscillation is a result of dynamic balance, as opposed to static balance, between two counter-acting driving “forces”. One such “force” is the aerodynamic loading of the blades, i.e. the pressure difference across the pressure and suction sides of the compressor blades created by the main through flow. Its counter-acting “force” is the unloading of the blades, i.e. the reduction of the pressure difference caused by the tip leakage cross flow that originates from the pressure side, rushes into the suction side through the tip clearance. At operating conditions in which both “forces” are strong and in the same order, their static balance will be broken. While a larger blade loading creates a stronger tip leakage flow, the tip leakage flow tends to diminish itself because its accompanying effect is to unload the blade. Since the weaker tip leakage flow cannot overcome the ability of the main through flow to recover the original aerodynamic loading for the blade, the whole process restarts and periodically oscillatory tip leakage flow forms. Furthermore, a dimensionless analysis shows that the onset of the observed unsteadiness is conditioned by the tip leakage flow, which can or cannot reach the neighboring blade before mixing with the main flow.

Turbine Pocket Blade: Structural Integrity and Tip Leakage Flow

2012 ◽  
Author(s):  
Loc Q. Duong ◽  
Nagamany Thayalakhandan
Keyword(s):  
Structural Integrity ◽  
Simultaneous Optimization ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Blade Tip ◽  
Mechanical Optimization ◽  
End Wall ◽  
Aerodynamic Simulation

The design of a turbine blade is a complex task involving the simultaneous optimization and compromise of different disciplines with the most important ones are aerodynamics and structures. Aerodynamics mainly involves optimizing blade profiles for minimum pressure loss while structures deals with fatigue and creep life. In small gas turbine application, the turbine pocket blade with aspect ratio less than unity is a typical case of such aero-mechanical optimization. The objective of this paper is to address two crucial topics encountered by such blade design configuration. They are (a) the integrity of the re-enforced pin and pocket fix-end wall under thermal cyclic loading resulting from combustor pattern factor and in combination with blade transient resonance and (b) the minimization of tip leakage flow to improve turbine efficiency. Finite element method and computational fluid dynamics are used to illustrate the blade pocket physical states and its underlying solutions. Structural analysis indicated that a bi-slotted pin is a suited solution to reduce loading of HCF nature at the blade wall-pin interface. Aerodynamic simulation showed that the pocket blade tip with scooped configuration reduced the tip leakage flow.

Improving Vibration Response of Radial Turbine in Variable Geometry Turbochargers With CFD Analysis

2021 ◽  
Author(s):  
Bipin Gupta ◽  
Toyotaka Yoshida ◽  
Shinji Ogawa ◽  
Yosuke Danmoto ◽  
Takashi Yoshimoto
Keyword(s):  
Safety Factor ◽  
Surface Pressure ◽  
Leading Edge ◽  
Operating Conditions ◽  
Wake Flow ◽  
Leakage Flow ◽  
Variable Geometry ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Nozzle Vane

Abstract Recent advancements in internal combustion engine for efficient fuel combustion, such as application of miller cycle, where the closing of engine intake valve is purposely delayed to provide more cooling of air-fuel mixture during compression stroke for better engine efficiency, has led to a requirement for turbochargers to function at a wider operating range and higher compression ratio. One of the methods which have been largely accepted is the use of variable geometry turbochargers. As compared to diesel engine, operating conditions for gasoline engine require the turbine to operate at higher exhaust temperature, which increases the risk of damaging the rotor. This paper discusses a detailed flow analysis of the effect of tip leakage and nozzle vane wake flow on surface pressure distribution of the turbine rotor, especially at the severe condition when vane trailing edge and rotor leading edge are in proximity. It was observed in steady and unsteady CFD simulations that the origination and propagation of tip leakage flow can be varied depending on the blade loading at the rotor leading edge, and the major interaction of nozzle wake can be switched from pressure surface to suction surface as rotor blade crossed a nozzle vane, which can drastically affect the alternating aerodynamic stresses. The sensitivity to this phenomenon has been evaluated by calculating the safety factor. The authors modified the rotor design to weaken the effect of tip leakage flow in order to suppress variations in rotor surface pressure as it crosses the nozzle vane. It significantly reduced the alternating stress and increased the safety factor at vibration mode 2 from 0.3 to 9.3 and mode 3 from 0.6 to 3.2 respectively.

Conceptual Design of an Axial Turbocharger Turbine

2017 ◽  
Author(s):  
Apostolos Pesiridis ◽  
Antonio Ferrara ◽  
Raffaele Tuccillo ◽  
Hua Chen
Keyword(s):  
Internal Combustion Engines ◽  
Fluid Dynamic ◽  
Axial Flow ◽  
Initial Response ◽  
Operating Conditions ◽  
Combustion Engines ◽  
Turbine Efficiency ◽  
Transient Events ◽  
Engine Operating Point ◽  
Original Concept

Despite engine turbocharging being a widespread technology, there are still drawbacks present in current turbocharging systems stemming from the apparent mismatch between the periodic operation of a piston engine operating in conjunction with an essentially steady-state, rotordynamic machine (turbocharger). The primary issue remains the provision of adequate transient response thereby suppressing the issue of turbocharger lag (turbo-lag) or the poor initial response of the turbocharger to driver-commanded, engine operating point changes due to its inertia. Another problem is engine-turbocharger matching and operation under pulsating conditions in the exhaust manifold and generally unsteady engine operating conditions. The exhaust flows of internal combustion engines are characterized by pulsating flows at constant engine speeds (local pulsating effect) as well as “global” unsteadiness during engine transient events. Because of the volute volume and the length of the flow path, this unsteadiness generates a phase shift between mass flow, temperature and pressure at rotor inlet, and a stronger circumferential variation of the rotor inlet condition than in steady flow conditions. The shift and the variation increase the losses in the turbine, resulting in lower turbine efficiency. The current paper develops original concept work carried out at Brunel University London to develop an innovative fluid-dynamic design for an axial turbine for turbocharger application. An axial flow turbine coupled with a specially-designed, outflow volute, arranged in a non-classical way, are the target of this work. CFD analysis and 1D simulation of an engine coupled with the innovative turbine have been performed to highlight the design potential.

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