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.

The Development of Turbine Exit Flow in a Swan-Necked Inter-Stage Diffuser

2003 ◽  
Author(s):  
R. J. Miller ◽  
R. W. Moss ◽  
R. W. Ainsworth ◽  
N. W. Harvey
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Inlet Flow ◽  
Time Resolved ◽  
Tip Leakage ◽  
Numerical Predictions

This paper describes both the migration and dissipation of flow phenomena downstream of a transonic high-pressure turbine stage. The geometry of the HP stage exit duct considered is a swan-necked diffuser similar to those likely to be used in future engine designs. The paper contains results both from an experimental programme in a turbine test facility and from numerical predictions. Experimental data was acquired using three fast-response aerodynamic probes capable of measuring Mach number, whirl angle, pitch angle, total pressure and static pressure. The probes were used to make time-resolved area traverses at two axial locations downstream of the rotor trailing edge. A 3D time-unsteady viscous Navier-Stokes solver was used for the numerical predictions. The unsteady exit flow from a turbine stage is formed from rotor-dependent phenomena (such as the rotor wake, the rotor trailing edge recompression shock, the tip-leakage flow and the hub secondary flow) and vane-rotor interaction dependant phenomena. This paper describes the time-resolved behaviour and three-dimensional migration paths of both of these phenomena as they convect downstream. It is shown that the inlet flow to a downstream vane is dominated by two corotating vortices, the first caused by the rotor tip-leakage flow and the second by the rotor hub secondary flow. At the inlet plane of the downstream vane the wake is extremely weak and the radial pressure gradient is shown to have caused the majority of the high loss wake fluid to be located between the mid-height of the passage and the casing wall. The structure of the flow indicates that between a high pressure stage and a downstream vane simple two-dimensional blade row interaction does not occur. The results presented in this paper indicate that the presence of an upstream stage is likely to significantly alter the structure of the secondary flow within a downstream vane. The paper also shows that vane-rotor interaction within the upstream stage causes a 10° circumferential variation in the inlet flow angle of the 2nd stage vane.

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.

Tip Leakage Flows Near Partial Squealer Rims in an Axial Flow Turbine Stage

2003 ◽  
Author(s):  
Cengiz Camci ◽  
Debashis Dey ◽  
Levent Kavurmacioglu
Keyword(s):  
Total Pressure ◽  
Axial Flow ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Edge Zone ◽  
Tip Leakage ◽  
Partial Length

This paper deals with an experimental investigation of aerodynamic characteristics of full and partial-length squealer rims in a turbine stage. Full and partial-length squealer rims are investigated separately on the pressure side and on the suction side in the “Axial Flow Turbine Research Facility” (AFTRF) of the Pennsylvania State University. The streamwise length of these “partial squealer tips” and their chordwise position are varied to find an optimal aerodynamic tip configuration. The optimal configuration in this cold turbine study is defined as the one that is minimizing the stage exit total pressure defect in the tip vortex dominated zone. A new “channel arrangement” diverting some of the leakage flow into the trailing edge zone is also studied. Current results indicate that the use of “partial squealer rims” in axial flow turbines can positively affect the local aerodynamic field by weakening the tip leakage vortex. Results also show that the suction side partial squealers are aerodynamically superior to the pressure side squealers and the channel arrangement. The suction side partial squealers are capable of reducing the stage exit total pressure defect associated with the tip leakage flow to a significant degree.

Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Sergen Sakaoglu ◽  
Harika S. Kahveci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

Abstract The pressure difference between suction and pressure sides of a turbine blade leads to tip leakage flow, which adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are exposed to extreme thermal conditions requiring cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to leakage. Therefore, the compromise between the aerodynamic loss and the gain in tip-cooling effectiveness must be optimized. In this paper, the effect of tip-cooling configuration on the turbine blade tip is investigated numerically from both aerodynamics and thermal aspects to determine the optimum configuration. Computations are performed using the tip cross section of GE-E3 HP turbine first-stage blade for squealer and flat tips, where the number, location, and diameter of holes are varied. The study presents a discussion on the overall loss coefficient, total pressure loss across the tip clearance, and variation in heat transfer on the blade tip. Increasing the coolant mass flow rate using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor. Both aerodynamic and thermal response of squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with a larger number of cooling holes located toward the pressure side is highlighted to have the best cooling performance.

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.

Clearance Reduction and Performance Gain Using Abradable Material in Gas Turbines

2008 ◽  
Author(s):  
Iacopo Giovannetti ◽  
Manuele Bigi ◽  
Massimo Giannozzi ◽  
Dieter R. Sporer ◽  
Filippo Cappuccini ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Leakage Flow ◽  
Performance Gain ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Hot Gas ◽  
Industrial Gas Turbines ◽  
Basic Parameters ◽  
Component Shape ◽  
And Performance

An improvement in the energy efficiency of industrial gas turbines can be accomplished by developing abradable seals to reduce the stator/rotor gap to decrease the tip leakage flow of gases in the hot gas components of the turbine. “ABRANEW” is a project funded by the European Commission aimed at developing a high temperature abradable material capable of controlled abrasion and resistant to erosion and oxidation. In order to define the basic parameters such as the component shape, the existing gap, the expected gap reduction, the seal thickness and other geometric parameters, a comprehensive review of the design of the blade/shroud/casing system was performed.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

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.

scholarly journals Effects of Double-Side Labyrinth Seals on Aerodynamic Performance in a Transonic Shrouded Turbine Stage

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Weihang Li ◽  
Shaowen Chen ◽  
Hongyan Liu ◽  
Zhihua Zhou ◽  
Songtao Wang
Keyword(s):  
Labyrinth Seal ◽  
Aerodynamic Performance ◽  
Maximum Efficiency ◽  
Outlet Section ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Labyrinth Seals ◽  
Tip Leakage ◽  
Transonic Turbine

Abstract Labyrinth seals on both rotor casing and blade tip as an effective method to control the leakage flowrate of the shroud and improve aerodynamic performances in a transonic turbine stage are investigated in this study. Compared to the case without the labyrinth seal structure, the cases with three different types of sealing teeth have been shown to reduce significantly the tip leakage flow by computational simulations. The double-side sealing teeth case reduces the leakage flowrate mleakage/mpassage from 3.4% to 1.3% and increases the efficiency by 1.4%, which is the maximum efficiency improvement of all cases. The sealing structures increase the loss inside the shroud while reducing the momentum mixing between shroud leakage flow and mainstream. Therefore, the circumferential distribution of leakage velocity is changed, as well as the distribution of high-loss zones at turbine outlet. Furthermore, the leakage-vortex loss, which is associated with the blockage effect of sealing structure to the tip leakage flow, gains more improvement than the passage-vortex at the rotor outlet section in double-side seal case. In addition, it has also been found that with a larger gap at tip, the double-side seal has better effects of reducing the leakage flow and improving the aerodynamic performance in the transonic turbine stage.

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