Endwall Contouring Using Continuous Diffusion: A Breakthrough Method and its Application to a Three-Stage High Pressure Turbine

2011 ◽  
Author(s):  
M. T. Schobeiri ◽  
K. Lu
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Positive Impact ◽  
Leading Edge ◽  
Secondary Flows ◽  
Moderate Increase ◽  
Aerodynamic Efficiency ◽  
Drag Forces ◽  
Numerical Result ◽  
Endwall Contouring

Blades of high pressure turbines have a relatively small aspect ratio that produce major secondary flow regions close to the hub and tip. The secondary flows caused by a system of hub and tip vortices induce drag forces resulting in an increase of secondary flow losses and thus a reduction of stage efficiency. Given the high level of technological maturity and the current state of turbine aerodynamic efficiency, major efficiency improvement, if any, can be achieved only by significant R&D effort. In contrast, moderate increase in aerodynamic efficiency is attainable by reducing the effect of parasitic vortices such as those mentioned above. Introducing an appropriate non-axisymmetric endwall contouring reduces the secondary flow effect caused by the pressure difference between pressure and suction surfaces. Likewise, attaching leading edge fillets reduces the strength of horse shoe vortices. While an appropriate endwall contouring design requires special care, the design of the leading edge fillet is straight forward. In this paper we present a physics based method which enables researchers and engineers to design endwall contours for any arbitrary blade type regardless of the blade loading, degree of reaction, stage load and flow coefficients. A thorough step-by-step design instruction is followed by its application to the second rotor of the three-stage research turbine of Turbomchinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. Comprehensive numerical calculations of the flow field including the secondary flow show the positive impact of an appropriately designed endwall contouring on the efficiency. The results also show, how an inappropriately designed contour can be detrimental to turbine efficiency. The numerical result of the efficiency calculations is compared with the experimentally obtained efficiency for the reference non-contoured turbine.

Endwall Contouring Using Continuous Diffusion: A New Method and its Application to a Three-Stage High Pressure Turbine

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
M. T. Schobeiri ◽  
K. Lu
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Positive Impact ◽  
Leading Edge ◽  
Secondary Flows ◽  
Moderate Increase ◽  
Aerodynamic Efficiency ◽  
Drag Forces ◽  
Endwall Contouring ◽  
High Level

Blades of high pressure turbines have a relatively small aspect ratio that produces major secondary flow regions close to the hub and tip. The secondary flows caused by a system of hub and tip vortices induce drag forces resulting in an increase of secondary flow losses, and thus, a reduction of stage efficiency. Given the high level of technological maturity and the current state of turbine aerodynamic efficiency, major efficiency improvement, if any, can be achieved only by significant R&D effort. In contrast, a moderate increase in aerodynamic efficiency is attainable by reducing the effect of parasitic vortices such as those mentioned above. Introducing an appropriate nonaxisymmetric endwall contouring reduces the secondary flow effect caused by the pressure difference between pressure and suction surfaces. Likewise, attaching leading edge fillets reduces the strength of horseshoe vortices. While an appropriate endwall contouring design requires special care, the design of the leading edge fillet is straightforward. In this paper, we present a physics based method which enables researchers and engineers to design endwall contours for any arbitrary blade type regardless of the blade loading, degree of reaction, stage load and flow coefficients. A thorough step-by-step design instruction is followed by its application to the second rotor row of the three-stage research turbine of the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. Comprehensive numerical calculations of the flow field, including the secondary flow, show the positive impact of an appropriately designed endwall contouring on the efficiency. The results also show how an inappropriately designed contour can be detrimental to turbine efficiency.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Design Optimization of Profiled Endwall With Consideration of Cooling and Rim Seal Flow Effects

2016 ◽  
Author(s):  
Huimin Tang ◽  
Shuaiqiang Liu ◽  
Hualing Luo
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Great Influence ◽  
Optimization Procedure ◽  
Secondary Flows ◽  
High Pressure Turbine ◽  
Operation Condition ◽  
Turbine Performance

Profiled endwall is an effective method to improve aerodynamic performance of turbine. This approach has been widely studied in the past decade on many engines. When automatic design optimisation is considered, most of the researches are usually based on the assumption of a simplified simulation model without considering cooling and rim seal flows. However, many researchers find out that some of the benefits achieved by optimization procedure are lost when applying the high-fidelity geometry configuration. Previously, an optimization procedure has been implemented by integrating the in-house geometry manipulator, a commercial three-dimensional CFD flow solver and the optimization driver, IsightTM. This optimization procedure has been executed [12] to design profiled endwalls for a turbine cascade and a one-and-half stage axial turbine. Improvements of the turbine performance have been achieved. As the profiled endwall is applied to a high pressure turbine, the problems of cooling and rim seal flows should be addressed. In this work, the effects of rim seal flow and cooling on the flow field of two-stage high pressure turbine have been presented. Three optimization runs are performed to design the profiled endwall of Rotor-One with different optimization model to consider the effects of rim flow and cooling separately. It is found that the rim seal flow has a significant impact on the flow field. The cooling is able to change the operation condition greatly, but barely affects the secondary flow in the turbine. The influences of the profiled endwalls on the flow field in turbine and cavities have been analyzed in detail. A significant reduction of secondary flows and corresponding increase of performance are achieved when taking account of the rim flows into the optimization. The traditional optimization mechanism of profiled endwall is to reduce the cross passage gradient, which has great influence on the strength of the secondary flow. However, with considering the rim seal flows, the profiled endwall improves the turbine performance mainly by controlling the path of rim seal flow. Then the optimization procedure with consideration of rim seal flow has also been applied to the design of the profiled endwall for Stator Two.

The Effect of Coolant Injection on the Endwall Flow of a High Pressure Turbine

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Jonathan Ong ◽  
Robert J. Miller ◽  
Sumiu Uchida
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Penetration Depth ◽  
Three Dimensional ◽  
Fast Response ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Leakage Flow ◽  
Speed Test ◽  
Coolant Injection

This paper presents a study of the effects of two types of hub coolant injection on the rotor of a high pressure gas turbine stage. The first involves the leakage flow from the hub cavity into the mainstream. The second involves a deliberate injection of coolant from a row of angled holes from the edge of the stator hub. The aim of this study is to improve the distribution of the injected coolant on the rotor hub wall. To achieve this, it is necessary to understand how the coolant and leakage flows interact with the rotor secondary flows. The first part of the paper shows that the hub leakage flow is entrained into the rotor hub secondary flow and the negative incidence of the leakage strengthens the secondary flow and increases its penetration depth. Three-dimensional unsteady calculations were found to agree with fast response pressure probe measurements at the rotor exit of a low speed test turbine. The second part of the paper shows that increasing the injected coolant swirl angle reduced the secondary flow penetration depth, improves the coolant distribution on the rotor hub, and improves stage efficiency. Most of the coolant however, was still found to be entrained into the rotor secondary flow.

Endwall Effusion Cooling System Behaviour Within a High-Pressure Turbine Cascade: Part 1—Aerodynamic Measurements

2010 ◽  
Author(s):  
Marco Sacchi ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Stefano Zecchi
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Secondary Flow ◽  
Measurement Techniques ◽  
Secondary Flows ◽  
Turbine Cascade ◽  
High Pressure Turbine ◽  
Tangential Plane ◽  
Cooling Effects ◽  
Secondary Flow Field

The secondary flow field in a large-scale high-pressure turbine cascade with micro-holed endwall cooling has been investigated at the Genova Laboratory of Aerodynamics and Turbomachinery in cooperation with Avio S.p.A in the framework of the European Project AITEB-2. The experimental investigation has been performed for the baseline configuration, with a smooth solid endwall installed, and for the cooled configuration with a micro-holed endwall providing micro-jets ejection from the wall. Two different cooling flow rates were investigated and the experimental results are reported in the paper. Different measurement techniques have been employed to analyze the secondary flow field along the channel and in a downstream tangential plane. Particle Image Velocimetry has been utilized to quantify the blade-to-blade velocity components in a plane located close to the endwall and in the midspan plane. Hot-wire measurements have been performed in a tangential plane downstream of the blade trailing edges in order to survey the micro-jets effects on the secondary flows behavior. The total pressure distributions, for the different blowing conditions, have been measured in the downstream tangential plane by means of a Kiel pneumatic probe. The results, represented in color plots of velocity, pressure loss coefficient and turbulent kinetic energy distributions, allow the identification of the endwall effusion cooling effects on location and strength of the secondary vortical structures. The thermal investigation of the effusion system is discussed in Part 2 of the paper.

The Behavior of Turbine Center Frames Under the Presence of Purge Flows

2017 ◽  
Author(s):  
S. Zerobin ◽  
A. Peters ◽  
S. Bauinger ◽  
A. Ramesh ◽  
M. Steiner ◽  
...  
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Pressure Loss ◽  
Measurement Data ◽  
Leading Edge ◽  
Turbine Rotor ◽  
High Pressure Turbine ◽  
Oil Flow ◽  
Purge Flow ◽  
Cooling Air

This paper deals with the influence of high-pressure turbine purge flows on the aerodynamic performance of turbine center frames. Measurements were carried out in a product-representative one and a half stage turbine test setup, installed in the Transonic Test Turbine Facility at Graz University of Technology. The rig allows testing at engine-relevant flow conditions, matching Mach, Reynolds, and Strouhal number at the inlet of the turbine center frame. Four individual purge mass flows differing in flow rate, pressure, and temperature were injected through the hub and tip, forward and aft cavities of the unshrouded high-pressure turbine rotor. Two turbine center frame designs (differing in area distribution and inlet-to-exit radial offset), equipped with non-turning struts, were tested and compared. For both configurations, aerodynamic measurements at the duct inlet and outlet as well as oil flow visualizations through the turbine center frame were performed. The acquired measurement data illustrate that the interaction of the ejected purge flow with the main flow enhances the secondary flow structures through the turbine center frame duct. Depending on the purge flow rates, the radial migration of purge air onto the strut surfaces directly impacts the loss behavior of the duct. While the duct loss is demonstrated to be primarily driven by the core flow between two duct struts, the losses associated with the flow close to the struts and in the strut wakes are highly dependent on the relative position between the high-pressure turbine vane and the strut leading edge, as well as the interaction between vane wake and ejected purge flow. Hence, while the turbine center frame duct pressure loss depends on the duct geometric characteristics it is also influenced by the presence and rate of the high-pressure turbine purge flows. This first-time experimental assessment demonstrates that a reduction in the high-pressure turbine purge and cooling air requirement not only benefits the engine system performance by decreasing the secondary flow taken from the high-pressure compressor but also by lowering the turbine center frame total pressure loss.

Investigation of 3D Blading and Non-Axisymmetric Hub Endwall Contouring to a Dual-Stage Counter-Rotating Compressor in Multistage Environment

2014 ◽  
Author(s):  
Peng Zhang ◽  
Bo Liu ◽  
Guochen Zhang ◽  
Zhenzhe Na
Keyword(s):  
Secondary Flow ◽  
Flow Separation ◽  
Guide Vane ◽  
Aerodynamic Performance ◽  
Secondary Flows ◽  
Flow Losses ◽  
Dual Stage ◽  
Endwall Contouring

3D blading technique is an effective way to mitigate flow separation and improve the performance of turbomachinery. Non-axisymmetric endwall contouring technique is widely used to reduce transverse secondary flows near the endwall region in turbines, while the application of non-axisymmetric endwall contouring to compressors is rare. The investigation rig is the Northwestern Polytechnical University dual-stage counter-rotating compressor. In order to further improve the aerodynamic performance of the compressor, 3D blading optimization of the two rotors and outlet guide vane (OGV) was done in multistage environment at near stall condition. After 3D blading optimization, the radial secondary flows of the two rotors and the separation vortex at the tip of OGV are obviously reduced. However, the transverse secondary flows at the hub endwalls of the two rotors are scarcely improved. Based on the 3D blading optimization, non-axisymmetric hub endwall contouring optimization of the two rotors was carried out afterwards and the circumferential secondary flow losses of the two rotors are reduced effectively. The efficiency of the counter-rotating compressor on optimization point increases and the aerodynamic performance is improved largely after 3D blading and non-axisymmetric hub endwall contouring optimization.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Christopher J. Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio ◽  
End Wall

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high end-wall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy (SKE) of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet end-wall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent current practice for a low aspect ratio vane, a design exempt from thickness constraints, and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitter geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flow field was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

The Effect of Coolant Injection on the Endwall Flow of a High Pressure Turbine

2006 ◽  
Author(s):  
Jonathan H. P. Ong ◽  
Robert J. Miller ◽  
Sumiu Uchida
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Penetration Depth ◽  
Three Dimensional ◽  
Fast Response ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Leakage Flow ◽  
Speed Test ◽  
Coolant Injection

This paper presents a study of the effects of two types of hub coolant injection on the rotor of a high pressure gas turbine stage. The first involves the leakage flow from the hub cavity into the mainstream. The second involves a deliberate injection of coolant from a row of angled holes from the edge of the stator hub. The aim of this study is to improve the distribution of the injected coolant on the rotor hub wall. To achieve this, it is necessary to understand how the coolant and leakage flows interact with the rotor secondary flows. The first part of the paper shows that the hub leakage flow is entrained into the rotor hub secondary flow and the negative incidence of the leakage strengthens the secondary flow and increases its penetration depth. Three dimensional unsteady calculations were found to agree with fast response pressure probe measurements at the rotor exit of a low speed test turbine. The second part of the paper shows that increasing the injected coolant swirl angle reduced the secondary flow penetration depth, improves the coolant distribution on the rotor hub and improves stage efficiency. Most of the coolant however, was still found to be entrained into the rotor secondary flow.

Migration of Combustor Exit Profiles Through High Pressure Turbine Vanes

2007 ◽  
Author(s):  
M. D. Barringer ◽  
M. D. Polanka ◽  
J. P. Clark ◽  
P. J. Koch ◽  
K. A. Thole
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Total Pressure ◽  
Secondary Flows ◽  
Working Fluid ◽  
Outer Diameter ◽  
High Pressure Turbine ◽  
Flow Angle ◽  
Radial Temperature ◽  
Turbine Vane

The high pressure turbine stage within gas turbine engines is exposed to combustor exit flows that are nonuniform in both stagnation pressure and temperature. These highly turbulent flows typically enter the first stage vanes with significant spatial gradients near the inner and outer diameter endwalls. These gradients can result in secondary flow development within the vane passage that is different than what classical secondary flow models predict. The heat transfer between the working fluid and the turbine vane surface and endwalls is directly related to the secondary flows. The goal of the current study was to examine the migration of different inlet radial temperature and pressure profiles through the high turbine vane of a modern turbine engine. The tests were performed using an inlet profile generator located in the Turbine Research Facility (TRF) at the Air Force Research Laboratory (AFRL). Comparisons of area-averaged radial exit profiles are reported as well as profiles at three vane pitch locations to document the circumferential variation in the profiles. The results show that the shape of the total pressure profile near the endwalls at the inlet of the vane can alter the redistribution of stagnation enthalpy through the airfoil passage significantly. Total pressure loss and exit flow angle variations are also examined for the different inlet profiles.

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