Influence of Leading Edge Fillet and Nonaxisymmetric Contoured Endwall on Turbine NGV Exit Flow Structure and Interactions With the Rim Seal Flow

2013 ◽  
Author(s):  
Özhan H. Turgut ◽  
Cengiz Camcı
Keyword(s):  
Flow Structure ◽  
Total Pressure ◽  
Guide Vane ◽  
Axial Flow ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Constant Thickness ◽  
Computational Evaluation ◽  
Nozzle Guide

Three different ways are employed in the present paper to reduce the secondary flow related total pressure loss. These are nonaxisymmetric endwall contouring, leading edge (LE) fillet, and the combination of these two approaches. Experimental investigation and computational simulations are applied for the performance assessments. The experiments are carried out in the Axial Flow Turbine Research Facility (AFTRF) having a diameter of 91.66cm. The NGV exit flow structure was examined under the influence of a 29 bladed high pressure turbine rotor assembly operating at 1300 rpm. For the experimental measurement comparison, a reference Flat Insert endwall is installed in the nozzle guide vane (NGV) passage. It has a constant thickness with a cylindrical surface and is manufactured by a stereolithography (SLA) method. Four different LE fillets are designed, and they are attached to both cylindrical Flat Insert and the contoured endwall. Total pressure measurements are taken at rotor inlet plane with Kiel probe. The probe traversing is completed with one vane pitch and from 8% to 38% span. For one of the designs, area averaged loss is reduced by 15.06%. The simulation estimated this reduction as 7.11%. Computational evaluation is performed with the rotating domain and the rim seal flow between the NGV and the rotor blades. The most effective design reduced the mass averaged loss by 1.28% over the whole passage at the NGV exit.

Experimental Investigation and Computational Evaluation of Contoured Endwall and Leading Edge Fillet Configurations in a Turbine NGV

2012 ◽  
Author(s):  
Özhan H. Turgut ◽  
Cengiz Camcı
Keyword(s):  
Experimental Investigation ◽  
Secondary Flow ◽  
Total Pressure ◽  
Computational Study ◽  
Guide Vane ◽  
Axial Flow ◽  
Leading Edge ◽  
Constant Thickness ◽  
Computational Evaluation ◽  
Flow Minimization

Secondary flow minimization is a crucial problem in a turbine passage. In the present paper, three different ways are employed to reduce the secondary flow related total pressure loss. These are nonaxisymmetric endwall contouring, leading edge (LE) fillet, and the combination of these two approaches. Experimental investigation and computational assessment are applied for the performance calculations. The experiments are carried out in an annular Axial Flow Turbine Research Facility (AFTRF) having a diameter of 91.66cm. For the experimental measurement comparison, a reference Flat Insert is installed in the nozzle guide vane (NGV) passage. It has a constant thickness with cylindrical surface and is manufactured by stereolithography (SLA) method. Also, Flat Insert has a backward facing step at the NGV exit, and the effect of this step is analyzed computationally. Four different LE fillets are designed, and they are attached to both cylindrical Flat Insert and the contoured endwall. Total pressure measurements are taken at rotor inlet plane with Kiel probe. The probe traversing is completed with one vane pitch and from 8% to 38% span. For one of the designs, area-averaged loss is reduced by 15.06%. The simulation estimated this reduction as 6.95%. Computational evaluation is also performed at the NGV exit plane. The most effective design reduced the mass-averaged loss by 1.84% on the whole passage. The computational study did not include the rim seal flow between the vane and rotor domain and also rotor simulation was absent. The difference between the measurements and the simulation comes from these two important effects.

A Nonaxisymmetric Endwall Design Methodology for Turbine Nozzle Guide Vanes and its Computational Fluid Dynamics Evaluation

2011 ◽  
Author(s):  
O¨zhan H. Turgut ◽  
Cengiz Camcı
Keyword(s):  
Total Pressure ◽  
Design Methodology ◽  
Computational Study ◽  
Guide Vane ◽  
Leading Edge ◽  
Cavity Flow ◽  
Subsequent Paper ◽  
Rotor Stator Interaction ◽  
Endwall Contouring ◽  
Nozzle Guide

Nonaxisymmetric endwall contouring has recently become one of the ways to minimize the secondary flow related losses in a turbine nozzle guide vane (NGV) passage. In this study, a specific nonaxisymmetric endwall contouring design methodology is introduced. Fourier series based splines at different axial locations are generated and combined with the help of stream-wise B-splines within solid modeling program. Eight different contoured endwalls are presented in this paper. Computational study of these designs are performed by the finite-volume flow solver. The SST k–ω turbulence model is selected and a body-fitted structured grid is used. Total pressure distribution at the NGV exit shows that contouring the endwall effectively changes the results. Among from these various designs, the most promising one is with the contouring extended in the upstream of the vane leading edge. Mass-averaged value of 3.2% total pressure loss reduction is achieved at the NGV exit plane. The current study was performed in a rotating turbine rig simulating a state of the art HP turbine stage. An NGV only simulation is performed. This approach is helpful in isolating rotor-stator influence and the possible upstream flow modifications of the rim seal cavity flow existing in the rotating turbine research rig. The investigation including the rotor-stator interaction and rim seal cavity flow is the topic of a subsequent paper currently under progress.

Aerothermal Performance of Shielded Vane Design

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Ioanna Aslanidou ◽  
Budimir Rosic
Keyword(s):  
Heat Transfer ◽  
Total Pressure ◽  
High Speed ◽  
Guide Vane ◽  
Leading Edge ◽  
Experimental Facility ◽  
Numerical Studies ◽  
Nozzle Guide Vane ◽  
Inlet Conditions ◽  
Nozzle Guide

This paper presents an experimental investigation of the concept of using the combustor transition duct wall to shield the nozzle guide vane leading edge. The new vane is tested in a high-speed experimental facility, demonstrating the improved aerodynamic and thermal performance of the shielded vane. The new design is shown to have a lower average total pressure loss than the original vane, and the heat transfer on the vane surface is overall reduced. The peak heat transfer on the vane leading edge–endwall junction is moved further upstream, to a region that can be effectively cooled as shown in previously published numerical studies. Experimental results under engine-representative inlet conditions showed that the better performance of the shielded vane is maintained under a variety of inlet conditions.

A Computational Validation of Turbine Nozzle Guide Vane Aerodynamic Experiments in an HP Turbine Stage

2011 ◽  
Author(s):  
O¨zhan H. Turgut ◽  
Cengiz Camcı
Keyword(s):  
Validation Study ◽  
Total Pressure ◽  
Guide Vane ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Turbine Stage ◽  
Aerodynamic Loss ◽  
Nozzle Guide Vane ◽  
Nozzle Guide ◽  
Computational Validation

A computational validation study related to aerodynamic loss generation mechanisms is performed in an axial flow turbine nozzle guide vane (NGV). The 91.66 cm diameter axial flow turbine research facility has a stationary nozzle guide vane assembly and a 29 bladed HP turbine rotor. The NGV inlet and exit Reynolds numbers based on midspan axial chord are around 300000 and 900000, respectively. The effect of grid structure on aerodynamic loss generation is investigated. GAMBIT and TGRID combination is used for unstructured grid, whereas GRIDPRO is the structured grid generator. For both cases, y+ values are kept below unity. The finite-volume flow solver ANSYS CFX with SST k–ω turbulence model is employed. Experimental flow conditions are imposed at the boundaries. The flow transition effect and the influence of corner fillets at the vane-endwall junction are also studied in this paper. Grid independence study is performed with static pressure coefficient distribution at the mid-span of the vane and the total pressure coefficient at the NGV exit. The velocity distributions and the total pressure coefficient at the NGV exit plane are in very good agreement with the experimental data. This validation study shows that the effect of future geometrical modifications on the endwalls and the vane will be predicted reasonably accurately. The current study shows that an accurately measured turbine stage geometry, a properly prepared block structured/body fitted grid, a state of the art transitional flow implementation, and realistic boundary conditions coming from high resolution turbine experiments are all essential ingredients of a successful NGV aerodynamic loss quantification via computations.

Aerodynamic Influence of Endwall Fences Located in the Vicinity of the Leading Edge-Endwall Junction of Nozzle Guide Vanes

2011 ◽  
Author(s):  
Zeki Ozgur Gokce ◽  
Cengiz Camci
Keyword(s):  
Total Pressure ◽  
Numerical Study ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Vertical Cylinder ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Horseshoe Vortices ◽  
Nozzle Guide

Secondary flow characteristics like horseshoe vortices and related total pressure losses decrease turbine efficiency. Computerized simulations of potentially favorable modifications in turbine systems could provide a fast, numerical and inexpensive method of evaluating their effects on flow properties: This paper consists of a comparative numerical study of the flow characteristics of a domain containing a vertical cylinder subjected to cross flow and upstream endwall modifications. Analyzing the flow around a turbine nozzle guide vane (NGV) could be simplified by modeling it as a vertical cylinder with a diameter proportional to the leading edge diameter of the blade, and adding upstream endwall fences of varying dimensions and alignments could attenuate the development of a horseshoe vortex. A commercial computational fluid dynamics (CFD) software package, Fluent, was used for the numerical analysis. To validate the modeling strategy, experimental data previously reported in the literature for conventional cylinders in cross flow were compared to the current predictions. A grid independence study was also performed. The lateral distance between the two legs of the horseshoe vortex downstream of the cylinder was decreased by 7% to 14%. All fence types effectively changed the location of the main horseshoe vortex roll-up. The height of the fence was more influential than the length of the fence in modifying flow characteristics. The existence of the fences slightly increased the mass-averaged total pressure loss far downstream of the cylinder; however, beneficial near-fence flow characteristics were observed in all cases. Also, it was noted that an endwall fence could possibly result in decreased interaction between the horseshoe vortices created by consecutive blades in a row of NGV blades, which would be expected to result in improved flow conditions within actual turbine passages.

Nozzle Guide Vane Shock Wave Propagation and Bifurcation in a Transonic Turbine Rotor

1990 ◽  
Author(s):  
A. B. Johnson ◽  
M. L. G. Oldfield ◽  
M. J. Rigby ◽  
M. B. Giles
Keyword(s):  
Shock Wave ◽  
Thermal Loading ◽  
Guide Vane ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Incoming Wave ◽  
Pressure Surface ◽  
Nozzle Guide Vane ◽  
Transonic Turbine ◽  
Nozzle Guide

A study of the propagation of a Nozzle Guide Vane (NGV) trailing edge shock wave through a transonic turbine rotor passage is presented. The work was based on experimental tests carried out in the Isentropic Light Piston Tunnel in Oxford University using a rotating bar NGV shock wave simulator, together with schlieren photography and wide band width surface pressure and heat transfer rate measurements. The study identifies a previously unexplained interaction between the incoming wave and the rotor leading edge, which causes the nucleation of a Vortical Bubble. This bubble has been shown to enhance the thermal loading on the early pressure surface of the blade. A method of controlling this bubble and heat loading is also considered. A previously unseen “Lambda” interaction between the shock wave and the rotor pressure surface is also identified.

Aerodynamic Tip Desensitization of an Axial Turbine Rotor Using Tip Platform Extensions

2001 ◽  
Author(s):  
Debashis Dey ◽  
Cengiz Camci
Keyword(s):  
Total Pressure ◽  
Axial Flow ◽  
Suction Side ◽  
Tangential Direction ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Pressure Probe ◽  
Total Efficiency ◽  
Efficiency Gain ◽  
Pressure Side

Aerodynamic losses due to the formation of a leakage vortex near the tip section of rotor blades form a significant part of viscous losses in axial flow turbines. The leakage flow, mainly induced by the pressure differential between the pressure side and suction side of a rotor tip section, usually rolls into a streamwise vortical structure near the suction side part of the blade tip. The current study uses the concept of a tip platform extension that is a very short “winglet” obtained by slightly extending the tip platform in the tangential direction. The use of a pressure side tip extension can significantly affect the local aerodynamic field by weakening the leakage vortex structure. Phase averaged, time accurate total pressure measurements downstream of a single stage turbine facility are provided from a total pressure probe that has a time response of 150 kHz. Complete total pressure maps in all of the 29 rotor exit planes are measured accurately. Various pressure and suction side extension configurations are compared against a baseline case. The current investigation performed in the Axial Flow Turbine Research Facility (AFTRF) of the Pennsylvania State University shows that significant total to total efficiency gain is possible by the use of tip platform extensions.

The Thermodynamics of Wake Blade Interaction in Axial Flow Turbines: Combined Experimental and Computational Study

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Martin Rose ◽  
Peter Schüpbach ◽  
Michel Mansour
Keyword(s):  
Computational Study ◽  
Guide Vane ◽  
Axial Flow ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Strong Impact ◽  
Property Variation ◽  
Experimental Vehicle ◽  
Mach Numbers ◽  
Nozzle Guide

This paper reports on insights into the detailed thermodynamics of axial turbine nozzle guide vane (NGV) wakes as they interact with the rotor blades. The evidence presented is both computational and experimental. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations are used to compare the experimental observations with theoretical predictions. Output processing with both Eulerian and Lagrangian approaches is used to track the property variation of the fluid particles. The wake is found to be hot and loses heat to the surrounding fluid. The Lagrangian output processing shows that the entropy of the wake will fall due to heat loss as it passes through the rotor and this is corroborated experimentally. The experimental vehicle is a 1.5-stage shroudless turbine with modest Mach numbers of 0.5 and high response instrumentation. The entropy reduction of the wake is determined to be about four times the average entropy rise of the whole flow across the rotor. The results show that the work done by the wake fluid on the rotor is approximately 24% lower than that of the free-stream. The apparent experimental efficiency of the wake fluid is 114% but the overall efficiency of the turbine at midheight is around 95%. It is concluded that intrafluid heat transfer has a strong impact on the loss distribution even in a nominally adiabatic turbine with moderate row exit Mach numbers of 0.5.

Some Aspects of Wake-Wake Interactions Regarding Turbine Stator Clocking

2000 ◽  
Vol 123 (3) ◽  
pp. 526-533 ◽  
Author(s):  
Maik Tiedemann ◽  
Friedrich Kost
Keyword(s):  
Total Pressure ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Turbine Stage ◽  
Flow Angle ◽  
Wake Interactions ◽  
Turbulence Data ◽  
Number Flow ◽  
Nozzle Guide

This investigation is aimed at an experimental determination of the unsteady flowfield downstream of a transonic high pressure turbine stage. The single stage measurements, which were part of a joined European project, were conducted in the windtunnel for rotating cascades of the DLR Go¨ttingen. Laser-2-focus (L2F) measurements were carried out in order to determine the Mach number, flow angle, and turbulence distributions. Furthermore, a fast response pitot probe was utilized to determine the total pressure distribution. The measurement position for both systems was 0.5 axial rotor chord downstream of the rotor trailing edge at midspan. While the measurement position remained fixed, the nozzle guide vane (NGV) was “clocked” to 12 positions covering one NGV pitch. The periodic fluctuations of the total pressure downstream of the turbine stage indicate that the NGV wake damps the total pressure fluctuations caused by the rotor wakes. Furthermore, the random fluctuations are significantly lower in the NGV wake affected region. Similar conclusions were drawn from the L2F turbulence data. Since the location of the interaction between NGV wake and rotor wake is determined by the NGV position, the described effects are potential causes for the benefits of “stator clocking” which have been observed by many researchers.

Computational Design and Experimental Evaluation of Using a Leading Edge Fillet on a Gas Turbine Vane

2001 ◽  
Author(s):  
G. A. Zess ◽  
K. A. Thole
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Pressure Gradient ◽  
Gas Turbine ◽  
Total Pressure ◽  
Guide Vane ◽  
Leading Edge ◽  
Field Measurements ◽  
Computational Design ◽  
Horseshoe Vortex

With the desire for increased power output for a gas turbine engine comes the continual push to achieve higher turbine inlet temperatures. Higher temperatures result in large thermal and mechanical stresses particularly along the nozzle guide vane. One critical region along a vane is the leading edge-endwall juncture. Based on the assumption that the approaching flow to this juncture is similar to a two-dimensional boundary layer, previous studies have shown that a horseshoe vortex forms. This vortex forms because of a radial total pressure gradient from the approaching boundary layer. This paper documents the computational design and experimental validation of a fillet placed at the leading edge-endwall juncture of a guide vane to eliminate the horseshoe vortex. The fillet design effectively accelerated the incoming boundary layer thereby mitigating the effect of the total pressure gradient. To verify the CFD studies used to design the leading edge fillet, flow field measurements were performed in a large-scale, linear, vane cascade. The flow field measurements were performed with a laser Doppler velocimeter in four planes orientated orthogonal to the vane. Good agreement between the CFD predictions and the experimental measurements verified the effectiveness of the leading edge fillet at eliminating the horseshoe vortex. The flowfield results showed that the turbulent kinetic energy levels were significantly reduced in the endwall region because of the absence of the unsteady horseshoe vortex.

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