Effects of Upstream Step Geometry on Axisymmetric Converging Vane Endwall Secondary Flow and Heat Transfer at Transonic Conditions

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Zhigang Li ◽  
Luxuan Liu ◽  
Jun Li ◽  
Ridge A. Sibold ◽  
Wing F. Ng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Thermal Load ◽  
Numerical Study ◽  
Guide Vane ◽  
Leading Edge ◽  
Step Height ◽  
Temperature History ◽  
Flow And Heat Transfer ◽  
High Thermal Load

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5×106. A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88Cx (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward-facing step located just before the gap at 0.88Cx (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely, Nusselt number, was derived. This paper also presents a comparison with computational fluid dynamics (CFD) predictions performed by solving the steady-state Reynolds-averaged Navier–Stokes with Reynolds stress model using the commercial CFD solver ansysfluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25% to 0% span), and five backward-facing, upstream step geometries (step heights from 0% to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures and explain the effects of upstream step geometry. Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient (HTC) level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the HTC (by ∼10% to 40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3–1.3%) because of the forward-facing upstream step geometry but is slightly reduced (by 0.1–0.3%) by the presence of the backward upstream step geometry.

Effects of Upstream Step Geometry on Axisymmetric Converging Vane Endwall Secondary Flow and Heat Transfer at Transonic Conditions

2018 ◽  
Author(s):  
Zhigang Li ◽  
Luxuan Liu ◽  
Jun Li ◽  
Ridge A. Sibold ◽  
Wing F. Ng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Secondary Flow ◽  
Thermal Load ◽  
Leading Edge ◽  
Step Height ◽  
Flow And Heat Transfer ◽  
High Thermal Load ◽  
The Heat Transfer Coefficient

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5 × 106. A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88Cx (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward facing step located just before the gap at 0.88Cx (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely Nusselt number, were derived. This paper also presents a comparison with CFD predictions performed by solving the steady-state Reynolds Averaged Navier Stokes (RANS) with Reynolds Stress Model using the commercial CFD solver ANSYS Fluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25 to 0% span), and five backward-facing, upstream step geometries (step heights from 0 to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures, and explain the effects of upstream step geometry. Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the heat transfer coefficient (by ∼10%–40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3%–1.3%) as a result of the forward-facing upstream step geometry, but is slightly reduced (by 0.1%–0.3%) by the presence of the backward upstream step geometry.

Experimental and Numerical Conjugate Flow and Heat Transfer Investigation of a Shower-Head Cooled Turbine Guide Vane

1997 ◽  
Author(s):  
Dieter E. Bohn ◽  
Volker J. Becker ◽  
Agnes U. Rungen
Keyword(s):  
Heat Transfer ◽  
Thermal Analysis ◽  
Guide Vane ◽  
Leading Edge ◽  
Operating Conditions ◽  
Main Stream ◽  
Temperature Ratio ◽  
Stagnation Line ◽  
Flow And Heat Transfer ◽  
Turbine Guide Vane

This paper presents investigations of the development for a shower-head cooling configuration for a modern industrial turbine guide vane. One aim is to find suitable locations for cooling gas ejection with the lowest cooling gas mass flow possible. The investigations begin with a numerical experiment. After the prediction of a suitable configuration and operating parameters, the aerodynamics are investigated experimentally using a non-intrusive LDA technique. Once the aerodynamics had been validated, the numerical experiments were expanded to a thermal analysis of the vane. Our conjugate flow and heat transfer simulation enables thermal analysis of the vane body without us having to derive any heat transfer data beforehand. The calculations were performed for a temperature ratio of 0.5 between cooling gas and main stream. This temperature ratio is similar to the operating conditions found in current designs. The stagnation line moves under the influence of cooling gas ejection, which significantly influences the cooling gas distribution on the vane surface. The temperature distribution inside the vane is compared to a non-cooled test case. The simulation shows that the temperature peaks at the leading edge are reduced by between 18% and 44%.

3-D Conjugate Flow and Heat Transfer Investigations of a Film-Cooled Turbine Guide Vane With Different Blowing Ratios

1997 ◽  
Author(s):  
Dieter E. Bohn ◽  
Tom Heuer ◽  
Karsten A. Kusterer
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Guide Vane ◽  
Leading Edge ◽  
Cooling Fluid ◽  
Hot Gas ◽  
Flow And Heat Transfer ◽  
Passage Vortex ◽  
Turbine Guide Vane ◽  
Conjugate Calculation

Film-cooling has become a widely used cooling method in present day gas turbines. Cooling gas ejection at the leading edge serves to protect the entire vane surface from contact with the hot gas. With doing this, material temperatures are reduced in order to guarantee an economically acceptable life span of the vane. This paper describes the application of a numerical method for the conjugate calculation of internal and external fluid flows and the heat transfer in and through the blade walls of a film-cooled turbine guide vane. The advantage of this approach is that it is possible to predict fluid flow properties and wall temperatures without the need for additional heat transfer conditions or temperature conditions at the external surfaces of the vane. This is a great advantage because the desired data are either unknown or not available for the calculation in the design process of new cooled blades or vanes. In a complete calculation of external and internal flows, no additional boundary conditions at the internal surfaces of the cooling geometry are needed either. Another advantage is the interaction of fluid flow and heat transfer which is taken into account by the conjugate calculation. In the 3-D numerical experiment to be presented, the influence of leading edge cooling fluid ejection on the temperature distribution in the vane material is investigated. The cooling fluid is ejected through two slots at the leading edge. The calculations are performed for three blowing ratios in order to investigate the efficiency of the cooling method. Realistic temperature ratios of cooling-fluid flow and main flow are considered. Such information is very useful in the aero thermal design process of new cooling configurations, since the amount of experimental work can be minimized. The results show the influence of complex 3-D flow phenomena (e.g. passage vortex) on the cooling fluid distribution on the vane surface as a function of the chosen blowing factor. Due to the influence of the passage vortex, the cooling fluid is displaced and leaves the vane surface near the side-wall uncovered against the hot gas. Furthermore, cooling fluid displacement on the pressure side according to the ejection slot geometry leads to another unprotected region on the vane surface. These effects have severe consequences on the thermal load of the vane and can reduce its life span.

scholarly journals Effects of Blade Fillet Structures on Flow Field and Surface Heat Transfer in a Large Meridional Expansion Turbine

Energies ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 3035
Author(s):  
Fusheng Meng ◽  
Qun Zheng ◽  
Jian Zhang
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Thermal Load ◽  
Three Dimensional ◽  
Leading Edge ◽  
Flow State ◽  
Aerodynamic Loss ◽  
Expansion Turbine ◽  
Large Expansion ◽  
High Thermal Load

This paper is a continuation of the previous work, aiming to explore the influence of fillet configurations on flow and heat transfer in a large meridional expansion turbine. The endwall of large meridional expansion turbine stator has a large expansion angle, which leads to early separation of the endwall boundary layer, resulting in excessive aerodynamic loss and local thermal load. In order to improve the flow state and reduce the local high thermal load, five typical fillet distribution rules are designed. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solver for viscous turbulent flows was used to investigate the different fillet configurations of the second stage stator blades of a 1.5-stage turbine, and which fillet distribution is suitable for large meridional expansion turbines. The influence of fillet structures on the vortex system and loss characteristics was analyzed, and its impact on wall thermal load was studied in detail. The fillet structure mainly affects the formation of horseshoe vortexes at the leading edge of the blade so as to reduce the loss caused by horseshoe vortexes and passage vortexes. The fillet structure suitable for the large meridional expansion turbine was obtained through the research. Reasonable fillet structure distribution can not only improve the flow state but also reduce the high thermal load on the wall surface of the meridional expansion turbine. It has a positive engineering guiding value.

THERMAL BARRIER COATING AND TURBULENCE INTENSITY EFFECTS ON LEADING EDGE COOLING USING CONJUGATE HEAT TRANSFER ANALYSIS

2017 ◽  
Vol 41 (2) ◽  
pp. 249-263 ◽  
Author(s):  
Prasert Prapamonthon ◽  
Huazhao Xu ◽  
Zhaoqing Ke ◽  
Wenshuo Yang ◽  
Jianhua Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Barrier Coating ◽  
Conjugate Heat Transfer ◽  
Numerical Study ◽  
Guide Vane ◽  
Leading Edge ◽  
Heat Transfer Analysis ◽  
Thermal Barrier ◽  
Free Stream Turbulence ◽  
Barrier Coating

This is a numerical study of thermal barrier coating (TBC) and turbulence on leading edge (LE) cooling of a guide vane. Numerical results were carried out using 3D CFD with conjugate heat transfer analysis. Important phenomena were revealed. (1) TBC is effective in the LE region especially when free stream turbulence (Tu) increases. (2) At each Tu, TBC near the hub of the vane provides the most effective protection and at the highest Tu, TBC improves overall cooling effectiveness there by about 25%. (3) Near the exits of film hole, TBC may have negative effect, because of heat transfer impedance from the solid structure into the mixing fluid between mainstream and cooling air emitted from film holes.

Numerical Study of Fluid Flow and Heat Transfer in the Enhanced Microchannel With Oblique Fins

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Y. J. Lee ◽  
P. S. Lee ◽  
S. K. Chou
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Numerical Study ◽  
Leading Edge ◽  
Secondary Flows ◽  
Microchannel Heat Sink ◽  
Transfer Enhancement ◽  
Flow And Heat Transfer

Sectional oblique fins are employed in contrast to continuous fins in order to modulate flow in microchannel heat sink. The breakage of continuous fin into oblique sections leads to the reinitialization of both hydrodynamic and thermal boundary layers at the leading edge of each oblique fin, effectively reducing the thickness of boundary layer. This regeneration of entrance effect causes the flow to be always in a developing state thus resulting in better heat transfer. In addition, the presence of smaller oblique channels diverts a small fraction of flow into the adjacent main channels. The secondary flows thus created improve fluid mixing which serves to further enhance the heat transfer. Detailed numerical study on the fluid flow and heat transfer of this passive heat transfer enhancement technique provides insight to the local hydrodynamics and thermal development along the oblique fin. The uniquely skewed hydrodynamic and thermal profiles are identified as the key to the highly augmented and uniform heat transfer performance across the heat sink. The associated pressure drop penalty is much smaller than the achieved heat transfer enhancement, rendering it as an effective heat transfer enhancement scheme for single phase microchannel heat sink.

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