Investigation of Innovative Trailing Edge Cooling Configurations With Enlarged Pedestals and Square or Semicircular Ribs: Part II—Numerical Results

2008 ◽  
Author(s):  
Emiliano Di Carmine ◽  
Bruno Facchini ◽  
Luca Mangani
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Convective Heat Transfer Coefficient ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Trailing Edge ◽  
Pressure Losses ◽  
Structural Resistance ◽  
Pin Fins ◽  
Rib Turbulators

Trailing edge is a critical region for turbine airfoils since this part of the blade has to match aerodynamic, cooling and structural requirements at the same time. In fact aerodynamic losses are strictly related to trailing edge thickness which, on the contrary, tends to be increased to implement an internal cooling system, in order to face high thermal loads. At the moment the most employed devices consist of pin fins of various shapes, which contribute to both heat transfer enhancement and structural resistance improvement. Enlarged pedestals decrease pressure losses in comparison with multirow pin fins, even if the heat transfer increase is limited. This work deals with the investigation of the usage of enlarged pedestals, inserted in a wedge shaped duct, in conjunction with square or semicircular rib turbulators. The aim of the analysis is the evaluation of the convective Heat Transfer Coefficient (HTC) distribution over the endwall surface and the pressure drop of the converging duct. Numerical analysis used 3D RANS calculations. An in-house modified object-oriented CFD code and a commercial one were used. Several turbulence models and mesh types were tested. Numerical calculations were compared with experimental results obtained on the same geometries using a transient Thermochromic Liquid Crystals (TLC) based technique. Goals of this comparison are both the evaluation of the accuracy of CFD packages with standard two equation turbulence models in heat transfer problems with complex geometries and the analysis of flow details to complete and support experimental activity.

Computation of flow and heat transfer through channels with periodic dimple/protrusion walls using low-Reynolds number turbulence models

2019 ◽  
Vol 29 (3) ◽  
pp. 1178-1207 ◽  
Author(s):  
Mohammad Fazli ◽  
Mehrdad Raisee
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Correction Term ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Recirculation Bubble ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Numerical Predictions

PurposeThis paper aims to predict turbulent flow and heat transfer through different channels with periodic dimple/protrusion walls. More specifically, the performance of various low-Rek-ε turbulence models in prediction of local heat transfer coefficient is evaluated.Design/methodology/approachThree low-Re numberk-εturbulence models (the zonalk-ε, the lineark-εand the nonlineark-ε) are used. Computations are performed for three geometries, namely, a channel with a single dimpled wall, a channel with double dimpled walls and a channel with a single dimple/protrusion wall. The predictions are obtained using an in house finite volume code.FindingsThe numerical predictions indicate that the nonlineark-εmodel predicts a larger recirculation bubble inside the dimple with stronger impingement and upwash flow than the zonal and lineark-εmodels. The heat transfer results show that the zonalk-εmodel returns weak thermal predictions in all test cases in comparison to other turbulence models. Use of the lineark-εmodel leads to improvement in heat transfer predictions inside the dimples and their back rim. However, the most accurate thermal predictions are obtained via the nonlineark-εmodel. As expected, the replacement of the algebraic length-scale correction term with the differential version improves the heat transfer predictions of both linear and nonlineark-εmodels.Originality/valueThe most reliable turbulence model of the current study (i.e. nonlineark-εmodel) may be used for design and optimization of various thermal systems using dimples for heat transfer enhancement (e.g. heat exchangers and internal cooling system of gas turbine blades).

Effect of Rotation on Heat Transfer in AR = 2:1 and AR = 4:1 Channels Connected by a Series of Crossover Jets

2021 ◽  
pp. 1-19
Author(s):  
Srivatsan Madhavan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Flow Direction ◽  
Gas Turbine Blade ◽  
Trailing Edge ◽  
Cooling Flow ◽  
Liquid Crystal Thermography ◽  
Pin Fins ◽  
Rib Turbulators

Abstract Detailed heat transfer measurements using transient liquid crystal thermography were performed on a novel cooling design covering the mid-chord and trailing edge region of a typical gas turbine blade under rotation. The test section comprised of two channels with aspect ratio (AR) of 2:1 and 4:1, where the coolant was fed into the AR = 2:1 channel. Rib turbulators with a pitch-to-rib height ratio (p/e) of 10 and rib height-to-channel hydraulic diameter ratio (e/Dh) of 0.075 were placed in the AR = 2:1 channel at 60° relative to flow direction. The coolant after entering this section was routed to the AR = 4:1 section through a set of crossover jets. The 4:1 section had a realistic trapezoidal shape that mimics the trailing edge of an actual gas turbine blade. The pin fins were arranged in a staggered array with a center-to-center spacing of 2.5 times pin diameter. The trailing edge section consisted of radial and cutback exit holes for flow exit. Experiments were performed for Reynolds number of 20,000 at Rotation numbers (Ro) of 0, 0.1 and 0.14. The channel averaged heat transfer coefficient on trailing side was ~28% (AR = 2:1) and ~7.6% (AR = 4:1) higher than the leading side for Ro = 0.1. It is shown that the combination of crossover jets and pin-fins can be an effective method for cooling wedge shaped trailing edge channels over axial cooling flow designs.

Experimental Survey on Heat Transfer in a Trailing Edge Cooling System: Effects of Rotation in Internal Cooling Ducts

2012 ◽  
Author(s):  
L. Bonanni ◽  
C. Carcasci ◽  
B. Facchini ◽  
L. Tarchi
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Cooling System ◽  
Internal Cooling ◽  
Test Rig ◽  
Trailing Edge ◽  
Tip Mass

The high thermal loads, the heavy structural stresses and the small thickness required for aerodynamic performances make the trailing edge cooling (TE) cooling of high pressure gas turbine blades a critical challenge. The presented paper point out an experimental study focusing the aerothermal performance of a TE internal cooling system of a high pressure gas turbine blade, evaluated under stationary and rotating conditions. The investigated geometry consists of a 30:1 scaled model reproducing the typical wedge shaped discharge duct with one row of enlarged pedestals. The airflow pattern inside the device simulates a highly loaded rotor blade cooling scheme with a 90° turning flow from the radial hub inlet to the tangential TE outlet. Two different tip configurations were tested, the first one with a completely closed section, the second one with 5 holes on the tip outlet surfaces discharging at ambient pressure. To investigate the rotation effects on the trailing edge cooling system performance, a rotating test rig was purposely developed and manufactured. The test rig is composed by a rotating arm that holds the PMMA TE model and the instrumentation. A thin Inconel heating foil and wide band Thermo-chromic Liquid Crystals are used to perform steady state heat transfer measurements. A rotary joint ensures the pneumatic connection between the blower and the rotating apparatus, moreover several slip rings are used for both instrumentation power supply and thermocouple connection. Heat transfer coefficient measurements were made with fixed Reynolds number close to 20k in the hub inlet section and with variable rotating speed in order to set the Rotation number from 0 (non rotational test) up to 0.3. Six different configurations were tested: two different tip mass flow rates (the first one with a completely closed tip, the second one with the 12.5% of the inlet flow discharged from the tip) and three different surface conditions: the first one consists in the flat plate case and the others in two ribbed cases, with different angular orientation (60° and −60° respect to the radial direction). Results are reported in terms of detailed heat transfer coefficient 2D maps on the suction side surface as well as span-wise profiles inside the pedestal ducts. The reported work has been supported by the Italian Ministry of Education, University and Research (MIUR).

Heat Transfer in Rotating, Trailing Edge, Converging Channels With Full and Partial Height Strip-Fins

2021 ◽  
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Direction ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Cooling Channels ◽  
Heat Transfer Coefficients ◽  
Pin Fins ◽  
Full Height

Abstract A wide variety of pin-fins have been used to enhance heat transfer in internal cooling channels. However, due to their large blockage in the flow direction, they result in an undesirable high pressure drop. This experimental study aims to reduce pressure drop while increasing the heat transfer surface area by utilizing strip-fins in converging internal cooling channels. The channel is designed with a trapezoidal cross-section, converges in both transverse and longitudinal directions, and is also skewed β = 120° with respect to the direction of rotation in order to model a trailing edge cooling channel. Only the leading and trailing surfaces of the channel are instrumented, and each surface is divided into eighteen isolated copper plates to measure the regionally averaged heat transfer coefficient. Utilizing pressure taps at the inlet and outlet of the channel, the pressure drop is obtained. Three staggered arrays of strip-fins are investigated: one full height configuration and two partial fin height arrangements (Sz = 2mm and 1mm). In all cases, the strip fins are 2mm wide (W) and 10mm long (Lf) in the flow direction. The fins are spaced such that Sy/Lf = 1 in the streamwise direction. However, due to the convergence the spanwise spacing Sx/W, was varied from 8 to 6.2 along the channel. The rotation number of the channel varied up to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300rpm. It is found that the full height strip-fin channel results in a more non-uniform spanwise heat transfer distribution than the partial height strip-fin channel. Both trailing and leading surface heat transfer coefficients are enhanced under rotation conditions. The 2mm height partial strip-fin channel provided the best thermal performance, and it is comparable to the performance of the converging channels with partial length circular pins. The strip-fin channel can be a design option when the pressure drop penalty is a major concern.

scholarly journals Heat Transfer Augmentation Technologies for Internal Cooling of Turbine Components of Gas Turbine Engines

2013 ◽  
Vol 2013 ◽  
pp. 1-32 ◽  
Author(s):  
Phil Ligrani
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Thermal Performance ◽  
Density Ratio ◽  
Extensive Literature ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Heat Transfer Augmentation ◽  
Pin Fins ◽  
Rib Turbulators

To provide an overview of the current state of the art of heat transfer augmentation schemes employed for internal cooling of turbine blades and components, results from an extensive literature review are presented with data from internal cooling channels, both with and without rotation. According to this survey, a very small number of existing investigations consider the use of combination devices for internal passage heat transfer augmentation. Examples are rib turbulators, pin fins, and dimples together, a combination of pin fins and dimples, and rib turbulators and pin fins in combination. The results of such studies are compared with data obtained prior to 2003 without rotation influences. Those data are comprised of heat transfer augmentation results for internal cooling channels, with rib turbulators, pin fins, dimpled surfaces, surfaces with protrusions, swirl chambers, or surface roughness. This comparison reveals that all of the new data, obtained since 2003, collect within the distribution of globally averaged data obtained from investigations conducted prior to 2003 (without rotation influences). The same conclusion in regard to data distributions is also reached in regard to globally averaged thermal performance parameters as they vary with friction factor ratio. These comparisons, made on the basis of such judgment criteria, lead to the conclusion that improvements in our ability to provide better spatially-averaged thermal protection have been minimal since 2003. When rotation is present, existing investigations provide little evidence of overall increases or decreases in overall thermal performance characteristics with rotation, at any value of rotation number, buoyancy parameter, density ratio, or Reynolds number. Comparisons between existing rotating channel experimental data and the results obtained prior to 2003, without rotation influences, also show that rotation has little effect on overall spatially-averaged thermal performance as a function of friction factor.

Detailed Heat Transfer Coefficient Measurements on a Scaled Realistic Turbine Blade Internal Cooling System

2019 ◽  
Vol 12 (3) ◽  
Author(s):  
Chao-Cheng Shiau ◽  
Andrew F. Chen ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Cooling System ◽  
Plastic Material ◽  
Local Heat Transfer ◽  
Transfer Characteristic ◽  
Internal Cooling ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Trailing Edge

Abstract A realistic internal cooling system of a turbine blade includes both ribs and pin-fins inside the passages to enhance the heat transfer. However, the majority studies in the open literature assessing the heat transfer characteristics on a simplified cooling model by examining ribbed-roughen passages and pin-finned passage separately. This work presents the high-resolution heat transfer coefficients of a scaled realistic turbine blade internal cooling design. The cooling system, using a 3D-printed plastic material, consists of an S-shaped inlet, four serpentine passages (three U-bends) of variable aspect ratio, and the trailing edge ejection. Angled ribs are implemented inside the passages and the elongated fins and pins are used near the trailing edge. Two dust holes are realized on the blade tip, the injections are individually controlled to reflect the realistic coolant flowrate variation inside the entire internal cooling system. The tests are conducted at two Reynolds number, 45,000 and 60,000 based on the hydraulic diameter of the inlet passage. Transient heat transfer technique using thermochromic liquid crystal is applied to obtain the detailed heat transfer characteristic inside the cooling channel. The local and averaged Nusselt numbers are also compared with the correlations in the open literature. This paper provides gas turbine designers the difference of local heat transfer distributions between the realistic and simplified internal cooling designs.

Evaluation of Wall Heat Transfer in Blade Trailing-Edge Cooling Passage

2013 ◽  
Vol 284-287 ◽  
pp. 738-742 ◽  
Author(s):  
Yu Feng Yao ◽  
Marwan Effendy ◽  
Jun Yao
Keyword(s):  
Heat Transfer ◽  
Transfer Model ◽  
Internal Cooling ◽  
Wall Heat Transfer ◽  
Trailing Edge ◽  
Pin Fin ◽  
Pin Fins ◽  
Cooling Passage ◽  
End Wall ◽  
Good Agreement

Model configurations of turbine blade trailing-edge internal cooling passage with staggered elliptic pin-fins in streamwise and spanwise are adopted for numerical investigation using computational fluid dynamics (CFD). Grid refinement study is performed at first to identify a baseline mesh, followed by validation study of passage total pressure loss, which gives 2% and 4% discrepancies respectively for two chosen configurations in comparison with experimental measurements. Further investigations are focused on evaluation of wall heat transfer coefficient (HTC) of both pin-fin and end walls, and it is found that CFD predicted pin-fin wall HTC are generally in good agreement with test data for the streamwise staggered elliptic pin-fins, but not the spanwise staggered elliptic pin-fins in which some discrepancies occur. CFD predicted end wall HTC have shown reasonable good agreement for the first three rows, but discrepancies seen in downstream rows are around a factor of 2-3. A ratio of averaged pin-fin and end walls HTC is estimated 1.3-1.5, close to that from a circular pin-fin configuration that has 1.8-2.1. Further study should focus on improving end wall HTC predictions, probably through a conjugate heat transfer model.

Concavity Enhanced Heat Transfer in an Internal Cooling Passage

1997 ◽  
Author(s):  
M. K. Chyu ◽  
Y. Yu ◽  
H. Ding ◽  
J. P. Downs ◽  
F. O. Soechting
Keyword(s):  
Heat Transfer ◽  
Imaging System ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Pressure Losses ◽  
Turbine Cooling ◽  
Rib Turbulators ◽  
Cooling Passage

The present study evaluates an innovative approach for enhancement of surface heat transfer in a channel using concavities, rather than protruding elements. Serving as a vortex generator, a concavity is expected to promote turbulent mixing in the flow bulk and enhance the heat transfer. Using a transient liquid crystal imaging system, local heat transfer distribution on the surface roughened by an staggered array based on two different shapes of concavities, i.e. hemispheric and tear-drop shaped, have been obtained, analyzed and compared. The results reveal that both concavity configurations induce a heat transfer enhancement similar to that of continuous rib turbulators, about 2.5 times their smooth counterparts 10,000 ≤ Re ≤ 50,000. In addition, both concavity arrays reveal remarkably low pressure losses that are nearly one-half the magnitudes incurred with protruding elements. In turbine cooling applications, the concavity approach is particularly attractive in reducing system weight and ease of manufacturing.

Conjugate Heat Transfer Analysis of Internally Cooled Turbine Blade

2012 ◽  
Author(s):  
Ilhan Gorgulu ◽  
Baris Gumusel ◽  
I. Sinan Akmandor
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Turbulence Model ◽  
Conjugate Heat Transfer ◽  
Turbulence Models ◽  
Heat Transfer Analysis ◽  
Internal Cooling ◽  
Turbine Blade Cooling ◽  
Internally Cooled ◽  
Rib Turbulators

There are different characters of air flow in a conventional gas turbine blade cooling channel. These flow characters; including high streamline curvature caused from 180 degree bends, sequential flow separations caused from rib turbulators and pin-fin structures are analyzed separately with available commercial software for different turbulence models and validated against reliable experimental data from open literature. Also coupled conjugate heat transfer analyses on NASA C3X vane, which has only radial holes through blade span for cooling, are conducted with the same turbulence models. The accuracy information gathered from all these analyses; each interested with a single character of air and coupled conjugate heat transfer are put together and applied to a conjugate numerical analysis of internally cooled (VKI) LS-89 turbine blade. Internal cooling scheme which is applied to (VKI) LS-89 turbine blade encompassed the aforementioned flow characters and analyses are performed under realistic conditions. Because of the high temperature values occurring at realistic conditions, thermal conductivity and specific heat capacity of air and metal (Inconel 718) are modeled as temperature dependent material properties instead of using constant values. Conducted research revealed that 4 eqn. V2-f turbulence model gives similar results compared to the 2 eqn. Realizable k-e, k-w SST turbulence models for 180 degree bend and rib turbulator cases. However, at NASA C3X vane analyses V2-f turbulence model results are far more accurate than other two turbulence models in the manner of heat transfer coefficient and surface temperature distribution.

Heat Transfer in a Rib and Pin Roughened Rotating Multipass Channel With Hub Turning Vane and Trailing-Edge Slot Ejection

2017 ◽  
Vol 10 (2) ◽  
Author(s):  
Hao-Wei Wu ◽  
Hootan Zirakzadeh ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Orientation Angle ◽  
Side Wall ◽  
Internal Cooling ◽  
Test Model ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Pin Fin ◽  
Pin Fins ◽  
Cooling Air

A multipassage internal cooling test model with a 180 deg U-bend at the hub was investigated. The flow is radially inward at the inlet passage while it is radially outward at the trailing edge passage. The aspect ratio (AR) of the inlet passage is 2:1 (AR = 2) while the trailing edge passage is wedge-shaped with side wall slot ejections. The squared ribs with P/e = 8, e/Dh = 0.1, α = 45 deg, were configured on both leading surface (LE) and trailing surface (TR) along the inlet passage, and also at the inner half of the trailing edge passage. Three rows of cylinder-shaped pin fins with a diameter of 3 mm were placed at both LE and TR at the outer half of the trailing edge passage. For without turning vane case, heat transfer on LE at hub turn region is increased by rotation while it is decreased on the TR. The presence of turning vane reduces the effect of rotation on hub turn portion. The combination of ribs, pin-fin array, and mass loss of cooling air through side wall slot ejection results in the heat transfer coefficient gradually decreased along the trailing edge passage. Correlation between regional heat transfer coefficients and rotation numbers is presented for with and without turning vane cases, and with channel orientation angle β at 90 deg and 45 deg.

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