HEAT TRANSFER IN ROTATING, TRAILING EDGE, CONVERGING CHANNELS WITH FULL AND PARTIAL HEIGHT STRIP-FINS

2022 ◽  
pp. 1-32
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Rotation Speed ◽  
Flow Direction ◽  
Internal Cooling ◽  
Enhance Heat Transfer ◽  
Trailing Edge ◽  
Cooling Channels ◽  
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

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.

Heat Transfer and Pressure Drop in a Converging Pedestal Array With Exit Area Variation

2018 ◽  
Author(s):  
L. W. Soma ◽  
F. E. Ames ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Rate ◽  
Film Cooling ◽  
Reynolds Numbers ◽  
Flow Path ◽  
Internal Cooling ◽  
Channel Measurements ◽  
Trailing Edge ◽  
Cooling Air

The trailing edge of a vane is one of the most difficult areas to cool due to a narrowing flow path, high external heat transfer rates, and deteriorating external film cooling protection. Converging pedestal arrays are often used as a means to provide internal cooling in this region. The thermally induced stresses in the trailing edge region of these converging arrays have been known to cause failure in the pedestals of conventional solidity arrays. The present paper documents the heat transfer and pressure drop through two high solidity converging rounded diamond pedestal arrays. These arrays have a 45 percent pedestal solidity. One array which was tested has nine rows of pedestals with an exit area in the last row consistent with the convergence. The other array has eight rows with an expanded exit in the last row to enable a higher cooling air flow rate. The expanded exit of the eight row array allows a 30% increase in the coolant flow rate compared with the nine row array for the same pressure drop. Heat transfer levels correlate well based on local Reynolds numbers but fall slightly below non converging arrays. The pressure drop across the array naturally increases toward the trailing edge with the convergence of the flow passage. A portion of the cooling air pressure drop can be attributed to acceleration while a portion can be attributed to flow path losses. Detailed array static pressure measurements provide a means to develop a correlation for the prediction of pressure drop across the cooling channel. Measurements have been acquired over Reynolds numbers based on exit flow conditions and the characteristic pedestal length scale ranging from 5000 to over 70,000.

scholarly journals Effects of Channel Outlet Configuration and Dimple/Protrusion Arrangement on the Blade Trailing Edge Cooling Performance

2019 ◽  
Vol 9 (14) ◽  
pp. 2900
Author(s):  
Qi Jing ◽  
Yonghui Xie ◽  
Di Zhang
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
High Heat ◽  
Wake Flow ◽  
Internal Cooling ◽  
Trailing Edge ◽  
Cooling Channels ◽  
High Heat Transfer ◽  
Channel Outlet ◽  
Staggered Arrangement

The trailing edge regions of high-temperature gas turbine blades are subjected to extremely high thermal loads and are affected by the external wake flow during operation, thus creating great challenges in internal cooling design. With the development of cooling technology, the dimple and protrusion have attracted wide attention for its excellent performance in heat transfer enhancement and flow resistance reduction. Based on the typical internal cooling structure of the turbine blade trailing edge, trapezoidal cooling channels with lateral extraction slots are modeled in this paper. Five channel outlet configurations, i.e., no second passage (OC1), radially inward flow second passage (OC2), radially outward flow second passage (OC3), top region outflow (OC4), both sides extractions (OC5), and three dimple/protrusion arrangements (all dimple, all protrusion, dimple–protrusion staggered arrangement) are considered. Numerical investigations are carried out, within the Re range of 10,000–100,000, to analyze the flow structures, heat transfer distributions, average heat transfer and friction characteristics and overall thermal performances in detail. The results show that the OC4 and OC5 cases have high heat transfer levels in general, while the heat transfer deterioration occurs in the OC1, OC2, and OC3 cases. For different dimple/protrusion arrangements, the protrusion case produces the best overall thermal performance. In conclusion, for the design of trailing edge cooling structures with lateral slots, the outlet configurations of top region outflow and both sides extractions, and the all protrusion arrangement, are recommended.

Topology Optimization of Serpentine Channels for Minimization of Pressure Loss and Maximization of Heat Transfer Performance As Applied for Additive Manufacturing

2019 ◽  
Author(s):  
Shinjan Ghosh ◽  
Jayanta S. Kapat
Keyword(s):  
Heat Transfer ◽  
Topology Optimization ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Blade Cooling

Abstract Gas Turbine blade cooling is an important topic of research, as a high turbine inlet temperature (TIT) essentially means an increase in efficiency of gas turbine cycles. Internal cooling channels in gas turbine blades are key to the cooling and prevention of thermal failure of the material. Serpentine channels are a common feature in internal blade cooling. Optimization methods are often employed in the design of blade internal cooling channels to improve heat-transfer and reduce pressure drop. Topology optimization uses a variable porosity approach to manipulate flow geometries by adding or removing material. Such a method has been employed in the current work to modify the geometric configuration of a serpentine channel to improve total heat transferred and reduce the pressure drop. An in-house OpenFOAM solver has been used to create non-traditional geometries from two generic designs. Geometry-1 is a 2-D serpentine passage with an inlet and 4 bleeding holes as outlets for ejection into the trailing edge. Geometry-2 is a 3-D serpentine passage with an aspect ratio of 3:1 and consists of two 180-degree bends. The inlet velocity for both the geometries was used as 20 m/s. The governing equations employ a “Brinkman porosity parameter” to account for the porous cells in the flow domain. Results have shown a change in shape of the channel walls to enhance heat-transfer in the passage. Additive manufacturing can be employed to make such unconventional shapes.

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.

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.

scholarly journals Heat Transfer and Pressure Drop Evaluation in Thin Wedge-Shaped Trailing Edge

2003 ◽  
Author(s):  
C. Carcassi ◽  
B. Facchini ◽  
L. Innocenti
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Bottom Surface ◽  
Moderate Pressure ◽  
Trailing Edge ◽  
Number Range ◽  
Trailing Edges ◽  
Pin Fins

In modern high loaded transonic turbines the aerodynamic losses of turbine airfoils are mostly covered by the thickness and the wedge angle of the blade trailing edges. Due to the aerodynamic requirements the thin trailing edges are the life limiting parts of the airfoils. The aerodynamic design requirements lead to trailing edge slots with extreme aspect ratio and huge fillet radius in relation to the internal slot geometry. In most cases, the conventional design tools are not validated for these geometries, therefore an improved knowledge of flow and heat transfer in this area is necessary. This paper discusses the measurements of endwall heat transfer coefficient and pressure drops in a wedge-shaped duct with two different turbulators arrangement. The first one is concerning five different long ribs (pedestals) configurations disposed streamwise while the other one is related to three configurations of staggered pin fins. Pedestals and pin fins stand vertically on the bottom surface of the wedge–shaped duct. This surface, named endwall, is coated with a thin layer of thermochromic liquid crystals and several transient tests are run to obtain detailed heat transfer coefficient distributions. Both for the pedestal and pin fins several parametric studies has been performed, varying both Reynolds number range (from 9000 to 27000) and turbulators configurations while outlet Mach number was set to 0.3 for all tests. Investigated pedestal configurations are different for turbulators spanwise pitch while pin fins geometry have different pin diameter values. In all cases the wedge duct angle is 10°. Results indicate that the smallest long ribs pitch and pin fin diameter are most recommended because of its significant endwall heat transfer and moderate pressure-drop penalty. Long ribs and pin-fins are aluminium made in order to evaluate an average value of the heat transfer coefficient on their side surface. So a valuation of global heat transfer coefficient in the internal trailing edge cooling duct become possible.

Heat Transfer in Trailing Edge, Wedge-Shaped Cooling Channels Under High Rotation Numbers

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Lesley M. Wright ◽  
Yao-Hsien Liu ◽  
Je-Chin Han ◽  
Sanjay Chopra
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Cooling Channels ◽  
Heat Transfer Coefficients ◽  
Buoyancy Parameter ◽  
Cooling Passage

Heat transfer coefficients are experimentally measured in a rotating cooling channel used to model an internal cooling passage near the trailing edge of a gas turbine blade. The regionally averaged heat transfer coefficients are measured in a wedge-shaped cooling channel (Dh=2.22cm, Ac=7.62cm2). The Reynolds number of the coolant varies from 10,000 to 40,000. By varying the rotational speed of the channel, the rotation number and buoyancy parameter range from 0 to 1.0 and 0 to 3.5, respectively. Significant variation of the heat transfer coefficients in both the spanwise and streamwise directions is apparent. Spanwise variation is the result of the wedge-shaped design, and streamwise variation is the result of the sharp entrance into the channel and the 180deg turn at the outlet of the channel. With the channel rotating at 135° with respect to the direction of rotation, the heat transfer coefficients are enhanced on every surface of the channel. Both the nondimensional rotation number and buoyancy parameter have proven to be excellent parameters to quantify the effect of rotation over the extended ranges achieved in this study.

scholarly journals Pressure Drop Distribution in a Rotating Rectangular Channel With One Ribbed Surface

1997 ◽  
Author(s):  
S. V. Prabhu ◽  
R. P. Vedula
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Turbine Rotor ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Turbine Rotor Blade ◽  
Blade Thickness

A modified geometry for the internal cooling passages of a gas turbine rotor blade is suggested here. In this modified geometry, the Coriolis force induced enhanced heat transfer coefficients are experienced by both the coolant channel walls adjacent to the blade pressure and blade suction surfaces. This is made possible by permitting the flow to have a radially outward and a radially inward direction at different locations along the blade thickness at a given chordwise location. However, the flow geometry is complex and the corresponding pressure losses are also likely to be larger. The present investigation is a preliminary study of the pressure drop characteristics for the modified channel suggested above and the simplest case of a straight channel with ribs on only one surface is reported here. The pressure drop in a rectangular cross-sectioned duct with an aspect ratio of 2.0 rotating about an axis normal to the free-stream direction in the presence of rib turbulators glued on one of the surfaces of the test section with ribs normal to the flow direction is measured. The study has been conducted for Reynolds number varying from 10000–17000 and the rotation number varying from 0–0.21. Experiments were carried out for various pitch-to-rib height ratios (P/e) of 3, 5, 7.5 & 10 with a constant rib height-to-hydraulic diameter ratio (e/D) of 0.15. A significant increase of the friction factor is observed when the ribbed surface is the coolant channel trailing (pressure) surface in the presence of rotation. The highest friction factor is observed in a channel with a P/e ratio of 5 which would imply that there could be a significant increase in the heat transfer coefficient for this configuration. A pitch-to-height ratio of about 10, which is the most preferred choice for a stationary configuration, no longer appears to be the optimum in the presence of rotation.

Heat Transfer in Rotating, Trailing Edge, Converging Channels With Partial Length Pin-Fins

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Slight Reduction ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Partial Length ◽  
Pin Fins ◽  
Cooling Passage

Abstract In the current study, the heat transfer and pressure drop characteristics of a rotating, partial pin-finned, cooling channel that has a trapezoidal cross section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. To model the geometry of an internal trailing edge cooling passage, the channel is oriented with respect to the direction of rotation (β = 120 deg). Isolated copper plates are used to obtain regionally averaged heat transfer coefficients on the leading and trailing surfaces. Pressure drop is measured using pressure taps placed at the inlet and outlet of the channel. Utilizing Dp = 5 mm diameter pins, a staggered array is created. For this array, the streamwise pin-spacing, Sy/Dp = 2.1, was kept constant; however, the spanwise pin-spacing, Sx/Dp, was varied from the hub to tip between 3 and 2.6 due to the channel convergence. Experiments were conducted for two partial pin-fin sets having pin length-to-diameter ratios of Sz/Dp = 0.4 and 0.2. The rotation number was varied from 0 to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300 rpm. A significant decrease in pressure loss and a slight reduction in heat transfer enhancement are observed with the use of partial pin-fins compared with the previously reported full pin-fin converging channel study. This provides better thermal performances of the partial pin-fin arrays compared with the full pin-fin array, in the converging channels.

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