A213 A Study on the Effect of Angled Pin Fins on Endwall Heat Transfer(Gas Turbine-7)

Almost all measurements of the heat-transfer coefficient (HTC) or Nusselt number (Nu) in gas-turbine cooling passages with heat-transfer enhancement features such as pin fins and ribs have been made under conditions, where the wall-to-bulk temperature, Tw/Tb, is near unity. Since Tw/Tb in gas-turbine cooling passages can be as high as 2.2 and vary appreciably along the passage, this study examines if it is necessary to match the rate of change in Tw/Tb when measuring Nu, whether Nu measured at Tw/Tb near unity needs to be scaled before used in design and analysis of turbine cooling, and could that scaling for ducts with heat-transfer enhancement features be obtained from scaling factors for smooth ducts because those scaling factors exist in the literature. In this study, a review of the data in the literature shows that it is unnecessary to match the rate of change in Tw/Tb for smooth ducts at least for the rates that occur in gas turbines. For ducts with heat-transfer enhancement features, it is still an open question. This study also shows Nu measured at Tw/Tb near unity needs to be scale to the correct Tw/Tb before it can be used for engine conditions. By using steady RANS analysis of the flow and heat transfer in a cooling channel with a staggered array of pin fins, the usefulness of the scaling factor, (Tw/Tb)r, from the literature for smooth ducts was examined. Nuengine, computed under engine conditions, was compared with those computed under laboratory conditions, Nulab, and scaled by (Tw/Tb)r; i.e., Nulab,scaled = Nulab (Tw/Tb)r. Results obtained show the error in Nulab,scaled relative to Nuengine can be as high as 36.6% if r = −0.7 and Tw/Tb = 1.573 in the “fully” developed region. Thus, (Tw/Tb)r based on smooth duct should not be used as a scaling factor for Nu in cooling passages with heat-transfer enhancement features. To address this inadequacy, a method is proposed for generating scaling factors, and a scaling factor was developed to scale the heat transfer from laboratory to engine conditions for a channel with pin fins.

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Effect of Variation of Pin-fin Height on Jet Impingement Heat Transfer on a Rotating Surface

ASME 2021 Heat Transfer Summer Conference ◽

10.1115/ht2021-63946 ◽

2021 ◽

Author(s):

Pratik S. Bhansali ◽

Srinath V. Ekkad

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Nusselt Number ◽

Gas Turbine ◽

Average Nusselt Number ◽

Jet Impingement ◽

Impinging Jet ◽

Rotating Disc ◽

Disc Surface ◽

Pin Fins

Abstract Heat transfer over rotating surfaces is of particular interest in rotating machinery such as gas turbine engines. The rotation of the gas turbine disc creates a radially outward flow on the disc surface, which may lead to ingress of hot gases into the narrow cavity between the disc and the stator. Impingement of cooling jet is an effective way of cooling the disc and countering the ingress of the hot gases. Present study focusses on investigating the effect of introducing pin-fins over the rotating disc on the heat transfer. The jet Reynolds number has been varied from 5000 to 18000, and the rotating Reynolds number has been varied from 5487 to 12803 for an aluminum disc of thickness 6.35mm and diameter 10.16 cm, over which square pins have been arranged in an inline fashion. Steady state temperature measurements have been taken using thermocouples embedded in the disc close to the target surface, and area average Nusselt number has been calculated. The effects of varying the height of the pin-fins, distance between nozzle and the disc surface and the inclination of the impinging jet with the axis of rotation have also been studied. The results have been compared with those for a smooth aluminum disc of equal dimensions and without any pin-fins. The average Nusselt number is significantly enhanced by the presence of pin fins. In the impingement dominant regime, where the effect of disc rotation is minimal for a smooth disc, the heat transfer increases with rotational speed in case of pin fins. The effect of inclination angle of the impinging jet is insignificant in the range explored in this paper (0° to 20°).

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Heat Transfer Measurements of Oblong Pins

Volume 5A: Heat Transfer ◽

10.1115/gt2014-25370 ◽

2014 ◽

Cited By ~ 1

Author(s):

Kathryn L. Kirsch ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Flow Direction ◽

Effective Means ◽

Transfer Enhancement ◽

Pin Fin ◽

The Third ◽

Pin Fins ◽

Two Peaks ◽

Pin Fin Arrays

Pin fin arrays are employed as an effective means for heat transfer enhancement in the internal passages of a gas turbine blade, specifically in the blade’s trailing edge. Various shapes of the pin itself have been used in such arrays. In this study, oblong pin fins are investigated whereby their long axis is perpendicular to the flow direction. Heat transfer measurements were taken at the pin mid-span with unheated endwalls to isolate the pin heat transfer. Results show important differences in the heat transfer patterns between a pin in the first row and a pin in the third row. In the third row, wider spanwise spacing allows for two peaks in heat transfer over the pin surface. Additionally, closer streamwise spacing leads to consistently higher heat transfer for the same spanwise spacing. Due to the blunt orientation of the pins, the peak in heat transfer occurs off the stagnation point.

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Effects of Geometry, Spacing, and Number of Pin Fins in Additively Manufactured Microchannel Pin Fin Arrays

Journal of Turbomachinery ◽

10.1115/1.4038179 ◽

2017 ◽

Vol 140 (1) ◽

Cited By ~ 17

Author(s):

Katharine K. Ferster ◽

Kathryn L. Kirsch ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Pressure Loss ◽

Reynolds Numbers ◽

Turbine Engine ◽

Pin Fin ◽

Study Results ◽

Pin Fins ◽

Turbine Airfoils ◽

Pin Fin Arrays

The demand for higher efficiency is ever present in the gas turbine field and can be achieved through many different approaches. While additively manufactured parts have only recently been introduced into the hot section of a gas turbine engine, the manufacturing technology shows promise for more widespread implementation since the process allows a designer to push the limits on capabilities of traditional machining and potentially impact turbine efficiencies. Pin fins are conventionally used in turbine airfoils to remove heat from locations in which high thermal and mechanical stresses are present. This study employs the benefits of additive manufacturing to make uniquely shaped pin fins, with the goal of increased performance over conventional cylindrical pin fin arrays. Triangular, star, and spherical shaped pin fins placed in microchannel test coupons were manufactured using direct metal laser sintering (DMLS). These coupons were experimentally investigated for pressure loss and heat transfer at a range of Reynolds numbers. Spacing, number of pin fins in the array, and pin fin geometry were variables that changed pressure loss and heat transfer in this study. Results indicate that the additively manufactured triangles and cylinders outperform conventional pin fin arrays, while stars and dimpled spheres did not.

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

Journal of Turbomachinery ◽

10.1115/1.4053237 ◽

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.

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Numerical Studies on Effect of Channel Orientation in a Rotating Smooth Wedge-Shaped Cooling Channel

Volume 5A: Heat Transfer ◽

10.1115/gt2014-26560 ◽

2014 ◽

Cited By ~ 3

Author(s):

Balamurugan Srinivasan ◽

Anand Dhamarla ◽

Chandiran Jayamurugan ◽

Amarnath Balu Rajan

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Gas Turbine ◽

Turbine Blade ◽

Cooling Channel ◽

Transfer Enhancement ◽

Trailing Edge ◽

Pin Fins ◽

Channel Orientation ◽

The Heat Transfer Coefficient

The increasing demands of better efficiency of modern advanced gas turbine require higher turbine inlet temperatures, which gives great challenges to turbine blade designers. However, the temperature limits of turbine blade material are not high enough to ensure its survival in such incredible operating temperature. Hence, both internal and external cooling approaches have been developed and widely used in today’s turbine blade. To internal cooling problems, a variety of cooling enhancement approaches, such as impingement and turbulators, are employed in order to meet the different needs in leading, middle and trailing region. One of the most critical parts in turbine blade is trailing edge where it is hard to cool due to its narrow shape. Pin-fins are widely used to cool the trailing edge of rotor and stator blades of gas turbine engine. Pin-fins offer significant heat transfer enhancement, they are relatively easy to fabricate and offer structural support to the hollow trailing edge region. The flow physics in a pin-fin roughened channel is very complicated and three-dimensional. In this work, we have studied the effect of channel orientation on heat transfer in a rotating wedge-shaped cooling channel using numerical methods. Qiu [1] studied experimentally heat transfer effects of 5 different angles of wedge shaped channel orientation for the inlet Reynolds number (5100 to 21000) and rotational speed (zero to 1000 rpm), which results in the inlet Rotation number variation from 0 to 0.68. They observed that compared to the non-rotating condition, there is about 35% overall heat transfer enhancement under highest rotation number. The above said results are validated using current studies with Computational Fluid Dynamics (CFD) revealed that rotation increases significantly the heat transfer coefficient on the trailing surface and reduces the heat transfer coefficient on the leading surface. This is due to the higher velocities associated with the converging geometry near trailing surface.

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Effect of Pin-fins On Jet Impingement Heat Transfer Over a Rotating Disk

Journal of Heat Transfer ◽

10.1115/1.4053371 ◽

2021 ◽

Author(s):

Pratik S. Bhansali ◽

Kishore Ranganath Ramakrishnan ◽

Srinath V. Ekkad

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Gas Turbines ◽

Jet Impingement ◽

Reynolds Numbers ◽

High Heat ◽

Maximum Enhancement ◽

Pin Fin ◽

Smooth Disk ◽

Pin Fins

Abstract Many engineering applications consist of rotating components which experience high heat load. For instance, applications like the gas turbine engine consist of rotating disks and the study of heat transfer over such rotating surfaces is of particular interest. In the case of gas turbines, the disk also needs to be protected from the ingress of hot turbine gases caused by the low pressure region created due to the radially outward pumping of fluid close to the rotating surface. Present experimental study investigates the effects of introducing pin-fins on heat transfer over surface of a rotating gas turbine disk. Experiments were conducted at rotational Reynolds numbers (ReR) of 5487 - 12803 and jet Reynolds numbers (Re) of 5000 - 18000, nozzle to target spacing (z/d = 2 - 6), impingement eccentricities (e = 0 -0.67), angles of impingement (0°-20°), and the pin fin height (Hf = 3.05mm - 19.05mm). Steady state temperature measurements were taken using thermocouples embedded in the disk, and area average Nusselt number (Nu) was calculated. The results have been compared with those for a smooth aluminum disk. Nu was significantly enhanced by the presence of pin-fins. The enhancement was higher for lower Re and the maximum enhancement was found to be 3.9 times that of a smooth disk for Re = 5000. Qualitative visualization of flow field has been performed for smooth and the pin-fin case using the commercial simulation package Ansys Fluent to further understand the flow features that result in the enhancement.

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Simulation of Impinging Cooling Performance with Pin Fins and Mist Cooling Adopted in a Simplified Gas Turbine Transition Piece

Advances in Mathematical Physics ◽

10.1155/2014/327590 ◽

2014 ◽

Vol 2014 ◽

pp. 1-11 ◽

Cited By ~ 1

Author(s):

Tao Xu ◽

Hang Xiu ◽

Junlou Li ◽

Haichao Ge ◽

Qing Shao ◽

...

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Weighted Average ◽

Two Phase ◽

Cooling Performance ◽

Pin Fin ◽

Pin Fins ◽

Mist Cooling ◽

Transition Piece ◽

Impinging Cooling

The gas turbine transition piece was simplified to a one-four cylinder double chamber model with a single row of impinging holes in the outer wall. Heat transfer augmentation in the coolant chamber was achieved through the use of pin fin structure and mist cooling, which could increase the turbulence and heat transfer efficiency. The present research is focused on heat transfer and pressure characteristics of the impinging cooling in the coolant chamber using FLUENT software. With the given diameter of impinging hole, pin fin diameter ratiosD/dhave been numerically studied in ranges from 1 to 2. Three different detachedLwere simulated. The impinging cooling performance in all cases was compared between single-phase and two-phase (imported appropriate mist) flow in the coolant chamber. All the simulation results reveal that the factors ofLandD/dhave significant effects on the convective heat transfer. After the pin fin structure was taken, the resulting temperature decrease of 38.77 K at most compared with the result of structure without pin fins. And with the mist injecting into the cooling chamber, the area weighted average temperature got a lower value without excess pressure loss, which could satisfy the more stringent requirements in engineering.

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Effects of Geometry and Spacing in Additively Manufactured Microchannel Pin Fin Arrays

Volume 5C: Heat Transfer ◽

10.1115/gt2017-63442 ◽

2017 ◽

Author(s):

Katharine K. Ferster ◽

Kathryn L. Kirsch ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Pressure Loss ◽

Reynolds Numbers ◽

Turbine Engine ◽

Pin Fin ◽

Study Results ◽

Pin Fins ◽

Turbine Airfoils ◽

Pin Fin Arrays

The demand for higher efficiency is ever-present in the gas turbine field and can be achieved through many different approaches. While additively manufactured parts have only recently been introduced into the hot section of a gas turbine engine, the manufacturing technology shows promise for more widespread implementation since the process allows a designer to push the limits on capabilities of traditional machining and potentially impact turbine efficiencies. Pin fins are conventionally used in turbine airfoils to remove heat from locations in which high thermal and mechanical stresses are present. This study employs the benefits of additive manufacturing to make uniquely shaped pin fins, with the goal of increased performance over conventional cylindrical pin fin arrays. Triangular, star, and spherical shaped pin fins placed in microchannel test coupons were manufactured using Direct Metal Laser Sintering. These coupons were experimentally investigated for pressure loss and heat transfer at a range of Reynolds numbers. Spacing, number of pin fins in the array, and pin fin geometry were variables that changed pressure loss and heat transfer in this study. Results indicate that the additively manufactured triangles and cylinders outperform conventional pin fin arrays, while stars and dimpled spheres did not.

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Heat Transfer Measurements of Oblong Pins

Journal of Turbomachinery ◽

10.1115/1.4029124 ◽

2015 ◽

Vol 137 (7) ◽

Cited By ~ 1

Author(s):

Kathryn L. Kirsch ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Flow Direction ◽

Effective Means ◽

Transfer Enhancement ◽

Pin Fin ◽

The Third ◽

Pin Fins ◽

Two Peaks ◽

Pin Fin Arrays

Pin fin arrays are employed as an effective means for heat transfer enhancement in the internal passages of a gas turbine blade, specifically in the blade's trailing edge. Various shapes of the pin itself have been used in such arrays. In this study, oblong pin fins are investigated whereby their long axis is perpendicular to the flow direction. Heat transfer measurements were taken at the pin midspan with unheated endwalls to isolate the pin heat transfer. Results show important differences in the heat transfer patterns between a pin in the first row and a pin in the third row. In the third row, wider spanwise spacing allows for two peaks in heat transfer over the pin surface. Additionally, closer streamwise spacing leads to consistently higher heat transfer for the same spanwise spacing. Due to the blunt orientation of the pins, the peak in heat transfer occurs off the stagnation point.

Download Full-text