Heat Transfer of a Chordwise-Oriented Internal Cooling Passage Around a Turbine Airfoil

2001 ◽  
Author(s):  
M. K. Chyu ◽  
O. B. Ojo ◽  
C. H. Yen ◽  
R. S. Nordlund
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Trailing Edge ◽  
Cooling Passage

Abstract An innovative design of closed-loop cooling system for a stator airfoil consists of a number of internal cooling passages wrapping around both pressure and suction sides of the airfoil. The cooling passages feature (1) jet impingement post a sharp 90-degree turn at the passage inlet, (2) turbulators on the outermost wall, and (3) a nearly 180-degree turn in the trailing edge. In addition, the passage has an irregular cross-section and varies throughout its entire length. A series of heat transfer tests have been performed at Re = 17,000 ∼ 61,000, compared to this tests which uses a new approach, so-called the hybrid liquid crystal technique. The magnitude of local heat transfer coefficient rises sharply in three regions. The first maximum occurs in the region subjected to direct jet impingement as the flow turns into the channel. Compounded with the inlet effect, this maximum, in fact, is the highest heat transfer coefficient over the entire passage. The second and third peaks, both are comparable in magnitude, locate near the trailing edge of the airfoil where the flow experiences a 180-degree turn and near the passage exit with a 90-degree turn. The average value of heat transfer coefficient over the entire passage is about 1.9∼ 2.5 times higher than that with fully developed turbulent flow in a straight channel. This level of enhancement is comparable to that of the conventional ribturbulators with a 90-degree angle-of-attack.

Detailed Experimental Characterization of Heat Transfer Coefficient Over the Internal Cooling Passages of an Additive Manufactured Turbine Airfoil

2016 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Jae Y. Um ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Scale Model ◽  
Internal Cooling ◽  
Trailing Edge

This report describes the detailed experimental study to characterize the local heat transfer coefficient distribution over the internal cooling passages of a simplified generic airfoil. The airfoil is manufactured through additive manufacturing based on actual geometry and dimensions (1X scale model) of row one airfoil, applicable in large gas turbine system. At the mainbody section, the serpentine channel consists of three passages without any surface features or vortex generators. Both the leading edge and trailing edge sections are subjected to direct impingement. The trailing edge section is divided into three chambers, separated by two rows of blockages. This study employs the well-documented transient liquid crystal technique, where the local heat transfer coefficient on both pressure and suction sides is deduced. The experiments were performed at varying Reynolds number, ranging from approximately 31,000–63,000. The heat transfer distribution on the pressure side and suction side is largely comparable in the first and third pass, except for the second pass. Highest heat transfer occurs at the trailing edge region, which is ultimately dominated by impingement due to the presence of three rows of blockages. A cursory numerical calculation is performed using commercially available software, ANSYS CFX to obtain detailed flow field distribution within the airfoil, which explains the heat transfer behavior at each passage. The flow parameter results revealed that the pressure ratio is strongly proportional with increasing Reynolds number.

Three-Dimensional Transient Heat Conduction Equation Solution for Accurate Quantification of Heat Transfer Coefficient in Transient Liquid Crystal Experiments

2019 ◽  
Author(s):  
Shoaib Ahmed ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Conduction Model

Abstract Liquid crystal thermography and infrared thermography techniques are typically employed to measure detailed surface temperatures, where local heat transfer coefficient (HTC) values are calculated by employing suitable conduction models. One such practice, which is very popular and easy to use, is the transient liquid crystal thermography using one-dimensional semi-infinite conduction model. In these experiments, a test surface with low thermal conductivity and low thermal diffusivity (e.g. acrylic) is used where a step-change in coolant air temperature is induced and surface temperature response is recorded. An error minimization routine is then employed to guess heat transfer coefficients of each pixel, where wall temperature evolution is known through an analytical expression. The assumption that heat flow in the solid is essentially in one-dimension, often leads to errors in HTC determination and this error depends on true HTC, wall temperature evolution and HTC gradient. A representative case of array jet impingement under maximum crossflow condition has been considered here. This heat transfer enhancement concept is widely used in gas turbine leading edge and electronics cooling. Jet impingement is a popular cooling technique which results in high convective heat rates and has steep gradients in heat transfer coefficient distribution. In this paper, we have presented a procedure for solution of three-dimensional transient conduction equation using alternating direction implicit method and an error minimization routine to find accurate heat transfer coefficients at relatively lower computational cost. The HTC results obtained using 1D semi-infinite conduction model and 3D conduction model were compared and it was found that the heat transfer coefficient obtained using the 3D model was consistently higher than the conventional 1D model by 3–16%. Significant deviations, as high as 8–20% in local heat transfer at the stagnation points of the jets were observed between h1D and h3D.

Effects of Pin Detached Space on Heat Transfer in a Rib Roughened Channel

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Hybrid Technique ◽  
Pin Fins ◽  
Cooling Passage ◽  
Rib Roughened

An experimental study is performed to investigate the heat transfer characteristics and frictional losses in a rib roughened channel combined with detached pin-fins. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = [1/4]E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e., C/D = 0, 1, 2, respectively. The rib height-to-channel height ratio is 0.0625. Two newly proposed cross ribs, namely the broken rib and full rib are evaluated in this effort. The broken ribs are positioned in between two consecutive rows of pin-fins, while the full ribs are fully extended adjacent to the pin-fins. The Reynolds number, based on the hydraulic diameter of the unobstructed cross section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all pin elements. The presence of ribs enhances local heat transfer coefficient on the endwall substantially by approximately 20% to 50% as compared to the neighboring endwall. In addition, affected by the rib geometry, which is a relatively low profile as compared to the overall height of the channel, the pressure loss seems to be insensitive to the presence of the ribs. However, from the overall heat transfer enhancement standpoint, the baseline cases (without ribs) outperform cases with broken ribs or full ribs.

Effects of Pin Detached Space on Heat Transfer in a Rib Roughened Channel

2011 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Hybrid Technique ◽  
Pin Fins ◽  
Cooling Passage ◽  
Rib Roughened

An experimental study is performed to investigate the heat transfer characteristics and frictional losses in a rib roughened walls combined with detached pin-fins. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = 1/4E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e. C/D = 0, 1, 2, respectively. The rib height-to-channel height ratio is 0.0625. Two newly proposed cross-ribs, namely the broken ribs and full ribs are evaluated in this effort. The broken ribs are positioned in between two consecutive rows of pin-fins, while the full ribs are fully extended adjacent to the pin fins. The Reynolds number, based on the hydraulic diameter of the unobstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. The presence of ribs has enhanced the local heat transfer coefficient on the endwall substantially by about 20% up to 50% as compared to the neighboring endwall. In addition, affected by the rib geometry, which is a relatively low profile as compared to the overall height of the channel, the pressure loss seems to be insensitive to the presence of the ribs. However, from the overall heat transfer enhancement standpoint, the baseline cases (without ribs) outperforms cases with broken ribs and full ribs.

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).

scholarly journals Determination of Local Heat Transfer Coefficient Based on Bulk Mean Temperature Using a Transient Liquid Crystals Technique

1997 ◽  
Author(s):  
M. K. Chyu ◽  
H. Ding ◽  
J. P. Downs ◽  
A. Van Sutendael ◽  
F. O. Soechting
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Inlet Temperature ◽  
Test Model ◽  
Mean Temperature ◽  
Cooling Passage

Recent advances in thermochromic liquid crystal (TLC) thermography have improved its usefulness as a very effective temperature and heat transfer measurement technique. One of the approaches to determine the local heat transfer coefficient, known as the transient technique, is to monitor the temporal evolution of surface temperature in conjunction with the solution of a transient heat conduction model penetrating to the wall substrate. The local heat transfer coefficient resulted from such a transient test, by nature, has its reference temperature based on the inlet temperature of the test rig, rather than the local bulk mean temperature. The latter during a transient test varies with both time and streamwise location. The heat transfer coefficient based on the inlet temperature presents difficulty in data interpretation in designs of turbine cooling passages, particularly for passages with large length-to-diameter ratios. This study evaluates four different approaches and theoretical background associated for determining the local bulk mean temperature and the sensible local heat transfer coefficient. Using a test model of an internal cooling passage with delta-wing shaped vortex generators mounted on one of the passage walls, the magnitudes of the sensible heat transfer coefficient resulted from various approaches vary as much as 40%. Validated with the experimental data, two of the four methods yield superb data accuracy. Nevertheless, one of them stands out as the best choice, as it requires much less post-processing time and implementation effort.

Thermal Transport From a Rotating Disk During Partially Confined Liquid Jet Impingement

2007 ◽  
Author(s):  
Jorge Lallave ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jet ◽  
Interface Temperature

This paper presents a numerical study that characterizes the conjugate heat transfer results of a semi–confined liquid jet impingement on a uniformly heated spinning solid disk of finite thickness and radius. The model covers the entire fluid region including the impinging jet on a flat circular disk and flow spreading out downstream under the confined insulated wall that ultimately gets exposed to a free surface boundary condition. The solution is made under steady state and laminar conditions. The model examines how the heat transfer is affected by adding a secondary rotational flow under semi-confined jet impingement. The study considered various standard materials, namely aluminum, copper, silver, Constantan and silicon; covering a range of flow Reynolds number (220–900), under a broad rotational rate range from 0 to 750 rpm, or Ekman number (7.08×10−5 – ∞), nozzle to target spacing (β = 0.25 – 1.0), disk thicknesses to nozzle diameter ratio (b/dn = 0.25 – 1.67), Prandtl number (1.29 – 124.44) using ammonia (NH3), water (H2O), flouroinert (FC-77) and oil (MIL-7808) as working fluids and solid to fluid thermal conductivity ratio (36.91 – 2222). High thermal conductivity plate materials maintained more uniform and lower interface temperature distributions. Higher Reynolds number increased local heat transfer coefficient reducing the interface temperature difference over the entire wall. Rotational rate increases local heat transfer coefficient under most conditions. These findings are important for the design improvement and control of semi-confined liquid jet impingement under a secondary rotation induced motion.

Local Heat Transfer in a Rotating Square Channel With Jet Impingement

1999 ◽  
Vol 121 (4) ◽  
pp. 811-818 ◽  
Author(s):  
S.-S. Hsieh ◽  
J.-T. Huang ◽  
C.-F. Liu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient

The influence of rotation and jet mass flow rate on the local heat transfer coefficient for a single confined impinging round jet with a fixed jet-to-wall spacing of H/d = 5 was studied for the jet Reynolds number from 6500 to 26,000 and the rotational Reynolds number from 0 to 112,000. The local heat transfer coefficient along the surface is measured and the effect of the rotation on the stagnation (peak) point, local and average Nusselt number, is presented and discussed. Furthermore, a correlation was developed for the average Nusselt number in terms of the parameters of Rej and ReΩ. In general, the combined jet impingement and rotation effect are shown to affect the heat transfer response. Rotation decreases the average Nusselt number values from 15 to 25 percent in outward and inward radial flow, respectively. Finally, comparisons of the present data with existing results for multijets with rotation were also made.

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