Effects of Rotation on Heat Transfer for a Single Row Jet Impingement Array With Crossflow

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Justin A. Lamont ◽  
Srinath V. Ekkad ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Rotation Number ◽  
Coriolis Force ◽  
Room Temperature ◽  
Turbine Blades ◽  
Target Surface ◽  
Channel Height ◽  
Potential Core ◽  
Single Row

The effects of the Coriolis force are investigated in rotating internal serpentine coolant channels in turbine blades. For complex flow in rotating channels, detailed measurements of the heat transfer over the channel surface will greatly enhance the blade designers’ ability to predict hot spots so coolant may be distributed more effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer in a rotating, radially outward channel with impingement jets. A simple case with a single row of constant pitch impinging jets with the crossflow effect is presented to demonstrate the novel liquid crystal technique and document the baseline effects for this type of geometry. The present study examines the differences in heat transfer distributions due to variations in jet Rotation number, Roj, and jet orifice-to-target surface distance (H/dj = 1,2, and 3). Colder air, below room temperature, is passed through a room temperature test section to cause a color change in the liquid crystals. This ensures that buoyancy is acting in a similar direction as in actual turbine blades where walls are hotter than the coolant fluid. Three parameters were controlled in the testing: jet coolant-to-wall temperature ratio, average jet Reynolds number, Rej, and average jet Rotation number, Roj. Results show, such as serpentine channels, the trailing side experiences an increase in heat transfer and the leading side experiences a decrease for all jet channel height-to-jet diameter ratios (H/dj). At a jet channel height-to-jet diameter ratio of 1, the crossflow from upstream spent jets greatly affects impingement heat transfer behavior in the channel. For H/dj = 2 and 3, the effects of the crossflow are not as prevalent as H/dj = 1: however, it still plays a detrimental role. The stationary case shows that heat transfer increases with higher H/dj values, so that H/dj = 3 has the highest results of the three examined. However, during rotation the H/dj = 2 case shows the highest heat transfer values for both the leading and trailing sides. The Coriolis force may have a considerable effect on the developing length of the potential core, affecting the resulting heat transfer on the target surface.

Effects of Rotation on Jet Impingement Channel Heat Transfer

2011 ◽  
Author(s):  
Justin A. Lamont ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Rotation Number ◽  
Room Temperature ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Coolant Fluid ◽  
Channel Height ◽  
Constant Pitch

The effects of the Coriolis force and centrifugal buoyancy is investigated in rotating internal serpentine coolant channels in turbine blades. For complex flow in rotating channels, detailed measurements of the heat transfer over the channel surface will greatly enhance the blade designer’s ability to predict hot spots so coolant air may be distributed more effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer in a rotating, radially outward channel with impingement jets. This is the beginning of a comprehensive study on rotational effects on jet impingement. A simple case with a single row of constant pitch impinging jets with crossflow effect is presented to demonstrate the novel liquid crystal technique and document the baseline effects for this type of geoemtry. The present study examines the differences in heat transfer distributions due to variations in jet Rotation number and jet orifice-to-target surface distance. Colder air below room temperature is passed through a room temperature test section to simulate the centrifugal buoyancy effect seen in a real engine environment. This ensures that buoyancy is acting in a similar direction as in actual turbine blades where walls are hotter than the coolant fluid. Three parameters were controlled in the testing: jet coolant-to-wall temperature ratio, average jet Reynolds number, and average jet Rotation number. Results show, like serpentine channels, the trailing side experiences an increase in heat transfer and the leading side experiences a decrease for all jet channel height to jet diameter ratios (H/dj). At a jet channel height to jet diameter ratio of 1, the cross-flow from upstream spent jets greatly affects impingement heat transfer behavior in the channel.

scholarly journals Investigations of Flow and Heat Transfer Characteristics in a Channel Impingement Cooling Configuration with a Single Row of Water Jets

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4327
Author(s):  
Min-Seob Shin ◽  
Santhosh Senguttuvan ◽  
Sung-Min Kim
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Channel Height ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
Average Heat ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The present study experimentally and numerically investigates the effect of channel height on the flow and heat transfer characteristics of a channel impingement cooling configuration for various jet Reynolds numbers in the range of 2000–8600. A single array consisting of eleven jets with 0.8 mm diameter injects water into the channel with 2 mm width at four different channel heights (3, 4, 5, and 6 mm). The average heat transfer coefficients at the target surface are measured by maintaining a temperature difference between the jet exit and the target surface in the range of 15–17 °C for each channel height. The experimental results show the average heat transfer coefficient at the target surface increases with the jet Reynolds number and decreases with the channel height. An average Nusselt number correlation is developed based on 85 experimentally measured data points with a mean absolute error of less than 4.31%. The numerical simulation accurately predicts the overall heat transfer rate within 10% error. The numerical results are analyzed to investigate the flow structure and its effect on the local heat transfer characteristics. The present study advances the primary understanding of the flow and heat transfer characteristics of the channel impingement cooling configuration with liquid jets.

Heat Transfer in a Radially Rotating Square-Sectioned Duct With Two Opposite Walls Roughened by 45Deg Staggered Ribs at High Rotation Numbers

2006 ◽  
Vol 129 (2) ◽  
pp. 188-199 ◽  
Author(s):  
Shyy Woei Chang ◽  
Tong-Minn Liou ◽  
Jui-Hung Hung ◽  
Wen-Hsien Yeh
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Coriolis Force ◽  
Density Ratio ◽  
Inertial Force ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Test Channel ◽  
Rib Roughened

This paper describes an experimental study of heat transfer in a radially rotating square duct with two opposite walls roughened by 45deg staggered ribs. Air coolant flows radially outward in the test channel with experiments to be undertaken that match the actual engine conditions. Laboratory-scale heat transfer measurements along centerlines of two rib-roughened surfaces are performed with Reynolds number (Re), rotation number (Ro), and density ratio (Δρ∕ρ) in the ranges of 7500–15,000, 0–1.8, and 0.076–0.294. The experimental rig permits the heat transfer study with the rotation number considerably higher than those studied in other researches to date. The rotational influences on cooling performance of the rib-roughened channel due to Coriolis forces and rotating buoyancy are studied. A selection of experimental data illustrates the individual and interactive impacts of Re, Ro, and buoyancy number on local heat transfer. A number of experimental-based observations reveal that the Coriolis force and rotating buoyancy interact to modify heat transfer even if the rib induced secondary flows persist in the rotating channel. Local heat transfer ratios between rotating and static channels along the centerlines of stable and unstable rib-roughened surfaces with Ro varying from 0.1 to 1.8 are in the ranges of 0.6–1.6 and 1–2.2, respectively. Empirical correlations for periodic flow regions are developed to permit the evaluation of interactive and individual effects of ribflows, convective inertial force, Coriolis force, and rotating buoyancy on heat transfer.

Experimental Investigation of Crossflow Diverters in Jet Impingement Cooling

2019 ◽  
Author(s):  
Srivatsan Madhavan ◽  
Kishore Ranganath Ramakrishnan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Target Surface ◽  
Pumping Power ◽  
Detailed Measurement ◽  
To Come

Abstract Jet impingement is a cooling technique commonly employed in combustor liner cooling and high-pressure gas turbine blades. However, jets from upstream impingement holes reduce the effectiveness of downstream jets due to jet deflection in the direction of crossflow. In order to avoid this phenomenon and provide an enhanced cooling on the target surface, we have attempted to come up with a novel design called “crossflow diverters”. Crossflow diverters are U-shaped ribs that are placed between jets in the crossflow direction (under maximum crossflow condition). In this study, the baseline case is jet impingement onto a smooth surface with 10 rows of jet impingement holes, jet-to-jet spacing of X/D = Y/D = 6 and jet-to-target spacing of Z/D = 2. Crossflow diverters with thickness ‘t’ of 1.5875 mm, height ‘h’ of 2D placed in the streamwise direction at a distance of X = 2D from center of the jet have been investigated experimentally. Transient liquid crystal thermography technique has been used to obtain detailed measurement of heat transfer coefficient for four jet diameter based Reynolds numbers of 3500, 5000, 7500, 12000. It has been observed that crossflow diverters protect the downstream jets from upstream jet deflection thereby maximizing their stagnation cooling potential. An average of 15–30% enhancement in Nusselt number is obtained over the flow range tested. However, this comes at the expense of increase in pumping power. Pressure drop for the enhanced geometry is 1–1.5 times the pressure drop for baseline impingement case. At a constant pumping power, crossflow diverters produce 9–15% enhancement in heat transfer coefficient as compared to baseline smooth case.

Heat Transfer in a Radially Rotating Square-Sectioned Duct With Two Opposite Walls Roughened by 45° Staggered Ribs

2006 ◽  
Author(s):  
Shyy Woei Chang ◽  
Tong-Minn Liou ◽  
Wen-Hsien Yeh ◽  
Jui-Hung Hung
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Coriolis Force ◽  
Density Ratio ◽  
Inertial Force ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Test Channel ◽  
Rib Roughened

This paper describes an experimental study of heat transfer in a radially rotating square duct with two opposite walls roughened by 45° staggered ribs. Air coolant flows radially outward in the test channel with experiments to be undertaken that match the actual engine conditions. Laboratory-scale heat transfer measurements along centerlines of two rib-roughened surfaces are performed with Reynolds number (Re), rotation number (Ro) and density ratio (Δρ/ρ) in the ranges of 7500–15000, 0–1.8 and 0.076–0.294. The experimental rig permits the heat transfer study with the rotation number considerably higher than those studied in other researches to date. The rotational influences on cooling performance of the rib-roughened channel due to Coriolis forces and rotating buoyancy are studied. A selection of experimental data illustrates the individual and interactive impacts of Re, Ro and buoyancy number on local heat transfer. A number of experimental-based observations reveal that the Coriolis force and rotating buoyancy interact to modify heat transfer even if the rib induced secondary flows persist in the rotating channel. Local heat transfer ratios between rotating and static channels along the centerlines of stable and unstable rib-roughened surfaces with Ro varying from 0.1 to 1.8 are in the ranges of 0.6–1.6 and 1–2.2 respectively. Empirical correlations for periodic flow regions are developed to permit the evaluation of interactive and individual effects of rib-flows, convective inertial force, Coriolis force and rotating buoyancy on heat transfer.

The Effect of Turning Vanes on Pressure Loss and Heat Transfer of a Ribbed Rectangular Two-Pass Internal Cooling Channel

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Marco Schüler ◽  
Frank Zehnder ◽  
Bernhard Weigand ◽  
Jens von Wolfersdorf ◽  
Sven Olaf Neumann
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Width Ratio ◽  
Channel Height ◽  
Internal Cooling ◽  
Thermochromic Liquid Crystal ◽  
Sharp Turn

Gas turbine blades are usually cooled by using ribbed serpentine internal cooling passages, which are fed by extracted compressor air. The individual straight ducts are connected by sharp 180 deg bends. The integration of turning vanes in the bend region lets one expect a significant reduction in pressure loss while keeping the heat transfer levels high. Therefore, the objective of the present study was to investigate the influence of different turning vane configurations on pressure loss and local heat transfer distribution. The investigations were conducted in a rectangular two-pass channel connected by a 180 deg sharp turn with a channel height-to-width ratio of H/W=2. The channel was equipped with 45 deg skewed ribs in a parallel arrangement with e/dh=0.1 and P/e=10. The tip-to-web distance was kept constant at Wel/W=1. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Furthermore static pressure measurements were conducted in order to determine the influence of turning vane configurations on pressure loss. Additionally, the configurations were investigated numerically by solving the Reynolds-averaged Navier–Stokes equations using the finite-volume solver FLUENT. The numerical grids were generated by the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f turbulence model. The results showed a significant influence of the turning vane configuration on pressure loss and heat transfer in the bend region and the outlet pass. While using an appropriate turning vane configuration, pressure loss was reduced by about 25%, keeping the heat transfer at nearly the same level in the bend region. An inappropriate configuration led to an increase in pressure loss while the heat transfer was reduced in the bend region and outlet pass.

Heat Transfer in Internal Cooling Channels of Gas Turbine Blades: Buoyancy and Density Ratio Effects

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Mandana S. Saravani ◽  
Nicholas J. DiPasquale ◽  
Saman Beyhaghi ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Rotational Speed ◽  
Turbine Blades ◽  
Density Ratio ◽  
Internal Cooling ◽  
Buoyancy Effect ◽  
First Case ◽  
Buoyancy Forces ◽  
The Impact

The present work investigates the effects of buoyancy and wall heating condition on the thermal performance of a rotating two-pass square channel with smooth walls. The U-bend channel has a square cross section with a hydraulic diameter of 5.08 cm (2 in.). The lengths of the first and second passes are 514 mm and 460 mm, respectively. The turbulent flow entered the channel with Reynolds numbers of up to 34,000. The rotational speed varied from 0 to 600 rpm with rotational numbers up to 0.75. For this study, two approaches were considered for tracking the buoyancy effect on heat transfer. In the first case, the density ratio was set constant, and the rotational speed was varied. In the second case, the density ratio was changed in the stationary case, and the effect of density ratio was discussed. The range of buoyancy number along the channel is 0–6. The objective was to investigate the impact of buoyancy forces on a broader range of rotation number (0–0.75) and buoyancy number scales (0–6), and their combined effects on heat transfer coefficient for a channel with an aspect ratio of 1 : 1. Results showed that increasing the density ratio increased the heat transfer ratio in both stationary and rotational cases. Furthermore, in rotational cases, buoyancy force effects were very significant. Increasing the rotation number induced more buoyancy forces, which led to an enhancement in heat transfer. The buoyancy effect was more visible in the turning region than any other region.

Aerothermal Investigation of a Single Row Divergent Narrow Impingement Channel by Particle Image Velocimetry and Liquid Crystal Thermography

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Alexandros Terzis ◽  
Christoforos Skourides ◽  
Peter Ott ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Particle Image Velocimetry ◽  
Liquid Crystal ◽  
Flow Field ◽  
Particle Image ◽  
Field Measurements ◽  
Single Row ◽  
Transient Techniques ◽  
Liquid Crystal Thermography ◽  
Image Velocimetry

Integrally cast turbine airfoils with wall-integrated cooling cavities are greatly applicable in modern turbines providing enhanced heat exchange capabilities compared to conventional cooling passages. In such arrangements, narrow impingement channels can be formed where the generated crossflow is an important design parameter for the achievement of the desired cooling efficiency. In this study, a regulation of the generated crossflow for a narrow impingement channel consisting of a single row of five inline jets is obtained by varying the width of the channel in the streamwise direction. A divergent impingement channel is therefore investigated and compared to a uniform channel of the same open area ratio. Flow field and wall heat transfer experiments are carried out at engine representative Reynolds numbers using particle image velocimetry (PIV) and liquid crystal thermography (LCT). The PIV measurements are taken at planes normal to the target wall along the centerline for each individual jet, providing quantitative flow visualization of jet and crossflow interactions. The heat transfer distributions on the target plate of the channels are evaluated with transient techniques and a multilayer of liquid crystals (LCs). Effects of channel divergence are investigated combining both the heat transfer and flow field measurements. The applicability of existing heat transfer correlations for uniform jet arrays to divergent geometries is also discussed.

Leading Edge Jet Impingement Under High Rotation Numbers

2012 ◽  
Author(s):  
Cassius A. Elston ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Test Cases ◽  
Nusselt Numbers ◽  
Supply Channel ◽  
Cooling Air

The effect of rotation on jet impingement cooling is experimentally investigated in this study. Pressurized cooling air is supplied to a smooth, square channel in the radial outward direction. To model leading edge impingement in a gas turbine, jets are formed from a single row of discrete holes. The cooling air from the first pass is expelled through the holes, with the jets impinging on a semi-circular, concave surface. The inlet Reynolds number varied from 10000–40000 in the square supply channel. The rotation number and buoyancy parameter varied from 0–1.4 and 0–6.6 near the inlet of the channel, and as coolant is extracted for jet impingement, the rotation and buoyancy numbers can exceed 10 and 500 near the end of the passage. The average jet Reynolds number varied from 6000–24000, and the jet rotation number varied from 0–0.13. For all test cases, the jet-to-jet spacing (s/djet = 4), the jet-to-target surface spacing (l/djet = 3.2), and the impingement surface diameter-to-diameter (D/djet = 6.4) were held constant. A steady state technique was implemented to determine regionally averaged Nusselt numbers on the leading and trailing surfaces inside the supply channel and three spanwise locations on the concave target surface. It was observed that in all rotating test cases, the Nusselt numbers deviated from those measured in a non-rotating channel. The degree of separation between the leading and trailing surface increased with increasing rotation number. Near the inlet of the channel, heat transfer was dominated by entrance effects, however moving downstream, the local rotation number increased and the effect of rotation was more pronounced. The effect of rotation on the target surface was most clearly seen in the absence of crossflow. With pure jet impingement, the deflection of the impinging jet combined with the rotation induced secondary flows offered increased mixing within the impingement cavity and enhanced heat transfer. In the presence of strong crossflow of the spent air, the same level of heat transfer is measured in both the stationary and rotating channels.

Detailed Heat Transfer Measurements Inside Rotating Ribbed Channels Using the Transient Liquid Crystal Technique

2012 ◽  
Vol 4 (1) ◽  
Author(s):  
Justin A. Lamont ◽  
Srinath V. Ekkad ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Test Section ◽  
Turbine Blades ◽  
Density Ratio ◽  
Complex Nature ◽  
Detailed Knowledge ◽  
Channel Surface ◽  
Transient Liquid Crystal Technique ◽  
Temperature Test

Coolant flow in rotating internal serpentine channels is highly complex due to the effects of the Coriolis force and centrifugal buoyancy. Detailed knowledge of the heat transfer over a surface will greatly enhance the blade designers’ ability to predict hot spots so coolant may be distributed effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer on a rotating two-pass channel surface with chilled inlet air. The present study examines the differences in heat transfer distributions on channel surfaces with smooth walls, 90 deg rib and W-shaped rib turbulated walls. The test section is made up of two passes to model radially inward and outward flows. To account for centrifugal buoyancy, cold air is passed through a room temperature test section. This ensures that buoyancy is acting in a similar direction to real turbine blades. The inlet coolant-to-wall density ratio is fixed at 0.08, Re = 16,000, and Ro = 0.08. The present study shows that the W-shaped ribs enhance heat transfer in all cases (stationary and rotating) approximately 1.75 times more than the 90 deg ribs. The W-shaped rib channel is least affected by rotation, which may be due to the complex nature of the secondary flow generated by the geometry. A higher pressure drop is associated with the W-shaped ribs than the 90 deg ribs, however, the overall thermal-hydraulic performance of the W-shaped ribs still exceeds that set by the 90 deg ribs.

Sign in / Sign up

Export Citation Format

Share Document