Rotation Effects on the Heat Transfer Distribution in a Two-Pass Rotating Internal Cooling Channel Equipped With Triangular Ribs

2017 ◽  
Author(s):  
Ignacio Mayo ◽  
Tony Arts ◽  
Nicolas Van de Wyer
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Channel Model ◽  
Flow Direction ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Experimental Conditions ◽  
Cfd Validation ◽  
The Impact

The present paper addresses the detailed heat transfer pattern in a two-pass rotating internal cooling channel model, with a square cross section and equipped with triangular ribs on one of its walls. The turn region consists of a smooth high curvature U-bend that generates a complex flow field and wall heat transfer. The investigation is based on Liquid Crystal Thermography (LCT) measurements in a rotating facility at Reynolds numbers varying from 20,000 to 60,000, and a maximum rotation number equal to 0.20. For these experimental conditions, the centripetal buoyancy effects are negligible. The channel is rotated around an axis perpendicular to the main flow direction in clockwise and counter-clockwise senses, in order to observe the impact of cyclonic and anti-cyclonic behavior on the heat transfer in both legs. The objective of the present study is two-fold: firstly, it aims to understand the flow physics and heat transfer phenomena at different regimes. Secondly, the detailed heat transfer measurements are intended to be a reference set for Computational Fluid Dynamics (CFD) validation. The measurements obtained in the first leg have been compared with previous experimental data in channels with square ribs and radially outward flow, showing a similar behavior in terms of heat transfer distribution and overall dependency on the rotation number. In the second leg, the heat transfer distribution is more complex. The heat transfer distribution is not symmetric, and high gradients are present in the span-wise direction. Nevertheless, the dependency of the heat transfer to increasing rotation shows a trend similar to the one observed in the first pass. The combined effects of rib-induced secondary flows stabilization/destabilization by rotation, Coriolis-induced stream-wise vortices and high streamline curvature on the heat transfer distribution are analyzed in the paper.

Heat Transfer in a Rotating Cooling Channel (AR = 2:1) With Rib Turbulators and a Tip Turning Vane

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Andrew F. Chen ◽  
Hao-Wei Wu ◽  
Nian Wang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Rotation Number ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Enhancement ◽  
Rib Turbulators ◽  
Effects Of Rotation ◽  
Cooling Passage ◽  
Turbine Airfoils

Experimental investigation on rotation and turning vane effects on heat transfer was performed in a two-pass rectangular internal cooling channel. The channel has an aspect ratio of AR = 2:1 and a 180 deg tip-turn, which is a scaled up model of a typical internal cooling passage of gas turbine airfoils. The leading surface (LS) and trailing surface (TS) are roughened with 45 deg angled parallel ribs (staggered P/e = 8, e/Dh = 0.1). Tests were performed in a pressurized vessel (570 kPa) where higher rotation numbers (Ro) can be achieved with a maximum Ro = 0.42. Five Reynolds numbers (Re) were examined (Re = 10,000–40,000). At each Reynolds number, five rotational speeds (Ω = 0–400 rpm) were considered. Results showed that rotation effects are stronger in the tip regions as compared to other surfaces. Heat transfer enhancement up to four times was observed on the tip wall at the highest rotation number. However, heat transfer enhancement is reduced to about 1.5 times with the presence of a tip turning vane at the highest rotation number. Generally, the tip turning vane reduces the effects of rotation, especially in the turn portion.

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.

Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels—Part II: Experimental Validation

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Filippo Coletti ◽  
Tom Verstraete ◽  
Jérémy Bulle ◽  
Timothée Van der Wielen ◽  
Nicolas Van den Berge ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Heat Transfer Performance ◽  
Internal Cooling ◽  
Transfer Performance ◽  
Cooling Channel ◽  
Piv Measurements ◽  
Cooling Channels ◽  
Numerical Predictions ◽  
The Impact

This two-part paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter, as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In the first part of the paper, the design methodology of the cooling channel was presented. In this second part, the optimized design is validated. The results obtained with the numerical methodology described in Part I are checked against pressure measurements and particle image velocimetry (PIV) measurements. The experimental campaign is carried out on a magnified model of a two-legged cooling channel that reproduces the geometrical and aerodynamical features of its numerical counterpart. Both the original profile and the optimized profile are tested. The latter proves to outperform the original geometry by about 36%, in good agreement with the numerical predictions. Two-dimensional PIV measurements performed in planes parallel to the plane of the bend highlight merits and limits of the computational model. Despite the well-known limits of the employed eddy viscosity model, the overall trends are captured. To assess the impact of the aerodynamic optimization on the heat transfer performance, detailed heat transfer measurements are carried out by means of liquid crystals thermography. The optimized geometry presents overall Nusselt number levels only 6% lower with respect to the standard U-bend. The study demonstrates that the proposed optimization method based on an evolutionary algorithm, a Navier–Stokes solver, and a metamodel of it is a valid design tool to minimize the pressure loss across a U-bend in internal cooling channels without leading to a substantial loss in heat transfer performance.

Spatially Resolved Heat Transfer Coefficient in a Rib-Roughened Channel Under Coriolis Effects

2013 ◽  
Author(s):  
Ignacio Mayo ◽  
Tony Arts ◽  
Julien Clinckemaillie ◽  
Aude Lahalle
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Shear Layer ◽  
Rotation Number ◽  
Rectangular Cross Section ◽  
Flow Direction ◽  
Secondary Flows ◽  
Uniform Heat Flux ◽  
Flux Boundary Condition ◽  
Coriolis Forces

Heat transfer in a magnified rotating ribbed channel is studied by means of liquid crystal thermometry. The test section consists of four Plexiglas walls, forming a rectangular cross section, mounted on a large rotating disk together with the complete necessary measurement chain. The investigated wall is equipped with ribs perpendicular to the main flow direction, it is heated in such a way to achieve a uniform heat flux boundary condition. Facing the need of two-dimensional experimental heat transfer data, tets were carried out in order to quantify the convective heat transfer distribution on the wall between two consecutive ribs under rotating conditions. Different Rotation numbers (0, 0.06, 0.11 and 0.17) were tested at a Reynolds number of 15,000. For the selected heat flux and rotation rates, and based on previous aerodynamic and thermal investigations presented in open literature, no effect of buoyancy is expected, while the Coriolis forces play an important role in the determination of heat transfer. The rotating cases were performed in both senses of rotation in order to allow the studied wall to act as both a trailing and a leading side. At the highest Rotation number, the results confirm that heat transfer is enhanced up to 17% along the trailing side compared with the non-rotating case. This is due to the secondary flows and shear layer instability instigated by the Coriolis forces. On the other hand, heat transfer on the leading side is reduced up to 19% at the highest rotation number; this is caused by the stabilization of the shear layer and the contribution of the secondary flows.

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.

Heat Transfer Measurements in Rectangular Channels With Orthogonal Mode Rotation

1991 ◽  
Vol 113 (3) ◽  
pp. 339-345 ◽  
Author(s):  
W. D. Morris ◽  
G. Ghavami-Nasr
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Rotor Blades ◽  
Coolant Temperature ◽  
Internal Cooling ◽  
General Terms

The influence of rotation on local heat transfer in a rectangular-sectioned duct has been experimentally studied for the case where the duct rotates about an axis orthogonal to its own central axis. The coolant used was air with the flow direction in the radially outward direction. This rotating flow geometry is encountered in the internal cooling of gas turbine rotor blades. Local Nusselt number variations along the duct have been determined over the trailing and leading surfaces. In general terms Coriolis-induced secondary flows are shown to enhance local heat transfer over the trailing surface compared to a stationary duct forced convection situation. The converse is true on the leading surface where significant impediment to local heat transfer can occur. Centripetal buoyancy is shown to influence the heat transfer response with heat transfer being improved on both leading and trailing surfaces as the wall-to-coolant temperature difference is increased with other controlling parameters held constant. Correlating equations are proposed and the results compared with those of other workers in the field.

Effect of Entrance Geometry and Rotation on Heat Transfer in a Narrow (AR = 1:4) Rectangular Internal Cooling Channel

2014 ◽  
Author(s):  
Krishnendu Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Flow Distribution ◽  
Leading Edge ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Cross Sectional ◽  
Density Ratios

This paper studies the effect of entrance geometries on the heat transfer and fluid flow in a narrow aspect ratio (AR = 1:4) rectangular internal cooling channel, representative of a leading edge of a gas turbine blade, under rotating condition. Numerical simulations are performed to understand the role of the rotation generated forces on the flow for different entrance geometries representative of those encountered in practice. Three different entrance geometries are tested: a S-shape entrance, a 90 degree bend entrance and a twisted entrance that changes its aspect ratio along its length. Numerical simulations are run at a constant Reynolds number (Re = 15000), for a range of rotation numbers (Ro = 0–0.2) and density ratios (DR = 0–0.4). Detailed heat transfer coefficient data at the leading and trailing walls are presented along with streamline profiles at different cross sectional planes that provide an insight into the flow field. It is seen that the entrance profile upstream of the actual test section is significantly different for the different entrance geometries, and has a significant impact on the rotation generated secondary flows. Non-uniformity in flow distribution at the exit of entrance geometry is small for the S-shape entrance while the non-uniformity is prominent at the exit of the changing AR entrance geometry. The entrance effect dies down as the flow progresses further downstream inside the cooling channel and the rotation effect becomes dominant.

Experimental Investigation of Heat Transfer on the Internal Tip Wall in a Rotating Two-Pass Rectangular Channel

2019 ◽  
Author(s):  
Kai-Chieh Chia ◽  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Channel Wall ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Three Dimensional Flow ◽  
Smooth Channel ◽  
Blade Tip ◽  
The Impact

Abstract The current study experimentally studied heat transfer characteristics of the blade tip wall in a rotating internal cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180° turn, complex three dimensional flow significantly affected heat transfer on the internal tip surface. The liquid crystal method is used to capture the heat transfer contour on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45° angled ribs. The Reynolds number inside the pressurize two-pass cooling channel ranged from 10,000 to 30,000 at both stationary and rotating conditions. Furthermore, two channel orientations (90° and 135°) were tested. The effect of Coriolis force on heat transfer is studied with the rotation number up to 0.53. The tip heat transfer from the smooth channel wall was more sensitive to rotation and the largest heat transfer enhancement as a result of rotation was 68%.

Heat Transfer Enhancement Using Angled Grooves as Turbulence Promoters

2013 ◽  
Author(s):  
Krishnendu Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Enhancement ◽  
Number Range ◽  
Pressure Drops ◽  
Friction Factors ◽  
Mainstream Flow ◽  
Turbine Airfoils

An experimental study is conducted on a simulated internal cooling channel of a turbine airfoil using angled grooves and combination of grooves-ribs to enhance the heat transfer from the wall. The grooves are angled at 45° to the mainstream flow direction and combinations of four different geometries are studied that include: (1) angled grooves with a pitch, p/δ = 10, (2) angled groove with a larger pitch, p/δ = 15, (3) combination of angled groove and 45° angled rib, and (4) combination of angled groove with transverse rib. Transient liquid crystal experiments are conducted for a Reynolds number range of 13,000–55,000, and local and averaged heat transfer coefficient values are presented for all the geometries. Pressure drops are measured between the inlet and the exit of the grooved channel and friction factors are calculated. The combination of the angled groove and 45° angled rib provided the highest performance factor of the four cases considered, and these values were higher or comparable to among the best-performing rib geometries (45-degree broken ribs) commonly used in gas turbine airfoils.

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