scholarly journals Coriolis and buoyancy effects on heat transfer in viewpoint of field synergy principle and secondary flow intensity for maximization of internal cooling

2021 ◽  
Author(s):  
Seyed Mostafa Hosseinalipour ◽  
Hamidreza Shahbazian ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Secondary Flow ◽  
Rotation Number ◽  
Numerical Results ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Field Synergy ◽  
Field Synergy Principle ◽  
Flow Intensity

AbstractThe present investigation emphases on rotation effects on internal cooling of gas turbine blades both numerically and experimentally. The primary motivation behind this work is to investigate the possibility of heat transfer enhancement by dean vortices generated by Coriolis force and U-bend with developing turbulent in the view point of the field synergy principle and secondary flow intensity analysis. A two-passage internal cooling channel model with a 180° U-turn at the hub section is used in the analysis. The flow is radially outward at the first passage of the square channel and then it will be inward at the second passage. The study covers a Reynolds number (Re) of 10,000, Rotation number (Ro) in the range of 0–0.25, and Density Ratios (DR) at the inlet between 0.1–1.5. The numerical results are compared to experimental data from a rotating facility. Results obtained with the basic RANS SST k-ω model are assessed completely as well. A field synergy principle analysis is consistent with the numerical results too. The results state that the secondary flows due to rotation can considerably improve the synergy between the velocity and temperature gradients up to 20%, which is the most fundamental reason why the rotation can enhance the heat transfer. In addition, the Reynolds number and centrifugal buoyancy variations are found to have no remarkable impact on increasing the synergy angle. Moreover, vortices induced by Rotation number and amplified by Reynolds number increase considerable secondary flow intensity which is exactly in compliance with Nusselt number enhancement.

Lattice Boltzmann Method Simulation of Backward-Facing Step Flow With Double Plates Aligned at Angle to Flow Direction

2006 ◽  
Vol 128 (11) ◽  
pp. 1176-1184 ◽  
Author(s):  
Chao-Kuang Chen ◽  
Tzu-Shuang Yen ◽  
Yue-Tzu Yang
Keyword(s):  
Reynolds Number ◽  
Temperature Gradient ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Numerical Results ◽  
Field Synergy ◽  
Backward Facing Step ◽  
Number Range ◽  
Field Synergy Principle ◽  
Boltzmann Method

This study applies the lattice Boltzmann method (LBM) to simulate incompressible steady low Reynolds number backward-facing step flows. In order to restrict the simulations to two-dimensional flows, the investigated Reynolds number range is limited to a maximum value of Re=200. The field synergy principle is applied to demonstrate that the increased interruption within the fluid caused by the introduction of two inclined plates reduces the intersection angle between the velocity vector and the temperature gradient. The present results obtained for the velocity and temperature fields are found to be in good agreement with the published experimental and numerical results. Furthermore, the numerical results confirm the relationship between the velocity and temperature gradient predicted by the field synergy principle.

Numerical Modelling Techniques for Turbine Blade Internal Cooling Passages

2015 ◽  
Author(s):  
Priyanka Dhopade ◽  
Luigi Capone ◽  
Matthew McGilvray ◽  
David Gillespie ◽  
Peter Ireland
Keyword(s):  
Heat Transfer ◽  
Numerical Modelling ◽  
Secondary Flow ◽  
Mesh Generation ◽  
Fluid Dynamic ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Modelling Techniques

Numerical modelling of internal cooling passages in gas turbine blades is a challenging task due to their physical characteristics, such as rounded duct corners, the presence of rib turbulators and their staggered locations between surfaces. This results in complex fluid dynamic phenomenon such as counter-rotating vortices and other secondary flow structures that can drive the heat transfer. Heat transfer mechanisms in such passages are inherently coupled with momentum transport and diffusion. Current industry practices for numerical modelling of such passages use unstructured mesh generation tools, steady Reynolds-averaged Navier-Stokes (RANS) equations and two-equation turbulence models such as k-ε and k-ω SST. This paper investigates two generic, engine-representative rib geometries using current numerical practices to determine their limitations. Three mesh generation tools and two turbulence models are compared across two rib geometries. The results are qualitatively and quantitatively compared to detailed experimental Nusselt numbers on the passage walls. It was found that as long as the rib geometry results in a secondary flow that directly impinges onto the wall, the meshing tools and turbulence models agree reasonably well with experiments. When the passage includes wall-wrapped ribs resulting in more complex secondary flows, this decreases the validity of the numerical tools, suggesting that more sophisticated modelling techniques are required as rib geometries continue to evolve.

Flow and Heat Transfer in Microchannels With Dimples and Protrusions

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Jibing Lan ◽  
Yonghui Xie ◽  
Di Zhang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Characteristics ◽  
Field Synergy ◽  
Transfer Enhancement ◽  
Rectangular Microchannel ◽  
Field Synergy Principle ◽  
Flow And Heat Transfer ◽  
Better Than

Flow characteristics and heat transfer performances in a rectangular microchannel with dimples/protrusions are studied numerically in this research. The height and the width of the microchannel is 200 μm and 50 μm, respectively. The dimple/protrusion diameter is 100 μm, and the depth is 20 μm. The effects of Reynolds number, streamwise pitch, and arrangement pattern are examined. The numerical simulations are conducted using water as the coolant with the Reynolds number ranging from 100 to 900. The results show that dimple/protrusion technique in mcirochannel has the potential to provide heat transfer enhancement with low pressure penalty. The normalized Nusselt number is within the range from 1.12 to 4.77, and the corresponding normalized friction factor is within the range from 0.94 to 2.03. The thermal performance values show that the dimple + protrusion cases perform better than the dimple + smooth cases. The flow characteristics of the dimples/protrusions in microchannel are similar to those in conventional channel. Furthermore, from the viewpoint of energy saving, dimples/protrusions in microchannel behave better than those in conventional channel. Also from the viewpoint of field synergy principle, the synergy of the dimple + protrusion cases are much better than the dimple + smooth cases. Moreover, the synergy becomes worse with the increase in the Reynolds number and decrease in the streamwise pitch.

Experimental and Numerical Study of the Turbulent Flow and Heat Transfer in a Wedge-shaped Channel with Guiding Pin Fin Arrays under Rotating Conditions

2022 ◽  
pp. 1-28
Author(s):  
Ce Liang ◽  
Yu Rao ◽  
Jianian Chen ◽  
Peng Zhang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Rotation Number ◽  
Internal Cooling ◽  
Number Range ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Pin Fin Arrays

Abstract Experiments and numerical simulations under stationary and rotating conditions have been conducted to investigate turbulent flow and heat transfer characteristics of innovative guiding pin fin arrays in a wedge-shaped channel, which models the internal cooling passages for gas turbine blade trailing edge. The Reynolds number range is 10,000-80,000, and the inlet rotation number range is 0-0.46. With the increase of Reynolds numbers, the enhancement of heat transfer performance with guiding pin fin arrays is significantly higher than that with conventional circular pin fin arrays. At the highest Reynolds number of Re=80,000, the overall Nusselt number of the channel with guiding pin fin arrays is about 33.7% higher than that of the channel with circular pin fin arrays under the stationary condition, and is about 23.0% higher than the latter under the rotating conditions. At the highest inlet rotation number of Ro=0.46, the heat transfer difference between the trailing side and leading side of the channel is significantly lower with the guiding pin fin arrays. Both the experiments and numerical simulations indicate that the heat transfer uniformity and enhancement of the channel endwall is significantly improved by the guiding pin fin arrays under stationary and rotating conditions, which provide more reasonable flow distribution in the wedge-shaped channel, and can further produce obviously improved heat transfer in the tip region for the trailing edge internal cooling channel.

Effects of Freestream Turbulence Intensity, Turbulence Length Scale, and Exit Reynolds Number on Vane Endwall Secondary Flow and Heat Transfer in a Transonic Turbine Cascade

2020 ◽  
Author(s):  
Zhigang Li ◽  
Bo Bai ◽  
Luxuan Liu ◽  
Jun Li ◽  
Shuo Mao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Secondary Flow ◽  
Turbulence Intensity ◽  
Thermal Load ◽  
Secondary Flows ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Turbulence Length ◽  
Turbulence Length Scale

Abstract In gas turbine engines, the first-stage vanes usually suffer harsh incoming flow conditions from the combustor with high pressure, high temperature and high turbulence. The combustor-generated high freestream turbulence and strong secondary flows in a gas turbine vane passage have been reported to augment the endwall thermal load significantly. This paper presents a detailed numerical study on the effects of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the endwall secondary flow pattern and heat transfer distribution of a transonic linear turbine vane passage at realistic engine Mach numbers, with a flat endwall no cooling. Numerical simulations were conducted at a range of different operation conditions: six freestream turbulence intensities (Tu = 1%, 5%, 10%, 13%, 16% and 20%), six turbulence length scales (normalized by the vane pitch of Λ/P = 0.01, 0.04, 0.07, 0.12, 0.24, 0.36), and three exit isentropic Mach number (Maex = 0.6, 0.85 and 1.02 corresponding exit Reynolds number Reex = 1.1 × 106, 1.7 × 106 and 2.2 × 106, respectively, based on the vane chord). Detailed comparisons were presented for endwall heat transfer coefficient distribution, endwall secondary flow field at different operation conditions, while paying special attention to the link between endwall thermal load patterns and the secondary flow structures. Results show that the freestream turbulence intensity and length scale have a significant influence on the endwall secondary flow field, but the influence of the exit Reynolds number is very weak. The Nusselt number patterns for the higher turbulence intensities (Tu = 16%, 20%) appear to be less affected by the endwall secondary flows than the lower turbulence cases. The thermal load distribution in the arc region around the vane leading edge and the banded region along the vane pressure side are influenced most strongly by the freestream turbulence intensity. In general, the higher freestream turbulence intensities make the vane endwall thermal load more uniform. The Nusselt number distribution is only weakly affected by the turbulence length scale when Λ/P is larger than 0.04. The heat transfer level appears to have a significant uniform augmentation over the whole endwall region with the increasing Maex. The endwall thermal load distribution is classified into four typical regions, and the effects of freestream turbulence, exit Reynolds number in each region were discussed in detail.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (AR=4:1 to 2:1) With Profiled 60 Deg Angled Ribs

2018 ◽  
Author(s):  
Andrew F. Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Cross Section ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Internal Cooling ◽  
First Passage ◽  
Aspect Ratios

The internal cooling channels of an advanced gas turbine blade typically have varying aspect ratios from one pass to another due to the varying thickness of the blade profile. Most of the fundamental internal cooling studies found in the open literature used a fixed aspect ratio for multi-pass channels. Studies on a reduced cross-section and aspect ratio channel are scarce. The current study features a two-pass rectangular channel with an aspect ratio AR = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180 deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross-section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ≈ 0.11, parallel and inline). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all surfaces within the flow passages. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. Rotation effects on both heat transfer and pressure loss coefficient for the smooth and rib-roughened cases are presented. The results showed that the turn induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction on the tip wall was seen in both the smooth and ribbed cases under rotating condition. A reduced overall pressure penalty was seen for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

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.

Numerical Investigation on Mist/Air Cooling in Rectangular Ribbed Channels With Various Aspect Ratios

2017 ◽  
Author(s):  
Junxiong Zeng ◽  
Tieyu Gao ◽  
Jun Li ◽  
Jianying Gong
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Secondary Flows ◽  
Air Cooling ◽  
Mass Ratio ◽  
Aspect Ratios

Continuously increasing gas turbine inlet temperature to further improve thermal efficiency and power output of gas turbines leads to acquiring a higher cooling effectiveness of gas turbine blades and vanes to protect them from high temperature corrosion and creeping damage. One of the new and promising technologies to greatly increase heat transfer is mist cooling by injecting a small amount of tiny droplets into coolant flow. This paper aims to numerically study the flow and heat transfer behaviors of mist/air coolant in rectangular ribbed channels with various aspect ratios of 1/4, 1/2, 1/1, 2/1 and rib angle of 60°. In addition, the distribution of secondary flows in the four ribbed channels and its effect on heat transfer are analyzed in detail. The effects of Reynolds number ranging from 10,000 to 60,000, mist mass ratios ranging from 1% to 4%, and droplet sizes ranging from 5 μm to 20 μm on heat transfer characteristics of mist/air cooling are investigated. As a comparison, the air-only coolant is also considered in the present study. The Eulerian-Lagrangian particle tracking method is adopted in this study to simulate the two-phase flow mist/air cooling. Turbulence model validation has been conducted for air-only, indicating that the numerical results with SST k-ω model are fairly consistent with experimental data. The results show that the aspect ratio has insignificant influence on longitudinal secondary flow distribution in the four ribbed channels, but greatly affects the size of main secondary flows. The channel with a smaller aspect ratio obtains a larger size of main secondary flow, which may result in decreasing the heat transfer coefficient. The average Nu on ribbed surfaces presents an increasing trend with Reynolds number and mist mass ratio for mist/air cooling. The heat transfer enhancement of mist/air as compared to air-only increases from 12.3% to 91.86% when Reynolds number ranges from 10,000 to 60,000 with injecting 2% mist into air coolant, while that increases from 7.96% to 113.15% when mist mass ratio increases from 1% to 4%. The average Nu initially increases with droplet size and then decreases. A peak value of average Nu is obtained in the case of 15μm mist among all the sizes of droplets. The case of AR = 2/1 obtains the highest average Nu, followed by the cases of AR = 1/2, 1/1 and 1/4 for both air-only and mist/air. The channel with aspect ratio of 1/2 obtains the best thermal performance in mist/air cooling channel.

Heat Transfer Enhancement by Criss-Cross Pattern Formed by 45° Angled Rib Turbulators in a Straight Square Duct

2017 ◽  
Author(s):  
Prashant Singh ◽  
Yongbin Ji ◽  
Mingyang Zhang ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Hydraulic Performance ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Conduction Model ◽  
Square Duct ◽  
Rib Turbulators

The need for higher turbine efficiency has been constantly pushing the turbine inlet temperatures to elevated levels. Hot gas path temperatures are much higher than the typical blade material yield temperature. Efficient internal cooling technologies are required for safe operation of gas turbine. Several internal cooling technologies have been developed in order to enhance the heat transfer from relatively hotter walls of turbine blade. For mid-chord region of turbine blade, rib turbulators are typically installed in multi-pass channels. Rib turbulators trip the boundary layer, induce secondary flows which enhance near wall shear as well as enhance turbulent mixing when they interact with surrounding walls. Research has been carried out on several aspects of rib turbulated passages in order to achieve higher thermal hydraulic performance. Generally, rib turbulators are installed on two opposite walls of serpentine passages in order to enhance heat transfer from both pressure and suction sides of blade through coolant flowing through complicated paths. Typical arrangement of rib turbulators were parallel to each other or having some offset from each other. In the present study, an attempt has been made to arrange 45° angled ribs in a way that they form a Criss-Cross pattern. Two ribbed configurations with Criss-Cross pattern - Inline and staggered, have been studied where the baseline case was smooth duct with no rib turbulators. The effective rib-pitch-to-rib-height ratio (p/e) was 8.6 and rib-height-to-channel-hydraulic diameter ratio (e/dh) was 0.1. The channel had a total length of 20 hydraulic diameters and the rib turbulators were installed at a distance of six hydraulic diameters from the inlet of the test section to allow flow development. Detailed heat transfer coefficients were measured using transient liquid crystal thermography employing 1D semi-infinite conduction model. Globally averaged Nusselt numbers are calculated from the detailed measurements and thermal hydraulic performance of configurations have been reported with respect to Reynolds number. The aim of this study was to develop a cooling configuration which has higher thermal-hydraulic performance compared to other traditional rib configurations. It has been found that the heat transfer characteristics of the inline and staggered configurations were similar to each other and ranged between three times D-B correlation to 2.7 times, for Reynolds number ranging from 30000 to 60000. Inline configuration had relatively lower frictional losses, however the thermal hydraulic performances of both the configurations were similar.

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