scholarly journals Flow and Heat Transfer Mechanisms in a Rotating Compressor Cavity Under Centrifugal Buoyancy-Driven Convection

2021 ◽  
Author(s):  
Feng Gao ◽  
John W. Chew
Keyword(s):  
Heat Transfer ◽  
Operating Conditions ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Ekman Layers ◽  
Convection Correlation ◽  
Buoyancy Driven Convection ◽  
Rayleigh Numbers ◽  
Transfer Mechanisms ◽  
Level Of Agreement

Abstract This paper presents a systematic study of flow and heat transfer mechanisms in a compressor disc cavity with an axial throughflow under centrifugal buoyancy-driven convection, comparing with previously published experimental data. Wall-modelled large-eddy simulations are conducted for six operating conditions, covering a range of rotational Reynolds number (3.2x10^5 - 2.2x10^6), buoyancy parameter (0.11 - 0.26) and Rossby number (0.4 - 0.8). Numerical accuracy and computational efficiency of the simulations are considered. Wall heat transfer predictions are compared with measured data with a good level of agreement. A constant rothalpy core occurs at high Eckert number, appearing to reduce the driving buoyancy force. The flow in the cavity is turbulent with unsteady laminar Ekman layers observed on both discs except in the bore flow affected region on the downstream disc cob. The shroud heat transfer Nusselt number-Rayleigh number scaling agrees with that of natural convection under gravity for high Rayleigh numbers. Disc heat transfer is dominated by conduction across unsteady Ekman layers, except on the downstream disc cob. The disc bore heat transfer is close to a pipe flow forced convection correlation. The unsteady flow structure is investigated showing strong unsteadiness in the cavity that extends into the axial throughflow.

scholarly journals Flow and Heat Transfer Mechanisms in a Rotating Compressor Cavity Under Centrifugal Buoyancy-Driven Convection

2021 ◽  
Author(s):  
Feng Gao ◽  
John W. Chew
Keyword(s):  
Heat Transfer ◽  
Operating Conditions ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Ekman Layers ◽  
Convection Correlation ◽  
Buoyancy Driven Convection ◽  
Rayleigh Numbers ◽  
Transfer Mechanisms ◽  
Level Of Agreement

Abstract This paper presents a systematic study of flow and heat transfer mechanisms in a compressor disc cavity with an axial throughflow under centrifugal buoyancy-driven convection, comparing with previously published experimental data. Wall-modelled large-eddy simulations are conducted for six operating conditions, covering a range of rotational Reynolds number (3.2 × 105 – 2.2 × 106), buoyancy parameter (0.11 – 0.26) and Rossby number (0.4 – 0.8). Numerical accuracy and computational efficiency of the simulations are considered. Wall heat transfer predictions are compared with measured data with a good level of agreement. A constant rothalpy core occurs at high Eckert number, appearing to reduce the driving buoyancy force. The flow in the cavity is turbulent with unsteady laminar Ekman layers observed on both discs except in the bore flow affected region on the downstream disc cob. The shroud heat transfer Nusselt number-Rayleigh number scaling agrees with that of natural convection under gravity for high Rayleigh numbers. Disc heat transfer is dominated by conduction across unsteady Ekman layers, except on the downstream disc cob. The disc bore heat transfer is close to a pipe flow forced convection correlation. The unsteady flow structure is investigated showing strong unsteadiness in the cavity that extends into the axial throughflow.

Modeling of Turbulent Flow and Heat Transfer in Graphitic Foams

2010 ◽  
Vol 297-301 ◽  
pp. 739-744
Author(s):  
J. Cepek ◽  
Anthony G. Straatman
Keyword(s):  
Heat Transfer ◽  
Temperature Fields ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Order Of Magnitude ◽  
Void Shape ◽  
Energy Balances ◽  
Les Model ◽  
Transfer Mechanisms

We describe a study conducted to examine the influence of turbulence on the flow and heat transfer in graphitic foams. In this study, a Large Eddy Simulation (LES) model was used to characterize turbulence in the momentum and energy balances, and calculations were done to produce transient results of the velocity and temperature fields inside the spherical pores of the foam. The LES simulations enable excellent insight into the pore-level heat transfer mechanisms for the spherical void shape, and show that the heat transfer increases by a factor of 4.7 for an order of magnitude increase in the Reynolds number.

scholarly journals Large-Eddy Simulation Study of Flow and Heat Transfer in Swirling and Non-Swirling Impinging Jets on a Semi-Cylinder Concave Target

2021 ◽  
Vol 11 (15) ◽  
pp. 7167
Author(s):  
Liang Xu ◽  
Xu Zhao ◽  
Lei Xi ◽  
Yonghao Ma ◽  
Jianmin Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Wall Temperature ◽  
Target Surface ◽  
Impinging Jets ◽  
Small Scale ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy

Swirling impinging jet (SIJ) is considered as an effective means to achieve uniform cooling at high heat transfer rates, and the complex flow structure and its mechanism of enhancing heat transfer have attracted much attention in recent years. The large eddy simulation (LES) technique is employed to analyze the flow fields of swirling and non-swirling impinging jet emanating from a hole with four spiral and straight grooves, respectively, at a relatively high Reynolds number (Re) of 16,000 and a small jet spacing of H/D = 2 on a concave surface with uniform heat flux. Firstly, this work analyzes two different sub-grid stress models, and LES with the wall-adapting local eddy-viscosity model (WALEM) is established for accurately predicting flow and heat transfer performance of SIJ on a flat surface. The complex flow field structures, spectral characteristics, time-averaged flow characteristics and heat transfer on the target surface for the swirling and non-swirling impinging jets are compared in detail using the established method. The results show that small-scale recirculation vortices near the wall change the nearby flow into an unstable microwave state, resulting in small-scale fluctuation of the local Nusselt number (Nu) of the wall. There is a stable recirculation vortex at the stagnation point of the target surface, and the axial and radial fluctuating speeds are consistent with the fluctuating wall temperature. With the increase in the radial radius away from the stagnation point, the main frequency of the fluctuation of wall temperature coincides with the main frequency of the fluctuation of radial fluctuating velocity at x/D = 0.5. Compared with 0° straight hole, 45° spiral hole has a larger fluctuating speed because of speed deflection, resulting in a larger turbulence intensity and a stronger air transport capacity. The heat transfer intensity of the 45° spiral hole on the target surface is slightly improved within 5–10%.

Numerical Simulation of Gas Flow and Heat Transfer in Cross-Wavy Primary Surface Channel for Microtubine Recuperators

2005 ◽  
Author(s):  
H. X. Liang ◽  
Q. W. Wang ◽  
L. Q. Luo ◽  
Z. P. Feng
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Gas Turbine ◽  
Numerical Study ◽  
High Reliability ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
The Cross

Three-dimensional numerical simulation was conducted to investigate the flow field and heat transfer performance of the Cross-Wavy Primary Surface (CWPS) recuperators for microturbines. Using high-effective compact recuperators to achieve high thermal efficiency is one of the key techniques in the development of microturbine in recent years. Recuperators need to have minimum volume and weight, high reliability and durability. Most important of all, they need to have high thermal-effectiveness and low pressure-losses so that the gas turbine system can achieve high thermal performances. These requirements have attracted some research efforts in designing and implementing low-cost and compact recuperators for gas turbine engines recently. One of the promising techniques to achieve this goal is the so-called primary surface channels with small hydraulic dimensions. In this paper, we conducted a three-dimensional numerical study of flow and heat transfer for the Cross-Wavy Primary Surface (CWPS) channels with two different geometries. In the CWPS configurations the secondary flow is created by means of curved and interrupted surfaces, which may disturb the thermal boundary layers and thus improve the thermal performances of the channels. To facilitate comparison, we chose the identical hydraulic diameters for the above four CWPS channels. Since our experiments on real recuperators showed that the Reynolds number ranges from 150 to 500 under the operating conditions, we implemented all the simulations under laminar flow situations. By analyzing the correlations of Nusselt numbers and friction factors vs. Reynolds numbers of the four CWPS channels, we found that the CWPS channels have superior and comprehensive thermal performance with high compactness, i.e., high heat transfer area to volume ratio, indicating excellent commercialized application in the compact recuperators.

LES Simulations of Rotating Two-Pass Ribbed Duct With Coriolis and Centrifugal Buoyancy Forces at Re=100,000

2016 ◽  
Author(s):  
Cody Dowd ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Large Eddy Simulations ◽  
The Other ◽  
Coriolis Forces ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Buoyancy Forces ◽  
First Pass ◽  
Duct Geometry

The focus of this research is to predict the flow and heat transfer in a rotating two-pass duct geometry with staggered ribs using Large-Eddy Simulations (LES). The geometry consists of a U-Bend with 17 ribs in each pass. The ribs are staggered with an e/Dh = 0.1 and P/e = 10. LES is performed at a Reynolds number of 100,000, a rotation number of 0.2 and buoyancy parameters (Bo) of 0.5 and 1.0. The effects of Coriolis forces and centrifugal buoyancy are isolated and studied individually. In all cases it is found that increasing Bo from 0.5 to 1.0 at Ro = 0.2 has little impact on heat transfer. It is found that in the first pass, the heat transfer is quite receptive to Coriolis forces which augment and attenuate heat transfer at the trailing and leading walls, respectively. Centrifugal buoyancy, on the other hand has a bigger effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On contrary, it aids heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. The heat transfer in the second pass is dominated by the highly turbulent flow exiting the bend. Coriolis forces have no impact on the augmentation of heat transfer on the leading wall till the second half of the passage whereas it attenuates heat transfer at the trailing wall as soon as the flow exits the bend. Contrary to phenomenological arguments, inclusion of centrifugal buoyancy augments heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass.

Large Eddy Simulation of Flow and Heat Transfer Mechanism in Matrix Cooling Channel

2017 ◽  
Author(s):  
Yigang Luan ◽  
Lianfeng Yang ◽  
Bo Wan ◽  
Tao Sun
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Gas Turbine ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Longitudinal Vortices ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy

Gas turbine engines have been widely used in modern industry especially in the aviation, marine and energy fields. The efficiency of gas turbines directly affects the economy and emissions. It’s acknowledged that the higher turbine inlet temperatures contribute to the overall gas turbine engine efficiency. Since the components are subject to the heat load, the internal cooling technology of turbine blades is of vital importance to ensure the safe and normal operation. This paper is focused on exploring the flow and heat transfer mechanism in matrix cooling channels. In order to analyze the internal flow field characteristics of this cooling configuration at a Reynolds number of 30000 accurately, large eddy simulation method is carried out. Methods of vortex identification and field synergy are employed to study its flow field. Cross-sectional views of velocity in three subchannels at different positions have been presented. The results show that the airflow is strongly disturbed by the bending part. It’s concluded that due to the bending structure, the airflow becomes complex and disordered. When the airflow goes from the inlet to the turning, some small-sized and discontinuous vortices are formed. Behind the bending structure, the size of the vortices becomes big and the vortices fill the subchannels. Because of the structure of latticework, the airflow is affected by each other. Airflow in one subchannel can exert a shear force on another airflow in the opposite subchannel. It’s the force whose direction is the same as the vortex that enhances the longitudinal vortices. And the longitudinal vortices contribute to the energy exchange of the internal airflow and the heat transfer between airflow and walls. Besides, a comparison of the CFD results and the experimental data is made to prove that the numerical simulation methods are reasonable and acceptable.

scholarly journals Effect of Rayleigh Number on Internal Eccentricity in a Heated Horizontal Elliptical Cylinder to its Coaxial Square Enclosure

2020 ◽  
Vol 25 (3) ◽  
pp. 17-29
Author(s):  
Abdelkrim Bouras ◽  
Djedid Taloub ◽  
Zied Driss
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Outer Cylinder ◽  
Boussinesq Approximation ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Commercial Code ◽  
Volume Method ◽  
Rayleigh Numbers

AbstractThis paper deals with numerical investigation of a natural convective flow in a horizontal annular space between a heated square inner cylinder and a cold elliptical outer cylinder with a Newtonian fluid. Uniform temperatures are imposed along walls of the enclosure. The governing equations of the problem were solved numerically by the commercial code Fluent, based on the finite volume method and the Boussinesq approximation. The effects of Geometry Ratio GR and Rayleigh numbers on fluid flow and heat transfer performance are investigated. The Rayleigh number is varied from 103 to 106. Throughout the study the relevant results are presented in terms of isotherms, and streamlines. From the results, we found that the increase in the Geometry Ratio B leads to an increase of the heat transfer coefficient. The heat transfer rate in the annulus is translated in terms of the average Nusselt numbers along the enclosure’s sides. Tecplot 7 program was used to plot the curves which cleared these relations and isotherms and streamlines which illustrate the behavior of air through the channel and its variation with other parameters. The results for the streamlines, isotherms, local and average Nusselt numbers average Nusselt numbers are compared with previous works and show good agreement.

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