scholarly journals Thermo-Hydraulic Characteristics of Micro-Scale Surface Roughness Topology of Additively Manufactured Surface Model: Modal Decomposition Perspective

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7650
Author(s):  
Sina Lohrasbi ◽  
René Hammer ◽  
Werner Eßl ◽  
Georg Reiss ◽  
Stefan Defregger ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Additive Manufacturing ◽  
Numerical Study ◽  
Rapid Development ◽  
Surface Model ◽  
Micro Scale ◽  
Roughness Elements ◽  
Flow Mechanisms ◽  
Scale Surface

As a consequence of rapid development of additive manufacturing (3D printing) methods, the academic/industrial demand has been continuously increasing. One field of application is the manufacturing of heat exchanging devices using this promising method. In this regard, understanding the underlying mechanisms from a thermo-hydraulic viewpoint becomes important. Therefore, in this study, scale-resolving large eddy simulation (LES) is applied to reveal the flow details in combination with a model of roughness topology occurring in additive manufacturing. To process the transient LES results, proper orthogonal decomposition (POD) is used to extract the coherent flow structures, and the extended POD is used to rank the flow modes based on thermal importance. The main aim of the present work is to go beyond the conventionally applied methodologies used for the evaluation of surface roughness, i.e., averaged numerical study or experimental overall performance evaluation of the flow/thermal response of additively manufactured surfaces in heat exchangers. This is necessary to reveal the underlying flow mechanisms hidden in the conventional studies. In this study, the behavior of the flow over the micro-scale surface roughness model and its effects on heat transfer are studied by assuming cone-shaped roughness elements with regular placement as the dominant surface roughness structures. The major discussions reveal the footprint of flow mechanisms on the heat transfer coefficient spatial modes on the rough surface. Moreover, comparative study on the flow/thermal behavior at different levels of roughness heights shows the key role of the height-to-base-diameter ratio of the roughness elements in thermal performance.

Boundary Slope Control in Topology Optimization for Additive Manufacturing: For Self-Support and Surface Roughness

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Cunfu Wang ◽  
Xiaoping Qian ◽  
William D. Gerstler ◽  
Jeff Shubrooks
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Topology Optimization ◽  
Additive Manufacturing ◽  
Density Gradient ◽  
Transfer Efficiency ◽  
Global Constraints ◽  
Optimization Approach ◽  
Heat Transfer Efficiency ◽  
Boundary Slope

This paper studies how to control boundary slope of optimized parts in density-based topology optimization for additive manufacturing (AM). Boundary slope of a part affects the amount of support structure required during its fabrication by additive processes. Boundary slope also has a direct relation with the resulting surface roughness from the AM processes, which in turn affects the heat transfer efficiency. By constraining the minimal boundary slope, support structures can be eliminated or reduced for AM, and thus, material and postprocessing costs are reduced; by constraining the maximal boundary slope, high-surface roughness can be attained, and thus, the heat transfer efficiency is increased. In this paper, the boundary slope is controlled through a constraint between the density gradient and the given build direction. This allows us to explicitly control the boundary slope through density gradient in the density-based topology optimization approach. We control the boundary slope through two single global constraints. An adaptive scheme is also proposed to select the thresholds of these two boundary slope constraints. Numerical examples of linear elastic problem, heat conduction problem, and thermoelastic problems demonstrate the effectiveness and efficiency of the proposed formulation in controlling boundary slopes for additive manufacturing. Experimental results from metal 3D printed parts confirm that our boundary slope-based formulation is effective for controlling part self-support during printing and for affecting surface roughness of the printed parts.

Effect of Additive Manufacturing Process Parameters on Turbine Cooling

2019 ◽  
Author(s):  
Jacob C. Snyder ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Additive Manufacturing ◽  
Surface Morphology ◽  
Process Parameters ◽  
Manufacturing Process ◽  
Pressure Loss ◽  
Cooling Performance ◽  
Micro Scale ◽  
Turbine Cooling ◽  
External Cooling

Abstract Turbine cooling is a prime application for additive manufacturing because it enables quick development and implementation of innovative designs optimized for efficient heat removal, especially at the micro-scale. At the micro-scale, however, the surface finish plays a significant role in the heat transfer and pressure loss of any cooling design. Previous research on additively manufactured cooling channels has shown the surface roughness increases both heat transfer and pressure loss to similar levels as highly-engineered turbine cooling schemes. What has not been shown, however, is whether opportunities exist to tailor additively manufactured surfaces through control of the process parameters to further enhance the desired heat transfer and pressure loss characteristics. The results presented in this paper uniquely show the potential of manipulating the parameters within the additive manufacturing process to control the surface morphology, directly influencing turbine cooling. To determine the effect of parameters on cooling performance, coupons were additively manufactured for common internal and external cooling methods using different laser powers, scan speeds, and scanning strategies. Internal and external cooling tests were performed at engine relevant conditions to measure appropriate metrics of performance. Results showed the process parameters have a significant impact on the surface morphology leading to differences in cooling performance. Specifically, internal and external cooling geometries react differently to changes in parameters, highlighting the opportunity to consider process parameters when implementing additive manufacturing for turbine cooling applications.

Predicting Skin Friction and Heat Transfer for Turbulent Flow Over Real Gas-Turbine Surface Roughness Using the Discrete-Element Method

2003 ◽  
Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Wind Tunnel ◽  
Discrete Element Method ◽  
Skin Friction ◽  
Gas Turbine ◽  
Discrete Element ◽  
Real Gas ◽  
Roughness Elements ◽  
Element Method

The discrete-element method considers the total aerodynamic drag on a rough surface to be the sum of shear drag on the flat part of the surface and the form drag on the individual roughness elements. The total heat transfer from a rough surface is the sum of convection through the fluid on the flat part of the surface and the convection from each of the roughness elements. The discrete-element method has been widely used and validated for predicting heat transfer and skin friction for rough surfaces composed of sparse, ordered, and deterministic elements. Real gas-turbine surface roughness is different from surfaces with sparse, ordered, and deterministic roughness elements. Modifications made to the discrete-element roughness method to extend the validation to real gas-turbine surface roughness are detailed. Two rough surfaces found on high-hour gas-turbine blades were characterized using a Taylor-Hobson Form Talysurf Series 2 profilometer. Two rough surfaces and two elliptical-analog surfaces were generated for wind-tunnel testing using a three-dimensional printer. The printed surfaces were scaled to maintain similar boundary-layer thickness to roughness height ratio in the wind tunnel as found in gas-turbine operation. The results of the wind tunnel skin friction and Stanton number measurements and the discrete-element method predictions for each of the four surfaces are presented and discussed. The discrete-element predictions made considering the gas-turbine roughness modifications are within 7% of the experimentally-measured skin friction coefficients and are within 16% of the experimentally-measured Stanton numbers.

scholarly journals An Experimental and Numerical Study of Heat Transfer From Arrays of Impinging Jets With Surface Ribs

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Sebastian Spring ◽  
Yunfei Xing ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Cross Flow ◽  
Impinging Jets ◽  
Separation Distance ◽  
Distance Measures ◽  
Impingement Plate ◽  
Roughness Elements ◽  
Staggered Arrangement ◽  
The Heat Transfer Coefficient

A combined experimental and numerical investigation of the heat transfer characteristics within arrays of impinging jets with rib-roughened surfaces is presented. Two configurations are considered: One with an inline arrangement of jets and ribs oriented perpendicular to the direction of cross-flow and one with a staggered arrangement of jets and broken ribs aligned with the direction of cross-flow. For both cases, the jet Reynolds number is 35,000, the separation distance measures H/D = 3, the spent air is routed through one exit contributing to the maximum cross-flow condition, and the rib height and width is both 1 D. The experiments are carried out in perspex models using the transient liquid crystal method. Local jet temperatures are measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. In addition to the measurements, a numerical analysis using the commercial CFD software package ANSYSCFX is conducted. Heat transfer predictions are compared with those obtained from experiments with regards to local distributions as well as averaged quantities. A good overall agreement is found but discrepancies for local values need to be accepted. The present investigation also emphasizes that configurations including rib roughness elements should be compared based on the amount of transferred heat flux in order to account for the area enlarging effect. This allows a correct evaluation of the thermal performance.

Heat Transfer at Aluminum-Water Interfaces: Effect of Surface Roughness

2012 ◽  
Author(s):  
H. Sam Huang ◽  
Jennifer L. Wohlwend ◽  
Vikas Varshney ◽  
Ajit K. Roy
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Surface Roughness ◽  
Finite Element ◽  
Thermal Conductance ◽  
Md Simulations ◽  
Macroscopic Scale ◽  
Microscopic Scale ◽  
Scale Surface ◽  
Element Method

In this paper, we studied the effect of microscopic surface roughness on heat transfer between aluminum and water by molecular dynamic (MD) simulations and macroscopic surface roughness on heat transfer between aluminum and water by finite element (FE) method. It was observed that as the microscopic scale surface roughness increased, the thermal boundary conductance increased. The thermal conductance increases 20% when the ratio of the amplitude of the surface roughness to the width of the system was changed from 0 to 1. At the macroscopic scale, different degrees of surface roughness were studied by finite element method. The heat transfer was observed to enhance as the surface roughness increases. The surface roughness was found to enhance the heat transfer both at the microscopic scale and at the macroscopic scale. Based upon the calculations at the microscopic scale by MD simulations and at the macroscopic scale by Finite Element method, a procedure was proposed to obtain the thermal conductance of surface roughness at the length scale of macroscopic and able to include the macroscopic scale surface roughness.

scholarly journals Micro scale jet impingement cooling and its efficacy on turbine vanes : a numerical study

2021 ◽  
Author(s):  
Santhiya Jayaraman
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Leading Edge ◽  
Jet Impingement ◽  
3D Analysis ◽  
Transfer Rates ◽  
Impingement Cooling ◽  
Micro Scale ◽  
Turbine Vane ◽  
Nozzle Configuration

A numerical analysis of effectiveness of micro-jet impingement cooling on leading edge of a turbine vane is presented. An axisymmetric single round jet was assessed for its ability and consistency as a preliminary study including the investigation of parameters influencing the heat transfer distribution. The analysis revealed that an increase in Nusselt number was attributed to increase in Reynolds number, decrease in jet diameter and H/D < 3. Significant improvement in heat transfer was observed for tapering nozzle configuration. The study was then further expanded to 3D analysis of leading edge cooling of turbine vane. Effect of nozzle diameter to micro-scale was studied, which showed 65% enhancement in the heat transfer rates.

scholarly journals A highly stretchable and robust non-fluorinated superhydrophobic surface

2017 ◽  
Vol 5 (31) ◽  
pp. 16273-16280 ◽  
Author(s):  
Jie Ju ◽  
Xi Yao ◽  
Xu Hou ◽  
Qihan Liu ◽  
Yu Shrike Zhang ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Superhydrophobic Surface ◽  
Silicone Elastomer ◽  
Micro Scale ◽  
Highly Stretchable ◽  
Silica Microparticles ◽  
Scale Surface

A stretchable, rub-proof superhydrophobic surface was realized by a chemically bonded silicone elastomer network covering the surface of silica microparticles to form enhanced micro-scale surface roughness.

Influences of Target Surface Roughness on Impingement Jet Array Heat Transfer: Part 2 — Effects of Roughness Shape, and Reynolds Number

2016 ◽  
Author(s):  
W. Buzzard ◽  
Z. Ren ◽  
P. M. Ligrani ◽  
C. Nakamata ◽  
S. Ueguchi
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Target Surface ◽  
Impingement Cooling ◽  
Impingement Jet ◽  
Heat Transfer Augmentation ◽  
Small Triangle ◽  
Roughness Elements ◽  
Jet Array

The present investigation considers the effects of special roughness patterns on impingement target surfaces to improve the effectiveness and surface heat transfer augmentation levels of impingement jet array cooling. This investigation utilizes various sizes, distributions, shapes, and patterns of surface roughness elements for impingement cooling augmentation. The surface roughness shapes considered here are rectangle and triangle, in combination with larger rectangular pins. Configurations considered include: (i) arrays of small rectangular roughness, (ii) arrays of small triangle roughness, (iii) combinations of small rectangle roughness and large pins together, and (iv) combinations of small triangle roughness and large pins together. Tests are performed at impingement jet Reynolds numbers of 900, 1500, 5000, and 11000. Local and overall impingement cooling performance depends upon the shape of the roughness elements, as well as upon the jet Reynolds number. Depending upon the magnitude of jet Reynolds number, different behavior and trends are observed for the arrays of small rectangle roughness, compared with arrays of small triangle roughness. These differences are related to the abilities of the two different roughness shapes to generate different distributions of local mixing and vorticity at different length and time scales. Overall, results demonstrate the remarkable ability of target surface roughness to produce increased surface heat transfer augmentation levels of impingement jet array cooling, relative to target surfaces which are smooth.

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