Simulating Heat Exchange and Friction in a Thin Laminar Boundary Layer of Air over the Lateral Surface of a Blunted Cone Featuring a Low Aspect Ratio

2020 ◽  
pp. 4-20
Author(s):  
V.V. Gorskiy ◽  
A.G. Loktionova
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Differential Equations ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Solutions ◽  
Aircraft Design ◽  
Effective Length ◽  
Engineering Practice ◽  
Operation Conditions

It is not possible to obtain a high-quality solution to a convective heat transfer problem without numerically integrating the differential equations describing the boundary layer, which involves a whole range of computational issues. Developing relatively simple yet adequately accurate computation methods becomes crucial. Using the effective length method may be considered to be the first step towards solving this problem. This method boasts an accuracy of convective heat transfer calculation that is acceptable in practice, due to which it became prevalent in aircraft design. However, this method is also relatively labour-intensive, although significantly less so than numerical integration of the boundary layer differential equations. The most efficient approach to solving heat transfer and friction problems in engineering practice would be using simple algebraic equations based on fitting the results of rigorous numerical computations or experimental investigations. Regrettably, there is no information published regarding how accurate these equations are for various operation conditions. The paper presents a solution to this problem based on deriving systematic numerical solutions to the boundary layer equations in the most rigorous analytical statement, along with conducting a thorough analysis of the equation accuracy for both the equations derived and previously published

Heat Transfer and Friction in a Thin Air Laminar Boundary Layer over Semi-Sphere Surface

2020 ◽  
pp. 17-33
Author(s):  
V.V. Gorskiy ◽  
A.G. Loktionova
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Differential Equations ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Experimental Studies ◽  
Point Of View ◽  
Effective Length ◽  
Engineering Practice ◽  
Literary Sources

A qualitative solution to the problem of calculating convective heat transfer can be obtained only by numerically integrating the differential equations of the boundary layer, which is associated with overcoming a number of computational problems. Consequently, it is important to develop relatively simple, but fairly high-precision calculation methods. As a first approximation to solving this problem, we can consider the use of the effective length method. From the practical point of view, this method is characterized by satisfactory accuracy of calculating convective heat transfer, which has led to its widespread use in aeronautical design engineering. However, this method is also characterized by a relatively high complexity, although it is much lower than that in numerical integration of the differential equations of the boundary layer. The most effective approach to solving heat transfer and friction problems in engineering practice is to use simple algebraic formulae obtained on the basis of approximating the results of rigorous numerical calculations, or experimental studies. Unfortunately, there is no information in literary sources about the accuracy of these formulae under various conditions of product functioning. This problem is solved on the basis of a systematic numerical calculation of the equations of the boundary layer in the most rigorous theoretical calculation, as well as a detailed analysis of the accuracy of the obtained algebraic formulae and their literary analogues

scholarly journals On the question of computing convective heat transfer parameters in a laminar-to-turbulent boundary layer on an impermeable hemispherical surface

2019 ◽  
pp. 17-28
Author(s):  
V.V. Gorskiy ◽  
A.G. Leonov ◽  
A.G. Loktionova
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Solutions ◽  
Turbulent Viscosity ◽  
Effective Length ◽  
Viscosity Models ◽  
Transfer Parameters

In order to qualitatively solve the problem of computing convective heat transfer parameters in a laminar-to-turbulent boundary layer, it is necessary to numerically integrate differential equations descrybing that layer, completed by semiempirical turbulent viscosity models. These must be validated using results of experimental investigations where the gas dynamics of a gas flow around a body is correctly simulated. In terms of practical applications, developing relatively simple yet highly accurate computation methods is important. At present, the most widely used method to solve this type of problems in aviation and aerospace engineering is the effective length method developed by V.S. Avduevskiy, Academician. The paper shows that significant errors characterise computations using this method and traditional turbulent viscosity models to determine parameters of those blunted components of aircraft that are subjected to the highest temperatures. We present a solution to this problem, based on constructing systematic numerical solutions to the equations describing the laminar-to-turbulent boundary layer and subsequently approximating them. We prove that this approach ensures both acceptable computation accuracy and solution simplicity.

Mechanical Augmentation of Convective Heat Transfer in Air

1975 ◽  
Vol 97 (4) ◽  
pp. 516-520 ◽  
Author(s):  
J. K. Hagge ◽  
G. H. Junkhan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Boundary Layers ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Renewal Theory ◽  
Surface Renewal ◽  
Mechanical Removal ◽  
Blade Element

An experimental investigation was conducted into augmentation of forced convection heat transfer in air by mechanical removal of the boundary layer. A rotating blade element passing in close proximity to a flat plate convective surface was found to increase the rate of convective heat transfer by up to eleven times in certain situations. The blade element effectively scrapes away the boundary layer, thus reducing the resistance to heat flow. Parameters investigated include scraping frequency, scraper clearance, and type of boundary layer. Increased coefficients were found for higher scraping frequencies. Significant augmentation was obtained with clearance as large as 0.15 in. (0.0038 m) between the moving blade element and the convective surface. The technique appears most useful for laminar and transitional boundary layers, although some improvement was obtained for the turbulent boundary layers investigated. The simple surface renewal theory developed for scraped surface augmentation in liquids was found to approximately predict the coefficients obtained. A new relation is proposed which gives a better prediction and includes the effect of scraper clearance.

scholarly journals Slip Effects on Boundary Layer Flow and Heat Transfer Along a Stretching Cylinder

2013 ◽  
Vol 18 (2) ◽  
pp. 447-459 ◽  
Author(s):  
S. Mukhopadhyay ◽  
R.S.R Gorla
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Differential Equations ◽  
Boundary Layer Flow ◽  
Numerical Solutions ◽  
Velocity Slip ◽  
Heat Equations ◽  
Stretching Cylinder ◽  
Linear Ordinary Differential Equations ◽  
Layer Flow

An axi-symmetric laminar boundary layer flow of a viscous incompressible fluid and heat transfer towards a stretching cylinder is presented. Velocity slip is considered instead of the no-slip condition at the boundary. Similarity transformations are used to convert the partial differential equations corresponding to the momentum and heat equations into non-linear ordinary differential equations. Numerical solutions of these equations are obtained by the shooting method. It is found that the velocity decreases with increasing the slip parameter. The skin friction as well as the heat transfer rate at the surface is larger for a cylinder compared to those for a flat plate.

Heat Transfer Enhancement of Channel Flow via Vortex-Induced Vibration of Flexible Cylinder

2014 ◽  
Author(s):  
Junxiang Shi ◽  
Jingwen Hu ◽  
Steven R. Schafer ◽  
Chung-Lung (C. L. ) Chen
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Channel Flow ◽  
Convective Heat ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Thermal Boundary Layer ◽  
Flexible Cylinder

Thermal diffusion in a developed thermal boundary layer is considered as an obstacle for improving the forced convective heat transfer rate of a channel flow. In this work, a novel, self-agitating method that takes advantage of vortex-induced vibration (VIV) is introduced to disrupt the thermal boundary layer and thereby enhance the thermal performance. A flexible cylinder is placed at the centerline of a rectangular channel. The vortex shedding due to the cylinder gives rise to a periodic vibration of the cylinder. Consequently, the flow-structure-interaction (FSI) strengthens the disruption of the thermal boundary layer by vortex interaction with the walls, and improves the mixing process. This new concept for enhancing the convective heat transfer rate is demonstrated by a three-dimensional modeling study at different Reynolds numbers (84∼168). The fluid dynamics and thermal performance are analyzed in terms of vortex dynamics, temperature fields, local and average Nusselt numbers, and pressure loss. The channel with the self-agitated cylinder is verified to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% as opposed to the clean channel and the channel with a stationary cylinder, respectively.

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