Thermal Convection Field Research Articles

Experimental study of cross-correlation algorithm based on background schlieren quantization in natural thermal convection field

Abstract The background shading technology has shown a wide application potential in many fields. This study aims to study the thermal convection field above the flame. In this study, we established a large field shading system, which is used to observe the flow field distribution and the high temperature probe at the corresponding position above the flame flow field, and then the temperature change map of the corresponding position of the flow field is obtained. The experimental results show the advantages of the large field of view shading system based on background shading technology in the temperature distribution image of the flow field, and make up for the vacancy and deficiency of the application in the optical field. This study is also helpful to better reveal the nature of the combustion process. The development of research will provide a new perspective for the further application of background shading technology.

Characteristics and suppression of beam distortion in a high repetition rate nanosecond stimulated Brillouin scattering phase conjugation mirror

Abstract The stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) based on liquid media is widely used in high-power laser systems due to its robust thermal load capacity, high energy conversion efficiency and improved beam quality. Nevertheless, with an increase in the pump repetition rate, thermally-induced blooming and optical breakdown can emerge, leading to distortions in the Stokes beam. In this study, we delved into the thermal effects in liquid SBS-PCMs employing hydrodynamic analysis, establishing a relationship between beam profile distortion and the thermal convection field. We calculated the temperature and convection velocity distribution based on the pump light parameters and recorded the corresponding beam profiles. The intensities of the beam profiles were modulated in alignment with the convection directions, reaching a velocity peak of 2.85 mm/s at a pump pulse repetition rate of 250 Hz. The residual sum of squares (RSS) was employed to quantify the extent of beam profile distortion relative to a Gaussian distribution. The RSS escalated to 7.8, in contrast to 0.7 of the pump light at a pump pulse repetition rate of 500 Hz. By suppressing thermal convection using a high-viscosity medium, we effectively mitigated beam distortion. The RSS was reduced to 0.7 at a pump pulse repetition rate of 500 Hz, coinciding with a twentyfold increase in viscosity, thereby enhancing the beam quality. By integrating hydrodynamic analysis, we elucidated and mitigated distortion with targeted solutions. Our research offers an interdisciplinary perspective on studying thermal effects and contributes to the application of SBS-PCMs in high-repetition-rate laser systems by unveiling the mechanism of photothermal effects.

Physics-informed graph convolutional neural network for modeling fluid flow and heat convection

This paper introduces a novel surrogate model for two-dimensional adaptive steady-state thermal convection fields based on deep learning technology. The proposed model aims to overcome limitations in traditional frameworks caused by network types, such as the requirement for extensive training data, accuracy loss due to pixelated preprocessing of original data, and inability to predict information near the boundaries with precision. We propose a new framework that consists primarily of a physical-informed neural network (PINN) and a graph convolutional neural network (GCN). The GCN serves as the prediction module and predicts thermal convection in the two-dimensional computational domain by considering the mutual influence between unstructured nodes and their neighbors. On the other hand, the PINN acts as the physical constraint module of the framework by embedding the control equation of thermal convection into the loss function of the neural network, ensuring that the inference and prediction results of the GCN comply with the constraints of the control equation. The advantages of this framework lie in two aspects. First, the computation mechanism of the GCN is more in line with the actual evolution of temperature fields. Second, the PINN enhances the cognitive ability of the surrogate model toward the convection field information. It accurately describes the changes of temperature gradient information at the boundary position and reduces the model's demand for training data. To validate the advantages of the proposed model, we gradually analyzed the model's geometric adaptability and predictive accuracy from the single cylinder case to the double cylinder case. We also investigated the impact of the number of sampling points on model training and compared the model's prediction results with those of a purely data-driven model. The results show that the proposed model exhibits good geometric adaptability and stability. With only 20 training data, the mean error of the proposed model in predicting the velocity and temperature field is less than 1% and 0.6% for the single cylinder, and less than 2% and 1% for the double cylinder case, while the mean error of the purely data-driven GCN model in predicting the velocity and temperature field is 9.4% and 6.4% for the double cylinder case. These findings demonstrate the effectiveness of the proposed physics-informed graph convolutional neural network, allowing for more accurate prediction of fluid flow and heat convection using surrogate model.

A set of codes for numerical convection and geodynamo calculations

Abstract We present a set of codes for calculating and displaying solutions to diverse problems within thermal convection and magnetic field generation in rotating fluid-filled spheres and spherical shells. There are diverse programs for the kinematic dynamo problem, the onset of thermal convection, and boundary-locked thermal convection, and time-stepping codes for non-magnetic convection and the dynamo with either homogeneous or spatially varying thermal boundary conditions. Where possible, all programs have been benchmarked against other codes and tested by reproducing previously published results. Each program comes with the complete source code, a pdf instruction manual, and at least one example run with a sample input file and all necessary files for describing an initial condition. The only prerequisite for running most of the codes is a FORTRAN compiler. The plotting programs require in addition the PGPLOT graphics library. All source code, examples, input files, solutions, and instructions are available for download from github and Zenodo.

Significance of thermal stress in a convective-radiative annular fin with magnetic field and heat generation: application of DTM and MRPSM

The present paper explains the temperature attribute of a convective-radiative rectangular profiled annular fin with the impact of magnetic field. The effect of thermal radiation, convection, and magnetic field on thermal stress distribution is also studied in this investigation. The governing energy equation representing the steady-state heat conduction, convection, and radiation process is transformed into its dimensionless nonlinear ordinary differential equation (ODE) with corresponding boundary conditions using non-dimensional terms. The obtained ODE is then solved analytically by employing the Pade approximant-differential transform method (DTM) and modified residual power series method (MRPSM). Moreover, the important characteristics of the temperature field, the thermal stress, and the impact of some non-dimensional parameters are inspected graphically, and a physical explanation is provided to aid in comprehension. The significant findings of the investigation reveal that temperature distribution enhances with an increase in the magnitude of the heat generation parameter and thermal conductivity parameter, but it gradually decreases with an increment of convective-conductive parameter, Hartmann number, and radiative-conductive parameter. The thermal stress distribution of the fin varies considerably in the applied magnetic field effect.

Quantitative measurement of natural thermal convection temperature field based on color stripe background oriented schlieren (CSBOS)

In this study, a new color stripe background oriented schlieren (CSBOS) was proposed. Through multiple experiments, the oblique stripes with color alternating arrangements were selected to draw the background pattern, and the natural thermal convection temperature fields of premixed flame combustion in butane laminar flow with different equivalence ratios were analyzed and reconstructed. A color stripe background oriented schlieren experimental platform was built to collect images of the natural thermal convection field above the butane flame, which can improve the accuracy and spatial resolution, and analyze the influence of different equivalence ratios on the flow field morphology and temperature distribution. The root mean square error (RMSE) between the temperature reconstructed by CSBOS and the temperature measured by invasive measurement (the flow field is not destroyed) is 5.26 at different equivalence ratios, and the maximum measurement error between the reconstructed flow field temperature distribution and the contact measurement is only 2.7%, indicating that CSBOS can accurately reconstruct the temperature of the natural thermal convection field.

Shape Optimisation of a Heat Source in a Thermal Convection Field Considering Perimeter Constraint Condition

In this study, we present an investigation of shape optimisation analysis for a heat convection problem taking into account perimeter constraint condition. The incompressible Navier–Stokes equation using the Boussinesq approximation, the equation of continuity and the energy equation are employed for the governing equations in the heat convection field. The mixed interpolation method is applied to solve the flow field, and the quadratic and linear triangular elements are, respectively, employed for the velocity and the pressure. The quadratic triangular element is applied to interpolate the temperature. The purpose of this study is to find the optimal shape of a heat source so as to maximise the quantity of radiation on the outer boundary. The adjoint variable method is applied to obtain the optimal shape, and the perimeter constraint condition for the heat source is considered in this optimisation problem. The perimeter constraint condition is adapted in the traction method.

Shape optimization in thermal convection field considering a slight compressibility

Shape optimization in thermal convection field considering a slight compressibility

Shape design in unsteady forced thermal convection field considering pulsating flow

Shape design in unsteady forced thermal convection field considering pulsating flow

Natural Thermal Convection Field Measurement Technology Based on Background Oriented Schlieren Technology

Background oriented schlieren technology is developed from the combination of schlieren technology and PIV technology. It is an emerging non-contact flow field quantitative measurement method. The development and principle of background oriented schlieren technology are introduced in detail. A set of background oriented schlieren imaging system suitable for natural thermal convection field is built. The quantitative measurement research is carried out on the natural thermal convection field above the candle flame, and the density field is calculated. Distorted vector displacement map. The results show that the background oriented schlieren technology can be better applied to the quantitative measurement of natural thermal convection field, and it has broad development prospects.

Optimization of Heat Source Boundary Shape in Thermal Convection Field Based on the Adjoint Variable and the Finite Element Methods

Optimization of Heat Source Boundary Shape in Thermal Convection Field Based on the Adjoint Variable and the Finite Element Methods

Shape optimization in thermal convection field based on the adjoint variable and the finite element methods

Shape optimization in thermal convection field based on the adjoint variable and the finite element methods

Global, nonparametric, noniterative optimization of time-averaged quantities under small, time-varying forcing: An application to a thermal convection field

This study demonstrates a global, nonparametric, noniterative optimization of time-mean value of a kind of index vibrated by time-varying forcing. It is based on the fact that the (steady) forced vibration of nonautonomous ordinary differential equation systems is well approximated by an analytical solution when the amplitude of forcing is sufficiently small and its base state without forcing is linearly stable and steady. It is applied to optimize a time-averaged heat-transfer rate on a two-dimensional thermal convection field in a square cavity with horizontal temperature difference, and the globally optimal way of vibrational forcing, i.e. the globally optimal, spatial distribution of vibrational heat and vorticity sources, is first obtained. The maximized vibrational thermal convection corresponds well to the state of internal gravity wave resonance. In contrast, the minimized thermal convection is weak, keeping the boundary layers on both sidewalls thick.

Computer simulations of Jupiter’s deep internal dynamics help interpret what Juno sees

We describe computer simulations of thermal convection and magnetic field generation in Jupiter's deep interior: that is, its convective dynamo. Results from three different simulations highlight the importance of including the dynamics in the very deep interior, although much of the convection and field generation seems to be confined to the upper part of the interior. A long-debated question is to what depth do Jupiter's zonal winds extend below its surface. Our simulations suggest that, if global latitudinally banded patterns in Jupiter's near-surface magnetic and gravity fields were detected by Juno, NASA's orbiting spacecraft at Jupiter [Bolton S, et al. (2017) Science 356:821-825], they would provide evidence for Jupiter's zonal winds extending deep below the surface. One of our simulations has also maintained, for a couple simulated years, a deep axisymmetric inertial wave, with properties at the surface that depend on the size of the model's small rocky core. If such a wave was detected on Jupiter's surface, its latitudes and oscillation frequency would provide evidence for the existence and size of Jupiter's rocky core.

Thermal fluid-structure interaction and coupled thermal-stress analysis in a cable stayed bridge exposed to fire

In this paper, thermal fluid structure-interaction (TFSI) and coupled thermal-stress analysis are utilized to identify the effects of transient and steady-state heat-transfer on the vortex induced vibration and fatigue of a segmental bridge deck due to fire incidents. Numerical simulations of TFSI models of the deck are dedicated to calculate the lift and drag forces in addition to determining the lock-in regions once using fluid-structure interaction (FSI) models and another using TFSI models. Vorticity and thermal convection fields of three fire scenarios are simulated and analyzed. Simiu and Scanlan benchmark is used to validate the TFSI models, where a good agreement was manifested between the two results. Extended finite element method (XFEM) is adopted to create 3D models of the cable stayed bridge to simulate the fatigue of the deck considering three fire scenarios. Choi and Shin benchmark is used to validate the damaged models of the deck in which a good coincide was seen between them. The results revealed that TFSI models and coupled thermal-stress models are significant in detecting earlier vortex induced vibration and lock-in regions in addition to predicting damages and fatigue of the deck due to fire incidents.

Second-order approximation to forced oscillations of thermal convection under small time-varying forcing

This study presents a theory that approximates steady forced oscillations up to the second-order with respect to vibration amplitude a. This is the extension of the first-order approximation (linear theory) that enable us to obtain the optimal forcing without any parametric studies (Ishida et al., 2012). The theory is constructed on an ordinary differential equation system (ODEs) with an arbitrary small time-varying external forcing and is applicable to obtain the steady response including the contribution of the vibration to the direct-current component more accurately than the linear theory while a is relatively small. It also enables us to evaluate a sensitivity, i.e. the derivative of an objective measure, indicator, with respect to the amplitude a. Thereby the region of a where the linear theory is effective can be identified. The application of the second-order approximation to a thermal convection field in a square cavity subjected to a heat-flux vibration on the bottom wall shows that the second-order sensitivity (second derivative) well explains the parameter region where the nonlinearity appears. Outside the region we can utilize in a positive manner the useful linear theory. Moreover, the change in the time-mean skin friction on the wall surface is well evaluated by the second-order approximation while a is small enough.

Magnetic effect on thermally stratified nanofluid saturated non-Darcy porous medium under convective boundary condition

The flow, heat and nanoparticle mass transfer characteristics in the free convection from a vertical plate in a thermally linearly stratified nanofluid saturated non-Darcy porous medium under convective boundary condition is investigated. In addition, the magnetic field effect under convective boundary condition is incorporated in the nanofluid model. The transformed non-similar non-linear coupled partial differential equations representing the transport of mass, momentum, thermal energy, and the nanoparticles volume fraction are solved numerically by the Blottner [18] scheme, which is modified to accommodate the effect of the convective boundary condition. The accuracy of the numerical results is validated by a quantitative comparison of the heat transfer rates with previously published results for a special case and the results are found to be in good agreement. It is observed that the thermal transport is significantly affected due to the stratification of the medium and it is more significant with varying values of the parameters related to the nanofluid in the medium as well as the Biot number due to the convective boundary condition. The effects of thermal stratification, non-Darcy, convection and magnetic field parameters on the velocity, temperature, nanoparticle volume fraction, heat and nanoparticle mass transfer rates are illustrated graphically.

D111 任意微小振幅強制振動熱対流場に対する弱非線形解析の有効性(一般講演(5))

D111 任意微小振幅強制振動熱対流場に対する弱非線形解析の有効性(一般講演(5))

Forced oscillations, optimal forcing and resonance of thermal convection under small, time-varying forcing

This study proposes a method to obtain forced oscillation induced by arbitrary small time-varying forcing on a stable thermal convection field, and a framework for finding universal and inherent resonance modes on the field, independent of the ways of forced vibration, indicators of resonance and other information. It is based on an eigenvalue analysis of a Hermitian matrix relating to the frequency response function, and the typical forced oscillation at a resonance is given by the response to the optimal forcing as the eigenvector corresponding to the largest eigenvalue of the matrix. The method also provides indicators to quantify the efficiency in realizing a given resonance mode by a specific forced vibration. We can find thereby that heat-flux vibration not on the bottom wall but on the left-hand sidewall is preferred for realizing the internal gravity wave resonance.

Shape optimization of thermal forced convection fields

AbstractThis paper presents a numerical analysis method for solving two shape optimization problems, namely, determining temperature distributions in subdomains and maximizing the thermal dissipation on sub‐boundaries of steady‐state thermal convective fields. The square‐error integral between the actual temperature distributions and the prescribed temperature distributions in the prescribed subdomains is employed as the objective function for determining the temperature distribution. The shape gradients for these shape determination problems were derived theoretically using the adjoint variable method, the Lagrange multiplier method and the formulae of the material derivative. Reshaping was accomplished using a traction method that was proposed as a solution to the domain optimization problems. A new numerical procedure is proposed that applies the finite element method to the shape determination problems. The validity of this method was confirmed by 2D numerical analysis. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(5): 313–328, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20202