Instantaneous acoustic heating of a viscous fluid flow in a boundary layer is the subject of investigation. The governing equation of acoustic heating is derived by means of a special linear combination of conservation equations in the differential form, which reduces all acoustic terms in the linear part of the final equation but preserves terms belonging to the thermal mode. The procedure of decomposition is valid in a weakly nonlinear flow, it yields the nonlinear terms responsible for the modes interaction. Nonlinear acoustic terms form a source of acoustic heating in the case of the dominative sound. This acoustic source reflects the thermoviscous and dispersive properties of a fluid flow. The method of deriving the governing equations does not need averaging over the sound period, and the final governing dynamic equation of the thermal mode is instantaneous. Some examples of acoustic heating are illustrated and discussed, and conclusions about efficiency of heating caused by different waveforms of sound are made.
Presented work considers flow and thermal phenomena occurring during the single minijet impingement on curved surfaces, heated with a constant heat flux, as well as the array of minijets. Numerical analyses, based on the mass, momentum and energy conservation laws, were conducted, regarding single phase and two-phase simulations. Focus was placed on the proper model construction, in which turbulence and boundary layer modeling was crucial. Calculations were done for various inlet parameters. Initial single minijet results served as the basis for the main calculations, which were conducted for two jet arrays, with flat and curved heated surfaces. Such complex geometries came from the cooling systems of electrical devices, and the geometry of cylindrical heat exchanger. The results, regarding Nusselt number, heated surface temperature, turbulence kinetic energy, production of entropy and vorticity, were presented and discussed. For assumed geometrical parameters similar results were obtained.
This paper presents the numerical solution to the unsteady natural convection problem in micropolar fluid in the vicinity of a vertical plate, heat flux of which rises suddenly at a given moment. In order to solve this problem the method of finite differences was applied. The numerical results have been presented for a range of values of the dimensionless material properties and fluid Prandtl number. The analysis of the results shows that the intensity of the heat transfer in micropolar fluid is lower compared to the Newtonian fluid.
There is an airflow velocity boundary layer near tunnel wall when the air is flowing in the underground coal mine. The thickness and distribution of the airflow velocity boundary layer could influence the discharge of harmful and toxic gases that enter the ventilating airflow through this flow interface. It may also have a major impact in coal mine gas explosion. The results of field measurements and simulation experimental data are used to research airflow velocity boundary layer in a flat walled mine roadway, which is considered in turn: as unsupported, I-steel sectioned arch or bolted and shot create supported cross section. By referenced to other literature studies that consider boundary layer characteristics and the analysis of on-site and experimental data sets we obtain the corresponding airflow velocity boundary layer characteristics for each of the supported roadway sections. The airflow velocity within the boundary layer increase is assumed to follow a logarithmic law given by the expression: u = a Ln(x) + b. It is concluded that the thickness of the airflow velocity boundary layer is observed to significantly decrease with the airflow center velocity and to increase with roadway wall roughness. The airflow velocity distribution is found to be described by the equation: u = (m1v + n1)Ln(d) + m2v + n2, for the three types coal mine tunnel taking into account the influence of center airflow velocity.
The aim of present work is to investigate the mass transfer of steady incompressible hydromagnetic fluid near the stagnation point with deferment of dust particles over a stretching surface. Most researchers tried to improve the mass transfer by inclusion of cross-diffusion or dust particles due to their vast applications in industrial processes, extrusion process, chemical processing, manufacturing of various types of liquid drinks and in various engineering treatments. To encourage the mass transport phenomena in this study we incorporated dust with microorganisms. Conservation of mass, momentum, concentration and density of microorganisms are used in relevant flow equations. The arising system of nonlinear partial differential equations is transformed into nonlinear ordinary differential equations. The numerical solutions are obtained by the Runge-Kutta based shooting technique and the local Sherwood number is computed for various values of the physical governing parameters (Lewis number, Peclet number, Eckert number). An important finding of present work is that larger values of these parameters encourage the mass transfer rate, and the motile organisms density profiles are augmented with the larger values of fluid particle interaction parameter with reference to bioconvection, bioconvection Lewis number, and dust particle concentration parameter.
For a deeper understanding of the inner ear dynamics, a Finite-Element model of the human cochlea is developed. To describe the unsteady, viscous creeping flow of the liquid, a pressure-displacement-based Finite-Element formulation is used. This allows one to efficiently compute the basilar membrane vibrations resulting from the fluid-structure interaction leading to hearing nerve stimulation. The results show the formation of a travelingwave on the basilar membrane propagating with decreasing velocity towards the peaking at a frequency dependent position. This tonotopic behavior allows the brain to distinguish between sounds of different frequencies. Additionally, not only the middle ear, but also the transfer behavior of the cochlea contributes to the frequency dependence of the auditory threshold. Furthermore, the fluid velocity and pressure fields show the effect of viscous damping forces and allow us to deeper understand the formation of the pressure difference, responsible to excite the basilar membrane.
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