Vicinity Of Stagnation Point Research Articles

Transportation of melting heat in stratified Jeffrey fluid flow with heat generation and magnetic field

In current years, storage of energy is a challenging task for the scientists and researchers. So, they are interested to develop some extra ordinary techniques of energy storage. Thus, our main theme here is to focus on the latent heat energy (melting heat) which is more economical and sustainable. Transportation of melting heat in quadratic stratified Jeffrey fluid flow in the vicinity of stagnation point is scrutinized. The flow is deformed by linear stretchable sheet. Characteristics of heat transportation are scrutinized through viscous dissipation and heat generation or absorption. Constant magnetic field is implemented to electrically conducting fluid in vertical direction. The arising governing equations are converted in the non-dimensional state through suitable transformations. Homotopic technique is utilized for simulation of solutions. Graphical behavior of velocity and temperature fields is investigated corresponding to relevant parameters. As a conclusion, higher amount of energy can be achieved as melting phenomenon enhances, and also results in low temperature. Further, dominant stratification decays the temperature field. Current study will play key role in industrial liquids like polymer solutions to make high quality fiberglass, paints, silicone heat valves etc. This study will also deliberate efficiently for the storage of energy through phase change procedure i.e., melting phenomenon.

A thin layer lubricant surface applications due to nonlinear radiated hybrid nanoparticles with orthogonal stagnation point flow

ABSTRACT The improved thermal association of heat transfer is considerably observed due to hybrid nanoparticles. Being to suspension of base fluids with two distinct nanoparticles, the stable properties of hybrid nanofluids are measured. Current contribution reports the enhancement in thermal impact of water (base liquid) uniformly decomposed with hybrid nanoparticles theoretically. The hybrid nanofluid properties are justified with copper and aluminum oxide nanoparticles. With improved heat transfer mechanism, the motivations for observing the aspect of lubrication phenomenon in the vicinity of stagnation points are associated to the manufacturing systems and chemical processes ample applications in fluid bearing, assembling of thin films, coating and printing. Moreover, the treatment of heat transfer is further influenced by nonlinear radiation and mixed convection applications. The dimensionless variables successfully transformed the system into a dimensionless form, which is further solved using the Keller box method. The comparative heating transfer onsets are predicted for the traditional nanofluid with suspension and hybrid nanofluid with decomposition. The results show that the lubrication phenomenon controls the wall shear force while enhancement in Nusselt number is noticed. Increasing observations for skin friction and Nusselt number are resulted for hybrid nanofluid as compared to simple nanofluid.

Entropy analysis in thermally stratified Powell-Eyring magnesium-blood nanofluid convection past a stretching surface

Recently, researchers are very possessive to examine the treatment of diseases caused due to the deficiency of magnesium. The deficiency of magnesium in blood caused Hypomagnesaemia, which is further stimulus for various diseases such as vomiting, sleepiness, nausea, loss of appetite etc. In order to cover such deficiency, magnesium is injected in blood (base fluid) as a nanoparticle. Based on the above applications, the current research focuses to cover the deficiency of magnesium through Powell-Eyring (Magnesium-Blood) nanofluid flow deformed by the linearly stretchable sheet in the vicinity of stagnation point. Linear thermal stratification, viscous dissipation and Joule heating are incorporated to disclose the heat transport properties. Magnetic field is implemented to the nanofluid with an angle α. A system of dimensionless governing equations is achieved through appropriate transformations. Physical behaviors of temperature and velocity fields are elaborated through comparative graphs. Skin friction, entropy generation, rates of heat transfer and Bejan number is disclosed through graphs corresponding to pertinent parameters. The well-known convergence method (Homotopy analysis method) is utilized to achieve the solution of the model. Decrement occurs in temperature field for dominant melting and thermal stratification phenomenon. Entropy has same scenario in case of dominant melting while inverse behavior in term of thermal stratification. Bejan number is de-escalates with the escalation of Eckert number. Also, it is worth mentioning that the velocity outline accelerated and temperature profile decelerated with the enhancement of melting parameter. It shows that recovery rate of magnesium patients may be enhanced through medicine with enriched magnesium nanoparticles depending on the health of the patient.

Melting heat phenomenon in thermally stratified fluid reservoirs (Powell-Eyring fluid) with joule heating

The currant study focuses on the characteristics of melting heat phenomenon in the Powell-Eyring fluid flow deformed by the linearly stretchable sheet in the vicinity of stagnation point. Quadratic thermal stratification, thermal radiation, viscous dissipation and Joule heating are implemented to disclose the heat transport properties. Magnetic field is implemented to the fluid with an angle α. Mass diffusion is scrutinized through quadratic solutal stratification and constructive/ destructive chemical reactions. A system of dimensionless governing equations are achieved through appropriate transformations. Physical behaviors of temperature, velocity and concentration fields are elaborated through graphs. Skin friction, entropy generation, rates of mass and heat transfer are disclosed through graphs corresponding to pertinent parameters. Decrease occurs in temperature field for dominant melting and thermal stratification phenomenon. Entropy has inverse behavior in case of dominant thermal stratification while similar behavior of melting case. The interesting behavior in melting heat transfer phenomena is the increase of temperature as we raise the Prandtl number. Also, it is worth mentioning that the velocity outline accelerated and temperature profile decelerated with the enhancement of melting factor.

Statistical properties of streamline geometry in turbulent wall-flows

This study investigates the characteristics of streamline curvature and torsion in wall-bounded turbulence using DNS data from channel and boundary layer flows. The analysis includes characterizing the curvature of probability distributions as a function of the wall-normal distance. Far from the wall, the probability density function of the curvature decays with a -4 power dependence for the extreme events that are comparable with the Kolmogorov length scale. Consistent with previous studies, these large values of curvature are hypothesized to reflect the flow in the vicinity of stagnation points in the fluctuating field.

Model of spontaneous evaporating droplet on solid horizontal substrate

Free evaporation of sessile liquid non-isothermal drop on solid substrate is analyzed. Exact formulae for temperature and concentration fields are found out as functions of dimensionless parameters. The non-uniform temperature distribution at the drop surface creates the thermocapillar Marangonni forces that change their direction in the vicinity of stagnation points. Direction of the forces and disposition of the stagnation points are derived as function of contact angle and thermodynamic parameters of model. Conditions for the stagnation points to appear are found out. Moreover, maximal value of contact angle corresponding to presence of stagnation points in droplet is calculated as a function of the thermal conductivity ratio.

An experimental investigation on comparison of synthetic and continuous jets impingement heat transfer

The convective heat transfer characteristics under a normally synthetic jet impingement driven by a piston actuator are investigated experimentally in the present study. Particular attentions are paid to present the detailed local and laterally-averaged heat transfer comparison between synthetic jet and continuous jet, as well as the effect of orifice shape on the synthetic jet impingement. Three jet orifices including single-round, single-square, and single-rectangular are designed to have the approximately same exit area. In additional, heat transfer regimes for the synthetic jet impingement in the situation of large stroke length to jet-to-surface spacing are further identified. In the present, the equivalent convective heat transfer coefficient is defined in terms of the difference between target temperature and ambient temperature. The results show that continuous jet exhibits stronger local heat transfer than the synthetic jet in the vicinity of stagnation point. However, the synthetic jet produces much flatter and more uniform local heat transfer coefficient distributions over the surface, showing its advantage over the continuous jet on laterally-averaged convective heat transfer enhancement at a larger jet-to-surface spacing. For the piston-driven synthetic jet featured by low excitation frequency and large stroke length, there is evidence for a power law relationship between stagnation Nusselt number and jet Reynolds number with an exponent of approximately 0.32. Two kinds of heat transfer regimes are observed and a critical ratio of stroke length to jet-to-surface spacing is identified as 18 approximately regardless of orifice shape. The orifice shape has a moderate effect on the convective heat transfer. The single-rectangular synthetic jet produces a slightly better stagnation point heat transfer than the other orifices. The synthetic jet originated from the round-hole orifice seems to introduce favorable overall convective heat transfer achievement. The advantage of synthetic jet impingement in comparison to the corresponding continuous jet is relatively degraded for the square-hole orifice.

Domain Decomposition Technique for Solution of Acoustic Wave Scattering

A novel domain decomposition technique is applied that couples nonlinear and linear Euler solvers to model acoustic scattering of waves in the vicinity of high-velocity gradients and large-amplitude waves to reduce numerical resources. The linear solver is applied in domains in which the wave amplitude is small and linearization is applicable, whereas the nonlinear solver is used in the vicinity of high wave amplitudes and stagnation points. Three numerical models are compared in this paper: 1) a linear Euler, 2) a nonlinear Euler, and 3) the domain decomposition technique. For all three models, the finite difference dispersion relation preserving scheme is applied to all spatial derivatives and the low-dissipation–dispersion Runge–Kutta scheme is applied for the temporal integration. A perfectly matched layer is applied at the edges of the computational domain to absorb outgoing waves and minimize reflections. To include complex bodies and geometries, an overset mesh is applied. After model validation, the technique is applied to the acoustic scattering of a pulse and a periodic source from a circular cylinder in flow. The results conclude that a thin zone around a complex body is sufficient to accurately account for nonlinear effects in the vicinity of stagnation points and that the domain decomposition technique accurately predicts both the unsteady field and integral unsteady forces about bluff bodies compared with full nonlinear simulations. The results suggest that there is a 40% reduction in computational time using the domain decomposition technique compared with full nonlinear calculations.

Wall shear rates and stagnation mass transfer on a plate in axisymmetric and cross impinging jets

This article presents a study on the wall shear rate and mass transfer of impinging jets on a flat plate in the vicinity of stagnation point. The performance of a cross-shaped orifice nozzle was compared with a reference convergent circular nozzle having similar equivalent diameter. An array of electrodiffusion micro probes inserted into the plate was used for wall shear rates measurements. Mass transfer in the impinging region was calculated from the measured wall shear rates for a Reynolds number around 5500 and over a range of streamwise distances between the nozzle and the impinging plane within 1 to 5 nozzle equivalent diameters. The most important observation in the present investigation is that the wall shear rates and the mass transfer in the impingement region of the cross-shaped orifice nozzle are up to 175% and 40%, respectively, higher than that of the convergent nozzle. The performance of the cross-shaped orifice jet is probably related to its particular vortex dynamics characteristic of the near exit region. All the results confirm that the jet passive control enhance the mass transfer.

Curvature statistics of streamlines in various turbulent flows

Geometrical features of turbulent flows are analyzed by studying the curvature field of streamlines based on the instantaneous fluctuating velocity field of four different direct numerical simulations (DNS) at Taylor-based Reynolds numbers in the range Re λ = 50–300. Among the flows are two decaying homogeneous isotropic flows, one isotropic forced flow and the other homogeneous shear flow. Two different measures of curvature are extracted, the first one is the geometrical curvature of streamlines based on Frenet’s formulas, and the second one is the Gaussian curvature describing the divergence of streamlines. The two curvature fields are found to be related to each other by the divergence of the directional tensor of streamlines, which is also related to the total acceleration along streamlines. The latter identity allows the identification of the convective term in the Navier–Stokes equations, as the term determining the curvature-related geometrical features of streamlines. Based on the random sweeping hypothesis, a scaling of the standard deviation of the two curvatures of streamlines in turbulent flows with the inverse of the Taylor microscale is obtained. The curvature fields are in a first step analyzed via their probability density functions (pdfs) of the fluctuating fields (including their sign), and a normalization with the standard deviation yields a good collapse of the curves for different Reynolds numbers and flow types. Both, the positive and negative tails of the pdf display a pronounced algebraic tail with a decay exponent of −4. To analyze the curvatures as geometrical features of streamlines, the pdf of their absolute values normalized with their respective mean values are examined, and the curves are found to collapse well for the different Reynolds numbers. All pdfs again display an algebraic tail for large values of the curvature with a scaling exponent of −4. This result is theoretically explained based on the expression for the Gaussian curvature, and turns out to be related to the regions in the flow close to stagnation points where streamlines get strongly diverted. It turns out that at the origin the pdf of the Gaussian curvature is dominated by regions where the gradient of the absolute value in streamline direction us vanishes. us =0, However, it defines an isosurface in which all local extreme points of the field of the absolute value of the velocity u as well as those of the turbulent kinetic energy k lie. As stagnation points are absolute minima of the kinetic energy field, these points too lie in the isosurface. The topology of the isosurface is analyzed in the vicinity of stagnation points, and it is found that independent of the type of stagnation point, the isosurface is locally always a degenerated quadric surface of cone type, a conjecture that is verified based on the comparison of the analytical expansion and the DNS data.

Stream function–potential function coordinates for aeroacoustics and unsteady aerodynamics

‘Stream function as a coordinate approach’ (SFC) combined with compact high-order finite difference schemes has been developed and applied to aeroacoustics and unsteady aerodynamics problems. Straightforward implementation of SFC creates coarse grids at the vicinity of stagnation points that smears high-order numerical computations. Grid clustering is employed to resolve coarse grid near stagnations points. The agreement between numerical results and particle image velocimetry (PIV) measurements for flapping airfoil shows the robustness of the current approach for performing high-order computations.

On the validity of ideal MHD in the vicinity of stagnation points in the heliosphere and other astrospheres

The paradigm of ideal MHD is investigated in the vicinity of null points of flows and magnetic fields. These null points determine the location and geometrical shape of the heliopause (or other astropauses). We investigate the question whether regular and stable solutions of the ideal MHD equations in the vicinity of null points of flow and magnetic field exist. This is done to test the validity of ideal MHD in the vicinity of flow and magnetic field of the plasma boundaries of stellar winds and their local inter- stellar medium. We calculate the general solutions of ideal MHD in the vicinity of magnetic null points and use the stan- dard form of stagnation point flows to analyse all possible time evolutions of these plasma environments. We show that the solution space in 2-D consists almost exclusively of either exponentially (in time) growing velocity or mag- netic fields, or collapse solutions. Regular solutions must be three-dimensional and seem to be unstable with respect to small perturbations. This is an argument that reconnection has to take place in such regions and that therefore nonideal terms in Ohm's law are necessary, allowing for reconnec- tion. We conclude that the use of ideal MHD in the vicinity of singular points of flow and magnetic field has to be anal- ysed very carefully with respect to simulation results as those simulations show numerical dissipation (resistivity). These simulations can therefore produce unphysical reconnection regimes. Thus one has to search for a realistic Ohm's law, allowing for reconnection at the heliospheric boundaries.

A211 軸対称衝突噴流の三次元渦構造の抽出

A scanning stereo particle image velocimetry system was applied to measure the three-dimensional distribution of three-component velocity in an axisymmetric impinging jet. The jet formed by a round nozzle with an exit diameter of D=5 mm impinges vertically on the flat plate that was located at 45D from the nozzle. The jet Reynolds number was set at Re D ?? 1000 and a measurement region was set to contain the stagnation region. Appling Linear-Stochastic-Estimation to the measurement result, characteristic vortex structure in impinging region and time variations of that was estimated. It was confirmed that the structure was convected to streamwise direction with time passage through the vicinity of stagnation point, and was compressed axially and stretched to radial direction.

Molecular orientation of a commercial thermotropic liquid crystalline polymer in simple shear and complex flow

In-situ X-ray scattering methods have been used to measure the average degree of molecular orientation in the commercial thermotropic copolyesteramide, Vectra B. Experiments were conducted in both homogeneous shear flow and in extrusion-fed channel flows that provided mixed shear/extensional deformations. In the channel flows, extension has a dramatic effect on the average orientation state in the vicinity of stagnation points or expansions/contractions in cross-sectional area. Of particular note, a temporary increase and subsequent decay in orientation observed in a 4:1 slit-contraction flow provides additional indirect evidence supporting the hypothesis that Vectra B exhibits director tumbling. This is consistent with results from other fully aromatic copolyesters but contrasts with findings in “model” thermotropes incorporating flexible spacers. Thus, it seems that the stiffer backbone of commercial main chain LCPs is the main feature which, apparently, leads to tumbling. Measurements of average molecular orientation in transient shear flows show some connections with the corresponding mechanical response, but fail to show the distinctive characteristics that have previously been associated with either tumbling or aligning in LCPs using similar procedures. These experiments might be adversely affected by the comparatively slow rate of data acquisition, which leads to lengthy experiments in which the sample is more prone to degradation.

Fluid helicity and dynamo effect

Using the incompressible magnetohydrodynamic equations, we have numerically studied the dynamo eect in electrically conducting fluids. The necessary energy input into the system was modeled either by an explicit forcing term in the NavierStokes equation or fully selfconsistently by thermal convection in a fluid layer heated from below. If the fluid motion is capable of dynamo action, the dynamo eect appears in the form of a phase transition or bifurcation at some critical strength of the forcing. Both the dynamo bifurcation and subsequent bifurcations that occur when the strength of the forcing is further raised were studied, including the transition to chaotic states. Special attention was paid to the helicity of the flow as well as to the symmetries of the system and symmetry breaking in the bifurcations. The magnetic field tends to be accumulated in special regions of the flow, notably in the vicinity of stagnation points or near the boundaries of convection cells.

Effect of pressure gradient on viscous shear flow past an axisymmetric depression or protuberance on a plane wall

The effect of pressure gradient on the structure of unidirectional viscous shear flow over an axisymmetric depression or protuberance on a plane wall, possibly in the presence of an upper parallel plane wall in the configuration of two-dimensional Hagen–Poiseuille flow, is considered. The problem is formulated in terms of a system of three coupled Fredholm integral equations of the first kind for the first-order Fourier coefficients of the boundary traction, and the solution is found using a boundary element method. The numerical results illustrate the effect of the pressure gradient on the streamline pattern and on the distribution of the shear stress along the plane wall and over the depression or protuberance. The topology of the streamline pattern in three-dimensional flow is found to be generally similar to that in two-dimensional flow, but important differences arise in the vicinity of stagnation points. The structure of semi-infinite parabolic flow is similar to that of the channel pressure-driven flow, when the distance between the channel walls is roughly larger than six times the characteristic size of the depression of protuberance. The force and torque exerted on a protuberance are evaluated for pure shear flow, pure parabolic flow, and pressure-driven channel flow, and a linear combination of the results for the first two cases is shown to accurately describe the results for the third case when the channel is moderately wide.

Exchange Geometry Revealed by Float Trajectories in the Gulf Stream*

In an effort to understand the extent to which Lagrangian pathways in the Gulf Stream indicate fluid exchange between the stream and its surroundings, trajectories of RAFOS floats are viewed in a frame of reference moving with the dominant zonal phase speed associated with the periodic flow. In such a frame, geometrical structures emerge that more clearly delineate the position of the parcel in relation to the jet core and its surroundings. The basic premise of this work is that the pathways of fluid parcels in the vicinity of stagnation points, as defined in the moving frame of reference, are susceptible to changes in their pathways, thereby facilitating fluid exchange between different regions of the flow field. Four representative RAFOS float trajectories are shown to exhibit the expected behavior in the vicinity of stagnation points. To further examine the mechanism of exchange in the vicinity of these geometrical features, concepts from dynamical systems theory are applied to a numerically simulated flow field. The entrainment and detrainment of parcels from the jet core are explained in the context of stable and unstable manifolds and their associated lobes. It is shown that the Lagrangian pathways from the numerical flow and the observational trajectories exhibit a similarity based on the kinematics of a meandering flow field. Overall, this study provides the first look at RAFOS float trajectories in a moving frame and provides insight as to how the temporal variability of a jet creates chaotic exchange.

Flow in vicinity of blunt body stagnation point in diverging hypersonic stream

In the hypersonic thin shock layer approximation for a small ratio k of the densities before and after the normal shock wave the solution of [1] for the vicinity of the stagnation point of a smooth blunt body is extended to the case of nonuniform outer flow. It is shown that the effect of this nonuniformity can be taken into account with the aid of the effective shock wave radius of curvature R*, whose introduction makes it possible to reduce to universal relations the data for different nonuniform outer flows with practically the same similarity criterion k. The results of the study are compared with numerical calculations of highly underexpanded jet flow past a sphere.