Two-dimensional buoyant plumes in a uniform co-flow

The behaviour of turbulent, buoyant, planar plumes is fundamentally coupled to the environment within which they develop. The effect of a background stratification directly influences a plumes buoyancy and has been the subject of numerous studies. Conversely, the effect of an ambient co-flow, which directly influences the vertical momentum of a plume, has not previously been the subject of theoretical investigation. The governing conservation equations for the case of a uniform co-flow are derived and the local dynamical behaviour of the plume is shown to be characterised by the scaled source Richardson number and the relative magnitude of the co-flow and plume source velocities. For forced, pure and lazy plume release conditions the co-flow acts to narrow the plume and reduce both the dilution and the asymptotic Richardson number relative to the classic zero co-flow case. Analytical solutions are developed for pure plumes from line sources, and for highly forced and highly lazy releases from sources of finite width in a weak co-flow. Contrary to releases in quiescent surroundings, our solutions show that all classes of release can exhibit plume contraction and the associated necking. For entraining plumes, a dynamical invariance spatially only occurs for pure and forced releases and we derive the co-flow strengths that lead to this invariance.

NUMERICAL RESULTS OF MIXED CONVECTION FLOW OVER A FLAT PLATE WITH THE IMPOSED HEAT AND ANGLE OF INCLINATION

In this paper, the numerical results of mixed convection flow over a flat plate with the imposed heat and different angles of inclination are established by applying the finite difference method of Crank-Nicolson. We further compare these numerical results with the case of non-mixed convection flow. The velocity and temperature profiles are decreased when the different values of the Prandtl number (Pr) are increased. Meanwhile, the velocity profiles are increased, when the different values of angle of inclination (alfa) and mixed convection parameter (lambda) are increased. The mixed convection flow case (lambda=1.5) is affected by the external force, so the velocity of convection flow is higher than the non-mixed case (lambda=0).

Examination of Viscosity Effect on Cavitating Flow inside Poppet Valves Based on a Numerical Study

The higher susceptibility to cavitation in poppet valves due to the lower viscosity of water than the traditionally used mineral oil poses a challenge in fluid transmission technology. To reveal the underlying mechanism of cavitating flow physics associated with the variation in viscosity effect, the current paper examines both the water and oil cavitating flow dynamics inside poppet valves with varied structures through a numerical study. The simulation results are validated with a comparison to previous experimental data in terms of cavitation morphology and pressure distribution. According to the predicted cavitation distribution, three kinds of cavitation occurred at separated positions in both water- and oil-flow cases. The vortex cavitation, which in the oil-flow case displays a remarkable paired structure with favorable coherence, is featured with a scattered dispersion in the water-flow case, while the profound attached cavitation at the poppet trailing edge in the water-flow case almost disappears in the oil-flow case. Furthermore, the attached cavitation within the chamfered groove has higher stability in the oil-flow case, compared to the thorough detachment behavior featured with profound 3-dimensionality in the water-flow case. According to the potential core and vortex evolution, the strong 3-dimensionality due to the violent laminar-turbulent transition in the water-flow case together with the produced puff pattern of the potential core, to a large extent, interrupts the periodic behavior of cavitation, which is essentially preserved in the oil-flow case featured with favorable coherence.

The K-property for some unique equilibrium states in flows and homeomorphisms

We set out some general criteria to prove the K-property, refining the assumptions used in an earlier paper for the flow case, and introducing the analogous discrete-time result. We also introduce one-sided $\lambda $ -decompositions, as well as multiple techniques for checking the pressure gap required to show the K-property. We apply our results to the family of Mañé diffeomorphisms and the Katok map. Our argument builds on the orbit decomposition theory of Climenhaga and Thompson.

Nonlinear Mixed Convective Flow over a Moving Yawed Cylinder Driven by Buoyancy

The fluid flow over a yawed cylinder is useful in understanding practical significance for undersea applications, for example, managing transference and/or separation of the boundary layer above submerged blocks and in suppressing recirculating bubbles. The present analysis examines nonlinear mixed convection flow past a moving yawed cylinder with diffusion of liquid hydrogen. The coupled nonlinear control relations and the border restrictions pertinent to the present flow problem are nondimensionalized by using nonsimilar reduction. Further, implicit finite difference schemes and Quasilinearization methods are employed to solve the nondimensional governing equations. Impact of several nondimensional parameters of the analysis on the dimensionless velocity, temperature and species concentration patterns and also on Nusselt number, Sherwood number and friction parameter defined at the cylinder shell is analyzed through numerical results presented in various graphs. Velocity profiles can be enhanced, and the coefficients of friction at the surface can be reduced, for increasing values of velocity ratio parameters along chordwise as well as spanwise directions. Species concentration profile is reduced, while the Sherwood number is enhanced, for growth of the Schmidt number and yaw angles. Furthermore, for an increasing value of yaw angle, skin-friction coefficient in chordwise direction diminishes in opposing buoyancy flow case, whereas the results exhibit the opposite trend in assisting buoyancy flow case. Moreover, very importantly, for increasing magnitude of nonlinear convection characteristic, the liquid velocity and surface friction enhance in spanwise direction. Further, for increasing magnitude of combined convection characteristics, velocity profiles and coefficient of friction at the surface enhance in both spanwise and chordwise directions. Moreover, we have observed that there is no deviation for zero yaw angle in Nusselt number and Sherwood number.

Comparison of Optical, Electrical, and Surface Characteristics of InGaN Thin Films at Non-Flow and Small Nitrogen Flow Cases

InGaN films in the non-flow and a small flow of nitrogen cases were fabricated by the RFMS (Radio Frequency Magnetron Sputter) method to compare crucial physical characteristics of its material. From the XRD analysis, application of small nitrogen flow in InGaN thin film growth has been observed to result in changes in the crystal size, texture coefficient, and crystal structure parameters of the film. AFM results showed both films obtained have tightly packed granular, and almost homogeneous, and Nano-structural properties, but they are different in roughness, as increased by applying small nitrogen flow. Optical conductance peaks of the material in non-flow and small flow case were 1.3957 x 1010 and 1.1496 x 1010 (S/m), showed a decrement in optical conductance by small nitrogen flow. In the same manner, electrical conductance peaks of the material in non-flow and small flow case were 5.2512 x 1012 and 5.2236 x 1012 (S), showed a decrement in electrical conductance by small nitrogen flow. In addition, the electrical conductivity of the InGaN material has been obtained at higher than the optical conductivity value of the InGaN material in both cases. Also, it was noticed that direct allowed optical band gap energy non-flow and small flow cases were 2.4701 and 2.5225 eV, displayed increased by applied small nitrogen flow. Essentially, many noteworthy physical properties such as crystalline size, texture coefficient, optical/electrical conductivity, the surface roughness of the films have been compared and studied for the non-flow and a small flow of nitrogen cases.