Fluid Dynamics

The first flow bifurcation, in channels with a sudden geometry contraction, is controlled through shape optimization to delay the onset of asymmetry. First, we confirm the existence of a pitchfork type bifurcation instability, already reported in similar geometries. The global mode responsible for this bifurcation leads to asymmetric flow for Reynolds numbers beyond a critical value. Second, we propose a global shape optimization methodology to introduce small modifications in the channel geometry that lead to flows with enhanced stability. Our results include three contraction ratios C = 2, 4, and 8, where C is the ratio of upstream to downstream channel widths. The shape optimization aims at minimizing the growth rate of the unstable mode responsible for asymmetry. Sensitivity analysis is used to find an appropriate geometry parametrization, which is defined through super-elliptic curves, and limited to small deformations. Additionally, a dynamically updated surrogate model (based...

Most of the turbines used in Nepal are medium or high head turbines. These types of turbines are efficient but limited for rivers and streams in the mountain and hilly region which have considerably high head. Low head turbines should be used in the plain region if energy is to be extracted from the water sources there. This helps in the rural electrification and decentralized units in community, reducing the cost of construction of national grid and also to its dependency, in already aggravated crisis situation. There are good turbine designs for medium to high heads but traditional designs for heads under about 5m (i.e. cross flow turbine and waterwheel) are slow running, requiring substantial speed increase to drive an AC generator. Propeller turbines have a higher running speed but the airfoil blades are normally too complicated for micro hydro installations. Therefore, the open volute propeller turbine with constant thickness blades was ventured as possible solution. Such type ...

We prove existence and uniqueness of a solution to the Cauchy problem corresponding to the dynamics capillarity equation $$\begin{aligned} {\left\{ \begin{array}{ll} \partial _t u_{\varepsilon ,\delta } +\mathrm {div} {\mathfrak f}_{\varepsilon ,\delta }(\mathbf{x}, u_{\varepsilon ,\delta })=\varepsilon \Delta u_{\varepsilon ,\delta }+\delta (\varepsilon ) \partial _t \Delta u_{\varepsilon ,\delta }, \ \ \mathbf{x} \in M, \ \ t\ge 0\\ u|_{t=0}=u_0(\mathbf{x}). \end{array}\right. } \end{aligned}$$ ∂ t u ε , δ + div f ε , δ ( x , u ε , δ ) = ε Δ u ε , δ + δ ( ε ) ∂ t Δ u ε , δ , x ∈ M , t ≥ 0 u | t = 0 = u 0 ( x ) . Here, $${{\mathfrak {f}}}_{\varepsilon ,\delta }$$ f ε , δ and $$u_0$$ u 0 are smooth functions while $$\varepsilon $$ ε and $$\delta =\delta (\varepsilon )$$ δ = δ ( ε ) are fixed constants. Assuming $${{\mathfrak {f}}}_{\varepsilon ,\delta } \rightarrow {{\mathfrak {f}}}\in L^p( {\mathbb {R}}^d\times {\mathbb {R}};{\mathbb {R}}^d)$$ f ε , δ → f ∈ L p ( R d × R ; R d ) fo...

We present a comparison between the finite-element and the lattice-Boltzmann method for simulating fluid flow in a SMRX static mixer reactor. The SMRX static mixer is a piece of equipment with excellent mixing performance and it is used in highly efficient chemical reactors for viscous systems like polymers. The complex geometry of this mixer makes such 3D simulations nontrivial. An excellent agreement between the results of the two simulation methods and experimental data was found.

The objective of this study was to analyze the fluid flow of molten steel in a continuous casting tundish using numerical simulations for better inclusion floatation and its separation. The tundish geometry was designed using Autodesk FUSION 360 and the analysis were performed on ANSYS FLUENT. The investigations were done on steady-state as well as transient conditions. To scale back vortexing and turbulence within the tundish, turbo stoppers and flow modulators, e.g. dam and weirs were placed for an optimized and efficient flow inside the tundish and its behavior on the spacious flow structure was explored. The strategic placements of the flow modifiers produced higher turbulence in the recess region of the tundish resulting in better turbulent flow withinside the inlet region of the tundish. Thereby a more homogeneous fluid flow is formed with better conditions for particle separation. Analysing the flow behavior we have determined the inclusion floatation using particle tracking ...

In this paper, we introduce the non-conformable double Laplace transform. Its properties are studied, and it is applied to solve some fractional PDEs involving the nonconformable fractional derivative. Graphical representations of the obtained solutions are shown in figures. The study shows that this transform is effective and easy to apply to create an exact solution for types of fractional PDEs.

Effective cooling of data centers presents a dual challenge: increased cooling power to meet the ever increasing device heat loads, and the need for energy efficient cooling. Detailed analysis of the thermal and flow conditions within a data center are necessary for obtaining optimal ...

This paper investigates the stability of an incompressible viscous fluid flow between relatively moving horizontal parallel plates in the presence of a uniform vertical throughflow. A linear stability analysis has been performed by employing the method of normal modes and the resulting stability equation is solved numerically using the Chebyshev collocation method. Contrary to the stability of plane Couette flow (PCF) to small disturbances for all values of the Reynolds number in the absence of vertical throughflow, it is found that PCF becomes unstable owing to the change in the sign of growth rate depending on the magnitude of throughflow. The critical Reynolds number triggering the instability is computed for different values of throughflow dependent Reynolds number and it is shown that throughflow instills both stabilizing and destabilizing effect on the base flow. It is seen that the direction of throughflow has no influence on the stability of fluid flow. A comparative study b...

This study concentrates on steady collisionless gas flows inside arbitrary enclosures, which are either convex or concave, two-dimensional or three-dimensional, formed by several plates maintained at different temperatures. If the molecular reflections on these plates are completely diffuse, then at the final steady flow stage for any point inside the enclosures, the velocity distribution function (VDF) is completely determined, and macroscopic properties such as density, velocities, temperature, and heat flux can be exactly determined by integrating the VDF with different moments. The result from this study leads to many exact solutions for internal collisionless gas flow and thermal fields, such as those inside vacuum packaged micro-/nanoelectromechanical system devices. These solutions are applicable as base solutions to solve flows with a much smaller Knudsen number.

The application of 3D technology for fabrication of artificial porous media samples improves porous media flow studies. The geometrical characteristics of a porous media pore channel: the channel shape, size, porosity, specific surface, expansion ratio, contraction ratio, and the tortuous pathway of the channel can be controlled through advanced additive manufacturing techniques (3D printing), computed tomography imagery (CT imaging) and image analysis methods. These 3D technologies have here been applied to construct and analyze four homogeneous porous media samples with predefined geometrical properties that are otherwise impossible to construct with conventional methods. Uncertainties regarding the geometrical properties are minimized because the 3D-printed porous media samples can be evaluated with CT imaging after fabrication. It is this combination of 3D technology that improves the data acquisition and data interpretation and contributes to new insight into the phenomenon of ...

The DEVS formalism is a set of conventions introduced in 1976 for the specification of discrete event simulation models. This chapter explains the core concepts of DEVS by applying the formalism to a single ongoing example. First, the example is introduced as a set of informal requirements from which a formal specification is to be developed. Readers are then presented with alternative sets of modeling conventions which, lacking the DEVS formalism’s approach to representing state, prove inadequate for the example. The chapter exploits the DEVS formalism’s support for modular model design, as the system in the example is specified first in parts and later as a combination of those parts. The concept of legitimacy is demonstrated on various model specifications, and the relationship between DEVS and both object-oriented programming and parallel computing is discussed.

A rule of thumb - The condensate load used to design condensate pipelines should be twice the maximum production load.



Assumptions:       

1 . Most of the flow patterns for steam condensate headers fall within the annular or dispersed region on the baker map. Flow pattern falls in slug flow region. 

2 . Flashed steam is less than 30% by weight. 

3 . Vapour-liquid mixture throughout the condensate line is represented by the mixture condition near the end of the Line.   



Method:   

1 . The amount of condensate flashed is calculated. 

2 . Further to above the density of the mixture (Condensate + Flashed steam) is found out. 

3 . Using two pressure drop co-relations, Pressure per 100 ft is calculated. 

4 . If the velocity is lower than 5000 feet/min, the specified line size is said to be adequate.

Only limited information is available concerning the effects of low-shear modeled microgravity (LSMMG) on cell function and morphology. We examined the behavior of Saccharomyces cerevisiae grown in a high-aspect-ratio vessel, which simulates the low-shear and microgravity conditions encountered in spaceflight. With the exception of a shortened lag phase (90 min less than controls; P < 0.05), yeast cells grown under LSMMG conditions did not differ in growth rate, size, shape, or viability from the controls but did differ in the establishment of polarity as exhibited by aberrant (random) budding compared to the usual bipolar pattern of controls. The aberrant budding was accompanied by an increased tendency of cells to clump, as indicated by aggregates containing five or more cells. We also found significant changes (greater than or equal to twofold) in the expression of genes associated with the establishment of polarity ( BUD5 ), bipolar budding ( RAX1 , RAX2 , and BUD25 ), and ce...

We present a three‐dimensional study of the plasma dynamics at the flank magnetopause of the Earth's magnetosphere during mainly northward interplanetary magnetic field periods. Two‐fluid simulations show that the initial magnetic shear at the magnetopause and the field line bending caused by the dynamics itself (in a configuration taken as representative of the properties of the flank magnetopause) influence both the location where the Kelvin‐Helmholtz (KH) instability and the induced magnetic reconnection take place and their nonlinear development. The KH vortices develop asymmetrically with respect to the Earth's equatorial plane where the local KH linear growth rate is maximal. Vortex‐driven reconnection processes take place at different latitudes, ranging from the equatorial plane to midlatitude regions but only in the hemisphere that turns out to be the less KH unstable. These results suggest that KH‐induced reconnection is not limited to specific regions around the vo...

In a recent authors ’ paper, the general expression of Stokes drag experienced by a deformed sphere in both longitudinal and transverse flow situations was calculated in terms of the deformation parameter up to the second order. In this paper, Oseen’s correction to the axial Stokes drag on the deformed sphere is presented by using Brenner’s formula in general, first and then applied to prolate and oblate the deformed spheroid up to the second order of the deformation parameter. Numerical values of Oseen’s correction is obtained with respect to the deformation parameter and Reynolds number. The corresponding variations are depicted in figures. Some particular cases of a needle shaped body and flat circular disk are considered and found to be in good agreement with those existing in the literature. The important applications are also highlighted.

This study investigates the influence of loading and inflow conditions on tidal turbine performance from a hydrodynamic and hydroacoustic point of view. A boundary element method is utilized for the former to investigate turbine performance at various loading conditions under zero/non-zero yaw inflow. The boundary element method is selected as it has been selected, tested, and validated to be computationally efficient and accurate for marine hydrodynamic problems. Once the hydrodynamic solutions are obtained, such as the time-dependent surface pressures and periodic motion of the turbine blade, they are taken as the known noise sources for the subsequence hydroacoustic analysis based on the Ffowcs Williams-Hawkings formulation given in a form proposed by Farassat. This formulation is coupled with the boundary element method to fully consider the three-dimensional shape of the turbine and the speed of sound in the acoustic analysis. For validations, a model turbine is taken from a reference paper, and the comparison between numerical predictions and experimental data reveals satisfactory agreement in hydrodynamic performance. Importantly, this study shows that the noise patterns and sound pressure levels at both the near-and far-field are affected by different loading conditions and sensitive to the inclination imposed in the incoming flow.