Linear temporal stability analysis on cross sheared flow: the stabilization effects via cross shear

The stability features of the inviscid, homogenous, and free cross sheared flow, with base flow velocities U = tanh(z) in the primary direction, which is unstable, and V = nz^3 in the orthogonal direction, which is stable, are thoroughly examined with linear temporal stability analysis, where z is the transverse coordinate perpendicular to the flow and n is the cross shear ratio which is the ratio of the characteristic magnitudes of V to U. The map of the unstable regions directly related to v = n(b=a) is obtained, where (b=a) is the ratio between the orthogonal and primary wavenumbers. Further examination of the eigenfunctions shows that the eigenfunction structures divide into the orthogonal wavenumber (OW) mode where (b=a) dominates and the cross shear (CS) mode where n dominates. The cross shear is found necessary for stabilization in spite of different fashions for the OW and CS modes. The transition from the OW mode to the CS mode shows that the developments of the two modes inherently compete with each other, so that when w = (b=a)=n decreases the enhanced cross shear needs to deteriorate the OW mode before it helps the growth of the CS mode. Based on the magnitudes of the associated eigenfunctions in the enstrophy budget, the map of the OW, CS, and hybrid modes, which includes the mixed features of both the OW and CS modes, is produced and discussed

Collaboration modes and advantages in supply chain

This research aims to address supply chain collaboration with a perspective of broader three-dimensional relationship, not a linear two-dimensional relationship discussed broadly in previous research. Case study was adopted for this research, and data collection was mainly conducted via interview. The research results highlighted that supply chain collaborations are common practice across all levels of the pharmaceutical supply chain. The results also indicated that the different strengthen levels of barging power among collaborative partners will influence the achieved advantages at different supply chain levels, including strategic, operational and political levels

Smart manufacturing and supply chain management

In the fourth industrial revolution, smart manufacturing will be characterized by adaptability, resource efficiency and ergonomics as well as the integration of customers and business partners in business and value processes. Business model, operations management, workforce and manufacturing process all face substantial transformations to reasoning the manufacturing process. This paper explores the impacts of smart manufacturing on supply chain management, and develops several propositions to improve supply chain performance under the context of smart manufacturing

Direct numerical simulation of confined weak round fountains in homogeneous ambient

Fountains (negatively buoyant jets) are commonly used in numerous engineering applications, such as the natural ventilation in buildings and the smoke spread in compartment fires. In this study, the long-term behavior of weak round fountains in homogeneous ambient confined in a cylindrical container was analyzed using three-dimensional direct numerical simulation over a range of the Froude number (Fr), Reynolds number (Re), dimensionless radius of the container (λ), respectively. The confined weak round fountain behaves in the manner of a ‘fountain filling box’ flow, experiencing five development stages, i.e., the formation of the fountain flow, the intrusion flow, the wall fountain, the reversed flow and the stratification. Three stages of the development of the bulk entrainment rate are identified and the dominant mechanisms involved are analyzed. Fr = 1 and 2 are identified as the approximate critical values to distinguish the behavior of the intrusion, wall fountain and stratification. Re = 200 is determined as the approximate critical value to distinguish the influence of Re. These are consistent with the existing results about the round fountains

Scalings for unsteady natural convection boundary layer under time-varying heating flux in a small Prandtl number fluid

The unsteady natural convection boundary layer (NCBL) on a vertical wall heated by time varying flux in initially quiescent homogeneous fluid with a small Prandtl number (Pr) was studied. Scalings for the parameters typifying NCBL behavior, including plate temperature, maximum vertical velocity, thermal boundary-layer thickness, and velocity boundary-layer thickness, at different development stages, and the time for the transition from the start-up stage to the quasi-steady state, were developed by scaling analysis. The obtained scalings were compared to and validated by the numerical results with different values of Pr, the Rayleigh number Ra and the dimensionless time-varying heat flux frequency fn, over 106 ≤ Ra ≤ 109, 0.01 ≤ Pr ≤ 0.5, and 0.001 ≤ fn ≤ 0.025. It is also found that the development of the boundary layer at the start-up stage is one-dimensional and but becomes two-dimensional at the quasi-steady state

Linear temporal stability analysis on the inviscid sheared convective boundary layer flow

A linear temporal stability analysis is conducted for inviscid sheared convective boundary layer flow, in which the sheared instability with stable stratification coexists with and caps over the thermal instability with unstable stratification. The classic Taylor–Goldstein equation is applied with different stratification factors Js and Jb in the Brunt–Väisälä frequency, respectively. Two shear-thermal hybrid instabilities, the hybrid shear stratified (HSS) and hybrid Rayleigh–Bénard (HRB) modes, are obtained by solving the eigenvalue problems. It is found that the temporal growth rates of the HSS and HRB modes vary differently with increased Jb in two distinct wavenumber (~a) regions defined by the intersection point between the stability boundaries of the HSS and HRB modes. Based on Jb,cr where the temporal growth rate of the HSS and HRB are equal, a map of the unique critical boundary, which separates the effective regions of the HSS and HRB modes, is constructed and found to be dependent on Js, Jb, and ~a. The examinations of the subordinate eigenfunctions indicate that the shear instability is well developed in the HSS mode, in which the large vortex structures may prevail and suppress the formation of convective rolls; the shear instability in the HRB mode is either “partly developed” when Jb Jb,cr , thus only plays a secondary role to modify the dominant convective rolls, and as Jb increases, the eigenfunctions of the HSS mode exhibit different transitional behaviors in the two regions, signifying the “shear enhancement” and “shear sheltering” of the entrainment of buoyancy flux

Transient conjugate natural convection heat transfer in a differentially-heated square cavity with a partition of finite thickness and thermal conductivity

The transient conjugate natural convection heat transfer in a differentially-heated cavity with a partition of finite thickness and thermal conductivity are investigated numerically over the range of the Rayleigh number from 103 to 108, the thermal conductivity ratio of partition to that of fluid from 0.1 to 1000, and the dimensionless partition thickness from 0.05 to 0.2. An analysis of the obtained temperature contours and profiles, the time for the onset of stratification and the Nusselt number shows that the thermal conductivity ratio effect is significant only over the range of 0.1–10, when the role played by the partition changes, whereas the effect becomes negligible as the thermal conductivity ratio is very large (100 or beyond). It is also found that the scaling relations developed for the non-partitioned cavity are found to be applicable for the partitioned cavity. The results further show that the effect of the partition thickness on heat transfer is significant mainly when the thermal conductivity ratio is small

A Review of Gravitational Water Vortex Hydro Turbine Systems for Hydropower Generation

Hydropower is one of the most sustainable and desirable renewable energy sources. Gravitational water vortex hydro turbine (GWVHT) systems are one of the most suitable and sustainable renewable power generation devices for remote and rural areas, particularly in developing countries, owing to their small scales and low costs. There are various GWVHT systems with different configurations and various operating conditions. The main components of a GWVHT system include the inlet and outlet channels, a basin, and a turbine on which there are a number of blades attached. This paper presents a comprehensive review regarding the progress and development of various GWVHT systems, covering broad aspects of GWVHT systems, particularly various types of basins, inlet and outlet channels, turbines with blades which have different shapes, orientations, sizes, numbers, etc. The nature of the previous studies is summarised. The fundamentals of the vortex dynamics involved and the quantitative analysis of the performance of GWVHT systems are also described. The turbulence models and multiphase models used in some leading numerical simulation studies have been reviewed. As a case study, the implementation of a GWVHT system in PNG is presented. Based on the review of previous studies regarding GWVHT systems, the major issues and challenges are summarised, and some key topics are recommended for future research work on the performance of GWVHTsystems

The Influence of Geometry Variation and Heat Sink Angle on its Thermal Performance

Light-emitting diodes (LEDs) are becoming substantially more popular than traditional lighting methods. LED lights are high power density devices that need thermal management systems to extend their useful life. This paper presents an experimental study on radial aluminum heat sink fabricated by metal additive manufacturing process operating under natural convection conditions. New design considerations such as adapting the middle fin, fin height gradient towards the centre of the heat sink, along with fin perforations and a spiral cut out of the central pillar have been used to improve the thermal performance of the heat sink. For different fin numbers, the effect of the orientation on the natural heat transfer was studied. The performance of three different geometries with 6, 8 and 10 long fins (6LF, 8LF and 10LF) were evaluated under three different heat flux conditions (471.57W/m2, 943.14W/m2 and 1257.52W/m2) for 10 different orientation angles from 0 to 90. It was found that the orientation has a weaker effect on high-density heat sinks than on low ones due to the hindered convective fluid flow by the overlapping of thermal boundary layers. The Rayleigh number was showed to have a significant effect on heat transfer and this effect was the most prominent for the 6LF heat sink. The overall Nusselt number correlations to predict the heat transfer as a function of the Rayleigh number for the 6LF, 8LF and 10LF heat sinks are 0.2748Ra^0.3425, 0.3868Ra^0.2747 and 0.3317Ra^0.2708, respectively