Investigation on design flow of a millimeter-scale radial turbine for micro gas turbine

Microsystem Technologies - As compared to the conventional large scale gas turbines, the aerothermodynamics design of a micro gas turbine will be quite different not only due to the small scale...     

Viscoelastic flow past a cylinder: drag coefficient

The channel flow of a viscoelastic fluid past a circular cylinder is simulated using a parallelized unstructured Finite Volume Method (FVM) [H.-S. Dou, N. Phan-Thien, J. Non-Newtonian Fluid Mech. 77 (1998) 21–51] under a distributed computing environment through the Parallel Virtual Machine (PVM) libraries. The numerical method is based on the SIMPLER (Semi-Implicit Method for Pressure-Linked Equations Revised) algorithm, using the simplified Phan-Thien/Tanner (PTT) and the Upper Convective Maxwell (UCM) constitutive models, with the Elastic Viscous Split Stress (EVSS) formulation. The parallelization of the program is implemented by a domain decomposition strategy and the PVM software. It is found that the both shear thinning and normal stress contribute to the drag reduction. With the PTT model, the drag reduction is mainly due to shear thinning. With the UCM model, it is primarily due to the normal stress effect.     

Steady flow past a rotating cylinder

Numerical solutions have been obtained for steady viscous flow past a rotating circular cylinder. Results are presented for Reynolds numbers of 5 and 20 and ratios of the speed of the surface of the cylinder to the fluid speed at infinity from 0 to 0.5. The effects of using different boundary conditions on the stream function at large distances from the cylinder are presented and discussed.     

The past recaptured: in search of lost paradigms

In the mid 1980s, a cluster of HF professionals described a new paradigm in which technology would be designed for a better fit not just with individual users but also with organizational systems and dynamics. The term 'Macroergonomics' took hold to describe this broadening of perspective. This concept was a manifestation of the holistic design philosophy and values of the user-centred design (UCD) paradigm, but tended to place more emphasis on how technology fit into organizational systems than on either design or on individual use of technology. While the benefits in the quality of work life that were expected to result from paying more attention to how organizations managed technology and technological change were many, the track record has been disappointing. The promotion of a focus on the organizational context of technology did not lead directly to practical application or make companies more humane for either their workers or for external customers. Today, however, with the maturation and broadening application of user-centred design approaches, the time is ripe to apply them to the design of information systems within companies as vigorously as they are being applied to products and systems intended for consumers.     

Unsteady potential flow past a group of spheres

The problem of an unsteady potential flow past a group of stationary spheres is considered using the methods of images. The problem is formulated so that the number and location of the spheres is arbitrary so long as there is no overlap between adjacent spheres. Inertial and lift coefficients are determined for several different sphere arrangements. The inertial coefficient for a sphere can vary in either direction from its isolated-sphere value of 1·5. The controlling factors on this variation are the relative geometric position of the sphere within the group and its distance from its neighbors. These same factors determine, as is expected, the lift-coefficient values. In some example configurations, there is even a drag-type force generated on an individual sphere in the potential flow.     

Molecular dynamics simulation of flow past a plate

Molecular dynamics simulations with a soft-sphere potential have been carried out to model two dimensional fluid flow obstructed by a plate. At fluid velocities large enough to obtain adequate signal to noise resolution, two counter-circulating vortices are observed behind the obstruction. The stationary state length scale of these vortices is found to be roughly proportional to the average velocity in the system, as predicted by the hydrodynamic theory.     

Moving-target search: a real-time search for changing goals

Considers the case of heuristic search where the goal may change during the course of the search. For example, the goal may be a target that actively avoids the problem solver. The authors present a moving-target search algorithm (MTS) to solve this problem. The authors prove that if the average speed of the target is slower than that of the problem solver, then the problem solver is guaranteed to eventually reach the target in a connected problem space. The original MTS algorithm was constructed with the minimum operations necessary to guarantee its completeness, and hence is not very efficient. To improve its efficiency, the authors introduce ideas from the area of resource-bounded planning into MTS, including 1) commitment to goals, and 2) deliberation for selecting plans. Experimental results demonstrate that the improved MTS is 10 to 20 times more efficient than the original MTS in uncertain situations     

Unsteady flow computations for flow past multiple moving boundaries using LSKUM

We present the latest developments in the least squares kinetic upwind method (LSKUM), a kinetic theory based grid free approach for the solution of Euler equations. A single step higher order scheme through modified CIR splitting is presented. A new weighted least squares method has been used in the present work which simplifies the 2-D formulae to an equivalent 1-D form. This is achieved through diagonalisation of the least squares matrix through suitable choices of the weights. All these developments have been extended to problems with moving nodes and boundaries. A 2-D unsteady Euler code has been developed incorporating all the above ideas along with the well known dual time stepping procedure. The code has been verified and validated for the standard test case AGARD CT(5) which corresponds to unsteady flow past oscillating NACA0012 airfoil pitching about quarter chord. Good comparisons with the experimental values have been obtained. In order to demonstrate the ability of the method to handle multiple moving bodies we have computed unsteady flow past two oscillating NACA0012 airfoils one behind the other. Some interesting results are presented for this case.     

Variational multiscale large-eddy simulations of the flow past a circular cylinder: Reynolds number effects

Variational multiscale large-eddy simulations (VMS–LES) of the flow around a circular cylinder are carried out at different Reynolds numbers in the subcritical regime, viz. Re = 3900, 10,000 and 20,000, based on the cylinder diameter. A mixed finite-element/finite-volume discretization on unstructured grids is used. The separation between the largest and the smallest resolved scales is obtained through a variational projection operator and finite-volume cell agglomeration. The WALE subgrid scale model is used to account for the effects of the unresolved scales; in the VMS approach, it is only added to the smallest resolved ones. The capability of this methodology to accurately predict the aerodynamic forces acting on the cylinder and in capturing the flow features are evaluated for the different Reynolds numbers considered. The sensitivity of the results to different simulation parameters, viz. agglomeration level and numerical viscosity, is also investigated at Re = 20,000.     

Visualization of flashback in a premixed burner with swirling flow

In this study,the measurement object is a flame propagating in a premixed burner with swirling flow in order to investigate unsteady flame behavior in a gas turbine premixer.During flashback,the flame propagating upstream was visualized with a high-speed camera.Moreover,we established the technique to measure the instantaneous flow fields of unburned fuel-air mixture in a swirling premixed burner using particle image velocimetry(PIV).As a result,the characteristics of flame behavior propagating upstream wer...     

Resource scheduling based on energy consumption for sustainable manufacturing

The paper proposes an agent-based approach for measuring in real time energy consumption of resources in job-shop manufacturing processes. Data from industrial robots is collected, analysed and assigned to operation types, and then integrated in an optimization engine in order to estimate how alternating between makespan and energy consumption as objective functions affects the performances of the whole system. This study focuses on the optimization of energy consumption in manufacturing processes through operation scheduling on available resources. The decision making algorithm relies on a decentralized system collecting data about resources implementing thus an intelligent manufacturing control system; the optimization problem is implemented using IBM ILOG OPL.     

MHD flow past a circular cylinder using the immersed boundary method

The immersed boundary method (IB hereafter) is an efficient numerical methodology for treating purely hydrodynamic flows in geometrically complicated flow-domains. Recently Grigoriadis et als. [1] proposed an extension of the IB method that accounts for electromagnetic effects near non-conducting boundaries in magnetohydrodynamic (MHD) flows. The proposed extension (hereafter called MIB method) integrates naturally within the original IB concept and is suitable for magnetohydrodynamic (MHD) simulations of liquid metal flows. It is based on the proper definition of an externally applied current density field in order to satisfy the Maxwell equations in the presence of arbitrarily-shaped, non-conducting immersed boundaries. The efficiency of the proposed method is achieved by fast direct solutions of the two poisson equations for the hydrodynamic pressure and the electrostatic potential.The purpose of the present study is to establish the performance of the new MIB method in challenging configurations for which sufficient details are available in the literature. For this purpose, we have considered the classical MHD problem of a conducting fluid that is exposed to an external magnetic field while flowing across a circular cylinder with electrically insulated boundaries. Two- and three-dimensional, steady and unsteady, flow regimes were examined for Reynolds numbers Re_d ranging up to 200 based on the cylinder’s diameter. The intensity of the external magnetic field, as characterized by the magnetic interaction parameter N, varied from N=0 for the purely hydrodynamic cases up to N=5 for the MHD cases. For each simulation, a sufficiently fine Cartesian computational mesh was selected to ensure adequate resolution of the thin boundary layers developing due to the magnetic field, the so called Hartmann and sidewall layers. Results for a wide range of flow and magnetic field strength parameters show that the MIB method is capable of accurately reproducing integral parameters, such as the lift and drag coefficients, as well as the geometrical details of the recirculation zones. The results of the present study suggest that the proposed MIB methodology provides a powerful numerical tool for accurate MHD simulations, and that it can extend the applicability of existing Cartesian flow solvers as well as the range of computable MHD flows. Moreover, the new MIB method has been used to carrry out a series of accurate simulations allowing the determination of asymptotic laws for the lift and drag coefficients and the extent of the recirculation length as a function of the amplitude of the magnetic field. These results are reported herein.     

Parallel tabu search algorithm for the hybrid flow shop problem

The paper deals with the parallel variant of the scheduling algorithm dedicated to the hybrid flow shop problem. The problem derives from practice of automated manufacturing lines, e.g. for printed packages. The overall goal is to design a new algorithm which merges the performance of the best known sequential approach with the efficient exploitation of parallel calculation environments. In order to fulfill the above aim, there are two methods proposed in this paper: the original fast method of parallel calculation of the criterion function and the local neighborhood parallel search method embedded in the tabu search approach. The theoretical analysis, as well as the original implementation, with the use of vector processing instructions SSE2 supported by suitable data organization, are presented below. Numerical properties of the proposed algorithm are empirically verified on the multi-core processor.     

Research on group search optimizers for a reconfigurable flow shop sequencing problem

A reconfigurable manufacturing system is usually designed for quick re-adjusting of production capacity in response to market changes. In this paper, we study a flow shop sequencing problem (FSSP) with controllable processing times as a special case of reconfigurable manufacturing system. It is possible to speed up the processing times through assigning additional resources or control of machine speed. After formulating this problem mathematically, a novel evolutionary procedure, entitled group search optimizer (GSO), is devised as solution method. The adapted GSO is a population-based search tool which is devised based on the producer and scrounger behavior. GSO emphasizes on imitating searching model of real-world animals. The basic GSO with four promising improvements is elaborated and discussed for addressing the FSSP with controllable processing times. A set of computational experiments is also conducted to demonstrate the applicability of proposed FSSP and performance of improved GSOs.     

The numerical solution of the Navier-Stokes equations for laminar incompressible flow past a paraboloid of revolution

A numerical methods is presented for the solution of the Navier-Stokes equations for flow past a paraboloid of revolution. This method is based upon the ideas of van de Vooren and collaborators [1,2]. The flow field has been computed for a large range of Reynolds numbers. Results are presented for the skinfriction and the pressure together with their respective drag coefficients. The total drag has been checked by means of an application of the momentum theorem.     

Numerical simulation of thrust generating flow past a pitching airfoil

Earlier analytical and experimental studies predict that pitching motions at high frequency can generate thrust on the airfoil. The present work is an effort towards a systematic understanding of the influence of various parameters on thrust generation from a harmonically pitching airfoil. Quantitative instantaneous force computations have been discussed together with qualitative vortex patterns using a 2-D discrete vortex simulation of incompressible viscous flow. In general, thrust force increases with the oscillation frequency. The trend is very similar to the inviscid theory prediction. Further, the thrust force is seen to decrease with the increase in mean angle of attack. However, in a clear deviation from inviscid theory trends, pitching at high amplitudes about high mean angle of attack, only drag is observed for high values of reduced frequency considered. The effect of location of the pitching axis is also found to be significant on the propulsive characteristics of the airfoil.     

A numerical study of flow past a cylinder with cross flow and inline oscillation

Two-dimensional fluid flow around an oscillating circular cylinder is studied numerically at different values of oscillation frequency and amplitude. A novel finite element method which uses discretization along the characteristic line is used for simulation. The solver is coupled to a mesh movement scheme using the Arbitrary Lagrangian-Eulerian (ALE) formulation to account for body motion in the flow field. Two cases of cylinder motion have been studied, cross flow and inline oscillation. In both cases, occurrence of lock on is investigated and the bounds of the lock on region are determined. A comparison of the numerical results with the experimental data indicates that 2D simulation is valid up to Re = 300. Beyond that, 3D effects appear. By using flow visualization, effect of a cylinder oscillation on the flow field and wake pattern has been studied. Also, variation of the mean drag coefficient against the oscillation parameters is discussed. The numerical results are in good agreement with the experimental data available in the literature.     

Numerical solutions for high Reynolds number separated flow past a semi-infinite compression corner

The present paper addresses the high Reynolds number, two-dimensional, steady laminar flow separation phenomenon near an interior (concave) corner. A very fast Alternating Direction Implicit finite difference approach is used to solve the Interacting Boundary Layer approximation to the Navier Stokes equations in a conformal plane. Solutions are presented for corner angles up to 18° for Reynolds numbers (based on forebody length) up to 10⁸. Convergence properties and accuracy levels are identified in order to provide reliability estimates of the results. Limitations to the numerical algorithm for large separation regions at high Reynolds numbers are identified.     

Control of separated flow past a backward facing step in a microchannel

A key concern for microdevice design is its power consumption. When such a device involves microflows, actively controlling the flow losses often reduces the power requirements. In the present study, a microsynthetic jet is proposed as a flow control device. The method used is an automated design optimization methodology coupled with computational fluid dynamics. Microflows in the Knudsen number (Kn) range of 10^–3 to 10^–1 are modeled using a Navier–Stokes solver but with slip velocity and temperature jump boundary conditions derived for microsized geometries. First, an uncontrolled flow past a backward facing step in a channel is computed. Then, a synthetic jet actuator is placed downstream of the step where the separation occurs. A large number of test cases have been analyzed. It has been observed that the reattachment point of the separated flow and the flow dissipation are quite sensitive to the location and the geometry of the synthetic jet, as well as the parameters of the oscillating membrane. The best flow control, defined as the largest decrease in dissipation, is obtained when the actuator cavity width and the membrane oscillation amplitude are increased simultaneously.     

Laminar incompressible flow past a class of blunted wedges using the Navier-Stokes equations

The Navier-Stokes equations are solved, numerically, to determine the symmetric laminar incompressible flow past blunted wedges. Similarity-type variables are used in a coordinate system that comprises the optimal coordinates for the corresponding boundary-layer problem. This formulation leads to better numerical accuracy and produces the correct solution near the leading edge, far downstream and transversely far from the wedge surface. The flow over parabolas, the flat plate, and the verticval wall are obtained as particular cases of the present solutions and compare well with the available results for these problems. The numerical method that converges rapidly to accurate results.