Numerical Simulation of the Flow over a Model of the Cavities on a Butterfly Wing

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Influences of a Kind of Groove-blade on the Flow Field in a Compressor Cascade

This paper presents an experimental investigation of effects of a kind of streamwise-grooved blades on the flowfield in a compressor cascade.The flow field downstream the cascade and the boundary layer on the suctionsurface were measured using a mini 5-hole pressure probe at different incidence angles.The flow field in thegroove cascade was compared with that in the smooth cascade.The measurement results indicate that:(1)thegroove surface can restrain the development of the boundary layer on the suction surface;(2)the grooves canrestrain the radial migration of the low-energy fluids in the boundary layer on the suction surface;(3)the grooveblades can reduce total pressure loss and flow blockage in the cascade at the incidence angles of 0°,5°and 8°;(4)the maximum benefit of 8.6% loss reduction was obtained at the incidence angle of 5° while negative benefit of-3.0% loss reduction occurred at the incidence angle of-5°.     

Study on the Effects of Flow in the Volute Casing on the Performance of a Sirocco Fan

The flow at the exit from the runner blade of a centrifugal fan with forward curved blades (a sirocco fan) sometimes separates and becomes unstable. We have conducted many researches on the impeller shape of a sirocco fan, proper inlet and exit blade angles were considered to obtain optimum performance. In this paper, the casing shape were decided by changing the circumferential angle, magnifying angle and the width, 21 sorts of casings were used. Performance tests, inner flow velocity and pressure distributions were measured as well. Computational fluid dynamic calculations were also made and compared with the experimental results. Finally, the most suitable casing shape for best performance is considered.     

Study for the Gas Flow through a Critical Nozzle

In the present study, computational work using the axisymmetric, compressible, Navier-Stokes equations is carried out to predict the discharge coefficient and critical pressure ratio of gas flow through a critical nozzle. The Reynolds number effects are investigated with several nozzles with different throat diameter. Diffuser angle is varied to investigate the effects on the discharge coefficient and critical pressure ratio. The computational results are compared with the previous experimental ones. It is known that the discharge coefficient and critical pressure ratio are given by functions of the Reynolds number and boundary layer integral properties. It is also found that diffuser angle affects the critical pressure ratio.     

Flow Structure Around the Intake of a Vertical Pump

The flow structure around the intake of a vertical pump is investigated experimentally and numerically in order to obtain a guideline in designing the optimum shape of the intake of vertical pumps, in which their installation area is demanded to be minimum without losing the high performance. We concentrate our attention on the expansion ratio of the intake as a representative characteristic of the shape of the pumps and investigate the effect of the expansion ratio on pump performance. It is concluded that the optimum expansion ratio ranges in 1.1-1.2 if we take into consideration that the area needed for the installation of the pump should be minimum.     

A Solution for the Flow Between a Cone and a Plate at Low Reynolds Number

An analysis of the flow in the gap between a rotating cone and a stationary plate at low Reynolds numbers is presented. Using series expansions for the components of the mean velocity profile and the pressure gradient the Navier-Stokes equations and the continuity equation for a Newtonian fluid written in cylindrical coordinates are solved. It is found that the solution is stable and convergent for the local Reynolds numbers Re smaller than 1.2928. The computed angle of the wall streamlines is found to be in good agreement with experimental data.     

A Study of the Vortical Flow over a Delta Wing with a Leading Edge Extension

The present paper describes computational and experimental work on the vortex flow characteristics of a sharp-edged delta wing with a leading edge extension (LEX). Experiment was carried out using a low-speed wind tunnel that has a test section of 3.5 m(W)×2.45 m(H)×8.7 m(L). The angle of attack of the delta wing ranges from 10° to 30°. The free stream velocity is fixed at 20 m/s, which corresponds to Reynolds number of 0.88×106. Computations using the mass-averaged implicit 3D Navier-Stokes equations were applied to predict the complicated vortical flow over the delta wing. The governing equations were discretized in space using a fully implicit finite volume differencing formation. The standard k-e turbulent model was employed to close the governing equations. The present computations predicted the experimented flow field with a good accuracy.     

The Parametric Study on the Development of the Large-Scale Coherent Structures in a Mixing Layer

IntroductionDuring the past two decades, free shear layers haveattracted increasing attention afer the discovery of the1arge-scale coherent strUctllres which are the prondnentfeatures of such flows during their eary developmentand transition to ful1y turbulent flow.Wnant & Browand[l] observed the repeatedfOrmation and pairing of vortices in the spatiallydeveloping Inixing layer at moderate Reyno1ds numbers.They also fOund that the growth of a mixing layer iscontrolled by the pairing mechanis…     

A solution to the unit commitment problem—a review

Unit commitment (UC) is an optimization problem used to determine the operation schedule of the generating units at every hour interval with varying loads under different constraints and environments. Many algorithms have been invented in the past five decades for optimization of the UC problem, but still researchers are working in this field to find new hybrid algorithms to make the problem more realistic. The importance of UC is increasing with the constantly varying demands. Therefore, there is an urgent need in the power sector to keep track of the latest methodologies to further optimize the working criterions of the generating units. This paper focuses on providing a clear review of the latest techniques employed in optimizing UC problems for both stochastic and deterministic loads, which has been acquired from many peer reviewed published papers. It has been divided into many sections which include various constraints based on profit, security, emission and time. It emphasizes not only on deregulated and regulated environments but also on renewable energy and distributed generating systems. In terms of contributions, the detailed analysis of all the UC algorithms has been discussed for the benefit of new researchers interested in working in this field.     

Computational and Experimental Study of Pinch on the Performance of a Vaneless Diffuser in a Centrifugal Compressor

This study focuses on the vaneless diffuser of a centrifugal compressor.The examined stage consists of an un-shrouded impeller,a parallel wall vaneless diffuser and a volute.The walls of the diffuser were movable allowingdifferent pinch configurations to be investigated.The baseline geometry had no pinch i.e.the height of the dif-fuser was equal to the height of the impeller flow channel plus the axial running clearance.The work consists ofboth numerical and experimental parts.Quasi-steady, turbulent,fully 3D numerical simulations were conducted.The inlet cone,rotor and diffuser were modelled.Six different configurations were studied.The height of thepinch was altered and the pinch made to different walls was tested.Two of the numerically studied cases werealso experimentally investigated.The overall performance of the compressor,the circumferential static and totalpressure and the spanwise total pressure distribution before and after the diffuser were measured.The numericaland experimental studies showed that the pinch improved the efficiency of the compressor.     

Reconstruction of a heat exchanger network under industrial constraints — the case of a crude distillation unit

Heat exchanger network retrofit using a pinch based approach is presented. In this approach, the criterion of minimum sensitivity of heat exchanger to fouling effects is accounted for. The present paper introduces this criterion without explaining its details that are described in the literature. A summary is given of HEN reconstruction in a crude distillation unit processing 4.2 million ton crude oil per year. While the total heat quantity of hot streams is 110 MW, the heat recovery in the existing HEN is 60 MW. Using Pinch Analysis, the target value of heat recovery at ΔT_min=10 K was determined at 91 MW. Measurements were carried out on the existing HEN with the aim to determine the influence of fouling effects on the heat transfer in the exchangers. Taking local constraints including fouling into account, HEN reconstruction was proposed. The heat savings in the reconstructed HEN was estimated at 75 MW.     

Factors influencing the crack–system compliance of a piping system

With regard to the overall integrity of a piping system containing a circumferential through-wall crack, the crack–system compliance affects the integrity in various ways: (a) the onset and stability of crack extension and (b) leakage through a crack. This paper shows how this compliance depends on various factors: the mode of loading (displacement versus load control), system geometry, flexibility of mounting at the built-in ends, and the presence of supports and restraints. More particularly the paper quantifies, for a simple model system, how the compliance is affected by changes in these parameters, and especially with regard to changes in the system geometry, for which some interesting effects have been found.     

Flow of Viscous Oil in the Volute of a Centrifugal Pump

IntroductionIn a centrifugal pumP, the imPeller and the volutetogether decide its perfOrmance[']. Thus the volute is animportant element for a centrifugal pumP and theinvestigation into the flow in a volutC has drawn moreattenhons continuously. Bowerman and Acosta (l957)explored the flow in a volute and tWo-dimensionalcentrifugal impeller by using a Fltot probe[']. The resultshave shown that fOr efficien operation, the volute mustbe matched to the imPeller at the design flow rate. Atdesig…     

Relationship between the total energy efficiency of a sodium–sulfur battery system and the heat dissipation of the battery case

The relationship between the total energy efficiency of an Na/S battery system and the heat dissipation through its battery case, was investigated. The total energy efficiency was heavily influenced by the heat dissipation of the battery case, and little influenced by the energy efficiency of its cells. In order to obtain a higher total energy efficiency, it is essential to design the battery case with less heat dissipation.     

Economic forces in the European gas market — a 1985 prospective

Future gas supply and demand patterns of the European Community are simulated using a gas trade model (GTM). This study is intended to provide an economic background for exploring the future policies of the main suppliers of the Community, the type of price movements that can be expected and the possible role of high cost gas. Simulations are provided for both short-term (1985–1990) and long-term (1995–2000) developments. A decrease in Dutch gas prices, Algeria's price concession and abandonment of high prices for Norwegian gas are the main trends arising from the analysis. They all materialized between 1985 and the first half of 1986.     

A Study of the Gas Flow through a LNG Safety Valve

A safety valve functions to control an upper limit of pressure inside the LNG line of transportation.If the pressureinside the safety valve nozzle exceeds a pre-determined value on the valve sheet which plugs the nozzle,an ex-cess of LNG discharges through the gap between the nozzle exit and valve sheet.In this situation,the forces act-ing on the valve sheet are gasdynamic forces generated by the discharge of LNG and mechanical forces supportedby the spring behind the valve sheet. The flow through the gap is very complicated,involving vortices,flowseparation,and shock waves.These affect adversely on the system accompanying with noise and vibration.Thepresent study aims at understanding the flow physics of safety valve.A computational work using the two-dimensional,axisymmetric,compressible Navier-Stokes equations is carried out to simulate the gas flow betweenthe nozzle exit and valve sheet,and compared with the theoretical results. It has been found that there exists adistance between nozzle exit and valve sheet in which the thrust coefficient at the valve sheet increases abruptly.     

Natural convection in a shallow porous cavity—the Brinkman model

The natural convection in a shallow porous rectangular cavity with differentially heated sidewalls is examined using the Brinkman model. The heat transfer rate through the cavity is determined in terms of a Nusselt number, in the limit of vanishingly small aspect ratio. Two types of boundary conditions are considered. Case I deals with a cavity with all rigid boundaries so that the no-slip boundary conditions can be imposed. In case II, the cavity has a free upper surface. The present analysis shows that the Brinkman model and Darcy's law give virtually the same result for the heat transfer rate when the Darcy number, based on the depth of the cavity, is less than the order of 10⁻⁴. We also find that the presence of a free surface can significantly increase the heat transfer rate through the cavity, especially when the permeability of the medium is high.     

Reliable battery operation — a challenge for the battery management system

Advanced batteries, like lithium-ion batteries, are more sensitive in case of irregular operation than conventional batteries. Therefore, the operation of such batteries must be controlled by a management system. The features of a battery management system depend on the application, but in most cases, features like battery state determination, electrical management and safety management are necessary. This paper describes these functions of a battery management system. The use of a battery management system will lead to an increased lifetime and a safer operation of the battery.     

Experimental Study of the Viscous Pump with a Helical Channel Rotor： Torsion Effect of the Channel

The viscous pump, which has a rotor with a helical square channel, is studied experimentally. The non-dimensional channel curvature is taken to be about 0.1. Three types of torsion of the channel are made to investigate the torsion effect on the flow characteristics. We measure the flux through the channel at a constant rotor speed by changing the pressures at the entrance and exit of the pump. We also observe the secondary flow at a crosssection of the channel. Some of the results obtained are shown as follows： The friction factor along the channel to get the same flux is large for large channel torsion at a constant rotation, and becomes small when the favorable rotation of the rotor to the flow is applied. As for the secondary flow in a cross-section, there appear several types of vortex. When there is no rotation, the secondary flow is almost a symmetric two-vortex type for small flux as is the ordinary Dean vortex, but it changes to a four-vortex type when the flux is large. The secondary flow becomes asymmetric as the rotation is applied. We have unsteady flow patterns at large flux and rotation.