圆柱绕流的流动分离控制

流动分离现象在穿透自由液面的圆柱绕流过程中非常明显,也是造成各种海洋结构物阻力性能恶化的重要原因.针对此问题,开展了应用生涡器装置控制流动分离的试验研究和CFD模拟.通过生涡器可以在流动分离以前向边界层内触发小尺度涡,从而增加边界层底部的动量,抵抗流动分离的发生.圆柱绕流的拖曳试验结果表明,生涡器可有效抑制圆柱后体的流动分离,对于改善海洋结构物的阻力性能具有重要意义.

Study on High-Speed Centrifugal-Regenerative Pump with an Inducer

The study on high-speed centrifugal-regenerative pumps with an inducer (HCRP) is carried out. The combined structure of inducer, centrifugal impeller, and regenerative impeller is presented, and a theoretical parallel combinatorial hydraulic design method is investigated. The comparative experimental results show that efficiency in smaller capacity region, head coefficient and efficiency in larger capacity region of HCRPs is few lower, much higher and lower than those of high-speed centrifugal pumps, respectively, and that the suction performance of HCRPs is determined only by inducer. HCRPs can be more suitably applied to deliver small-capacity high-head liquids in chemical and petrochemical industries.

An empirical study on vortex-generator insert fitted in tubular heat exchangers with dilute Cu–water nanofluid flow

The heat transfer enhancement(HTE) in tubular heat exchangers fitted with vortex-generator(VG) inserts is experimentally investigated. The studied four parameters and ranges are: winglets-pitch ratio(1.33, 2.67, and 4),winglets-length ratio(0.33, 0.67, and 1), winglets-width ratio(0.2, 0.4, and 0.6), and Reynolds number(5200to 12200). The testing fluids are the water and Cu–water nanofluid at the volumetric fraction of 0.2%. The results obtained on HTE, pressure drop, and performance evaluation criterion(PEC) are compared with those for water in a smooth tube. It is found that the VG inserts with lower winglets-pitch ratio and higher winglets-length/width ratios present higher values of HTE and pressure drop. Over the range studied, the maximum PEC of 1.83 is detected with the Cu–water nanofluid inside the tube equipped with a VG insert at the winglets-width ratio of0.6 for the maximum Reynolds number, when the heat transfer rate and pressure drop are 1.24 times and 2.03 times of those in the smooth tube. Generalized regression equations of the Nusselt number, friction factor, and PEC are presented for the tubular heat exchangers with the VG inserts for both water and Cu–water nanofluid.It is concluded that the main advantage of the VG inserts is their simple fabrication and considerable performance, particularly at higher Reynolds number.

Experimental Investigation on Turbulent Convection in Solar Air Heater Channel Fitted with Delta Winglet Vortex Generator

The paper presents an experimental study on the heat transfer and flow friction characteristics in a solar air heater channel fitted with delta-winglet type vortex generators （DWs）. The experiments are conducted by varying the airflow rate for Reynolds number in the range of 5000 to 24000 in the test section with a uniform heat-flux applied on the upper channel wall. Firstly, the DW pairs are mounted only at the entrance of the lower wall of the test channel （called DW-E） to create multiple vortex flows at the entry. The effect of two transverse pitches （Re= Pt/H= 1 and 2） at three attack angles （a= 30°, 45° and 60°） of the DW-E with its relative height, b/H= 0.5 （half height of channel） is examined. Secondly, the 30° DWs with three different relative heights （blH = 0.3, 0.4 and 0.5） are placed on the upper wall only （absorber plate, called DW-A） of the test channel. The experimental result reveals that in the first case, the 60° DW-E at Rp = 1 provides the highest heat transfer and friction factor while the 30° DW-E at Rp = 1 performs overall better than the others. In the second case, the 30° DW-A at b/H= 0.5 yields the highest heat transfer and friction factor but the best thermal performance is found at b/H = 0.4.

Modeling a high output marine steam generator feedwater control system which uses parallel turbine-driven feed pumps

Parallel turbine-driven feedwater pumps are needed when ships travel at high speed. In order to study marine steam generator feedwater control systems which use parallel turbine-driven feed pumps, a mathematical model of marine steam generator feedwater control system was developed which includes mathematical models of two steam generators and parallel turbine-driven feed pumps as well as mathematical models of feedwater pipes and feed regulating valves. The operating condition points of the parallel ttu-bine-driven feed pumps were calculated by the Chebyshev curve fit method. A water level controller for the steam generator and a rotary speed controller for the turbine-driven feed pumps were also included in the model. The accuracy of the mathematical models and their controllers was verified by comparing their results with those from a simulator.

Heat transfer augmentation in a circular tube with winglet vortex generators

The article presents the influence of winglet vortex generators （WVGs） placed in the core flow area on ther- mal performance enhancement of a tube heat exchanger. The experiment was carried out in a uniform wall heat-fluxed tube by varying turbulent airflow for Reynolds number ranging from 5300 to 24000. In the pres- ent work, the WVGs with an attack angle of 30° were inserted into the test tube at four different winglet pitch ratios （Rp = P/D） and three winglet-width or blockage ratios （Ra = e/D）. The experimental results at various Rp and RB values were evaluated and compared with those for smooth tube and tubes with twist- ed tape or wire coil. The measurement reveals that the WVGs enhance considerably the heat transfer and friction loss above the plain tube, wire coil and twisted tape. The Nusselt number and friction factor increase with the increment Of RB and Re but with the decreasing Rp. The average Nusselt numbers for the WVGs with various Ra are in the range of 2.03-2.34 times above the plain tube. The thermal performance for the WVGs is found to be much higher than that for the wire coil and twisted tape and is in a range of 1.35-1.59. Also, a numerical investigation is conducted to study the flow structure and heat transfer enhancement mecha- nisms in the winglet-inserted tube.

Banshan Gas-Fired Turbine Generator Set Put into Operation

No.1 generator set of Banshan gas-fired power generation project, which is the first 9 FA heavy-duty gas turbine generator set in China that has drawn much attention, was successfully put into operation and merged into power grid at 21：30 in June 2, three months ahead of schedule.

Convective mass transfer enhancement in a membrane channel by delta winglets and their comparison with rectangular winglets

Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels equipped with delta winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications. The channel consists of an impermeable solid wall and a membrane. The delta winglets are attached to the solid wall surface to enhance the mass transfer near the membrane surface and suppress the concentration polarization. The winglet performance was evaluated in terms of concentration polarization factor versus consumed pumping power. Calculations were implemented for NaCl solution flow in a membrane channel having a height of 2.0 mm for Reynolds numbers ranging from 400 to 1000. The delta wing- lets were optimized under equal pumping power condition, and the results of optimization suggest winglet height of 5/6 of the channel height, aspect ratio of 2.0, attack angle of 30% and a winglet interval equal to the channel height The optimal delta winglets were compared with the optimal rectangular winglets we found previously, and it is shown that the rectangular winglets yield a somewhat better performance than the delta winglets. @ 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.

Turbulent forced convection in a heat exchanger square channel with wavy-ribs vortex generator

Turbulent forced convective heat transfer and flow con figurations in a square channel with wavy-ribs inserted diagonally are examined numerically. The in fluences of the 30° and 45° flow attack angles for wavy-ribs, blockage ratio, R B= b/H = 0.05–0.25 with single pitch ratio, R P= P/H = 1 are investigated for the Reynolds number based on the hydraulic diameter of the square channel, Re = 3000–20000. The use of the wavy-ribs, which inserted diagonal in the square channel, is aimed to help to improve the thermal performance in heat exchange systems.The finite volume method and SIMPLE algorithm are applied to the present numerical simulation. The results are presented on the periodic flow and heat transfer pro files, flow con figurations, heat transfer characteristics and the performance evaluations. The mathematical results reveal that the use of wavy-ribs leads to a higher heat transfer rate and friction loss over the smooth channel. The heat transfer enhancements are around 1.97–5.14 and 2.04–5.27 times over the smooth channel for 30° and 45° attack angles, respectively. However, the corresponding friction loss values for 30° and 45° are around 4.26–86.55 and 5.03–97.98 times higher than the smooth square channel, respectively. The optimum thermal enhancement factor on both cases is found at R B= 0.10 and the lowest Reynolds number, Re = 3000, to be about 1.47 and 1.52, respectively, for 30° and 45° wavy-ribs.

500-ton LOX/Kerosene Engine Joint Test Achieved Success

Recently,the first gas generator-turbopump joint test for the 500-ton LOX/kerosene engine was completed with success.The engine developed independently by the Academy of Aerospace Liquid Propulsion Technology（AALPT）will be used for the heavy-lift rocket.The 500-ton LOX/kerosene engine has the thrust of the largest ever developed by China and in the foreseeable future.

A Karman-Vortex Generator for passive separation control in a conical diffuser

Flow separation in a conical diffuser with large divergence angle （29.14°） and large area ratio （3.533） is eliminated by a novel passive flow control device called Karman-Vortex Generator （KVG）. The effect of the KVG is verified and investigated by the URANS, DES and DDES methods based on the SST model. CFD results show that the performance coefficient of the diffuser can be doubled by the KVG, and the total pressure recovery coefficient can be improved by about 1.2%. DES and DDES re- suits show that the KVG can introduce a Karman-vortex street frequency in the diffuser. This frequency decays rapidly, and could not be detected in the ending plane of the expansion section, Different KVG configurations with different locations and dimensions are numerically simulated and compared. Some suggestions are provided.

Modeling of delta-wing type vortex generators

A numerical model of delta-wing type vortex generator was developed in two steps.The first step was to obtain a parameterized model of the shedding vortex based on delta-wing theory,which relates the geometry parameters and flow field parameters to the strength of shedding vortex which directly decides the source term.In the second step,a method was proposed to add source terms into the flow control equations so that the shedding vortex could be simulated numerically.As soon as the numerical model was completed,two cases:One for a plate and another for an airfoil segment were investigated for test.Comparison showed that the flow field structure and aerodynamic performance agreed well with those obtained from cases with real vortex generators.

Simulation of shock wave buffet and its suppression on an OAT15A supercritical airfoil by IDDES

In the present paper,extremely unsteady shock wave buffet induced by strong shock wave/boundary-layer interactions (SWBLI) on the upper surface of an OAT15A supercritical airfoil at Mach number of 0.73 and angle of attack of 3.5 degrees is first numerically simulated by IDDES,one of the most advanced RANS/LES hybrid methods.The results imply that conventional URANS methods are unable to effectively predict the buffet phenomenon on the wing surface;IDDES,which involves more flow physics,predicted buffet phenomenon.Some complex flow phenomena are predicted and demonstrated,such as periodical oscillations of shock wave in the streamwise direction,strong shear layer detached from the shock wave due to SWBLI and plenty of small scale structures broken down by the shear layer instability and in the wake.The root mean square (RMS) of fluctuating pressure coefficients and streamwise range of shock wave oscillation reasonably agree with experimental data.Then,two vortex generators (VG) both with an inclination angle of 30 degrees to the main flow directions are mounted in front of the shock wave region on the upper surface to suppress shock wave buffet.The results show that shock wave buffet can be significantly suppressed by VGs,the RMS level of pressure in the buffet region is effectively reduced,and averaged shock wave position is obviously pushed downstream,resulting in increased total lift.

Investigation of micro vortex generators on controlling flow separation over SCCH high-lift configuration

For the problem that the flow separation on the flap lowers the aerodynamic performance of high lift system,an investigation was carried out on using micro vortex generators(VGs) to control the separation on flap of the swept constant chord half-model(SCCH) high-lift configuration,at a small to medium angle of attack,by experimental and numerical methods.The basic flow characteristics of SCCH landing configuration were analyzed by using numerical method to provide required information for the design of micro VGs.Then,by keeping the cruise configuration intact,the preliminary design procedure and design methods of micro VGs were established.In addition,the micro VGs were designed.The effects of VG's arrangement and geometric parameters,such as the arrangement mode,chordwise position,arrangement angle,height and spanwise distance,on controlling efficiency were investigated by using numerical method.Then the parameters of preliminary VGs were adjusted as the basis configuration for wind tunnel test.The experiments were accomplished in NH-2 wind tunnel for validating the numerical method,as well as obtaining the design principles and methods of micro VGs.The parameters of VGs were also optimized based on the experiments.The experimental results showed that the numerical design method can serve as an efficient and accurate design tool.The lift and drag were increased by 10% and 14%,respectively in landing state,which satisfied the requirements for landing.Finally,it was concluded that the established design principles and methods for micro VGs in this investigation can be used in engineering application.

Influence of Air-Jet Vortex Generator Diameter on Separation Region

Control of shock wave and boundary layer interaction continues to attract a lot of attention. In recent decades several methods of interaction control have been investigated. The research has mostly concerned solid (vane type) vortex generators and transpiration methods of suction and blowing. This investigation concerns interaction control using air-jets to generate streamwise vortices. The effectiveness of air-jet vortex generators in controlling separation has been proved in a previous research. The present paper focuses on the influence of the vortex generator diameter on the separation region. It presents the results of experimental investigations and provides new guidelines for the design of air-jet vortex generators to obtain more effective separation control.

The study of key design parameters effects on the vortex tube performance

In this paper, energy separation effect in a vortex tube has been investigated using a CFD model. Thenumerical simulation has been done due to the complex structure of flow. The governing equationshave been solved by FLUENT code in 2D and 3D compressible and turbulent model. The effects ofgeometrical and thermo-physical parameters have been investigated. The results have shown that theoptimum length to diameter ratio is from 25 to 35. Increasing the number of nozzles from 2 to 4 withconvergent shape is found to be an efficient configuration for the swirl generator. The optimum valueof orifice diameter to tube diameter ratio, for the maximum cold air temperature difference and efficiency,has been determined to be around 0.58. The results show that if the inlet pressure increases upto a critical value, the efficiency will increase. Nevertheless, if it increases to higher values, the efficiencywill decrease. Moreover, it is found out that increasing the cold fraction decreases the coldtemperature difference and efficiency.

Experimental investigation on flow characteristics of a transverse jet with an upstream vortex generator

This paper aims at probing the flow characteristics of a jet in supersonic crossflow(JISC)by installing a vortex generator(VG)upstream of the jet orifice.Nanoparticle planar laser scattering(NPLS)and stereo-particle image velocimetry(SPIV)technologies were employed to observe the flowfield,and three cases were designed for comparison.CASE0 stands for JISC without passive VG.In CASE1 and CASE2,VG is installed at 20 mm and 80 mm upstream away from the jet orifice,respectively.Transient flow structures show that two flow modes exist when the VG wake interacts with the JISC.In CASE1,vortices are induced from both sides of the jet plume because of the VG wake.This leads to a complex streamwise vortex system.Penetration and lateral diffusion are enhanced.In CASE2,intermittent large-scale eddies in the VG wake cause large streamwise vortices at the windward side of the jet.The penetration depth is also enhanced while the lateral diffusion is restrained.In addition,experimental results show that the penetration depth is approximately 8.5%higher in CASE1 than that in CASE0,and the lateral diffusion is larger by about 17.0%.In CASE2,the penetration is increased by about 26.2%,while the lateral diffusion is enhanced by just 0.5%.

Flow Control Effect on Unsteadiness of Shock Wave Induced Separation

In usual cases of significant pressure gradients and strong shocks, the front shock takes a fixed location along the wall, at which separation starts. Usually the rear shock is responding to vortex sheding by its deflection angle. In consequence main shock and rear shocks are moving whilst front shock is stable. The goal of the measurements presented here is to find out how the k-foot behaves during shock oscillations in the case when front shock is not fixed by the pressure gradient. Unsteady shock behaviour is also investigated when air jet vortex generators （AJVG） are used. Counteraction of the separation is directly related to the influence on unsteady processes in the shock wave induced separation.

Tailoring wind properties by various passive roughness elements in a bound- ary-layer wind tunnel

Boundary-layer wind tunnel provides a unique platform to reproduce urban, suburban and rural atmospheric boundary layer （ABL） by using roughness devices such as vortex generators, floor roughness, barrier wails, and slots in the extended test-section floor in the contraction cone. Each passive device impacts wind properties in a certain way. In this study, influence of various passive devices on wind properties has been investigated. Experi- ments using eighteen different configurations of the passive devices have been carried out to simulate urban, sub-urban, and rural climate conditions in a boundary-layer wind tunnel. The effect of each configuration on the wind characteristics is presented. It was found that higher barrier height and more number of roughness elements on the floor, generated higher turbulence and therefore higher model scale factors were obtained. However, in- creased slot width in the extended test-section floor in the contraction cone of the wind tunnel seemed to have a little effect on wind characteristics.

A Comparative Study of the Local Heat Transfer Distributions Around Various Surface Mounted Obstacles

In many engineering applications,heat transfer enhancement techniques are of vital importance in order to ensure reliable thermal designs of convective heat transfer applications.This study examines experimentally the heat transfer characteristics on the base plate around various surface mounted obstacles.Local convection coefficients are evaluated in the vicinity of each individual protruding body with great spatial resolution using the transient liquid crystal technique.Five different obstacles of constant height-to-hydraulic diameter ratio(~1.3) are considered.These include:a cylinder,a square,a triangle,a diamond and a vortex generator of delta wing shape design.The experiments were carried out over a range of freestream Reynolds numbers,based on the hydraulic diameter of each obstacle,varying from 4,000 to 13,000.The results indicate a negligible effect of the flow speed on the heat transfer topological structure and a considerable effect of the obstacle geometry on the level and distribution of heat transfer enhancement.