Enhanced heat transfer in rectangular duct with punched winglets

Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:punched delta-and elliptical-winglets(P-DW and P-EW)with four punched-hole sizes were tested at a fixed attack angle,optimal relative pitch and height.Also,data of solid delta-and elliptical-winglets(DW and EW)were included for comparison.The investigation has shown that the P-DW yields higher thermal-performance enhancement factor(η)than the P-EW.Although the solid DW and EW with no punch have the highest heat transfer and friction loss,the PWs yield betterηthan the solid ones.For PWs,the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct,respectively but the optimumηof 2.17 is seen for the one with a certain hole size.The PWs provideηat about 5%–8%above the solid winglets.

Lead-Free Piezoelectric Ceramics as Candidates on the Development of Morphing Winglets in Aircrafts

In this paper we discussed the development of a morphing wingtip device or winglet for aircraft.The aim of this research is enhancing the aerodynamic of aircrafts,by optimizing the winglet shape,angle and torsion,to reduce wingtip vortices at each flight stage,reduce drag,fuel consumption and increase its endurance.The development of a working physical wingtip device with morphing functionality,is possible by using piezoelectric MFCs(Macro Fiber Composites)as actuators in wing structures.Due to their excellent properties like flexibility,light weight,tolerant to damage and long term stability MFC fit most of the requirements and specifications of morphing structures.Unfortunately,they are based on the toxic compound of PbZrxTi1-xO3(PZT).Lead-free materials can replace lead based compounds.Also,other aim of this inquiry is the development of piezoelectric lead-free compounds based on the solid solution Ba1-xCaxTi0.9Zr0.1O3(BCZT)with x=0.1,0.125,0.15.The reason for choosing these compositions is because BZCT compounds could reach a piezoelectricity coefficient d33~400 pC/N.This value is comparable with commercial PZT,therefore it is a great candidate to replace it.

Variable Clearance Characteristics of High Subsonic Compressor Cascades with Blade Tip Winglets

The gas turbine is the main power equipment for naval ship and special civil ship,while the compressor is one of the core structures of the gas turbine.The existing tip clearance could prevent the compressor blade and casing collision.Therefore,the flow loss in the tip region caused by the tip clearance will degrade the performance of the compressor.To improve the variable clearance characteristics of the high subsonic compressor cascades,the cascades with tip clearances of 1%,2%and 3%chord length are studied through experimental measurements and numerical calculations.The research results prove that the pressure surface tip winglet can cause a significant improvement effect under most working conditions.If the blade tip clearance size is gradually increasing within a reasonable range,the improvement effect becomes more remarkable,and the optimal tip winglet case changes.When tip clearance is 1%chord length,the PTW1.0 case(the width of the pressure surface tip winglet is 1.0 time of the original tip)reduces the flow loss by 3.09%compared with the NTW case(No Tip Winglet).When tip clearance is 2%chord length,the flow loss of PTW1.5 case(the width of the pressure surface tip winglet is 1.5 times of the original tip)is reduced by 3.46%.When tip clearance is 3%chord length,all alternative tip winglets reduce the total pressure loss,and PTW2.0 case(the width of the pressure surface tip winglet is 2.0 times of the original tip)is the best choice,which has a 6.53%degree of improvement.

利用翼尖减阻装置提高碟形飞行器性能(英文)

Saucer-shaped aircraft adopts a novel aerodynamic configuration of blending fuselage with wing. In contrast to the ordinary aircraft configurations, this kind of configuration can totally eliminate the drag resulted from fuselage, bringing many advantages such as simple structure, compact scale, high load capability. But its small aspeet ratio makes the induced drag higher. Through wind tunnel experiments, it is discovered that a type of sweepback fin-shaped winglet can efficiently reduce the induced drag of this kind of aircraft. When this winglet is mounted to a model in wind tunnel experiment, the maximal ratio of lift to drag of the model can be increased by 75% as compared with the model without winglet at the speed of 30 m/s, and reached 15 at the speed of 50 m/s. In order to investigate the performance of this aircraft with winglet at low speed, test flights were processed. The results of test flights not only verify the conclusions of experiments in wind tunnel but also indicate that the load capability of the aircraft with winglet is increased and its lateral stability is even better than that of the aircraft without winglet.

膜通道内矩形翼对流传质强化效果的数值研究（英文）

Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with a spacing of 2.0 mm. The flow disturbers studied include rectangular winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications, as well as square prism, triangular prism, and circular cylinder, which are used here to mimic the traditional spacer filaments for comparison of their abilities in enhancing the convective mass transfer near the membrane surface to alleviate the concentration polarization. The disturber performance was evaluated in terms of concentration polarization factor versus consumed pumping power, with a larger factor meaning a more serious concentration polarization.Calculations were carried out for Na Cl solution flow with Reynolds numbers ranging from 400 to 1000. The results show that the traditional flow disturbers can considerably reduce the concentration polarization but cause a substantial pressure drop, while the rectangular winglets can effectively reduce the concentration polarization with a much less pressure drop penalty. The rectangular winglets were optimized in geometry under equal pumping power condition.

Influence of a Winglet Combined with a Groove Tip on the Performances of a Variable-Pitch Axial Flow Fan

Taking a two-stage variable-pitch axial fan as the research object,five schemes,including a single counter-flow rib layout grooved tip,are numerically simulated using the fluent software.The results indicate that,compared with the original blade tip,the total pressure rise and efficiency of the four proposed schemes have been improved to various degrees,with Scheme 4(groove tip with double counterflow ribs)displaying the best performances.The total pressure and efficiency are increased by 113.44 Pa and 0.955%,respectively.The blade tip leakage flow is reduced to varying degrees under different schemes,according to the following order:Scheme 1,Scheme 2,Scheme 4,and Scheme 3 leading to a reduction of 7.44%,6.46%,5.36%,and 4.35%,respectively.Steady results are used as the initial condition for the ensuing strength check and modal analysis.

Optimization and analysis of winglet configuration for solar aircraft

Installing winglets can notably improve the aerodynamic performance of solar aircraft.This paper proposes a multi-constraints optimization method of winglets for solar aircraft,aiming to enhance the corresponding uninterrupted cruising capability.An optimization objective function is formed and is separately studied in aerodynamic and structural terms.Qualitative analysis shows that the winglet design parameters are restricted by four special constraints(geometry,aerodynamics,energy and stability)of solar aircraft.The optimization process is constructed on the basis of a multi-island genetic algorithm,and carried out for a 15 m wingspan solar aircraft.Although the designed winglet is not as good as the traditional winglet in terms of drag and structural weight,the designed winglet provides a better 24 h cruising capability.The sensitivity between the objective function and the design parameters is investigated,and the winglet effects vary with respect to the wing aspect ratio(AR=10,15,19.6).The effect of the constraints is analysed quantitatively,and some basic laws are obtained.Moreover,the feasible design region and the possible optimal design parameters of winglets for different wing configurations are explored.The calculation results show that when the aspect ratio exceeds a certain value,the winglets will not benefit the aircraft.

Research Progress of Tip Winglet Technology in Compressor

In the present study,the research progress of tip winglets that control tip clearance leakage flow in compressors is reviewed.Firstly,the effects of tip leakage flow on the aerodynamic performance of the compressor are presented.Subsequently,the development of tip winglet technology is reviewed.Next,a series of studies on compressor tip winglet technology are conducted.Besides,the effects of tip winglets on the aerodynamic performance of rectangular cascades of low-speed and high-subsonic compressors,subsonic compressor rotor and transonic compressor rotor are discussed,respectively,and the control effect of tip winglet technology combined with tip groove design on tip leakage is investigated.Lastly,the subsequent development direction and research prospect of compressor tip winglet technology are presented.

Effect of blade tip winglet on the performance of a highly loaded transonic compressor rotor

The tip leakage flow has an important influence on the performance of transonic com- pressor. Blade tip winglet has been proved to be an effective method to control the tip leakage flow in compressor, while the physical mechanisms of blade tip winglet have been poorly understood. A numerical study for a highly loaded transonic compressor rotor has been conducted to understand the effect of varying the location of blade tip wing]et on the performance of the rotor. Two kinds of tip winglet were designed and investigated. The effects of blade tip winglet on the compressor over- all performance, stability and tip flow structure were presented and discussed, It is found that the interaction of the tip winglet with the flow in the tip region is different when the winglet is located at suction-side or pressure-side of the blade tip. Results indicate that the suction-side winglet （SW） is ineffective to improve the performance of compressor rotor. In addition, a significant stall range extension equivalent to 33.74% with a very small penalty in efficiency can be obtained by the pressure-side winglet （PW）. An attempt has been made to explain the fundamental mechanisms of blade tip winglet in detail.

Instability characteristics of a co-rotating wingtip vortex pair based on bi-global linear stability analysis

The Stereo Particle Image Velocimetry(SPIV)technology is applied to measure the wingtip vortices generated by the up-down symmetrical split winglet.Then,the temporal biglobal Linear Stability Analysis(bi-global LSA)is performed on this nearly equal-strength corotating vortex pair,which is composed of an upper vortex(vortex-u)and a down vortex(vortex-d).The results show that the instability eigenvalue spectrum illustrated by(ωr,ω_(i))contains two types of branches:discrete branch and continuous branch.The discrete branch contains the primary branches of vortex-u and vortex-d,the secondary branch of vortex-d and coupled branch,of which all of the eigenvalues are located in the unstable half-plane ofω_(i)>0,indicating that the wingtip vortex pair is temporally unstable.By contrast,the eigenvalues of the continuous branch are concentrated on the half-plane ofω_(i)<0 and the perturbation modes correspond to the freestream perturbation.In the primary branches of vortex-u and vortex-d,Mode P_(u) and Mode Pd are the primary perturbation modes,which exhibit the structures enclosed with azimuthal wavenumber m and radial wavenumber n,respectively.Besides,the results of stability curves for vortex-u and vortex-d demonstrate that the instability growth rates of vortex-u are larger than those of vortex-d,and the perturbation energy of Mode P_(u) is also larger than that of Mode Pd.Moreover,the perturbation energy of Mode P_(u) is up to 0.02650 and accounts for 33.56%percent in the corresponding branch,thereby indicating that the instability development of wingtip vortex is dominated by Mode P_(u).By further investigating the topological structures of Mode P_(u) and Mode Pd with streamwise wavenumbers,the most unstable perturbation mode with a large azimuthal wavenumber of m=5-6 is identified,which imposes on the entire core region of vortex-u.This large azimuthal wavenumber perturbation mode can suggest the potential physical-based flow control strategy by manipulating it.

Effects of Width Variation of Pressure-Side Winglet on Tip Flow Structure in a Transonic Rotor

Tip leakage flow has become one of the major triggers for rotating stall in tip region of high loading transonic compressor rotors.Comparing with active flow control method,it’s wise to use blade tip modification to enlarge the stable operating range of rotor.Therefore,three pressure-side winglets with the maximum width of 2.0,2.5 and 3.0 times of the baseline rotor,are designed and surrounded the blade tip of NASA rotor 37,and the three new rotors are named as RPW1,RPW2,and RPW3 respectively.The numerical results show that the width of pressure-side winglet has significant influence on the stall margin and the minimum throttling massflow of rotor,while it produces less effect on the choking massflow and the peak efficiency of new rotors.As the width of the pressure-side winglet increases from new rotor RPW1 to RPW3,the strength of leakage massflow has been attenuated dramatically and a reduction of 20%in leakage massflow rate has appeared in the new rotor RPW3.By contrast,the extended blade tip caused by winglet has not introduced much more aerodynamic losses in tip region of rotor,and the new rotors with different width of pressure-side winglet have the similar peak efficiency to the baseline.The new shape of the leakage channel over blade tip which replaces of the static pressure difference near blade tip has dominated the behavior of the leakage flow in tip gap.As both the new aerodynamic boundary and throat in tip gap have reshaped by the low-velocity flow near the solid wall of extended blade tip,the discharging velocity and massflow rate of leakage flow have been suppressed obviously in new rotors.In addition,the increasing inlet axial velocity at the entrance of new rotor has increased slightly as well,which is attributed to the less blockage in the tip region of new rotor.In consideration of the increased inlet axial velocity and the weakened leakage flow,the new rotor presents an appropriately linear increase of the stall margin when the width of pressure-side winglet increases,and has a nearly 15%increase in new rotor RPW3.

Numerical Study on Thermoelectric Power Generator in Combustor

Micro gas turbine is a typical distributed energy resource system. The temperature of the burning gas in the combustor reaches 1000 K or even more, which makes a huge temperature difference in the combustor an interesting topic for heat recovery. In this work, thermoelectric devices are used for heat recovery in the combustor of the micro gas turbine. A flow-thermal-electric multiple-physical numerical model is used for the combustor and thermoelectric device power generation system. The effect of the winglet vortex generators installed at the outer wall of the flame tube on the system performance is examined. The numerical results show that the best matching load is about 1.4 times the internal resistance which provides the maximum power output for the thermoelectric generator. Active cascade control of heat transfer enhancement elements on flame tube considering wall safety and conversion efficiency of thermoelectric generator under high temperature and large temperature drop is proposed. The numerical results show that the conversion efficiency of thermoelectric generator can be increased by more than 80%, and the average wall temperature can be reduced by 35 K by using non-uniform arrangement of the winglet vortex generators.

Effect of vortex dynamics and instability characteristics on the induced drag of trailing vortices

In this paper, trailing vortices generated by three wingtip configurations, namely the M6wing and the M6 wing with a blended or split winglet, are experimentally investigated using the Stereo Particle Image Velocimetry(SPIV) technology. Then, linear stability analysis is performed to investigate instability characteristics. Three corresponding trailing vortex patterns, including the isolated trailing vortex without wake(pattern v) and with wake(pattern v-w), co-rotating vortex pair(pattern v-v), are observed in experiments. The strength of trailing vortices, characterized by circulation, is reduced after installing winglets as expected, and the strength of pattern v-v can be further suppressed compared with pattern v-w. Moreover, instability characteristics, such as the eigenvalue spectrum and perturbation mode, are distinctive among these three vortex patterns.The distribution of eigenvalue spectrums indicates that pattern v and pattern v-w are temporally“marginally stable”, while pattern v-v is temporally “unstable.” The primary perturbation mode of pattern v and pattern v-w is the m =-1 helical mode, while |m|>1 for the case of pattern v-v.The effect of vortex dynamics and instability characteristics can be concluded in two aspects.Firstly, the value of induced drag is polluted by about 3% from vortex wandering since vortex wandering affects the tangential velocity and streamwise vorticity of trailing vortices. Secondly, the growth rate and penetration depth perturbation mode affect trailing vortex evolution and further affect induced drag. Specifically, the larger the growth rate and penetration depth are, the more turbulence injects inside the vortex core, thus leading to a quicker and more intense attenuation of trailing vortex, as well as a smaller induced drag. This finding can guide us to manipulate the induced drag in flow control.

A novelapproachforsuppressingleakage flow throughturbinebladetipgaps

Tip clearance leakage flow of the turbine bade is an important factor limiting the augment of the high pressure turbine efficiency,which should be suppressed utilizing certain methods.However,the passive control method with the traditional structure is more and more difficult to satisfy the suppressing ability of the advanced turbine demand.In the present paper,a synergetic suppressing method by combining the approach of blade shape modification and spontaneous injection is adopted,to construct a novel tip structure.The aerodynamic characteristics of the tip leakage flow(TLF)with different blade tip configurations,such as the squealer,squealer-winglet(SW)and squealer-winglet-spontaneous injection holes(SWS)composite configurations,are numerically investigated.The impacts of several key geometric parameters,such as the winglet width and the space ng of spontaneous injection holes,are also discussed.Due to the adjustment of the winglet,the SW tip configuration can get better suppressing effect on TLF than the squealer tip.The SWS synergetic suppression tip decrease the leakage flow rate and the leakage mixing loss on the basis of the SW tip due to the blocking effect of the spontaneous injection flow.The key geometric parameters study shows that the suppressing effect of the TLF can be improved by reasonably increasing the winglet width and reducing the spacing between spontaneous injection holes.