A STUDY ON THE MECHANISM OF HIGH-LIFT GENERATION BY AN AIRFOIL IN UNSTEADY MOTION AT LOW REYNOLDS NUMBER

The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first. The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period and (C) over bar (L), the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short 'vortex street' in front of the airfoil and the 'vortex street' induces a 'wind'; against this 'wind' the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.

Surface integral analogy approaches for predicting noise from 3D high-lift low-noise wings

Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings （FW-H） method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to con- struct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill＇s stress tensors on the noise pre-diction are then evaluated by comparing the results of the Curle method with the other two methods.

Numerical study of the influence of spoiler deflection on high-lift configuration

This paper numerically studies the influence of the downward spoiler deflection on the boundary layer flow of a high-lift two-element airfoil consisting of a droop nose, a main wing, a downward deflecting spoiler and a single slotted flap. Both of the boundary layer of the upper surface of the spoiler and the confluent boundary layer of the upper surface of the flap become thicker, as the downward spoiler deflection increases. Compared to the attached flow at the angle of attack of 10°, the flow of the upper surface of the spoiler becomes separated at the angle of attack of 16° when the spoiler deflection is large enough, which corresponds to the boundary layer flow reversal in velocity profiles.

Dynamic Stall on High-Lift Airfoil 30P30N in Ground Proximity

Computational prediction of stall aerodynamics in free air and in close proximity to the ground considering the 30P30N three-element high-lift configuration is carried out based on CFD simulations using the OpenFOAM code and Fluent software. Both the attached and separated flow regimes are simulated using the Reynolds Averaged Navier-Stokes (RANS) equations closed with the Spalart-Allamaras (SA) turbulence model for static conditions and pitch oscillations at Reynolds number, Re = 5 x 106 and Mach number, M = 0.2. The effects of closeness to the ground and dynamic stall are investigated and the reduction in the lift force in close proximity to the ground is discussed.

A novel hybrid method for aerodynamic noise prediction of high-lift devices

Aerodynamic noise of High-Lift Devices(HLDs)is one of the main sources of airframe noise,and has immediate impacts on the airworthiness certification,environmental protection and security of commercial aircraft.In this study,a novel hybrid method is proposed for the aerodynamic noise prediction of HLD.A negative Spalart-Allmaras(S-A)turbulence model based Improved Delayed Detached Eddy Simulation(IDDES)method coupling with AFT-2017b transition model is developed,in order to elaborately simulate the complex flow field around the HLD and thus obtain the information of acoustic sources.A Farassat-Kirchhoff hybrid method is developed to filter the spurious noise sources caused by the vortex motions in solving the Ffowcs Williams-Hawkings(FW-H)equation with permeable integral surfaces,and accurately predict the far-field noise radiation of the HLD.The results of the 30P30N HLD indicate that,the computational Sound Pressure Levels(SPLs)obtained by the Farassat-Kirchhoff hybrid method conform well with the experimental ones in the spectrum for the given observation point,and are more accurate than those obtained by the Farassat 1A method.Based on the hybrid method,the acoustic directivity of the HLD of a commercial aircraft is obtained,and the variation of the SPLs in the spectrum with the deflection angle of the slat is analyzed.

高扬程泵站虹吸式出水流道虹吸形成过程分析

为研究高扬程泵站虹吸式出水流道虹吸形成过程,以某高扬程泵站的出水流道及出水池为研究对象,建立三维模型并使用Fluent仿真计算了虹吸管流态变化。针对3种出水池水位使用VOF模型计算其压力、流速等参数。驼峰段原角度为段前150°、段后160°,在虹吸段顶端使用DN350的真空破坏阀,同时改变驼峰段角度进行优化,发现将段前角度增加10°后,虹吸形成时间为448 s,相较于优化前缩短了56 s,改善了泵启动过程。分析发现,不同水位下虹吸形成时压力分布较为均匀;水位较低时流速分布不均,不良流态产生,低水位造成的负面影响远大于高水位;在驼峰段安装DN350真空阀能减小水力损失,对虹吸形成过程起到促进作用;真空阀会影响经典断面处流速分布,产生高流速区,出水池水位较低时,该现象使得流速分布不均。

YKJ-01型附着式升降脚手架在330m超高层建筑的应用

针对某330 m超高层项目,详细介绍了附着式升降脚手架在超高层的应用,主要包括:附着式升降脚手架施工平面布置,附着式升降脚手架参数设计,附着式升降脚手架直爬与斜爬部位处理,建筑结构凹槽位置防护设计,附着式升降脚手架斜爬角度变化,避难层位置附着式升降脚手架处理,高区大堂处格构柱设计,塔式起重机附墙处附着式升降脚手架处理措施,施工电梯处附着式升降脚手架处理措施,卸料平台处附着式升降脚手架处理措施,附着式升降脚手架分片提升断口位置处理,附着式升降脚手架安装、提升、拆除等。

榆树林油田CCUS采油工程方案优化设计与实践

大庆榆树林油田扶杨油层属低孔、特低渗透储层,针对以往开发过程中存在注水困难、压裂有效期短、水驱开发难以有效动用的问题,开展CO_(2)驱油技术现场试验。从经济性、技术适应性、配套工艺成熟性等角度对采油工程方案进行综合评价,优选出单、双管分层注入工艺、高气液比举升工艺、注采两端个性化防腐工艺及物理化学组合解冻堵工艺等CCUS采油工程技术。结果表明:试验区投产初期及目前生产情况均达到了油藏预测指标;采出井平均泵效及检泵周期与外围油田平均水平相持平,注气井与采出井腐蚀速率小于行业指标;实现CO_(2)有效埋存108.9×10^(4) t,比水驱预测采出程度提高采收率4.39百分点,取得较好的驱油开发效果。研究成果为CCUS示范区的高效建设提供了技术支撑,开辟了大庆油田外围难采储量有效动用的新途径。

High-Lift Effect of Bionic Slat Based on Owl Wing

A slat without a cove is built on the basis of a bionic airfoil （i.e. stowed multi-element airfoil）, which is extracted from a long-eared owl wing. The three-dimensional models with a deployed slat and a stowed slat are measured in a low-turbulence wind tunnel. The results are used to characterize high-lift effect： compared with the stowed slat, the deployed slat works more like a spoiler at low angles of attack, but like a conventional slat or slot at high angles of attack. In addition, it can also increase stall angle and maximum lift coefficient, and postpone the decrease in the gradient of the lift coefficient. At the same time, the flow field visualized around both three-dimensional models suggests the leading-edge separation associated with the decrease in the gradient of the lift coefficient, Furthermore, the related two-dimensional simulation well agrees with the analysis of the lift coefficient, as the complement to the experiment. The bionic slat may be used as reference in the design of leading-edge slats without a cove.

Unsteady wakes-secondary flow interactions in a high-lift low-pressure turbine cascade

Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine(LPT)cascade.All of the measurements were conducted in both the presence and absence of incoming wakes,and numerical analysis was performed to elucidate the flow mechanism.With increasing Reynolds number,the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers,leading to a lower blade loading near the leading edge and suppression of the Pressure Side(PS)leg of the horseshoe vortex.However,the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side(SS)separation bubble and increased mixing loss in the free-flow region at high Reynolds numbers.Incoming wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,000.In contrast,at the high Reynolds number of 100,000,the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes,and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade.

Aerodynamic performance enhancement of co-flow jet airfoil with simple high-lift device

The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing.Computations have been accomplished by an in-house-programmed Reynoldsaveraged Navier-Stokes solver enclosed by k-ωshear stress transport turbulence model.Three crucial geometric parameters,viz.,injection slot location,suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift,drag,power consumption and equivalent lift-to-drag ratio.Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack.The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle.The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio.Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain,meanwhile,carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.

Investigation of water impingement on a multi-element high-lift airfoil by Lagrangian and Eulerian approach

McDonnell Douglas Aerospace(MDA)high-lift model is widely used in the study of multi-element airfoil,while there is still short knowledge of ice accretion and water impingement on it.In this paper,based on two-phase flow theory,two numerical models were presented by using both Eulerian approach and Lagrangian approach,respectively,in order to predict the water impingement efficiency on a two-dimensional(2D)multi-element high-lift airfoil.Both computational results were validated with the experiment data,which shown good agreements in the impingement limitations and tendency.The trend that how the attack angle and droplet diameter affect the feather of local water impingement characteristics on the different elements of MDA were further investigated.As shown in this research,the trends that the local impingement intensity and extent on flap of MDA varied differently as in general understanding due to the complex structures of flow field,which should be careful cognized in design of the ice protection system.

Aerodynamic optimization of a high-lift system with adaptive dropped hinge flap

The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performance. In this paper, aerodynamic optimization design of an ADHF high-lift system is conducted considering the mechanism performance. Shape and settings of both takeoff and landing configurations are optimized and analyzed, with considering the kinematic constraints of ADHF mechanism, and the desired optimization results were obtained after optimization. Sensitivity analysis proves the robustness of the optimal design. Comparison shows that the ADHF design has better comprehensive performance of both mechanism and aerodynamics than the conventional Fowler flap and simple hinge flap design.

民用飞机高升力系统扭矩限制器触发特性分析

扭矩限制器是民用飞机高升力系统中重要的过载保护装置,能够在触发后阻止过量的载荷沿传动线系传递。触发特性的研究对于扭矩限制器的设计有重要的意义。设计了一种滚子-摩擦片式的扭矩限制器,提出了一种球窝结构的建模方法,建立了动力学有限元仿真模型,研究了扭矩加载速率、动静摩擦片初始安装距离、预加碟簧力和球与球窝摩擦系数对触发特性的影响。研究结果表明,扭矩加载速率改变会影响触发时间但不改变触发扭矩值。相同初始安装距离时,触发扭矩分别与碟簧力和摩擦系数呈线性关系。研究为高升力系统的设计提供了参考。

特大桥高墩施工技术分析

为了深入研究特大桥高墩施工技术,以银昆高速太彭段LJ08-2标段为例,重点分析了特大桥高墩施工的实施要点和成效。针对特大桥高墩施工的关键环节和难点,采取了有效的施工措施方法。实践表明,采用大块定型钢模板(翻模)作为特大桥高墩成型的手段,同时把控好模板吊装及混凝土浇筑,并做好高墩线形控制,能够高效完成特大桥高墩的施工并实现质量验收100%的目标,为企业节约成本12.48万元,既保证了特大桥高墩的施工进度和安全,也实现了良好的经济效益和社会效益,对类似工程具有参考价值和应用指导意义。

节能视域下农田水利高扬程提水泵站技术研究

以实例简述高扬程提水泵站节能降耗转型存在的问题与优化措施。研究发现,泵站存在规定扬程远高于实际应用、配套设施不完善、管理运行效率较低、泥沙杂质导致设备腐蚀等问题。基于此,提出了选配合理水泵设备、优化动力机效率、优化管路设计、优化沉淀池设计、水泵系统智能启停管理、定期开展能源评估等措施,以实现高扬程水利灌溉的“节能降耗”目标。

海洋工程甲板片SPMT高位顶升技术应用

随着一体化建造施工在海洋工程甲板片建造领域的广泛应用,甲板片预制阶段的建造高度控制会直接影响施工的效率和一体化率。SPMT是一种模块化生产及组装的自行式模块运输载具,可根据装载货物的不同需求配置成各种尺寸,具有灵活、安全、载重量大等优势,应用在甲板片高位顶升作业中,具有良好的效果。

高扬程电力提灌工程可持续发展的研究和对策

鉴于水管单位作为积极推动高扬程电力提灌工程发展的管理主体,本文以高扬程水电提灌的实例,分析了高扬程提灌工程在可持续发展中的一些主要因素及存在的主要问题,提出了在强化可持续发展方面所采取的降低运行管理成本、建立合理的水价机制、微机化管理等措施,以期提高管道企业可持续发展的水平。

Aerodynamic characteristics of co-flow jet wing with simple high-lift devices

Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet(CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial parameters of CFJ wing, i.e., angle of attack, jet momentum and swept angle, are comprehensively examined. Additionally, the aerodynamic characteristics of two CFJ configurations, i.e., using open and discrete slots for injection, are compared. The results show that applying CFJ technique to a wing with simple high-lift device is able to generate more lift,reduce drag and enlarge stall margin with lower energy expenditure due to the super-circulation effect. Increasing the jet intensity can reduce the drag significantly, which is mainly contributed by the reaction jet force. The Oswald efficiency factor is, in some circumstances, larger than one,which indicates the potential of CFJ in reducing induced drag. Compared with clean wing configuration, using CFJ technique allows the aerodynamic force variation less sensitive to the swept angle, and such phenomenon is better observed for small swept angle region. Eventually, it is interesting to know that the discrete slotted CFJ configuration demonstrates a promising enhancement in aerodynamic performance in terms of high lift, low drag and efficiency.

超高层顶模安装施工技术应用

以某超高层塔楼为对象,通过智能顶升模架系统,使塔楼核心筒竖向结构施工有一个封闭、安全的作业空间某项目智能顶升模架系统安装高度为33.4 m。智能顶升模架系统安装重点是钢平台系统和挂架系统的安装;钢平台的安装原则“地面拼装、空中对装”,挂架安装原则“三跨单元、单元吊装”。