查洁法结合RANS方程的滑行艇阻力计算方法

针对雷诺平均Navier-Stokes(RANS)方程结合流体积法(VOF)计算滑行艇阻力耗时较长、现有滑行艇阻力估算公式精度较低且适用范围有限,提出了一种查洁法结合RANS方程的滑行艇阻力计算方法.通过求解艇体平衡方程,迭代求出艇体航态,动态计及升沉和纵倾角对艇体流场和阻力计算的影响.对于艇体航态变化显著时的阻力计算(体积傅氏数F>1.5),先采用查洁法估算初始纵倾角,再求解RANS方程可大幅提高计算效率.采用该方法计算了现代滑行艇模型4667-1和SM5的阻力、升沉和纵倾角,并与试验结果对比.结果表明:0.26≤F≤6.03,阻力计算值与试验值误差小于7%,升沉和纵倾角计算值与试验值吻合良好,从而验证了所提出的计算方法有效性.

圆碟形潜水器阻力性能研究

提出了一种新型碟形潜水器外形设计.在三维贴体坐标系下,采用有限体积法求解不可压缩的雷诺平均(RANS)方程,使用标准k-ε湍流模型实现方程的封闭,数值模拟了艇体周围的粘性流场.通过对不同雷诺数下的粘性绕流和阻力性能的研究,并与水池实验结果相比较,证明了数值计算在潜水器阻力性能研究方面的应用价值.

6种典型飞行器的RANS计算及大分离区域的DES分析

提出了一种将RANS(Reynolds averaged Navier-Stokes)与DES(detached eddy simulation)相结合计算流场的工程新算法,并用于第一代载人飞船Mercury、第二代载人飞船Gemini、人类第一枚成功到达火星上空的Fire-Ⅱ探测器、具有丰富风洞实验数据(来流Mach数从0.50变到2.86)的巡航导弹、高升阻比的Waverider(乘波体)以及具有大容积效率与高升阻比的CAV(common aero vehicle)等6种国际上著名飞行器的绕流计算.在流场计算中,采用分区技术,即首先对全流场采用RANS计算,然后对分离较大或者分离较严重的那些区域采用DES分析技术.文中所完成的6个典型算例总共63个工况的数值计算表明:仅在分离较大的区域采用DES分析技术,虽然从严格意义上讲这样的处理并非真正意义上的DES,但这样近似处理后所得到的流场数值结果(其中包括气动力和气动热)与相关实验数据较为贴近,并且流场的计算效率较全场进行DES计算时要高得多.

基于Delaunay图映射的动弹网格技术及其应用

在多块混合网格的基础上发展了一套基于Delaunay图映射方法的动弹网格技术,实现了针对气动弹性计算的网格变形运动方法,并使用基于多块混合网格的RANS方程的有限体积法耦合结构静平衡方程,针对大展弦比无人机在实际使用中可能出现的显著的静气动弹性问题进行了计算、分析和研究。研究结果表明,所发展的动弹网格方法为粘性混合网格的变形提供了较好的解决方案;RANS方程解算器具有较高的精度和较强的适用性,具备求解粘性流体与结构耦合等复杂航空气动弹性问题的能力。

运动潜体尾迹及其与随机海面相互作用的数值模拟

研究了水下运动物体产生的自由面尾迹与随机海面相互作用的问题.以三维非定常不可压缩雷诺平均(RANS)方程为控制方程,采用重整化群(RNG)k-ε湍流模型,应用体积分数(VOF)方法处理自由面,对水下运动球体产生的自由面尾迹特征进行了数值模拟与分析.结合海浪谱模型,数值分析了水下运动球体产生的自由面尾迹与随机海面的相互作用机理及其表现特征.

基于两种螺旋桨建模方法的全附体船模斜拖试验数值模拟

应用计算流体动力学(CFD)方法数值模拟约束模试验以获取船舶操纵水动力导数,是建立船舶操纵运动数学模型的有效方法.在数值模拟全附体约束模试验中,选定合适的螺旋桨建模方法,是既快速又准确地计算船体水动力的关键.应用CFD方法求解雷诺平均Navier-Stokes(RANS)方程,分别采用体积力法和基于实桨的滑移网格法对螺旋桨进行处理,数值模拟了全附体KCS船模的斜拖试验;通过水动力数值计算结果与基准试验数据的比较,验证了所采用的数值方法的可靠性.对两种螺旋桨建模方法的结果进行比较可以发现,综合考虑计算成本和计算精度,体积力法可以代替实桨方法进行全附体约束模斜拖试验数值模拟.

Flow Dynamics of a Spiral-groove Dry-gas Seal

The dry-gas seal has been widely used in different industries. With increased spin speed of the rotator shaft, turbulence occurs in the gas film between the stator and rotor seal faces. For the micro-scale flow in the gas film and grooves, turbulence can change the pressure distribution of the gas film. Hence, the seal performance is influenced. However, turbulence effects and methods for their evaluation are not considered in the existing industrial designs of dry-gas seal. The present paper numerically obtains the turbulent flow fields of a spiral-groove dry-gas seal to analyze turbulence effects on seal performance. The direct numerical simulation （DNS） and Reynolds-averaged Navier-Stokes （RANS） methods are utilized to predict the velocity field properties in the grooves and gas film. The key performance parameter, open force, is obtained by integrating the pressure distribution, and the obtained result is in good agreement with the experimental data of other researchers. Very large velocity gradients are found in the sealing gas film because of the geometrical effects of the grooves. Considering turbulence effects, the calculation results show that both the gas film pressure and open force decrease. The RANS method underestimates the performance, compared with the DNS. The solution of the conventional Reynolds lubrication equation without turbulence effects suffers from significant calculation errors and a small application scope. The present study helps elucidate the physical mechanism of the hydrodynamic effects of grooves for improving and optimizing the industrial design or seal face pattern of a dry-gas seal.

Numerical Simulation on Hydraulic Performances of Quarter Circular Breakwater

Quarter circular breakwater （QCB） is a new-type breakwater developed from senti-circular breakwater （SCB）. The superstructure of QCB is composed of a quarter circular front wall, a horizontal base slab and a vertical rear wall. The width of QCB＇ s base slab is about half that of SCB, which makes QCB suitable to be used on relatively finn soil foundation. The numerical wave flume based on the Reynolds averaged Navier-Stokes equations for impressible viscosity fluid is adopted in this paper to simulate the hydraulic performances of QCB. Since the geometry of both breakwaters is similar and SCB has been studied in depth, the hydraulic performances of QCB are given in comparison with those of SCB.

A VOF-based numerical model for breaking waves in surf zone

This paper introduces a numerical model for studying the evolution of a periodic wave train, shoaling, and breaking in surf zone. The model can solve the Reynolds averaged Navier-Stokes （RANS） equations for a mean flow, and the k-ε equations for turbulence kinetic energy k and turbulence dissipation rate ε. To track a free surface, the volume of fluid （VOF） function, satisfying the advection equation was introduced. In the numerical treatment, third-order upwind difference scheme was applied to the convection terms of the RANS equations in order to reduce the effect of numerical viscosity. The shoaling and breaking processes of a periodic wave train on gently sloping beaches were modeled. The computed wave heights of a sloping beach and the distribution of breaking wave pressure on a vertical wall were compared with laboratory data.

含层流分离泡的粘性绕流精确数值模拟方法研究

高精度CFD求解器是翼型设计的基础,而翼型流动转捩的准确预测是提高数值模拟精度的关键之一。eN方法是比较可靠的且可应用于翼型设计的转捩判断方法,但目前国内耦合eN转捩预测与二维雷诺平均N-S(RANS)方程求解器的研究仍需要通过求解层流边界层方程为转捩判断提供所需的边界层信息。这种方法不能处理含层流分离泡的流动。为解决上述问题,文章发展了一种直接求解RANS方程为转捩判断提供高精度的边界层解的方法,耦合基于线性稳定性理论的eN转捩判断方法实现了含层流分离泡流动的转捩点自动判断。采用文中方法对含层流分离泡的翼型绕流进行了数值模拟,转捩预测位置与实验值吻合较好,气动力计算精度得到了提高,验证了该方法的有效性。

AERODYNAMIC OPTIMIZATION FOR TURBINE BLADE BASED ON HIERARCHICAL FAIR COMPETITION GENETIC ALGORITHMS WITH DYNAMIC NICHE

A global optimization approach to turbine blade design based on hierarchical fair competition genetic algorithms with dynamic niche （HFCDN-GAs） coupled with Reynolds-averaged Navier-Stokes （RANS） equation is presented. In order to meet the search theory of GAs and the aerodynamic performances of turbine, Bezier curve is adopted to parameterize the turbine blade profile, and a fitness function pertaining to optimization is designed. The design variables are the control points＇ ordinates of characteristic polygon of Bezier curve representing the turbine blade profile. The object function is the maximum lift-drag ratio of the turbine blade. The constraint conditions take into account the leading and trailing edge metal angle, and the strength and aerodynamic performances of turbine blade. And the treatment method of the constraint conditions is the flexible penalty function. The convergence history of test function indicates that HFCDN-GAs can locate the global optimum within a few search steps and have high robustness. The lift-drag ratio of the optimized blade is 8.3% higher than that of the original one. The results show that the proposed global optimization approach is effective for turbine blade.

Entropy generation in bypass transitional boundary layer flows

The primary objective of this study is to evaluate the accuracy of using computational fluid dynamics （CFD） turbulence models to predict entropy generation rates in bypass transitional boundary layers flows under zero and adverse pressure gradients. Entropy generation rates in such flows are evaluated employing the commercial CFD software, ANSYS FLUENT. Various turbulence and transitional models are assessed by comparing their results with the direct numerical simulation （DNS） data and two recent CFD studies. A solution verification study is conducted on three systematically refined meshes. The factor of safety method is used to estimate the numerical error and grid uncertainties. Monotonic convergence is achieved for all simulations. The Reynolds number based on momentum thickness, Reo, skin-friction coefficient, Cf, approximate entropy generation rates, S, dissipation coefficient, Cd , and the intermittency, y, are calculated for bypass transition simulations. All Reynolds averaged Navier-Stokes （RANS） turbulence and transitional models show improvement over previous CFD results in predicting onset of transition. The transition SST k - ω 4 equation model shows closest agreement with DNS data for all flow conditions in this study due to a much finer grid and more accurate inlet boundary conditions. The other RANS models predict an early onset of transition and higher boundary layer entropy generation rates than the DNS shows.

An hybrid RANS/LES model for simulation of complex turbulent flow

A nonqinear eddy viscosity model （NLEVM） and a scalable hybrid Reynolds averaged Navier-Stokes/large eddy simula- tion （RANS/LES） strategy are developed to improve the capability of the eddy viscosity model （EVM） to simulate complex flows featuring separations and unsteady motions. To study the performance of the NLEVM, numerical simulations around S809 airfoil are carried out and the results show that the NLEVM performs much better when a large separation occurs. Calculated results of the flow around a triangular cylinder show that the NLEVM can improve the precision of the flow fields to some extents, but the error is still considerable, and the small turbulence structures can not be clearly captured as the EVM. Whereas the scalable hybrid RANS/LES model based on the NLEVM is fairy effective on resolving the turbulent structures and can give more satisfactory predictions of the flow fields.

A CFD study on the hydrodynamic response of a small-scale ice floe induced by a passing ship

A Reynolds averaged Navier-Stokes(RANS)computational fluid dynamics(CFD)model is built to investigate the hydrodynamic response of a circular ice floe under the influence of a passing ship in calm waters.The ship,mirroring the KRISO Container Ship’s hull design,progresses near an ice floe whose diameter is 30%of the ship’s length and its thickness is 3 m.The ship advances at a constant speed,which is handled by using the overset mesh technique.This study focuses on the ice floe’s motions and the hydrodynamic forces induced by three speeds and three transverse distances of the passing ship.Findings reveal that ship-generated wakes notably influence the ice floe’s motions,with a greater influence on sway than surge.Additionally,the ship’s speed and proximity distinctly affect the ice floe’s motions.

高升力翼型复杂流动模拟中湍流模型性能评估

采用软件Fluent中工程常用的7个涡黏湍流模型对某种高升力3段翼的降落阶段绕流进行了数值模拟.通过和试验及经过试验校验过的延迟脱体模拟(delayed detached eddy simulation,DDES)结果进行详细的对比分析,包括翼型压力系数、马赫数、涡量场和湍动能分布等,系统地研究了常用涡黏湍流模型对该高升力翼型的模拟性能.结果表明:对于平均流场,standard k-ω模型的模拟性能最好,能较好预测翼型压力系数、襟翼分离区位置和大小等;SST(shear stress transport)k-ω模型性能也较好,一方程SA(Spalart-Allmaras)模型和四方程v^2-f模型具有相近的性能,而k-ε系列模型性能相对较差.对于湍流场的模拟性能,和上述平均流场对比所得结论相一致,但所有湍流模型均未预测出襟翼分离区附近湍动能"最大"的分布特征.

Method to Calculate Resistance of High-Speed Displacement Ship Taking the Effect of Dynamic Sinkage and Trim and Fluid Viscosity into Account

A method is presented to calculate the resistance of a high-speed displacement ship taking the effect of sinkage and trim and viscosity of fluid into account.A free surface flow field is evaluated by solving Reynolds averaged Navier-Stokes(RANS) equations with volume of fluid(VoF) method.The sinkage and trim are computed by equating the vertical force and pitching moment to the hydrostatic restoring force and moment.The software Fluent,Maxsurf and MATLAB are used to implement this method.With dynamic mesh being used,the position of a ship is updated by the motion of "ship plus boundary layer" grid zone.The hull factors are introduced for fast calculating the running attitude of a ship.The method has been applied to the ship model INSEAN2340 for different Froude numbers and is found to be efficient for evaluating the flow field,resistance,sinkage and trim.

Hydrodynamics of the interceptor on a 2-D flat plate by CFD and experiments

Nowadays, the use of interceptor by both partial and total dynamic lift crafts is quite common. In this article, a lot of evidence is given regarding the effectiveness of interceptor. The interceptor, when placed at the stern region, changes the pressure distribution around the craft. Its presence affects drag force, lifting force and the position of pressure＇s center leading to a new trim. This study focuses on hydrodynamic effects of interceptors on a 2-D fiat plate based on both computational fluid dynamic （CFD） and experimental approaches. The Reynolds average Navier-Stokes （RANS） equations are used to model the flow around a fixed flat plate with an interceptor at different heights and attack angles. Based on finite volume method and SIMPLE algorithm which uses static structures, this model can be analyzed and the RANS results can be compared with the experimental data obtained in the current channel of the laboratory of waves and current of COPPE/UFRJ （LOC in Portuguese acronym）. According to the results, the increase of pressure at the end of the flat plate was proportional to the interceptor height. In addition, the existence of interceptors can significantly increase the lift force coefficient at high angles of attack also proportional to the interceptor height. The presence of interceptor at the end of the fiat plate increased both the lift coefficient and the drag coefficient but hydrodynamic drag did not grow as fast as the lift coefficient did. The lift coefficient increased much more. Furthermore, the results showed that the interceptor effectiveness is proportional to the boundary layer thickness at the end of the fiat plate. As the interceptor was inside the boundary layer alterations of flow speed led to changes in boundary layer thickness, directly affecting interceptor＇s efficiency. Optimum choice of interceptor height had a great effect on its efficiency, and in choosing it the flow speed and length of the boat must be taken into consideration.

Numerical Simulation of Focused Wave and Its Uncertainty Analysis

On the basis of the transient water wave(TWW) theory,focused wave is generated in the circulating water channel.Numerical simulation of the focused wave is carried out by solving the Reynolds averaged NavierStokes(RANS) equations.The dynamic grid technique is adopted to simulate the motion of the wave maker,and the volume of fluid(VOF) method is used to capture the free surface of the wave.The simulation results are compared with the measured data,and good agreement is obtained.For quantitative estimation of the numerical simulation error and uncertainty,the uncertainty analysis method recommended by the International Towing Tank Conference(ITTC) procedure is performed for the simulation results of the surface elevations at different positions.Both grid-convergence and time-step-size convergence studies are conducted using three types of grids and time step sizes.The simulation results are all monotonously convergent in the verification procedure,and the validations of the simulated surface elevations with the positions at 3.5,4.0 and 4.5 m are all achieved by comparing with the validation uncertainty.It is found that the numerical simulation errors caused by the grid and time-step-size in the convergence studies have the same order of magnitude.In addition,the numerical errors and uncertainties for the surface elevations at different positions are compared and discussed in detail.This paper presents the first attempt to carry out the uncertainty analysis of the simulation of focused wave,and the effectiveness of the proposed verification and validation procedures in the uncertainty analysis is demonstrated.

动力干扰下宽体客机机翼多目标优化设计

在机翼/机身/吊挂/动力短舱(WBPN)构型中开展了宽体客机机翼外形多目标优化设计。通过对动力短舱流场的动量积分,分析了直接用壁面积分"阻力"作为机体外形减阻优化设计目标函数的合理性。计算研究了短舱/吊挂的安装,以及发动机喷流对翼吊布局宽体客机机翼的干扰作用,展示了同时在安装效应和喷流干扰下设计机翼外形的重要性。运行搭建于超级计算机上的优化系统,求解雷诺平均Navier-Stokes(RANS)方程计算流场,实现了动力干扰下机翼外形的三点三目标优化设计。在80h内,完成了近20 000个方案的计算评估,遗传优化近40代。所选的最优方案阻力发散性能明显提高,自动优化后的人工修形设计使机翼剖面展向过渡和压力分布形态更为理想。动力构型下取得的减阻效果,在通气短舱构型下亦得到验证和确认。

Numerical study of high-pressure GO_2/GH_2 combustion of a single-element injector

A single-element shear-coaxial combustor using gaseous hydrogen(GH2) and oxygen(GO2) was designed and hot-tested.The wall temperature was measured.The combustion flowfield of this GH2 /GO2 single-element combustor was modeled by RANS(Reynolds Averaged Navier-Stokes) and LES(Large Eddy Simulation) methods respectively.The impact of using various turbulence and turbulent combustion models was investigated to obtain the model combination which best represented the experimental data in the RANS modeling.The flamelet model was used in the LES modeling and the validity of its application to the GH2 /GO2 combustion in the combustor was carefully examined.The combustor wall heat flux distributions of both RANS and LES results show good agreement with the experimental data.The experimental wall temperature distribution can be clearly explained through analyzing the inner flowfield structure.The results indicate that both RANS and LES used in this paper can give good predictions of the development of the whole flowfield and the combustion completion length.LES can resolve large-scale flow motions in the combustor and accurately predict the influence of the wall heat loss on the combustion efficiency.