两种湍流模型在高速旋转翼身组合弹箭中的对比研究

弹箭设计、弹道计算和稳定性研究都需要准确预测旋转弹箭的马格努斯力和力矩,国内针对旋转弹箭气动特性的数值模拟工作集中在旋成体上,对带翼外形进行完全时间相关的非定常研究鲜有见到;国外虽然有对带翼外形开展研究,但以验证方法为主,对湍流模型在复杂外形弹箭旋转中的研究未曾见到.采用完全时间相关的非定常N-S方程,对带翼弹箭开展计算,对比了一方程SA(Spalart-Allmaras)湍流模型和两方程k-ωSST(shear-stress-transport)湍流模型对马格努斯效应产生的影响,并分析了旋转导致的边界层和涡非对称畸变,以及周向压力分布和剪切应力分布非对称畸变.结果表明:旋转引起的物面流场参数变化主要体现在弹体中后部,SA和SST湍流模型预测的全弹马格努斯特性与阿诺德工程发展中心(Arnold Engineering Development Center,AEDC)实验及陆军研究实验室(Army Research Laboratory,ARL)的计算结果一致性很好,对动导数而言两湍流模型计算精度相当.两湍流模型计算的弹体左侧流场参数差异比右侧大,分析认为正向旋转使左侧壁面速度方向与来流速度相反,相互阻碍使气流脉动效应更强.壁面附近湍流黏性系数SA结果大于SST结果,y=0截面物面压力SA结果小于SST结果、最大相差6%,摩阻系数SA结果大于SST结果、最大相差35%.SA对旋转产生的分离抑制作用强于SST.     

绕振荡水翼流动及其转捩特性的数值计算研究简

通过对比标准k-ω SST 湍流模型和基于标准k-ω SST 湍流模型修正的γ-Re_θ 转捩湍流模型对绕振荡NACA66 水翼流动的数值计算结果与实验结果,对水翼振荡过程的水动力特性和流场结构变化进行了分析研究. 结果表明：与标准k-ω SST 湍流模型的数值计算结果相比,基于标准k-ω SST 湍流模型修正的γ-Re_θ 转捩湍流模型能有效预测绕振荡翼型流场结构和水动力特性,捕捉流场边界层发生的流动分离和转捩现象;绕振荡水翼的流动过程可分为5 个特征阶段,当来流攻角较小时,在水翼前缘发生层流向湍流的转捩现象,水翼动力特征曲线出现变化拐点;随着来流攻角的增大,顺时针尾缘涡逐渐形成并向水翼前缘发展;当攻角较大时,前缘涡分离导致动力失速,水翼的动力特征曲线出现大幅波动;水翼处于顺时针向下旋转阶段,绕水翼的流动状态逐渐由湍流过渡为层流.     

绕栅中水翼空化流动的数值和实验研究

采用数值计算和实验研究的方法研究了绕水翼和栅中水翼的非定常空化流动. 实验采用高速录像技术分别观察了绕水翼和栅中水翼云状空化形态随时间的变化, 测量了升阻力, 并对测量数据进行了频率分析. 计算时空化模型选用了能比较准确描述旋涡空化非定常特性的Kubota模型, 湍流模型采用能准确捕捉流场非定常特性的FBM模型. 计算模型的可靠性用实验结果进行验证. 结果表明, 计算与实验的结果基本一致, 相比绕单个水翼的空化流动, 绕栅中水翼的空穴厚度比较薄, 翼型近壁处的逆压梯度较小, 反向射流的速度较小, 且水汽混合区速度梯度较小, 空穴的脱落周期变长, 平均升阻力系数较小      

绕振荡水翼流动及其转捩特性的数值计算研究

通过对比标准k-ω SST 湍流模型和基于标准k-ω SST 湍流模型修正的γ-Re_θ 转捩湍流模型对绕振荡NACA66 水翼流动的数值计算结果与实验结果,对水翼振荡过程的水动力特性和流场结构变化进行了分析研究. 结果表明:与标准k-ω SST 湍流模型的数值计算结果相比,基于标准k-ω SST 湍流模型修正的γ-Re_θ 转捩湍流模型能有效预测绕振荡翼型流场结构和水动力特性,捕捉流场边界层发生的流动分离和转捩现象;绕振荡水翼的流动过程可分为5 个特征阶段,当来流攻角较小时,在水翼前缘发生层流向湍流的转捩现象,水翼动力特征曲线出现变化拐点;随着来流攻角的增大,顺时针尾缘涡逐渐形成并向水翼前缘发展;当攻角较大时,前缘涡分离导致动力失速,水翼的动力特征曲线出现大幅波动;水翼处于顺时针向下旋转阶段,绕水翼的流动状态逐渐由湍流过渡为层流.      

强吸气旋转圆筒壁面湍流边界层建模及计算

提出了湍流边界层的一种简单、快速计算方法, 用以求解强吸气作用下旋转圆筒表面边界层流动. 首先, 理论分析了同心圆筒间的旋转流体运动, 外筒静止、内筒旋转且为多孔吸气条件. 强吸气情况下旋转流动主要表现为内筒壁面附近的边界层流动, 基于这一事实得到了周向速度分布的解析表达式. 其次, 通过引入新参数扩展Cebeci-Smith代数湍流模型, 使其能考虑流线曲率、壁面吸气、低Reynolds数效应等因素. 针对这些因素的综合影响, 采用解析修正和经验参数对模型进行调整. 同时, 基于Reynolds应力湍流模型的仿真结果, 校准代数湍流模型中的经验参数. 最后, 给出基于广义Cebeci-Smith湍流模型的旋转壁面边界层流动的迭代算法, 该算法适用于需要特殊迭代过程的轴向及周向流动均匀情况. 计算了不同旋转速度和吸气强度组合工况下的边界层流动, 其周向速度和湍流强度分布与基于Reynolds应力湍流模型的计算结果非常接近. 并且表明, 当Reynolds应力湍流模型数值模拟预测内筒边界层为稳定层流时, 该方法也再现了相同初始条件下的层流边界层.      

三维内埋式弹舱流动特性及形状影响数值分析

采用多块结构化网格生成方法,基于三维雷诺平均 N-S 方程和 SST k-ω湍流模型,模拟了三维内埋式弹舱的流动特性.通过改变弹舱各壁面的倾角及宽深比,分析其对弹舱流动特性的影响,并研究了前缘锯齿对气动特性的影响.计算结果表明,在适当范围内:增大弹舱后壁倾角、减小侧壁倾角、增大宽深比可以改善弹舱流动特性;舱门前缘增加锯齿,有明显的减阻效果.     

MODELLING AND CALCULATION OF THE TURBULENT BOUNDARY LAYER ON A ROTATING CYLINDER SURFACE WITH STRONG SUCTION 1)

提出了湍流边界层的一种简单、快速计算方法, 用以求解强吸气作用下旋转圆筒表面边界层流动. 首先, 理论分析了同心圆筒间的旋转流体运动, 外筒静止、内筒旋转且为多孔吸气条件. 强吸气情况下旋转流动主要表现为内筒壁面附近的边界层流动, 基于这一事实得到了周向速度分布的解析表达式. 其次, 通过引入新参数扩展Cebeci-Smith代数湍流模型, 使其能考虑流线曲率、壁面吸气、低Reynolds数效应等因素. 针对这些因素的综合影响, 采用解析修正和经验参数对模型进行调整. 同时, 基于Reynolds应力湍流模型的仿真结果, 校准代数湍流模型中的经验参数. 最后, 给出基于广义Cebeci-Smith湍流模型的旋转壁面边界层流动的迭代算法, 该算法适用于需要特殊迭代过程的轴向及周向流动均匀情况. 计算了不同旋转速度和吸气强度组合工况下的边界层流动, 其周向速度和湍流强度分布与基于Reynolds应力湍流模型的计算结果非常接近. 并且表明, 当Reynolds应力湍流模型数值模拟预测内筒边界层为稳定层流时, 该方法也再现了相同初始条件下的层流边界层.     

非定常IV型激波－激波干扰数值模拟研究

对IV型激波-激波干扰非定常流动进行了数值模拟，采用有限体积法，结合空间半隐的二阶OC-TVD格式与时间二阶显式Runge-Kutta法求解三维全N-S方程，并且使用了Baldwin-Lomax代数湍流模型．得到了周期性流场变化结果，其中包括周期变化的双涡结构．壁面压强峰值的大小和位置均呈周期性振动，壁面压力系数和Stanton数的时均分布与定常实验结果符合得较好．并从一周期内流场结构的扰动传播出发，分析了结构变化的相位，说明了IV型激波一激波干扰内在的非定常性机理与影响因素。     

翼型、机翼非定常运动模式下动态数值模拟

基于RANS方程,通过刚性动网格技术实现对翼型和机翼典型运动模式的描述,采用双时间推进方法和Roe空间离散格式对流场求解,构建了一个非定常气动计算平台;以NACA0012翼型为算倒进行了动态数值模拟可信度验证。数值模拟结果与试验数据吻合较好,升力和俯仰力矩的最大计算误差分别为3％和10％,表明了该平台的可靠性。另外,还数值模拟了M6机翼的动态非定常流场,并分析了两种湍流模型对非定常流场激波的捕捉能力。结果表明非定常流动中S-A湍流模型对激波的捕捉较B-L模型更敏感。文中开发的非定常计算平台对进一步解决三维复杂流场的流动问题有很高的工程应用价值。     

基于深度神经网络的横流转捩预测

基于深度神经网络DNN构建了从层流流场无量纲速度梯度、流向涡强度等物理量到横流转捩模态下间歇因子间的映射关系,获得一种新的数据驱动转捩模型.通过将数据驱动转捩模型与SST k-ω湍流模型耦合,有效简化了转捩模型输运方程求解,实现高效、准确的亚音速三维边界层横流转捩流场计算. DNN训练数据来自变雷诺数的NLF(2)-0415无限展长后掠翼计算结果,并以两种工况进行测试,数据驱动转捩模型预测精度与γ-Reθ转捩模型近似.将数据驱动转捩模型用于其他典型横流转捩算例的计算,以验证其泛化能力.对于变后掠角的NLF(2)-0415后掠翼,数据驱动转捩模型与γ-Reθt-CF模型预测的转捩位置几乎一致,并且能够预测出后掠角从45°增长到65°的过程中,转捩位置先向前再向后移动的现象;对于标准椭球体,使用低分辨率网格进行计算,数据驱动转捩模型依然能够实现转捩位置预测,对椭球体表面Cf的计算结果与多个平台的横流转捩模型、实验结果基本一致.研究表明,以横流转捩相关物理量作为输入对DNN进行训练,并将获得的数据驱动转捩模型与SST k-ω湍流模型耦合,可以实现对横流转捩的有效预测,且具有较强的泛化能力.数...     

Numerical Simulation of the Negative Magnus Effect of a Two-Dimensional Spinning Circular Cylinder

Based on the finite volume method, the flow past a spinning circular cylinder at a low subcritical Reynolds number (Re =1 × 10 ⁵), high subcritical Reynolds number (Re =1.3 ×10 ⁵), and critical Reynolds number (Re =1.4 ×10 ⁵) were each simulated using the Navier-Stokes equations and the γ-Re _?? transition model coupled with the SST k?ω turbulence model. The system was solved using an implicit algorithm. The freestream turbulence intensity decay was effectively controlled by the source term method proposed by Spalart and Rumsey. The variations in the Magnus force as a function of the spin ratio, α were obtained for the three Reynolds numbers, and the flow mechanism was analyzed. The results indicate that the asymmetric transitions induced by spin affect the asymmetric separations at the top and bottom surfaces of the circular cylinder, which further affects the pressure distributions at the top and bottom surfaces of the circular cylinder and ultimately result in a negative Magnus force, whose direction is opposite to that of the classical Magnus force. This study is the first to use a numerical simulation method to predict a negative Magnus force acting on a spinning circular cylinder. At the low subcritical Reynolds number, the Magnus force remained positive for all spin ratios. At the high subcritical Reynolds number, the sign of the Magnus force changed twice over the range of the spin ratio. At the critical Reynolds number, the sign of the Magnus force changed only once over the range of the spin ratio. For relatively low spin ratios, the Magnus force significantly differed by Reynolds number; however, this variation diminished as the spin ratio increased.     

Aerodynamic analysis and validation by using three turbulence models for narrow trench configuration

Three turbulence models SST Gamma Theta, k-ω and k-ε which all found in ANSYS CFX were used. Velocity contours, pressure coefficient profiles and turbulence levels contours were discussed. Results indicate that three models calculated the cross flow boundary layer with different thicknesses. This leads to a difference in calculation each the momentum of the cross flow fluid closer to the jet exit and cooling performance. At M = 0.5 from range X/D = 5:40, the average centerline effectiveness values in case SST Gamma Theta model and k-ω model were 21 and 9.2 % larger than k-ε model, respectively. While at high blowing ratios 1 and 1.4, the effectiveness values in case SST Gamma Theta model and k-ω model were 16, 24.4 % and 32, 46 % less than k-ε model, respectively. k-ω model shows a larger backflow regions than others which a maximum negative value of u/u_∞ = ?0.198 is reached in zone 4.     

Turbulence modelling of problem aerospace flows

Unsteady Reynolds averaged Navier–Stokes (URANS) and detached eddy simulation (DES) related approaches are considered for high angle of attack NACA0012 airfoil, wing–flap, generic tilt‐rotor airfoil and double‐delta geometry flows. These are all found to be problem flows for URANS models. For DES fifth‐order upwinding is found too dissipative and the use of, for high speed flows, instability prone centred differencing essential. An existing hybrid ILES–RANS modelling approach, intended for flexible geometry, relatively high numerical dissipation codes is tested along with differential wall distance algorithms. The former gives promising results. The standard turbulence modelling approaches are found to give perhaps a surprising results variation. Results suggest that for the problem flows, the explicit algebraic stress and Menter shear stress transport (SST) URANS models are more accurate than the economical Spalart–Allmaras (SA). However, the explicit algebraic stress model (EASM) in its k–ε form is impractically expensive to converge. Here, SA predictions lack a rotation correction term and this is likely to improve these results. Copyright © 2005 John Wiley & Sons, Ltd.     

Two-equation turbulence models for prediction of heat transfer on a transonic turbine blade

Two versions of the two-equation k–ω model and a shear stress transport (SST) model are used in a three-dimensional, multi-block, Navier–Stokes code to compare the detailed heat transfer measurements on a transonic turbine blade. It is found that the SST model resolves the passage vortex better on the suction side of the blade, thus yielding a better comparison with the experimental data than either of the k–ω models. However, the comparison is still deficient on the suction side of the blade. Use of the SST model does require the computation of distance from a wall, which for a multi-block grid, such as in the present case, can be complicated. However, a relatively easy fix for this problem was devised. Also addressed are issues such as (1) computation of the production term in the turbulence equations for aerodynamic applications, and (2) the relation between the computational and experimental values for the turbulence length scale, and its influence on the passage vortex on the suction side of the turbine blade.     

A turbulent plane offset jet with small offset ratio

 Mean velocities and turbulence characteristics of a turbulent plane offset jet with a small offset ratio of 2.125 have been studied using laser Doppler anemometry (LDA). Static pressure measurements highlight the importance of side plates in enhancing two-dimensionality of the jet. The spatial distributions of turbulence intensities and Reynolds shear stress show a high turbulence recirculating flow region close to the nozzle plate between the jet and the offset plate. The LDA results have been used to examine the capability of three different turbulence models (i.e. k–ɛ, RNG and Reynolds stress) in predicting the velocity field of this jet. While all three models are able to predict qualitatively the recirculation, converging and reattachment regions observed experimentally, the standard k–ɛ turbulence model predicts a reattachment length that best agrees with the experimentally determined value. Received: 11 September 1996/Accepted: 30 May 1997     

Numerical simulations of non‐equilibrium turbulent boundary layer flowing over a bump

Large‐eddy simulation (LES) and Reynolds‐averaged Navier–Stokes simulation (RANS) with different turbulence models (including the standard k?ε, the standard k?ω, the shear stress transport k?ω (SST k?ω), and Spalart–Allmaras (S–A) turbulence models) have been employed to compute the turbulent flow of a two‐dimensional turbulent boundary layer over an unswept bump. The predictions of the simulations were compared with available experimental measurements in the literature. The comparisons of the LES and the SST k?ω model including the mean flow and turbulence stresses are in satisfied agreements with the available measurements. Although the flow experiences a strong adverse pressure gradient along the rear surface, the boundary layer is unique in that intermittent detachment occurring near the wall. The numerical results indicate that the boundary layer is not followed by mean‐flow separation or incipient separation as shown from the numerical results. The resolved turbulent shear stress is in a reasonable agreement with the experimental data, though the computational result of LES shows that its peak is overpredicted near the trailing edge of the bump, while the other used turbulence models, except the standard k?ε, underpredicts it. Analysis of the numerical results from LES confirms the experimental data, in which the existence of internal layers over the bump surface upstream of the summit and along the downstream flat plate. It also demonstrates that the quasi‐step increase in skin friction is due to perturbations in pressure gradient. The surface curvature enhances the near‐wall shear production of turbulent stresses, and is responsible for the formation of the internal layers. The aim of the present work is to examine the response and prediction capability of LES with the dynamic eddy viscosity model as a sub‐grid scale to the complex turbulence structure with the presence of streamline curvature generated by a bumpy surface. Aiming to reduce the computational costs with focus on the mean behavior of the non‐equilibrium turbulent boundary layer of flow over the bump surface, the present investigation also explains the best capability of one of the used RANS turbulence models to capture the driving mechanism for the surprisingly rapid return to equilibrium over the trailing flat plate found in the measurements. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and numerical study of turbulent flow and heat transfer inside hexagonal duct

Flow and heat transfer characteristics in transition and turbulent regions are studied experimentally and numerically in a horizontal smooth regular hexagonal duct under constant wall temperature boundary condition covering a range of Reynolds number from 2.3 × 10³ to 52 × 10³. Two types of k-omega (standard and shear stress transport (SST)) and three types of k-ε (standard, renormalization (RNG), and realizable) turbulence model are employed for transition and turbulent regions, respectively. Both average and fully developed Darcy friction factor and Nusselt number are presented as a function of Reynolds number. It is seen that k-omega SST and k-ε realizable turbulence models gave the best agreement with the experimental data in transition and turbulent regions, respectively. All the experimental results are correlated within an accuracy of ±13 % and ±7 % for Nusselt number and Darcy friction factor, respectively. Results obtained in this study are compared with circular duct results using hydraulic diameter.     

The transmission of turbulent boundary layer unsteady pressure and shear stress through a viscoelastic layer

The transmission of unsteady pressure and shear stress, generated by a turbulent boundary layer in water, through a viscoelastic layer backed by a rigid plate is investigated. Analytical models are used to estimate the unsteady pressure and shear stress from 10 to 1000 Hz for a flat plate boundary layer with zero pressure gradient. Additionally, models for the transfer of the unsteady pressures and shear stress through the viscoelastic layer are developed. The models are used to predict the unsteady pressure fluctuations, or flow noise, which would be seen by a finite size sensor embedded under the elastomer layer. The unsteady pressure levels are found to be 20 dB greater than the unsteady shear stress levels across all frequency ranges computed, in agreement with recent measurements. The unsteady pressure transfer functions have a peak at the shear wavenumber and are larger than the shear stress transfer magnitudes from 10 to 50 Hz. The unsteady shear stress transfer functions have a peak at the acoustic wavenumber and are larger than the pressure transfer magnitudes from 50 to 1000 Hz. Over the frequency range examined, the unsteady pressures were found to be the dominant contributor to the sensor flow noise due to the considerably larger magnitude of the unsteady pressures on the top of the viscoelastic layer.     

旋转圆球入水空泡特性与流场结构的大涡模拟研究

圆球旋转入水过程对于基于先导物投放的新型入水降载方式具有重要研究价值. 采用大涡模拟方法结合均质多相流模型和VOF界面捕捉算法, 对低弗劳德数条件下疏水圆球高速旋转入水的自由运动过程进行了数值模拟, 研究了转速对入水空泡演化、流场结构和水动力特性的影响. 采用动网格与滑移网格技术实现圆球的自由运动, 并基于试验结果对比验证了数值模拟的可靠性与正确性. 旋转运动的升力效应导致圆球入水弹道发生偏转并从水面携带横向楔形射流侵入空泡内部. 采用入水砰击速度与转速进行归一化分析, 结果表明入水转速的增加显著改变了圆球的动力特性: 水平方向的速度和位移以及升力峰值都随入水转速的增加而变大, 但升力峰值受到入水速度的限制; 而垂直方向的速度和加速度以及空泡断裂深度几乎不受转速增加的影响, 并且空泡深闭合发生前圆球转速变化不大. 入水转速的增加也使液面飞溅环和空泡断裂的非对称性增强, 在较低转速时发生空泡表面闭合, 而在较高转速时则发生空泡深闭合. 对于空泡深闭合模式, 入水转速的增加带来更强的横向楔形射流, 并且抑制了空泡断裂产生的高压以及相应涡结构的生成, 致使圆球在入水砰击阶段承受更低的侧向压力.      

k-ω SST湍流模式三维激波分离流动修正

“激波?边界层分离”是航空气动领域的典型湍流非平衡流动问题, 准确模拟激波分离对于跨声速飞行器气动性能评估和优化设计具有重要意义. 然而传统涡黏性湍流模式中涡黏性系数的定义方式并不适用于非平衡流动, k-ω SST湍流模式为此引入的Bradshaw假设在应用于三维强逆压梯度和较大分离流动时反而限制了雷诺应力的生成, 导致包括k-ω SST在内的常用涡黏性湍流模式均无法对此类流动进行准确模拟. 同时, 现有的非线性雷诺应力本构关系也并不能有效提高模拟精度. 为此, 针对k-ω SST模式分别提出了基于Bradshaw假设和基于长度尺度的两种激波分离流动修正方法. 前者通过提高Bradshaw常数的方式放宽了对雷诺应力生成的限制, 后者则从湍流长度尺度概念出发, 利用混合长度理论、湍动能生成/耗散之比和一种新定义的长度尺度之比构造了ω方程耗散项修正函数, 提高了模式在三维激波分离流动中的建模长度尺度. 两种方法对ONERA M6机翼跨声速大攻角流动均能得到较雷诺应力模式更好的模拟结果. 进一步的雷诺应力分析表明, 三维激波分离流动中“主雷诺应力分量”的概念不再成立, 各雷诺应力分量大小接近. 网格收敛性分析、对其他攻角状态的验证以及湍流平板边界层壁面律验证进一步确认了所提出的两种修正方法的合理性、有效性和通用性.