Despite being one of the oldest and most widely-used turbulence models in engineering computational fluid dynamics(CFD),the k-ωmodel has not been fully understood theoretically because of its high nonlinearity and co...Despite being one of the oldest and most widely-used turbulence models in engineering computational fluid dynamics(CFD),the k-ωmodel has not been fully understood theoretically because of its high nonlinearity and complex model parameter setting.Here,a multi-layer analytic expression is postulated for two lengths(stress and kinetic energy lengths),yielding an analytic solution for the k-ωmodel equations in pipe flow.Approximate local balance equations are analyzed to determine the key parameters in the solution,which are shown to be rather close to the empirically-measured values from the numerical solution of the Wilcox k-ωmodel,and hence the analytic construction is fully validated.The results provide clear evidence that the k-ωmodel sets in it a multilayer structure,which is similar to but different,in some insignificant details,from the Navier-Stokes(N-S)turbulence.This finding explains why the k-ωmodel is so popular,especially in computing the near-wall flow.Finally,the analysis is extended to a newlyrefined k-ωmodel called the structural ensemble dynamics(SED)k-ωmodel,showing that the SED k-ωmodel has improved the multi-layer structure in the outer flow but preserved the setting of the k-ωmodel in the inner region.展开更多
本文通过采用PISO(Pressure Implicit with Splitting of Operators)算法求解不可压缩RANS方程,对两类典型标准水面船型阻力和黏性流场问题进行数值计算验证.其中自由面的模拟采用单相Level set方法,湍流模式选取SST k-ω模型.首先以标...本文通过采用PISO(Pressure Implicit with Splitting of Operators)算法求解不可压缩RANS方程,对两类典型标准水面船型阻力和黏性流场问题进行数值计算验证.其中自由面的模拟采用单相Level set方法,湍流模式选取SST k-ω模型.首先以标准数学船型Wigley船为例,进行网格收敛性验证,讨论分析时间步长的选取和壁面网格参数的确定对计算结果的影响,为复杂问题的求解提供经验参考;然后在合适的网格及时间步长下计算不同Froude数(Fr)时Wigley船体受到的总阻力系数、摩擦阻力系数、船体表面波高图等,并分别与模型试验结果和经验公式估算结果对比,结果吻合很好,从而验证了该算法的可靠性.此外,还模拟计算了第二类标准船型DTMB5415的阻力系数和黏性流场,总阻力计算结果与实验结果吻合很好,船体波高图与实验结果相比稍有误差.数值计算结果和分析充分证明本文算法和计算程序的可靠性.展开更多
The Duogu Wind Farm, China Huadian Group Corporation’s first wind project in Yunnan, China, has been approved by the Provincial Development and Reform Commission. The acquired site is in Mengzi, in the south-east of ...The Duogu Wind Farm, China Huadian Group Corporation’s first wind project in Yunnan, China, has been approved by the Provincial Development and Reform Commission. The acquired site is in Mengzi, in the south-east of Yunnan Province. The developer has deployed thirty-three 1.5 MW turbines in this wind farm (49.5 MW), and the total cost of construction has been estimated to be CNY449.7 million ($69.61 million). The present study compared the prediction accuracy of two CFD software packages for simulating flow over an escarpment with a steep slope. The two software packages were: 1) Open FOAM (Turbulence model: SST k-ω RANS), which is a free, open source CFD software package developed by Open CFD Ltd at the ESI Group and distributed by the Open FOAM Foundation and 2) RIAM-COMPACT (Turbulence model: Standard Smagorinsky LES), which has been developed by the lead author of the present paper. Generally good agreement was obtained between the results from the simulations with Open FOAM and RIAM-COMPACT.展开更多
基金the National Numerical Wind Tunnel(No.NNW2019ZT1-A03)the National Natural Science Foundation of China(Nos.91952201,11372008,and 11452002)。
文摘Despite being one of the oldest and most widely-used turbulence models in engineering computational fluid dynamics(CFD),the k-ωmodel has not been fully understood theoretically because of its high nonlinearity and complex model parameter setting.Here,a multi-layer analytic expression is postulated for two lengths(stress and kinetic energy lengths),yielding an analytic solution for the k-ωmodel equations in pipe flow.Approximate local balance equations are analyzed to determine the key parameters in the solution,which are shown to be rather close to the empirically-measured values from the numerical solution of the Wilcox k-ωmodel,and hence the analytic construction is fully validated.The results provide clear evidence that the k-ωmodel sets in it a multilayer structure,which is similar to but different,in some insignificant details,from the Navier-Stokes(N-S)turbulence.This finding explains why the k-ωmodel is so popular,especially in computing the near-wall flow.Finally,the analysis is extended to a newlyrefined k-ωmodel called the structural ensemble dynamics(SED)k-ωmodel,showing that the SED k-ωmodel has improved the multi-layer structure in the outer flow but preserved the setting of the k-ωmodel in the inner region.
文摘本文通过采用PISO(Pressure Implicit with Splitting of Operators)算法求解不可压缩RANS方程,对两类典型标准水面船型阻力和黏性流场问题进行数值计算验证.其中自由面的模拟采用单相Level set方法,湍流模式选取SST k-ω模型.首先以标准数学船型Wigley船为例,进行网格收敛性验证,讨论分析时间步长的选取和壁面网格参数的确定对计算结果的影响,为复杂问题的求解提供经验参考;然后在合适的网格及时间步长下计算不同Froude数(Fr)时Wigley船体受到的总阻力系数、摩擦阻力系数、船体表面波高图等,并分别与模型试验结果和经验公式估算结果对比,结果吻合很好,从而验证了该算法的可靠性.此外,还模拟计算了第二类标准船型DTMB5415的阻力系数和黏性流场,总阻力计算结果与实验结果吻合很好,船体波高图与实验结果相比稍有误差.数值计算结果和分析充分证明本文算法和计算程序的可靠性.
文摘The Duogu Wind Farm, China Huadian Group Corporation’s first wind project in Yunnan, China, has been approved by the Provincial Development and Reform Commission. The acquired site is in Mengzi, in the south-east of Yunnan Province. The developer has deployed thirty-three 1.5 MW turbines in this wind farm (49.5 MW), and the total cost of construction has been estimated to be CNY449.7 million ($69.61 million). The present study compared the prediction accuracy of two CFD software packages for simulating flow over an escarpment with a steep slope. The two software packages were: 1) Open FOAM (Turbulence model: SST k-ω RANS), which is a free, open source CFD software package developed by Open CFD Ltd at the ESI Group and distributed by the Open FOAM Foundation and 2) RIAM-COMPACT (Turbulence model: Standard Smagorinsky LES), which has been developed by the lead author of the present paper. Generally good agreement was obtained between the results from the simulations with Open FOAM and RIAM-COMPACT.
