基于壁面模化大涡模拟的SUBOFF壁面脉动压力数值研究

该文基于开源计算流体力学平台OpenFOAM,采用壁面模化大涡模拟中的非平衡壁面模型,对雷诺数Re_L=1.2×10⁷(L为艇长)下的SUBOFF艇体绕流问题开展了数值研究。通过Liutex涡识别方法,该文给出了艇体近壁流动的涡结构分布,提取了艇体表面的时均压力系数,与实验数据进行了对比,并在此基础上重点研究了壁面模化大涡模拟对壁面脉动压力的预测,给出了不同区域的壁面脉动压力频率谱、平行中体处流向和周向波数-频率谱。研究结果表明：壁面模化大涡模拟能够准确预测艇体表面时均压力分布;脉动压力预测方面,艇体首部转捩区的压力脉动更为剧烈,脉动压力谱级整体高于充分发展湍流区;从脉动压力流向波数-频率谱中可观察到湍流能量集中的迁移脊,很好地反映了湍流的时空关联特性。     

水下航行体水动力辐射噪声预报方法研究

为评估水下航行体水动力辐射噪声性能,将航行体湿表面划分为若干子单元,运用功率谱的概念和模态平均法,计算子单元受湍流脉动压力激励振动声辐射,根据声能迭加原理建立航行体水动力辐射噪声的计算方法。数值计算表明,水下航行体水动力辐射噪声的预报与国外方法提供结果基本一致。6 m/s以上航速声压谱级最大偏差小于3 dB,所建立的方法可用于水下航行体水动力辐射噪声的预报和评估。     

水下航行体表面水动力激励力预测模型

水动力激励力由航行体壁面湍流脉动压力引起,是航行体水动力噪声预报的输入力源。该文利用回转体模型表面脉动压力风洞测试结果,参考流动激励力与边界层参数的经典关系,给出水下结构流激壁面湍流脉动压力归一化数学模型,经平板及回转体模型水洞实验考核,20 Hz以上频段,预测结果与实验结果有很好的一致性,偏差小于3 dB,为水下航行体水动力噪声定量评估提供激励力输入参数。     

大涡模拟在水下航行体周围黏性流场计算中的初步应用

在空间过滤得到的不可压缩流动的大涡模拟控制方程基础上,利用基于三阶迎风偏置格式的混合差分及二阶中心差分离散控制方程的对流项及耗散项,离散得到的线性方程组通过无矩阵计算的隐式LU-SGS（Lower-Upper Symmetric Gauss Seidel）分步迭代方法求解.利用大涡模拟（Large Eddy Simulation-LES）方法对水下航行体周围的黏性流场及水动力进行了定常数值模拟,计算得到的速度、压力分布及阻力值与试验吻合较好.     

重叠布置泄水建筑物坝面隔墙 脉动压力特性研究

采用数值模拟的方法,利用大涡模型对重叠布置泄水建筑物泄流工况进行模拟计算,试验数据验证结果表明数值模拟方法合理可行。根据实测数据和计算结果,对坝面隔墙处脉动压力特性进行分析研究。通过对流场分布、频谱分析以及脉动压力强度系数等研究,分析得出脉动压力的脉动源以及脉动压力在隔墙上的分布规律。     

某低水头混流式水轮机叶道涡特性数值分析

采用数值模拟手段,研究低水头混流式水轮机叶道涡的水力特性,依托某低水头混流式水轮机模型转轮试验结果和数值计算结果,选取三个单位转速下出现叶道涡的工况,基于N-S方程及SST湍流模型对水轮机进行单流道、全流道、定常和非定常流动数值模拟,分析叶道涡复杂流动的水力特性和压力脉动。结果表明,在叶道涡初生工况,叶片上冠正背面均有部分脱流现象,随着水流在叶片内部运动,转轮出口处,靠近上冠区域有较明显的脱流漩涡和失速区,这部分区域也是叶道涡产生的集中区域。分析转轮内部各个监测点的压力脉动数据,发现转轮内部各个测点会出现有规律的1倍转频的低频脉动和24倍高频脉动,1倍低频脉动与转轮自身转速有关,24倍高频脉动与活动导叶数量有关,是动静干涉影响的结果。测点位置的流态越差,该测点的压力脉动幅值会越高。     

尾水管导流栅的减振性能分析

针对尾水涡带的偏心运动对涡带压力脉动形成的影响,通过理论分析,推导了压力脉动力与涡带偏心距之间的关系表达式,同时对某实际模型在安装导流栅前后分别进行了全流道的三维湍流数值模拟,综合比较理论与模拟数据。结果表明,通过安装导流栅能起到限制涡带偏心运动的作用,从而达到降低压力脉动的效果。     

基于模态分析法的水下高速航行体流激振动声辐射特性研究

为了评估水下高速航行体的低频水动力噪声特性，该文基于模态分析法，将航行体简化为镶嵌在无限长刚性圆柱障板的圆柱壳模型，以流动激励力湍流脉动压力波数-频率谱作为输入，建立水下航行体流激结构振动声辐射计算方法，并通过回转体实验进行验证。研究结果表明：3～9 m/s流速范围内，80 Hz以上总声级偏差小于2 dB，计算结果与试验结果基本一致。该研究工作为水下航行体低频水动力噪声评估提供了一种理论方法。     

子格（SGS）模型在内流湍流中的大涡模拟

本文将子格模型应用于大涡模拟，对直方管，弯方管和弯曲槽道内充分展湍流，进行了数值模拟，并将所得的结果与实验数据作比较，计算表明，应用于子格模型的大涡模拟可以用来模拟比较复杂的内流，研究湍流运动的结构，检验湍流模型。     

水平管内螺旋流涡特性数值模拟

螺旋流是工程上常见的流动现象,具有增强湍流度、促进传热传质和提高对颗粒的携带能力等特性。该文采用雷诺应力湍流模型(RSM)对水平管内由短螺旋扭带起旋的螺旋流流动特性进行了数值模拟研究,通过激光多普勒测速仪(LDV)测速实验验证了数学模型的准确性和可靠性。结果表明,水平管内螺旋涡首先在扭带吸力面形成,且形成初期,涡量的大小受主涡影响较大,二次涡形成后,涡量大小主要受二次涡影响。在形成过程中二次涡增强了壁面附近的速度脉动,能够有效地增加介质的掺混。此外,由于二次螺旋涡的存在,使水平径向压力梯度增加,靠近壁面处的轴向速度减小,近壁处切向速度值增大1倍,且径向速度在螺旋流中不可忽略。     

Numerical simulation of cavity flow induced noise by LES and FW-H acoustic analogy

The predictions of cavity flow and flow-induced noise are two important and complex issues in fluid-acoustic coupling field. Numerical studies for these issues are performed in the paper by large eddy simulation (LES) and FW-H acoustic analogy. Firstly, the wall pressure fluctuations of plate, foil, shutter hole are computed and compared with experimental results. The robustness of large eddy simulation in unsteady flow calculation is analyzed. Secondly, the calculation of a 2-D cavity flow are accomplished. The power spectrum of pressure fluctuations is compared with measured data and the vorticity distribution is analyzed. Finally, the flow induced noises of two 3D cavities are predicted. The computed results are compared with experimental data of Large Circulation Channel in CSSRC. It shows that the numerical prediction method in the paper is credible.

     

Computation of vortical flow and flow induced noise by large eddy simulation with FW-H acoustic analogy and Powell vortex sound theory

The sound generated by a NACA0012 airfoil in the wake of a rod is numerically simulated by two approaches, one is the large eddy simulation(LES) with the FW-H acoustic analogy and the other is the LES with the Powell vortex sound theory, in order to compare the accuracies of their predictions. The vortical structures around the rod-airfoil are computed by the LES and captured by the vortex identification(Q). The acoustic predictions are verified by the measurements. It is shown that the computed results by the two hybrid approa- ches(LES and FW-H, LES and Powell) are very similar. Both are shown to be satisfactory in the prediction of the noise generated by an unsteady flow. Subsequently, the numerical simulations of the wall pressure fluctuations and the flow-induced noise of a NACA0015 airfoil are made by the two hybrid approaches. At two angles of attack(0 o and 8o), the wall pressure fluctuations of the NACA0015 airfoil are computed. The obtained power spectra of the wall pressure fluctuations are analyzed and compared with the measured data. And the vortical structures around the airfoil at two angles of attack are simulated and analyzed. After that, the flow induced noises of the NACA0015 airfoil at two angles of attack are predicted by the two hybrid approaches(LES and FW-H, LES and Powell). The radiated sound spectra are analyzed and compared with the experimental data. Comparisons show that both are robust, credible and satisfactory in the numerical prediction of the flow induced noise. All numerical simulations are carried out by parallel processing in the Wuxi supercomputing center.     

水下循迹航行器水动力学性能数值研究

为了研究低速水下循迹监测航行器的水动力学性能数值计算问题,采用FLUENT软件和SST剪切应力输运模型,通过雷诺时均N-S方程分析流速一定的情况下,取不同攻角、不同水平舵角作为来流条件,研究未安装推进器以及安装推进器且其安装位置不同时,航行器的升力系数、俯仰力矩系数、表面压力分布和流场速度的变化规律。结果表明:在未安装推进器以及推进器的安装位置不同时,随着攻角的变化,升力系数呈线性变化,俯仰力矩系数呈非线性变化;随着水平舵角的变化,升力系数和俯仰力矩系数呈线性变化。当推进器安装在航行器头部时,对航行器流场压力和流场速度变化影响最大;当安装在航行器尾部时,对二者影响最小。对于低速航行器,应尽量将推进器安装在中间靠后位置,以提高航行器的水动力性能。升力系数的试验结果与数值仿真结果之间最大相差7. 51%,阻力系数的试验结果与数值仿真结果最大相差5. 84%,均吻合较好。研究结果可以为低速水下循迹航行器的优化设计和发展提供理论参考。     

二维大涡模拟在双流道式污水泵叶轮流场分析中的应用

本文采用高斯型滤波函数对Navier—Stokes方程进行滤波处理，再引入亚格子雷诺应力模型推导出了在水力机械内部流场计算中实用的二维大涡模拟方程，并在贴体坐标系下得到计算平面二维大涡模拟方程及其离散形式，编制了数值计算程序，应用该程序计算了双流道式污水泵叶轮内部流场，得到了满意的速度分布和压力分布规律。在此基础上，我们对双流道式污水泵的叶轮进行了优化设计。     

An integral calculation approach for numerical simulation of cavitating flow around a marine propeller behind the ship hull

In this paper, the unsteady cavitating turbulent flow around a marine propeller is simulated based on the unsteady Reynolds averaged Navier-Stokes(URANS) with emphasis on the hull-propeller interaction by an integral calculation approach, which means the propeller and hull are treated as a whole when the cavitating flow is calculated. The whole calculational domain is split to an inner rotating domain containing a propeller and an outer domain containing a hull. And the two split sections are connected together in ANSYS CFX by using the GGI interfaces and the transient rotor stator frame change/mixing model. The alternate rotation model is employed for the advection term in the momentum equations in order to reduce the numerical error. Comparison of predictions with measurements shows that the propeller thrust coefficient can be predicted satisfactorily. The unsteady cavitating flow around the propeller behind the ship hull wake shows quasi-periodic features including cavity inception, growth and shrinking. These features are effectively reproduced in the simulations which compare well to available experimental data. In addition, significant pressure fluctuations on the ship hull surface induced by the unsteady propeller cavitation are compared with experimental data at monitoring points on the hull surface. The predicted amplitudes of the first components corresponding to the first blade passing frequencies match well with the experimental data. The maximum error between the predictions and the experimental data for the pressure pulsations is around 8%, which is acceptable in most engineering applications.     

Hydrodynamic performance of distributed pump-jet propulsion system for underwater vehicle

A type of distributed pump-jet propulsion system （DPJP） is developed with two or four specially designed pump-jet pods located around the axisymmetric underwater vehicle body symmetrically. The flow field is numerically simulated by solving the RANS equations with the finite volume method. The computational method is validated by comparing the calculated hull resistances of the SUBOFF AFF-3 model and the open water performance of a ducted propeller with experimental data. The hydrodynamic performances of the DPJP with different axial or radial positions and numbers of pump-jet pods are obtained to analyze the interactions between the hull and the pump-jet pods. It is shown in the calculated results that the decrease of the distance between the pods and the hull leads to an increase both in the efficiency of the pods and the thrust deduction factor due to the effect of the stern wake. And, a negative thrust deduction factor can be obtained by locating the DPJP at the parallel middle body near the aftbody of the vehicle to improve the hydrodynamic performance of the DPJP. Besides, the increase of the number of pods will cause a remarkable decrease of the total propulsive efficiency of the DPJP with the pods mounted on the stern planes, while a small decline of the total propulsive efficiency of the DPJP is observed with the pods mounted on the parallel middle body.     

Flow induced structural vibration and sound radiation of a hydrofoil with a cavity

The structural vibration and the sound radiation induced by the flow over a cavity on a hydrofoil are investigated experimentally and numerically. The large eddy simulation(LES) is adopted to calculate the flow field and the pressure fluctuation characteristics. A coupled finite element method/boundary element method approach is used to analyze the hydrofoil vibration and the structure-borne noise. The flow noise is calculated using an acoustic analogy by considering the surface pressure fluctuations as the dipole sources. A hollow hydrofoil with an orifice supported by four cylinder rods is constructed for the experiments. Modal tests are performed to obtain the natural frequencies of the hydrofoil in air and water. The vibro-acoustic experiments are carried out in the water tunnel at various free stream velocities with the orifice open and closed. A pressure transducer is used to measure the pressure fluctuations behind the downstream edge of the orifice. The triaxial accelerometers mounted on the side walls are used to measure the vibrational response of the hydrofoil. Furthermore, a hydrophone located in a box, filled with water is used to measure the sound radiation. The structure-borne noise and the flow noise are identified by their frequency properties. Reasonable agreements are observed between the numerical predictions and the experimental measurements.     

闸下有压渗流的边界拟合坐标变换数值解

建立了曲线拟合坐标系下闸下渗流的数学模型 ,给出了边界条件和求解方程。计算实例表明 ,该数学模型对水利工程中的复杂边界渗流的数值求解很有效 ,可应用于工程实际