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1.
高超声速飞行器大面积热防护系统的传热数值分析   总被引:1,自引:0,他引:1  
隔热毡是高超声速飞行器防热系统中重要的组成部分。隔热毡内存在复杂的多种传热形式的耦合,本文详细地分析了隔热结构内导热与辐射的复合换热问题,用光学厚极限法分析了隔热层纤维席内辐射热流。建立了高温绝热毡有效热导率的数值计算模型,分析了温度和压力对传热机制的影响。该模型预测的有效导热系数与试验结果最大误差不超过6%。通过应用数值分析方法得到有效导热系数,建立了防热结构一维瞬态传热模型,该模型结果与瞬态实验结果最大误差为8%。最后还计算出不同厚度隔热毡蒙皮结构的温度响应,并分析讨论了隔热毡厚度对隔热效果的影响。本文研究表明:TPS隔热毡的厚度达到63.3mm后,继续增加尺寸,其隔热效率将明显降低。  相似文献   

2.
曲线坐标系下平面二维浅水模型的修正与应用   总被引:1,自引:0,他引:1  
借鉴有关弯道水流流速分布的研究成果,计入弯道环流引起的横向的动量交换,对曲线坐标系平面二维浅水方程做了修正;采用边界处正交的曲线网格生成技术,处理复杂的计算区域边界。采用修正后的模型对90°弯道水流进行了数值模拟,并与原模型的计算结果及实测资料进行了比较,结果表明该模型能够有效地模拟流线弯曲的复杂水流的水力特性。  相似文献   

3.
为研究不同双方程湍流模型对制退机内复杂流场计算的适用性,以某火炮制退机为研究对象,建立了实际结构下的三维计算模型,利用动网格与滑移网格技术,实现了火炮实际后坐速度下的制退机内部三维运动流场的数值计算。分别采用标准k-ε模型、RNGk-ε模型和Realizable k-ε模型计算制退机内部各腔室压力,与实验曲线对比,结果表明,应用标准k-ε模型对后坐冲击过程的制退机内部压力计算的误差最小,与实验结果吻合最好。  相似文献   

4.
锥阀附近水力特性的三维数值模拟研究   总被引:1,自引:0,他引:1  
采用可压缩的两相流模型,辅以Realizable k-ε湍流模型来模拟锥阀附近的水流水力特性,对于自由水面的处理采用了VOF法。通过对计算的压力场以及流线的分析,指出锥阀在水力消能中的作用。数值模拟结果与试验资料的比较分析表明两者吻合较好,从而验证了该模型在锥阀湍流模拟中的可靠性。  相似文献   

5.
延性金属层裂模型比较   总被引:1,自引:1,他引:0  
在平面一维弹塑性流动有限差分计算程序中加入4种延性金属层裂模型,对平板撞击层裂实验进行数值模拟。结果表明:简单最大拉伸应力模型和简单损伤累积模型能定性反映层裂的物理现象,由于忽略损伤对本构的影响,计算结果和实验有偏差,但模型要求参数较少,对于一些精度要求不是很高的工程问题,可以采用;从材料损伤断裂物理本质出发,采用微损伤统计方法得到的NAG模型和封加波损伤度函数模型,能很好地再现实测的自由面速度剖面,数值计算结果与实验吻合很好。  相似文献   

6.
以广东某水坝为研究对象,给出一种基于Fluent平台和Ansys平台进行结构动力响应分析的方法。首先采用基于YOUNGS界面重构技术的VOF模型,对流动进行数值模拟,成功捕捉了闸门开启过程中自由面的变化,比较了在三种落差情况下水坝的受力差异。计算表明,即使在上游平稳的入流条件下,水坝所受到的湍流水压力也会出现波动现象,水压力对坝体的冲击为低频作用,下游水位的升高会减缓水压力的波动,这些特点都与现场观察的相符。然后将水动力作为激励条件导入结构动力分析平台Ansys后,进一步对坝体结构进行动力分析。结构的模态分析结果与实测结果一致。因此,方法可以应用于实际。  相似文献   

7.
涡旋式压缩机排气系统气流脉动现象研究   总被引:2,自引:0,他引:2  
研究了涡旋式空气压缩机排气系统的气流脉动现象,首次提出了排气孔口侵入现象及计算方法。由一维非定常流动理论建立了排气系统气流脉动的计算模型,利用匀熵修正理论进行了边界条件处理,并运用L-W两步计算法进行了数值计算。试验样机的实测结果与数值计算结果吻合较好。研究内容对于新型压缩机——涡旋式空气压缩机的设计具有指导意义。  相似文献   

8.
利用一级气炮对高导无氧铜(OFHC)进行了圆柱以205 m/s速度冲击平板实验,并进行了数值模拟。用锰铜应力计测试了靶中应力随时间的变化,并进行了回收观测。采用Johnson-Cook(J-C)、Zerilli-Armstrong(Z-A)、Steinberg-Cochran-Guinan(S-C-G)3种本构模型对实验进行了数值模拟。实验结果与数值模拟结果比较表明:就峰值应力而言,采用J-C、Z-A及S-C-G本构模型的计算结果都比较接近实验;就圆柱变形而言,Z-A及S-C-G模型的计算较J-C模型结果更符合实验。然而,速度为500 m/s冲击实验的数值模拟结果表明:3种本构模型的计算结果差异明显。  相似文献   

9.
以熔铸型含铝混合炸药熔奥梯铝为对象,研究铸装含铝混合炸药快速热点火后的燃烧转爆轰特性。建立了快速热点火燃烧转爆轰实验平台,由实验装置(加热装置、约束钢管、炸药)、压力测试系统、光纤测速系统组成;加热装置加热15 mm厚45钢钢板,峰值温度大于1 100 ℃,温升速率为85~95 ℃/s。开展了快速热点火带壳熔奥梯铝炸药燃烧转爆轰实验,由加热装置加热约束钢管内熔奥梯铝炸药,炸药化学反应阵面压力和传播速度分别由压电性高压压力传感器和光纤探针测定;实测阵面压力约1 GPa,传播速度最大约2 600 m/s。由光纤数据获得炸药化学反应阵面传播轨迹,通过特征线方法获得冲击形成点,半定量给出冲击形成距离大于850 mm;并比较了管体破片质量实测值与炸药完全爆轰时破片平均质量计算值,实测值远小于计算值。综合实测化学反应阵面传播速度和压力、冲击形成距离分析、破片质量比较,可确定熔奥梯铝炸药没有发生完全爆轰,其化学反应状态为爆燃。另外,采用Adams和Pack模型、CJ燃烧模型,都能够半定量的预估冲击形成距离和燃烧波后压力,为实验设计提供依据,但CJ燃烧模型的计算结果更接近于实测值。  相似文献   

10.
泡沫铝爆炸冲击特性的数值研究   总被引:1,自引:0,他引:1  
基于流体弹塑性模型,建立了泡沫铝在爆炸载荷下的冲击特性方程。采用Lagrange差分格式,在 均匀网格上对方程进行了离散。编写了数值计算程序,进行了炸药在空中和水中爆炸的一维数值计算。爆炸 场中考虑了泡沫铝密度、环境介质对泡沫铝材料冲击特性的影响。结果表明:数值计算结果与理论解、实验实 测结果基本吻合,证明所建立的泡沫铝的流体弹塑性本构方程可以用来描述泡沫铝的冲击特性;泡沫铝的密 度越低,泡沫铝中的压力峰值越小;在接触爆炸条件下,泡沫铝外侧环境介质的性质对临近环境介质端泡沫铝 中的压力影响明显,其中,环境介质若为空气,则临近空气端泡沫铝中的压力呈下降趋势,若环境介质为水,则 临近水端泡沫铝中的压力呈上升趋势。  相似文献   

11.
12.
Invert traps are used to trap sewer solids flowing into a sewer drainage system. The performance of the invert trap in an open rectangular channel was experimentally and numerically analysed using field sewer solids collected from a sewer drain. Experiments showed that the free water surface rises over the central opening (slot) of the invert trap, which reduces the velocity near the slot and allows more sediment to be trapped in comparison with the case for the fixed-lid model (assuming closed conduit flow with a shear-free top wall) used by earlier investigators. This phenomenon cannot be modelled using a closed conduit model as no extra space is provided for the fluctuation of the water surface, whereas this space is provided in the volume of fluid (VOF) model in the form of air space in ANSYS Fluent 14.0 software. Additionally, the zero atmospheric pressure at the free water surface cannot be modelled in a fixed-lid model. In the present study, experimental trap efficiencies of the invert trap using field sewer solids were fairly validated using a three-dimensional computational fluid dynamics model (VOF model) coupled with a stochastic discrete phase model. The flow field (i.e., velocities) predicted by the VOF model were compared with experimental velocities obtained employing particle image velocimetry. The water surface profile above the invert trap predicted by the VOF model was found to be in good agreement with the experimentally measured profile. The present study thus showed that the VOF model can be used with the stochastic discrete phase model to well predict the performance of invert traps.  相似文献   

13.
Aerated flow is a complex hydraulic phenomenon that exists widely in the field of environmental hydraulics. It is generally characterised by large deformation and violent fragmentation of the free surface. Compared to Euler methods (volume of fluid (VOF) method or rigid-lid hypothesis method), the existing single-phase Smooth Particle Hydrodynamics (SPH) method has performed well for solving particle motion. A lack of research on interphase interaction and air concentration, however, has affected the application of SPH model. In our study, an improved multiphase SPH model is presented to simulate aeration flows. A drag force was included in the momentum equation to ensure accuracy of the air particle slip velocity. Furthermore, a calculation method for air concentration is developed to analyse the air entrainment characteristics. Two studies were used to simulate the hydraulic and air entrainment characteristics. And, compared with the experimental results, the simulation results agree with the experimental results well.  相似文献   

14.
Experimental results are presented for a bubbly lubricated externally pressurized circular thrust bearing. The data consists of the measured radial pressure distribution together with the lubricant mass flow rate over a wide range of inlet pressure, air mass flow rate ratio, for an either stationary or rotating bearing.It is shown that the air injection always improves the pressure distribution in the bearing and so can completely avoid the negative pressure generated due to rotational inertia. Also it is shown that the bearing load carrying capacity increases as the injected air mass flow increases, especially at high inlet pressure. The lubricant mass flow rate is reduced by the increase of air mass flow rate and by the decrease of bearing rotational speed.Finally the experimental results described in this paper are in good agreement with the mathematical analysis, based on the homogeneous flow model presented previously.  相似文献   

15.
The characterization of tip leakage flow plays an important role for one-dimensional loss modeling and design in radial turbine research. Tip leakage losses can be expressed as function of fluid momentum and mass flow passing through the tip gap. Friction-driven flow and contrariwise oriented pressure gradient-driven flow are highly coupled. However, these numbers are mostly unknown and dependent on tip gap geometry and turbine running condition. Based on a commonly used definition of a non-dimensional tip leakage momentum ratio, a novel correlation has been derived. This allows a consistent characterization for variable tip gap sizes over a wide range of operating conditions. The correlation has been validated by means of CFD data with high variety in reduced speed tip gap geometry and expansion ratios. Results of the novel number show significant improvements of quantitative and qualitative results over a wide range of running conditions in comparison to existing correlations. Furthermore, correlations for tip leakage velocities, that can easily be used in one-dimensional models, have been derived. Finally, it has been demonstrated, that the influence of inlet flow momentum on the tip leakage flow can be analyzed with presented correlations.  相似文献   

16.
A three-dimensional method for the calculation of interface pressure in the computational modeling of free surfaces and interfaces is developed. The methodology is based on the calculation of the pressure force at the interfacial cell faces and is mainly designed for volume of fluid (VOF) interface capturing approach. The pressure forces at the interfacial cell faces are calculated according to the pressure imposed by each fluid on the portion of the cell face that is occupied by that fluid. Special formulations for the pressure in the interfacial cells are derived for different orientations of an interface. The present method, referred to as pressure calculation based on the interface location (PCIL), is applied to both static and dynamic cases. First, a three-dimensional motionless drop of liquid in an initially stagnant fluid with no gravity force is simulated as the static case and then two different small air bubbles in water are simulated as dynamic cases. A two-fluid, piecewise linear interface calculation VOF method is used for numerical simulation of the interfacial flow. For the static case, both the continuum surface force (CSF) and the continuum surface stress (CSS) methods are used for surface tension calculations. A wide range of Ohnesorge numbers and density and viscosity ratios of the two fluids are tested. It is shown that the presence of spurious currents (artificial velocities present in case of considerable capillary forces) is mainly due to the inaccurate calculation of pressure forces in the interfacial computational cells. The PCIL model reduces the spurious currents up to more than two orders of magnitude for the cases tested.

Also for the dynamic bubble rise case, it is shown that using the numerical solver employed here, without PCIL, the magnitude of spurious currents is so high that it is not possible to simulate this type of surface tension dominated flows, while using PCIL, we are able to simulate bubble rise and obtain results in close agreement with the experimental data.  相似文献   

17.
This paper studies in the one-dimensional formulation the flow of a reacting gas with account for the nonequilibrium behavior of the chemical reactions; the pressure distribution along the stream filament is given. Viscosity, heat conduction, diffusion, and ionization are not taken into account. It is assumed that there is equilibrium excitation of the translational, rotational, and vibrational degrees of freedom.Several studies have already been made of nonequilibrium flows in nozzles [1–5]. It is known that in the calculation of nonequilibrium flows considerable difficulty arises in selecting the integration step in those regions where the flow is nearly equilibrium. It is found that with the use for numerical integration of the explicit difference schemes of the type of the Euler, Runge-Kutta, etc., methods the integration step for carrying out a stable calculation must be so small that the calculation becomes practically impossible. The present study proposes a method for calculating nonequilibrium flows using a single implicit difference scheme to calculate with a high degree of accuracy and a quite large step (exceeding the step in the explicit schemes by several orders) both those flow regions which are close to equilibrium and those regions where the flow deviates markedly from equilibrium. A program was compiled using this method for the M-20 electronic digital computer which permitted calculating in the one-dimensional approximation flows in nozzles with account for the nonequilibrium behavior of the chemical reactions for mixtures containing H, O, C, and N atoms.Some qualitative peculiarities of the nonequilibrium flows are demonstrated using as an example nonequilibrium air discharge. A comparison is made with experimental and theoretical results of other authors.The authors wish to thank L. F. Kuz'mina for her assistance in carrying out the present study.  相似文献   

18.
19.
Multiphase flows are critical components of many physical systems; however, numerical models of multiphase flows with large parameter gradients can be challenging. Here, two different numerical methods, volume of fluid (VOF) and smoothed particle hydrodynamics (SPH), are used to model the buoyant rise of isolated gas bubbles through quiescent fluids for a range of Bond and Reynolds numbers. The VOF is an Eulerian grid–based method, whereas the SPH is Lagrangian and mesh free. Each method has unique strengths and weaknesses, and a comparison of the two approaches as applied to multiphase phenomena has not previously been performed. The VOF and SPH simulations are compared, verified, and validated. Results using two-dimensional VOF and SPH simulations are similar to each other and are able to reproduce numerical benchmarks and experimental results for sufficiently large Morton and Reynolds numbers. It is also shown that at low Reynolds numbers, the two methods, SPH and VOF, diverge in the transient regime of the bubble rise. Regimes that require simulations capable of representing three-dimensional drag are identified as well as regimes in which results from VOF and SPH diverge.  相似文献   

20.
In this paper, we introduce numerical methods that can simulate complex multiphase flows. The finite volume method, applying Cartesian cut-cell is used in the computational domain, containing fluid and solid, to conserve mass and momentum. With this method, flows in and around any geometry can be simulated without complex and time consuming meshing. For the fluid region, which involves liquid and gas, the ghost fluid method is employed to handle the stiffness of the interface discontinuity problem. The interaction between each phase is treated simply by wall function models or jump conditions of pressure, velocity and shear stress at the interface. The sharp interface method “coupled level set (LS) and volume of fluid (VOF)” is used to represent the interface between the two fluid phases. This approach will combine some advantages of both interface tracking/capturing methods, such as the excellent mass conservation from the VOF method and good accuracy of interface normal computation from the LS function. The first coupled LS and VOF will be generated to reconstruct the interface between solid and the other materials. The second will represent the interface between liquid and gas.  相似文献   

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