基于IDDES的螺旋桨叶空化及梢涡空化数值模拟

为了预测船舶螺旋桨运转时产生的叶空泡及梢涡空化现象,采用了计算流体力学对延迟分离涡修正的方法-改进延迟分离涡湍流模型及Schnerr-Sauer的空化模型,计算了PPTC螺旋桨敞水性能、叶片空泡、尾流梢涡空化等。将数值计算结果与试验数据进行对比,分析结果显示数据吻合较好,验证了湍流模型数值计算的准确性。计算结果表明,随着进速系数的增加,桨叶片空泡面积逐渐减小,桨叶导边处的空泡比随边处的空泡减少明显。当达到某一临界值时,空泡区域由吸力面转向压力面。桨尾部梢涡空泡融合现象会随着进速系数增加而减弱。

Impeller modeling and analysis based on UG NX/KF and Fluent

Parametric modeling of the impeller which drove a small wind device was built by knowledge fusion technology.NACA2410 airfoil blade was created by KF language.Using technology of UG/KF secondary development for the automatic modeling of wind turbine blade,the program can read in the airfoil data files automatically and the impeller model entity can be generated automatically.In order to modify the model,the aerodynamic characteristics of the impeller were analyzed for getting aerodynamic parameters by Fluent.The maximum force torch and best parameters of impeller were calculated.A physical prototype impeller was manufactured and the correctness of the design was verified,and the error of force torch between simulation and experimental results is about 10%.Parameterization design of the impeller model greatly improves the efficiency of modeling and flexibility of the CAD system.

Effect of blade tip geometry on tip leakage vortex dynamics and cavitation pattern in axial-flow pump

A series of blade tip geometries, including original plain tip, rounded tip on the pressure side and diverging tip towards the suction side, were adopted to investigate the effect of blade geometry on tip leakage vortex dynamics and cavitation pattern in an axial-flow pump. On the basis of the computation, it clearly shows the flow structure in the clearance for different tip configurations by the detailed data of axial velocity and turbulent kinetic energy. The in-plain trajectory, in aspects of the angle between the blade suction side and vortex core and the initial point of tip leakage vortex, was presented using the maximum swirling strength method. The most striking feature is that the inception location of tip leakage vortex is delayed for chamfered tip due to the change of blade loading on suction side. Some significant non-dimensional parameters, such as pressure, swirling strength and turbulent kinetic energy, were used to depict the characteristics of tip vortex core. By the distribution of circumferential vorticity which dominates the vortical flows near the tip region, it is observed that the endwall detachment as the leakage flow meets the mainstream varies considerably for tested cases. The present study also indicates that the shear layer feeds the turbulence into tip leakage vortex core, but the way is different. For the chamfered tip, high turbulence level in vortex core is mainly from the tip clearance where large turbulent kinetic energy emerges, while it is almost from a layer extending from the suction side corner for rounded tip. At last, the visualized observations show that tip clearance cavitation is eliminated dramatically for rounded tip but more intensive for chamfered tip, which can be associated with the vortex structure in the clearance.

Anti-cavitation performance of a splitter-bladed inducer under different flow rates and different inlet pressures

The anti-cavitation performance of a high-speed centrifugal pump with a splitter-bladed inducer is investigated under different flow rates and different inlet pressures. Simulations and external characteristics experiments are carried out. Static pressure and the vapor volume fraction distributions on the inducer and the impeller of the pump under various operation conditions are obtained. The results show that the cavitation developments on the impeller and on the inducer with the flow rates are reverse, while the development of the inlet pressure on the inducer and the impeller is the same. Cavitation on the impeller increases with the increase of flow rates, and it extends to the near passages with rotating, while cavitation on the inducer is more complex than that on the impeller. Cavitation at the inlet of the inducer decreases with the increase of flow rates, while cavitation at the outlet of the inducer is opposite. The results also show that cavitation development on the impeller and on the inducer with the inlet pressure is the same. Cavitation both decreases with the increase of the inlet pressure at the same flow rate. Furthermore, asymmetric cavitation on the impeller and on the inducer is both observed. And the asymmetric degree of cavitation on the impeller is higher than that on the inducer.

Blade Parameterization and Aerodynamic Design Optimization for a 3D Transonic Compressor Rotor

The present paper describes an optimization methodology for aerodynamic design of turbomachinery combined with a rapid 3D blade and grid generator （RAPID3DGRID）, a N.S. solver, a blade parameterization method （BPM）, a gradient-based parameterization-analyzing method （GPAM）, a response surface method （RSM） with zooming algorithm and a simple gradient method. By the use of blade parameterization method a transonic com- pressor rotor can be expressed by a set of polynomials, and then it enables us to transform coordinate-expressed blade data to parameter-expressed and then to reduce the number of parameters. With changing any one of the parameters and by applying grid generator and N.S. solver, we can obtain several groups of samples. Here only ten parameters were considered to search an optimized compressor rotor. As a result of optimization, the adiabatic efficiency was increased by 1.73%.

Spatio-temporal modelling of the effect of selected environmental and land-use factors on acid grassland vegetation

Acid grasslands are threatened both by agricultural intensification with nutrient addition and increased livestock densities as well as by land abandonment.In order to understand and quantify the effect of selected environmental and land-use factors on the observed variation and changes in the vegetation of acid grasslands,large-scale spatial and temporal pin-point plant cover monitoring data are fitted in a structural equation model.The important sources of measurement and sampling uncertainties have been included using a hierarchical model structure.Furthermore,uncertainties associated with the measurement and sampling are separated from the process uncertainty,which is important when generating ecological predictions that may feed into local conservation management decisions.Generally,increasing atmospheric nitrogen deposition led to more grass-dominated acid grassland habitats at the expense of the cover of forbs.Sandy soils were relatively more acidic,and the effects of soil type on the vegetation include both direct effects of soil type and indirect effects mediated by the effect of soil type on soil pH.Both soil type and soil pH affected the vegetation of acid grasslands.Even though only a relatively small proportion of the temporal variation in cover was explained by the model,it would still be useful to quantify the uncertainties when using the model for generating local ecological predictions and adaptive management plans.