SUMMARYHybrid three-dimensional algorithms for the numerical integration of the incompressible Navier-Stokes equations are analyzed with respect to hydrodynamic stability in both linear and nonlinear ÿelds. The computational schemes are mixed-spectral and ÿnite di erences-and are applied to the case of the channel ow driven by constant pressure gradient; time marching is handled with the fractional step method. Di erent formulations-fully explicit convective term, partially and fully implicit viscous term combined with uniform, stretched, staggered and non-staggered meshes, x-velocity splitted and nonsplitted in average and perturbation component -are analyzed by monitoring the evolution in time of both small and ÿnite amplitude perturbations of the mean ow. The results in the linear ÿeld are compared with correspondent solutions of the Orr-Sommerfeld equation; in the nonlinear ÿeld, the comparison is made with results obtained by other authors.
This paper addresses the methodology used to design the layout of the tip cooling nozzles of a high pressure rotor blade turbine. The methodology used is through a complete CAE approach, by means of a parametric CFD model which is run several times for the exploration of several designs by an optimizer. Hence the design is carried out automatically by parallel computations, with the optimization algorithms taking the decisions rather than the design engineer. The engineer instead takes decision regarding the physical settings of the CFD model to employ, the number and the extension of the geometrical parameters of the blade tip holes and the optimization algorithms to be employed. From CFD validation the final design of the tip cooling geometry found by the optimizer has proved to be better than the base design, which used mean values of all input parameters, and than the design proposed by an experienced heat transfer AVIO engineer, who used standard best practice methods. Furthermore the large number of experiences gained by the simulations run by the optimizer allowed the designer to find laws, functions and correlation between input parameters and performance output, with a further and deeper insight on this specific design problem.
Abstract. Image-based monitoring has emerged as a prevalent technique for sensing mountain environments. Monoscopic time-lapse cameras, which rely on digital image correlation to quantify glacier motion, have limitations due to the need for a Digital Elevation Model for deriving 3D flow velocity fields. Multi-camera systems overcome this limitation, as they allow for a 3D reconstruction of the scene. This paper presents a replicable low-cost stereoscopic system designed for 4D glacier monitoring. The system consists of independent and autonomous units, built from off-the-shelves components, such as a DSLR camera, an Arduino microcontroller, and a Raspberry Pi Zero, reducing costs compared to pre-built time-lapse cameras. The units are energetically self-sufficient and resistant to harsh alpine conditions. The system was successfully tested for more than a year to monitor the northwest terminus of the Belvedere Glacier (Italian Alps). Daily stereo-pairs acquired were processed with Structure-from-Motion to derive 3D point clouds of the glacier terminus and estimate glacier retreat and ice volume loss. By combining the information about ice volume loss with ablation estimates and ice flow velocity information, e.g., derived from monoscopic-camera time series, a multi-camera system enables a comprehensive understanding of sub-seasonal glacier dynamics.
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