The von Kármán street behind a circular cylinder: flow control through synthetic jet placed at the rear stagnation point

Abstrac

Influence of Machine Learning-based active flow control on the turbulent statistics of the flow over a circular cylinder

The aim of the present paper is to investigate the capabilities of Machine Learning (ML) to reduce the aerodynamic drag of a circular cylinder in cross flow, by actively controlling its wake with a synthetic jet

Effects of the stroke length and nozzle-to-plate distance on synthetic jet impingement heat transfer

This study focuses on the combined e ect of the nozzle-to-plate distance andof the stroke length on the cooling performances of impinging synthetic jets.Infrared thermography is used as temperature transducer in conjunction withthe heated thin foil heat transfer sensor to measure time- and phase-averagedconvective heat transfer...The authors wish to thank Mr. G. Sicardi for contributing the realization of the experimental setup. Carlo Salvatore Greco, Andrea Ianiro and Gennaro Cardone have been partially supported by Grant DPI2016-79401-R funded by the Spanish State Research Agency (SRA) and European Regional Development Fund (ERDF).Publicad

Experimental and numerical investigation of Rayleigh-Bénard convection

This thesis presents a combined experimental and numerical investigation of Rayleigh-Bénard convection without and with a background rotation. Rayleigh-Bénard convection, the buoyancy-driven flow induced by temperature gradients, is relevant to a wide variety of both natural phenomena (of which motions in the atmosphere and in the oceans are only the most straightforward examples) and technological applications (like melting of pure metals or flows in turbomachinery). Despite the numerous works on the subject, different aspects of this phenomenon are still unclear or deserving of further investigation. Due to its inherently turbulent nature, the analysis of the flow field makes three-dimensional measurements mandatory to get an unambiguous picture of the underlying rich dynamics. Three-dimensional whole-field velocity measurements are very rare in literature and anyway very recent; in consideration of this, the present work focuses on the application of a state-of-art optical investigation technique, namely the tomographic particle image velocimetry, to the study of such a phenomenon. An experimental apparatus suitable for this purpose is designed and developed. Some technical issues inherent to the optical measurements are extensively addressed; in particular, an innovative camera model is formulated to precisely account for the optical distortions caused by the cylinder sidewall, through which the measurement volume is imaged. In addition to experimental measurements, direct numerical simulations are performed, in which the non-adiabaticity of the lateral wall is accounted for by simulating the presence of the wall itself with its physical properties. The comparison between the experimental and numerical results offers the chance of validating the physical models and computational approaches used in the numerical environment and, at the same time, pointing out unavoidable non-idealities of the experimental setup that make the phenomenon to differ from the canonical problem addressed not only numerically, but also theoretically

Refraction correction for 3D optical measurements inside cylinders

The present work proposes a calibration camera model to precisely express the projection from 3D world to 2D image coordinates for measurements inside transparent cylinders. Snell's law is used to model the refraction of the optical rays at the external and internal surfaces of the cylindrical wall and a standard pinhole camera is used to describe the lens behavior. Making use of the perspective and refraction laws, the mapping function consists of a relatively small number of parameters and all of these have a clear geometrical or physical meaning. A calibration procedure for the proposed camera model is also outlined. Finally, the innovative model is comparatively assessed against the classical pinhole camera model and different polynomial-based models by using experimental data from an investigation of Rayleigh-Bénard convection. Although the model is tested for tomographic particle image velocimetry measurements in flows occurring inside cylinders, it can be used also in a variety of other imaging applications, as well

PAIRS: a free software application for robust and accurate digital particle image velocimetry

This contribution presents PAIRS (PArticle Image Reconstruction Software), a free software application designed to perform digital particle image velocimetry (PIV). PIV has become a standard tool in the fluid dynamics community for the analysis of turbulent flows. PAIRS, developed since 2000, includes several modules that allow to process also stereoscopic and tomographic PIV measurements. The current free release aims mainly at introducing the user to the module that handles the processing of double-frame or time-resolved 2D planar PIV images. PAIRS employs an iterative multi-grid approach based on image deformation. The user is allowed to select different types of process parameters in such a way to find the best compromise between accuracy and computational speed. Beyond this flexibility, preset strategies are also available for image analysis and designed for specific tasks like fast visualization of results in preliminary measurements or high accuracy in the final phase of investigation. PAIRS has been validated both numerically and experimentally and its accuracy and robustness have been proved during the 2nd and 3rd International PIV Challenges. PAIRS is based on a C library and relies on a user interface in Python to facilitate its usage and promote the diffusion

Machine Learning-based active control and PIV measurements of a circular cylinder wake

The aim of the present paper is to investigate the fluid dynamic evolution of a circular cylinder wake controlled by a synthetic jet (SJ) to reduce the related aerodynamic drag via Particle Image Velocimetry (PIV