Thermo-fluid-dynamics of impinging swirling jets

The superimposition of a tangential motion on a conventional round jet has been demonstrated to significantly affect the large-scale topology of the flow. Swirling flows are widely employed, in the impinging configuration, in several industrial processes which involve both non-reacting and reacting applications. In the present dissertation, the simultaneously acquired thermal and three-dimensional velocity fields of an impinging hot jet emerging from a custom swirl generator in a cold ambient are presented. The velocity and temperature fields are experimentally measured using time-resolved Tomographic PIV and high-speed Infrared thermography in a combined system. A detailed description of a custom swirl generator is provided, and the time-averaged velocity profiles of a free swirling flow are discussed in order to estimate the swirl number. The instantaneous three-dimensional dynamics in proximity of the nozzle is discussed and the main features of a free swirling jet are investigated through the application of Proper Orthogonal Decomposition technique. The time-dependent features of velocity and temperature fields of an impinging swirling jet are investigated through the description of the time sequences of the temperature fluctuations and the synchronised instantaneous vortical structures. Taking advantage of the simultaneous acquisition and of the knowledge of the relative positioning of thermal and velocity frames, two different correlation techniques are applied, and their outcomes discussed

Search for heavy resonances decaying into a vector boson and a Higgs boson in final states with charged leptons, neutrinos, and b quarks

Peer reviewe

Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at √s=8 TeV with the ATLAS detector

An analysis is presented of events containing jets including at least one b-tagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb−1 of pp collisions at √s=8 TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced four-top-quark production, pair production of chiral b′-quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral b′-quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models

Search for a new resonance decaying to a W or Z boson and a Higgs boson in the ll/lv/vv + bb final states with the ATLAS detector

A search for a new resonance decaying to a W or Z boson and a Higgs boson in the ll/lv/vv + bb final states is performed using 20.3 fb −1 of pp collision data recorded at √ s = 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the W H / Z H invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets

Search for single production of a heavy vector-like T quark decaying to a Higgs boson and a top quark with a lepton and jets in the final state

Peer reviewe

Search for pair and single production of new heavy quarks that decay to a Z boson and a third-generation quark in pp collisions at root s=8 TeV with the ATLAS detector

Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited

Towards enabling time-resolved measurements of turbulent convective heat transfer maps with IR thermography and a heated thin foil

The temperature of a heated foil, exposed to a turbulent flow, changes continuously in time due to the fluctuation of the convective heat transfer coefficient. Measuring with enough temporal resolution the foil temperature map and solving the unsteady energy balance of the foil can allow restoring the instantaneous value of the convective heat transfer coefficient. Nevertheless, the high characteristic frequencies of turbulent flows (especially in air) result in very small temperature fluctuations, which are typically hard to measure with an infrared camera. This work presents a novel filtering approach based on Proper Orthogonal Decomposition which allows to dramatically reduce the measurement random noise, thus enabling the detection of small temperature fluctuations and, as a consequence, to improve the estimate of instantaneous distributions of the convective heat transfer coefficient. The proposed methodology is tested on synthetic jets impinging on a foil, actuated with a loudspeaker at various actuation frequencies. The measurement capabilities of the present technique are assessed through comparison with measurements obtained from raw data and phase averaged measurements.The authors wish to thank Mr. G. Sicardi for contributing the realization of the experimental setup. Marco Raiola, Carlo Salvatore Greco, Stefano Discetti, and Andrea Ianiro have been partially supported by grant DPI2016-79401-R of the Spanish Ministry of Economy and Competitiveness

PIV measurements of sloshing flow in a rectangular tank induced by a sinusoidal inflow

An experimental study of the flow field in a rectangular tank filled with water and forced by a speaker has been carried out by using particle image velocimetry (PIV) technique. The employed experimental apparatus is sketched in figure 1. The speaker oscillation creates a disturbed field which determines a periodically waving of the free surface on the upper part of the tank. Phase-locked measurements have been performed sampling the investigated phenomenon each 12° obtaining 30 phases. Several depths d (8cm, 6cm and 4cm), working frequencies f (1.825 Hz, 2.8 Hz, 3.4 Hz) and wave amplitudes have been tested. In particular, for a fixed depth and working frequency, the wave amplitude equal or more than 10% compared to the maximum depth of the tank is obtained varying the supply voltage V. In figures are represented the PIV measurements in the following conditions: f = 2.8Hz, V = 800mV, d = 8cm of water. The phases φ=264° - φ=336° are characterized by the formation of a vortex structure such like a synthetic jet starting from the speaker outflow. This expulsion phase causes free surface oscillation with the formation of a non-sinusoidal free surface. The non-regular behavior of the free surface is caused by the contrast between the fluid going backward from the previous phases and the new injected fluid in forward direction. During the entire expulsion phase, the vortex structure is generated and convects downstream until it reaches a distance of about x=3.5w where the vortex dissolves. Simultaneously, the free surface has a sinusoidal trend as expected because of the periodical forcing. The vortex structure gets smaller while it proceeds along the tank floor because of two main reasons: diffusion of kinetic energy and interaction with the descending free surface. This interaction stops the downstream evolution of the vortex structure which collapses under the water mass moving downward. After the vortex has dissolved, the suction phase starts and causes the downward movement of the free surface at x 8w