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14:00   Numerical Methods and Data Analysis 5 14:00 15 mins #574 NUMERICAL ANALYSIS OF THE HEAT TRANSFER OF A NANO-FLUID IMMERSED IN A POROUS MEDIUM INSIDE A CENTRAL TOWER-TYPE SOLAR RECEIVER AGUSTIN MORA, MARIA BELEM ARCE, MARTIN SALAZAR, OSCAR LOPEZ, ADOLFO RENE CORREA Abstract: The objective of this work is to analyze by a numerical procedure, the contribution of a nanofluid immersed in a porous media on the improvement of convection heat transfer of turbulent flow in a solar central receiver tube. The convection heat transfer for incompressible flows through homogeneous and isotropic matrix porous, is modeled by the well-known continuity, momentum and energy transport equations. The Forcheimer-Brinkman model is adopted to describe the flow in the porous region. The nanofluid is composed of molten salt (NaNO3 and KNO3) and nanoparticles of (Si2O2-Al2O3). The present study uses the COMSOL Multiphysics Software to analyzed these phenomena. The results suggest that the local Nu number improve when the porosity and Re number increase. Is presented the influence of dimensionless parameter geometric. The heat transfer coefficient is higher for the mixture of base fluid with a concentration of 1% of nanoparticles, however, for higher values of a concentration the heat transfer coefficient decrease. The numerical simulation is compared against the CFD Simulation with Ansys Fluent Sotfware 14:15 15 mins #359 Direct Measurement of Vorticity in Transitional to Turbulent Flow Markus J. Schmidt, Thomas Roesgen Abstract: The direct measurement of vorticity in flow is an ongoing challenge in the field of experimental fluid mechanics. A recently proposed method utilizes the anisotropy of phosphorescence emission to obtain insights into flow phenomena. The latest development of this experimental technique is presented for a canonical turbulent flow. 14:30 15 mins #227 3D LAGRANGIAN PARTICLE TRACKING WITH MULTI-PULSE SHAKE-THE-BOX IN TURBULENT BOUNDARY LAYER FLOWS AT HIGH REYNOLDS NUMBERS Matteo Novara, Daniel Schanz, Reinhard Geisler, Sebastian Gesemann, Christina Voss, Andreas Schroeder Abstract: The recent introduction of the Multi-Pulse Shake-The-Box technique (MP-STB [3]) extended the capabilities of the ShakeThe-Box (STB [4]) 3D Lagrangian particle tracking (LPT) algorithm in terms of applicable flow velocity. In particular, the MP-STB allows for 3D LPT investigations at velocities relevant for industrial and aerodynamic applications in relatively large volumes where the adoption of a time-resolved recording strategy would result in significant compromises in terms of spatial range or resolution (in order to limit the particle displacement between subsequent recordings). Multi-pulse sequences are obtained by synchronizing multiple illumination systems to generate bursts of laser pulses (typically four) where the time separation can be freely adjusted down to less than a microsecond (e.g. for supersonic applications). A 3D imaging system consisting of dual-frame cameras is adopted, where each frame is double-exposed to record the four pulses [2]; the MP-STB technique makes use of an iterative approach to overcome the limitations posed by the short observation time offered by the multi-pulse recording sequence, and allows for the reconstruction of individual four-pulse particle tracks in 3D [3]. The acquisition of long sequences of four-pulse recordings at low frequency (10−15Hz) enables the evaluation of flow statistics. In the present study, the MP-STB technique is employed for the investigation of turbulent boundary layer (TBL) flows at relatively high Reynolds numbers. A TBL at 15 m/s (Reθ ≈ 10; 000) is investigated in the SWG facility at DLR Göttingen; approximately 95; 000 individual tracks are reconstructed within the 80×120×10 mm3 domain for each four-pulse recording. Spatial gradients, as well as the instantaneous 3D pressure field, are evaluated by means of the FlowFit data assimilation algorithm [1] (fig.1-left). A TBL with adverse pressure gradient (APG) at 29 m/s (Reθ ≈ 30; 000) is investigated in the atmospheric wind tunnel of the University of Armed Forces in Munich; both planar PIV and MP-STB in a 80 × 90 × 7 mm3 domain are employed; the direct comparison of the results in terms of turbulent fluctuations (fig.1-right) highlights the higher spatial resolution of the LPT approach which, unlike PIV, does not suffer from the signal modulation caused by the finite size of the cross-correlation window. In the final presentation the MP-STB processing technique will be introduced together with the main parameters affecting its performances. Moreover, results regarding the TBL structure and flow statistics (e.g. TBL profiles, two-point correlations) will be presented. 14:45 15 mins #130 Impact of Lagrangian trajectory filtering on turbulent statistics in 4D-PTV measurements of Von Karman Flow Adam Cheminet, Valentina Valori, Tarek Chaabo, Yasar Ostovan, Paul Debue, Christophe Cuvier, Bérengère Dubrulle, Jean-Philippe Laval, Jean-Marc Foucaut, Cécile Wiertel, Vincent Padilla, François Daviaud Abstract: Thanks to 4D-PTV measurement techniques [Schanz et al 2016], it is now possible to capture a spatially dense time-resolved Lagrangian flow field in turbulent flows. Moreover, the tracers density accessible allows for the interpolation of the Lagrangian flow field to obtain the Eulerian flow field. However, measurement noise still arises in the Lagrangian trajectory positions thus polluting the higher-order turbulent statistics based on both temporal and spatial small scale quantities. To mitigate this, different low-pass filters are used in the literature [Gesemann et al. 2016} & [Lawson et al. 2018]. The aim of this talk is to understand their impact on trajectory geometrical properties and turbulent statistics. To do so, I use results of a well resolved Direct Numerical Simulation of a forced Homogeneous Isotropic Turbulent flow at $R_{\lambda} = 62$. A pseudo-spectral scheme on a $768^3$ periodic cubic box of length $2\pi$ was used to solve the Navier-Stokes equations. More than $2.10^6$ tracers are introduced and convected in the flow by means of a classical $4^{th}$ order Runge-Kutta scheme (see Figure \ref{fig1} left). Noise is then added on the tracers positions. The noise level was calibrated from 4D-PTV measurements of a Von Karman flow. This allows for an optimization of the filtering frequency cutoff which is then re-applied in the measurements. Filtering techniques such as penalized B-spline smoothing (TrackFit) and wavelet smoothing are compared, and their impact on several Lagrangian and Eulerian turbulent statistics are investigated. The study focuses primarily on the geometrical properties of the Lagrangian trajectories (curvature and torsion) and on a spectral analysis of the Lagrangian and Eulerian flow field (see Figure \ref{fig1} middle and right). This will give us a better understanding of the temporal and spatial resolution of the measurement. 15:00 15 mins #171 Directional Sensitivity & Performance Comparison of Dantec Dynamics Triple Sensor Hotwire Probes F. Gökhan Ergin, Carsten Pedersen Abstract: Triple-sensor hotwire probes are important point measurement sensors during turbulent flow investigations. Coupled with high-performance constant-temperature anemometers they can provide high-bandwidth information on turbulence quantities such as normal stress, Reynolds stress, turbulent kinetic energy, production terms and dissipation terms. An accurate measurement depends on the correct conversion of the measured voltage to instantaneous velocity. Variations in prong / sensor geometry, directional calibration model (f. ex. the effective cooling velocity), type of sensor (wire or fiber-film), and temperature variations affect the conversion. Furthermore, the measurement system is often calibrated within a limited velocity range and the sensor often has a limited acceptance angle for the incoming flow vector. It has been reported that the accuracy decreases with increasing incidence angle. With the development of a new automated directional calibration tool, we aim to report and compare the directional sensitivity and performance of Dantec Dynamics-manufactured triple sensor probes in a subsonic velocity range; from 5m/s to 50m/s, and within an incidence angle of up to 40deg with respect to the probe axis. A total of five probes are included in the calibration campaign in air. Four of these are for parallel flows: 55P91, 55R91 (wire and fiber sensors on legendary claw-type prong geometry), 55P95 (Fig. 1a), 55R95 (wire and fiber sensors on new straight prong geometry); and one is for cross-flows: 55R97 (fiber sensors on special cross-flow prong geometry). Each probe has been subject to multiple directional calibrations; at different constant velocity and yaw angle settings in order to establish the directional dependence to calibration velocity and incidence angle. The aim is to calculate the true error (Fig. 1b) from the calibration data for a wide range of velocity and incidence angles, and this will allow different comparisons among the five sensors: (i) sensor type: wire vs. fiber sensors (ii) prong shape: claw vs. straight prongs and (iii) placement of sensor: parallel vs. cross-flow. The results form a reference database for researchers who plan to undertake triple-sensor hotwire anemometry experiments, and provide the expected measurement error for a given flow speed. 15:15 15 mins #632 Turbulence measurements in an open channel with a new ADV profiler Marie Burckbuchler, Stéphane Fischer Abstract: Turbulence measurements in an open channel with a new ADV profiler 15:30 15 mins #398 Deep Learning of Turbulent Velocity Signals Alessandro Corbetta, Roberto Benzi, Vlado Menkovski, Federico Toschi Abstract: See uploaded pdf.