Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H5: Jets II: Impinging |
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Chair: Tommaso Astarita, Universita degli Studi di Napoli Federico II Room: 104 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H5.00001: On the effect of fractal geometric parameters on the heat transfer features of circular impinging jets Tommaso Astarita, Giusy Castrillo, Gioacchino Cafiero Several solutions have been proposed over the last decades to increase the heat transfer rate of impinging jets. In all cases the heat transfer enhancement is obtained by exciting/altering the structure and organization of large scale turbulence, which is widely recognized to be the main agent in heat and mass transfer mechanism of impinging jets. Tampering with the large coherent turbulent structures is the key to achieve a significant heat transfer enhancement. In a recent work we demonstrated the effectiveness of fractal turbulence in this sense. Its effect is such that the heat transfer rate increases up to 63{\%} in the stagnation region with respect to the well-known circular jet under the same power input. However, a systematic analysis of the effect of the singular geometric parameters of the fractal grid (such thickness ratio and length ratio) onto the spatial distribution of the Nusselt number has not been proposed yet. In this work we propose the analysis of the heat transfer enhancement produced by a class of turbulence promoters located in correspondence of the nozzle exit section of a circular jet. The upward shift of the turbulence intensity profile due to the blockage effect induced by the growing shear layer is discussed in terms of heat transfer enhancement. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H5.00002: The effect of confinement on the development of an axisymmetric wall-jet in confined jet impingement Tianqi Guo, Matthew J. Rau, Pavlos P. Vlachos, Suresh V. Garimella An experimental study of a confined developing axisymmetric wall-jet is reported. The wall-jet is formed downstream of a circular, confined, impinging jet of water. Stereo particle image velocimetry (SPIV) experiments are conducted at three different nozzle-to-plate spacings (2, 4 and 8 jet diameters) and across Reynolds numbers ranging from 1000 to 9000. Special attention is paid to the development of the wall-jet. The growth rate of the boundary layer thickness, decay rate of the local maximum velocity, and velocity profile scaling for both the inner- and outer-layer are investigated. Measurements are obtained with a maximum spatial resolution of 25 $\mu $m and a temporal resolution of 750 Hz. Both ensemble-averaged and instantaneous time-resolved three-component, two-dimensional (3C-2D) flow fields are obtained and analyzed. The upper confinement plate is found to limit the supply of ambient liquid for both the impinging-jet and wall-jet entrainment, and thus significantly influences the wall-jet development; the growth and decay rate of the wall-jet are shown to be greatest at the smallest confinement height. The influence of these confining effects on recirculation patterns and coherent-structure evolution is also reported. These flow field measurements and analyses will serve to inform a variety of practical applications that use impinging jets. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H5.00003: Large Eddy Simulation of a cooling impinging jet to a turbulent crossflow Michail Georgiou, Miltiadis Papalexandris In this talk we report on Large Eddy Simulations of a cooling impinging jet to a turbulent channel flow. The impinging jet enters the turbulent stream in an oblique direction. This type of flow is relevant to the so-called ``Pressurized Thermal Shock'' phenomenon that can occur in pressurized water reactors. First we elaborate on issues related to the set-up of the simulations of the flow of interest such as, imposition of turbulent inflows, choice of subgrid-scale model and others. Also, the issue of the commutator error due to the anisotropy of the spatial cut-off filter induced by non-uniform grids is being discussed. In the second part of the talk we present results of our simulations. In particular, we focus on the high-shear and recirculation zones that are developed and on the characteristics of the temperature field. The budget for the mean kinetic energy of the resolved-scale turbulent velocity fluctuations is also discussed and analyzed. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H5.00004: Drop Characteristics of non-Newtonian Impinging Jets at High Generalized Bird-Carreau Jet Reynolds Numbers Paul E. Sojka, Neil S Rodrigues The current study investigates the drop characteristics of three Carboxymethylcellulose (CMC) sprays produced by the impingement of two liquid jets. The three water-based solutions used in this work (0.5 wt.-{\%} CMC-7MF, 0.8 wt.-{\%} CMC-7MF, and 1.4 wt.-{\%} CMC-7MF) exhibited strong shear-thinning, non-Newtonian behavior - characterized by the Bird-Carreau rheological model. A generalized Bird-Carreau jet Reynolds number was used as the primary parameter to characterize the drop size and the drop velocity, which were measured using Phase Doppler Anemometry (PDA). PDA optical configuration enabled a drop size measurement range of approximately 2.3 to 116.2 $\mu $m. 50,000 drops were measured at each test condition to ensure statistical significance. The arithmetic mean diameter ($D_{\mathrm{10}})$, Sauter mean diameter ($D_{\mathrm{32}})$, and mass median diameter (\textit{MMD}) were used as representative diameters to characterize drop size. The mean axial drop velocity $U_{\mathrm{z-mean\thinspace }}$along with its root-mean square $U_{\mathrm{z-rms}}$ were used to characterize drop velocity. Incredibly, measurements for all three CMC liquids and reference DI water sprays seemed to follow a single curve for $D_{\mathrm{32\thinspace }}$and \textit{MMD} drop diameters in the high generalized Bird-Carreau jet Reynolds number range considered in this work (9.21E$+$03 \textless \textit{Re}j,gen-BC \textless 2.81E$+$04). [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H5.00005: Proper Orthogonal Decomposition Analysis of Turbulent Jet Impingement on Rib-roughened Surface Prasanth Anand Kumar Lam, Arul Prakash Karaiyan A Proper Orthogonal Decomposition (POD) analysis on turbulent flow dynamics of confined slot jet impinging on rib-roughened surface is numerically investigated. The data for POD analysis has been obtained by solving mass, momentum and energy equations in Cartesian framework using Streamline Upwind/Petrov-Galerkin Finite element method. Further, turbulent kinetic energy (k) and its dissipation rate ($\varepsilon )$ are modeled using standard k-$\varepsilon $ turbulence model with standard wall functions. POD is applied to computational data for a wide range of Reynolds number (Re) $=$ 5000 - 30000 and non-dimensional channel height (H/L) $=$ 0.5 - 4.0 to reveal large scale vortical structures in the flow field. The simulated results demonstrate a better understanding on effect of turbulence and its influence on individual vortical structures for enhancement of heat transfer. The enhancement of heat transfer in stagnation region due to combined effect of oscillation in impingement position caused by large vortical structures and strong acceleration of fluid during impingement is quantified. Furthermore, non-dimensional correlations have been derived for pressure drop and Surface averaged Nusselt number. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H5.00006: Experimental Analysis of Impinging Single and Twin Circular Synthetic Jets Gennaro Cardone, Carlo Salvatore Greco, Giusy Castrillo, Tommaso Astarita The behavior of impinging single synthetic jet and twin circular synthetic jets in phase opposition is experimentally investigated by using Particle Image Velocimetry (PIV) at Reynolds and Strouhal numbers equal to 5100 and 0.024, respectively. Different inter-axes distances for the twin configuration and several nozzle-to-plate distances have been investigated. The time-averaged behavior of the all velocity components are reported and discussed. Their distributions, near the impinging plate, are described for both the synthetic jet configurations and for all the nozzle-to-plate distances. At low nozzle-to-plate distance (H/D \textless 4) the axial velocity profile near the impinging plate shows a double peak with a minimum on the jet axis. Instead, at high nozzle-to-plate distance (H/D \textgreater 6), the axial velocity profile is bell-shaped. This is ascribed to the adverse pressure gradient strength and the potential core-like region extension. Indeed, the turbulence distribution shows a region characterized by low values, resembling the potential core region of continuous jets. Comparing the two synthetic jet configurations, a higher centerline velocity and a smaller jet width have been found for the twin case. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H5.00007: Directional transport of impinging capillary jet on wettability engineered surfaces Aritra Ghosh, Souvick Chatterjee, Pallab Sinha Mahapatra, Ranjan Ganguly, Constantine Megaridis Impingement of capillary jet on a surface is important for applications like heat transfer, or for liquid manipulation in bio-microfluidic devices. Using wettability engineered surfaces, we demonstrate pump-less and directional transport of capillary jet on a flat surface. Spatial contrast of surface energy and a wedge-shape geometry of the wettability confined track on the substrate facilitate formation of instantaneous spherical bulges upon jet impingement; these bulges are further transported along the superhydrophilic tracks due to Laplace pressure gradient. Critical condition warranted for formation of liquid bulge along the varying width of the superhydrophilic track is calculated analytically and verified experimentally. The work throws light on novel fluid phenomena of unidirectional jet impingement on wettability confined surfaces and provides a platform for innovative liquid manipulation technique for further application. By varying the geometry and wettability contrast on the surface, one can achieve volume flow rates of $\sim$ O(100 $\mu $L/sec) and directionally guided transport of the jet liquid, pumplessly at speeds of $\sim$ O(10cm/sec). [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H5.00008: Two-phase liquid-liquid flows generated by impinging liquid jets Dimitrios Tsaoulidis, Qi Li, Panagiota Angeli Two-phase flows in intensified small-scale systems find increasing applications in (bio)chemical analysis and synthesis, fuel cells, polymerisation, and separation processes (solvent extraction). Current nuclear spent fuel reprocessing separation technologies have been developed many decades ago and have not taken account recent advances on process intensification which can drive down plant size and economics. In this work, intensified impinging jets will be developed to create dispersions by bringing the two liquid phases into contact through opposing small channels. A systematic set of experiments has been undertaken, to investigate the hydrodynamic characteristics, to develop predictive models, and enable comparisons with other contactors. Drop size distribution and mixing intensity will be investigated for liquid-liquid mixtures as a function of various parameters using high speed imaging and conductivity probes. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H5.00009: Dynamics of Bouncing-vs.-Merging Responses in Jet Collision Minglei Li, Abhishek Saha, Delin L. Zhu, Chao Sun, Chung K. Law Collision of two fluid masses is a common natural and industrial phenomenon. Many kinds of noncoalescence phenomena of collisional fluid masses, such as droplet {\&} droplet, droplet {\&} liquid film, have been studied, and the dynamics of the gas layer between the colliding liquid surfaces was found to play a crucial role. However, many fluid mass collision processes are nonstationary, making it difficult to study this air layer dynamics in detail. Jet bouncing can be in a stationary state with a geometrically simple gas layer, providing an ideal system to investigate the dynamics of the air film between the colliding interfaces. In this work, we observe an entire suite of possible jet collision outcomes of (soft) merging, bouncing and (hard) merging with increasing impact inertia. These transitions between these different regimes are characterized through scaling analysis by considering the competing effects of impact inertia, surface tension and viscous thinning of the interfacial air-gap leading to activate the van der Waals force to effect merging. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H5.00010: Characterization of an impinging jet into porous media Cong Wang, Salwan Alhani, Morteza Gharib In this work, characteristic behavior of a liquid jet into porous hydrophobic / hydrophilic particle media is investigated. In porous media, the capillary effect becomes significant, especially when the jet Reynolds Number is low. To analyze the cavity creation phenomena, the effect of jet's diameter, speed and acceleration as well as particles' size are carefully studied. Such knowledge of fluid behavior will provide guidance for medicine injection process. [Preview Abstract] |
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