Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q40: Jets: Impinging |
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Chair: Ahmed Naguib, Michigan State University Room: 6b |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q40.00001: Instability of micro jet impinging onto a pool Maoying Zhou, Bo Li, Jun Zou A micro liquid jet discharged into a downstream pool exhibits different instabilities at certain heights. For some nozzle heights, the water jet shows a steady wavy profile while for some other heights, the water jet oscillates around the nozzle axis at given frequency. A series of experiments are conducted to identify the regimes of jet state with respect to nozzle heights, Reynolds numbers and Weber numbers. For the oscillation regime, oscillating characteristics of the jet are investigated in terms of different liquid properties. A simple model is developed to describe and explain the phenomena. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q40.00002: Impinging Tone Identification of Under-expanded Impinging Jets by Large Eddy Simulation. Minghang Li, Shahram Karami, Richard Sandberg, Julio Soria, Andrew Ooi The acoustic and hydrodynamic feedback mechanism to predict discrete tones was first proposed by Powell ($J. Acoust. Soc. Am., vol. 83 (2),1988, pp. 515–533$). The mechanism consists of the receptivity of the shear layer at the nozzle lip as well as the acoustic contribution from the downstream sources. The first part of the mechanism has been commonly accepted, while the locations of the downstream sources are still under debate. To further understand the mechanism, this work aims to identify the locations of the impinging tones by a novel methodology utilising the cross correlation and a ray tracing method. Each potential source is found with a certain ray tracing back to the nozzle exit. Joint probability density functions are then used to identify the impinging tones. Since the mean temperature out of the main jet plume and the wall jet varies little, another simplified method that does not consider refraction effects is proposed. Data from a recent Large Eddy Simulation is used to validate the current methods. The identified source locations are quantitatively determined and consistent with the second maximum of the root mean square of the pressure on the wall. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q40.00003: Volumetric flow measurements of impinging jet on circular cylinder using STB Mirae Kim, Eunseop Yeom, Matteo Novara, Daniel Schanz, Reinhard Geisler, Janos Agocs, Andreas Schroeder, Kyung Chun Kim Jet impingement is a direct and efficient way to transfer heat and mass in various applications. In practical applications, most jet flows are impinging on curved surfaces, however, less attention has been given to circular jet impingements on convexly curved surfaces. Interactions of three-dimensional flow structures of a round jet impinging obliquely on a convex circular cylinder was studied using high-resolution volumetric flow measurements by dense 4D Lagrangian particle tracking using the Shake-The-Box method and data assimilations by FlowFit. The Lagrangian tracks and assimilated 3D3C flow field confirmed that the 3D curved wall jet spreads widely in spanwise direction after impingement then merged to the jet centerline downstream. The Coanda effect on 3D wall jet flow along the cylinder wall is vividly shown with the delay of separation up to 180 degrees. The strong shear layer near the impingement area produces large-scale vortices with high vorticity. These structures distribute throughout the surface and break down to multiple vortex structures with lower vorticity. Small-scale negative vortex structures are moved away from the wall jet and are sustained longer at the edge of the wall jet. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q40.00004: Effect of Bi-Modal Exciation of an Impinging Jet on Cooling of a Heated Impingement Surface Basil Abdelmegied, Ahmed Naguib Impinging jets have many engineering applications, such as heating, cooling, and drying. This work is part of a larger study focused on using different active flow control strategies for enhancement of the cooling effectiveness of impinging jet arrays. Here, we examine the influence of bi-modal acoustic forcing on the Nusselt number (\textit{Nu}) distribution resulting from an axisymmetric jet impinging on a heated flat surface. The forcing scheme utilizes two concurrent sinusoidal waves, at the jet's shear layer fundamental and sub-harmonic frequencies, to take advantage of the jet's sub-harmonic resonance. The~\textit{Nu}~distribution is measured using temperature-sensitive paint applied to a heated stretched stainless steel foil. Data are obtained for jet ~Reynolds number based on jet diameter of 4000, jet-exit-to-plate distance range of 2 to 4 diameters, and different forcing parameters. The results illustrate the influence of the control on the jet's cooling effectiveness and the dependence of this influence on the flow and the forcing parameters. Flow visualization is used to examine associated changes in the flow structure. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q40.00005: Transient model for characterizing the erosion mixing of stratified layer and turbulent impinging jet with both density and pressure gradients Wooyoung Lee, Simon Song, Young Su Na The erosion mixing phenomenon of a stratified hydrogen layer caused by a turbulent impinging jet determines the distribution and mixing characteristics of hydrogen gas in a containment building of nuclear power plants (NPPs) during a severe accident. The mixed hydrogen gas can explode when in contact with ignition sources. To prevent the risk of the hydrogen explosion, it is necessary to quantitatively analyze the transient erosion mixing process over a long period of time. We experimentally and theoretically investigate the long-term erosion mixing process by the interaction between a stratified layer and a turbulent impinging jet. As a result, we propose a transient model for predicting the interface displacement of the stratified layer and the mean axial velocity and half width of the jet. We found that the prediction accuracy strongly depends on the consideration of the density and pressure gradient of the stratified layer and the jet. The results show that the predictions are in good agreement with the experimental data. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q40.00006: Mixing of cold jets in cross flow into exhaust gases for cryogenic CO2 capture Robert Dibble, Francisco Hernandez Perez, Hong Im For over a century, the widely accepted route for removal of CO2 from a gas stream has been absorption by amines. The liquid amine is sprayed downward in a vertical tower in which the exhaust stream is coming upward. In this counter-current flow, the falling amine droplets absorb CO2. The CO2-rich droplets collected at the bottom of the tower are pumped to a boiler, after which pure CO2 is extracted by heat. A new emerging process is the cryogenic carbon capture (CCC) process, in which the exhaust stream is cooled to near -90C and a cold fluid, such as methane, at -150C, is injected into the exhaust stream. The cold methane mixing with the exhaust gases forms CO2 in the "dry ice snow" form as the temperature rapidly descends below the sublimation point of CO2 (about -100C). The CO2 snow is easily collected. The methane can be injected into the exhaust duct, from the wall, creating a classic "jet in cross flow" configuration. We find that more rapid mixing occurs if the methane is injected at 45 degree angle to duct wall, in both the flow direction and orthogonal to flow direction. The present study aims to explore the effect of the two angles on the mixing effectiveness. Simulations using LES show most rapid mixing is achieved by the 45/45 degrees configuration. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q40.00007: Liquid Jet Impingement Cooling on Superheated Superhydrophobic Surfaces Jacob Butterfield, Brian Iverson, Daniel Maynes, Julie Crockett Superhydrophobic (SH) surfaces form air cavities between nano- or micro-structures, resulting in self-cleaning properties. This is a potential solution for fouling in cooling applications, but the air cavities also impede heat transfer. Here, water jet impingement heat transfer on surfaces of varying microstructures and wettability is experimentally explored. Silicon wafers with micro-scale posts etched in a square pattern and Teflon-coated are heated to 280C using an epoxied electrical resistance heater. An axisymmetric water jet then impinged normal to and rapidly cooled the surface. High-speed optical and thermal cameras recorded boiling behavior on the surface as well as the transient temperature field beneath the wafer. Spatial and temporal surface boiling was correlated to the temperature changes, and overall local heat transfer coefficients were calculated. The heat diffusion equation was solved and modified to predictively model the heat flux as a function of surface superheat and wettability, jet Reynolds number, and radial distance from the jet. Cavities in the SH surface microstructure allow vapor to escape laterally across the wafer rather than rise directly to the water surface as bubbles, leading to significant heat transfer reduction and delayed cooling times. [Preview Abstract] |
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