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 A14: Industrial Applications I |
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Chair: Ruo-Qian Wang, MIT Room: 202 |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A14.00001: A Respiratory Airway-Inspired Low-Pressure, Self-Regulating Valve for Drip Irrigation Ruo-Qian Wang, Amos G. Winter One of the most significant barriers to achieving large-scale dissemination of drip irrigation is the cost of the pump and power system. An effective means of reducing power consumption is by reducing pumping pressure. The principle source of pressure drop in a drip system is the high flow resistance in the self-regulating flow resistors installed at the outlets of the pips, which evenly distribute water over a field. Traditional architectures require a minimum pressure of $\sim$1 bar to maintain a constant flow rate; our aim is to reduce this pressure by 90\% and correspondingly lower pumping power to facilitate the creation of low-cost, off-grid drip irrigation systems. This study presents a new Starling resistor architecture that enables the adjustment of flow rate with a fixed minimum pressure demand of $\sim$0.1 bar. A Starling resistor is a flexible tube subjected to a transmural pressure, which collapses the tube to restrict flow. Our design uses a single pressure source to drive flow through the flexible tube and apply a transmural pressure. Flow into the flexible tube is restricted with a needle valve, to increase the transmural pressure. Using this device, a series of experiments were conducted with different flexible tube diameters, lengths and wall thickness. We found that the resistance of the needle valve changes flow rate but not the minimum transmural pressure required to collapse the tube. A lumped-parameter model was developed to capture the relationships between valve openings, pressure, and flow rates. [Preview Abstract] |
Sunday, November 22, 2015 8:13AM - 8:26AM |
A14.00002: A Phase-Field Method for Simulating Fluid-Structure Interactions in Multi-Phase Flow Xiaoning Zheng, George Karniadakis We investigate two-phase flow instabilities by numerical simulations of fluid structure interactions in two-phase flow. The first case is a flexible pipe conveying two fluids, which exhibits self-sustained oscillations at high Reynolds number and tension related parameter. Well-defined two-phase flow patterns, i.e., slug flow and bubbly flow, are observed. The second case is external two-phase cross flow past a circular cylinder, which induces a Kelvin-Helmholtz instability due to density stratification. We solve the Navier-Stokes equation coupled with the Cahn-Hilliard equation and the structure equation in an arbitrary Lagrangian Eulerian (ALE) framework. For the fluid solver, a spectral/hp element method is employed for spatial discretization and backward differentiation for time discretization. For the structure solver, a Galerkin method is used in Lagrangian coordinates for spatial discretization and the Newmark-$\beta$ scheme for time discretization. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A14.00003: Shape optimisation of an underwater Bernoulli gripper Tim Flint, Mathieu Sellier In this work, we are interested in maximising the suction produced by an underwater Bernoulli gripper. Bernoulli grippers work by exploiting low pressure regions caused by the acceleration of a working fluid through a narrow channel, between the gripper and a surface, to provide a suction force. This mechanism allows for non-contact adhesion to various surfaces and may be used to hold a robot to the hull of a ship while it inspects welds for example. A Bernoulli type pressure analysis was used to model the system with a Darcy friction factor approximation to include the effects of frictional losses. The analysis involved a constrained optimisation in order to avoid cavitation within the mechanism which would result in decreased performance and damage to surfaces. A sensitivity based method and gradient descent approach was used to find the optimum shape of a discretised surface. The model's accuracy has been quantified against finite volume computational fluid dynamics simulation (ANSYS CFX) using the k-$\omega $ SST turbulence model. Preliminary results indicate significant improvement in suction force when compared to a simple geometry by retaining a pressure just above that at which cavitation would occur over as much surface area as possible. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A14.00004: Validated Analytical Model of a Pressure Compensation Drip Irrigation Emitter Pulkit Shamshery, Ruo- Qian Wang, Katherine Taylor, Davis Tran, Amos Winter This work is focused on analytically characterizing the behavior of pressure-compensating drip emitters in order to design low-cost, low-power irrigation solutions appropriate for off-grid communities in developing countries. There are 2.5 billion small acreage farmers worldwide who rely solely on their land for sustenance. Drip, compared to flood, irrigation leads to up to 70{\%} reduction in water consumption while increasing yields by 90{\%} -- important in countries like India which are quickly running out of water. To design a low-power drip system, there is a need to decrease the pumping pressure requirement at the emitters, as pumping power is the product of pressure and flow rate. To efficiently design such an emitter, the relationship between the fluid-structure interactions that occur in an emitter need to be understood. In this study, a 2D analytical model that captures the behavior of a common drip emitter was developed and validated through experiments. The effects of independently changing the channel depth, channel width, channel length and land height on the performance were studied. The model and the key parametric insights presented have the potential to be optimized in order to guide the design of low-pressure, clog-resistant, pressure-compensating emitters. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A14.00005: Flow control of a centrifugal fan in a commercial air conditioner Jiyu Kim, Kyeongtae Bang, Haecheon Choi, Eung Ryeol Seo, Yonghun Kang Air-conditioning fans require a low noise level to provide user comfort and quietness. The aerodynamic noise sources are generated by highly unsteady, turbulent structures near the fan blade. In this study, we investigate the flow characteristics of a centrifugal fan in an air-conditioner indoor unit and suggest control ideas to develop a low noise fan. The experiment is conducted at the operation condition where the Reynolds number is 163000 based on the blade tip velocity and chord length. Intermittent separation occurs at the blade leading edge and thus flow significantly fluctuates there, whereas vortex shedding occurs at the blade trailing edge. Furthermore, the discharge flow observed in the axial plane near the shroud shows low-frequency intermittent behaviors, resulting in high Reynolds stresses. To control these flow structures, we modify the shapes of the blade leading edge and shroud of the centrifugal fan and obtain noise reduction. The flow characteristics of the base and modified fans will be discussed. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A14.00006: The Other Source of Inducer Backflow Tate Fanning, Ryan Lundgreen, Daniel Maynes, Stephen Gorrell, Kerry Oliphant High suction performance inducers are used as a first stage in turbopumps to hinder cavitation and promote stable flow. Despite the distinct advantages of inducer use, an undesirable region of backflow and resulting cavitation can form near the tips of the inducer blades. This flow phenomenon has long been attributed to “tip leakage flow”, or the flow induced by the pressure differential between pressure and suction sides of an inducer blade at the tip. We examine backflow of a single inducer geometry at varying flow coefficients with a tip clearance of 0.4 mm and a tip clearance of 0 mm. Removing the tip clearance removes any potential tip leakage flow. Despite the removal of the tip leakage flow, backflow persists, and is essentially unaffected. We have observed backflow penetrating 1.1 tip diameters upstream of the leading edge in the inducer with tip clearance, and 0.95 tip diameters in the inducer without tip clearance under the same flow coefficient. A comprehensive analysis of these simulations suggests that blade inlet diffusion, not tip leakage flow, is the driving force for the formation of tip backflow. [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A14.00007: Abstract Withdrawn
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Sunday, November 22, 2015 9:31AM - 9:44AM |
A14.00008: Addressing heat transfer and uniformity of flow in the \emph{Muon g-2} tracker design Nicholas A. Pohlman, Guanrong Luo, Andrew Behnke Recent experiments in high energy physics found a possible deviation in the predicted value in the magnetic dipole moment of the muon particle within the standard model. To explore this term with higher precision, the \emph{Muon g-2} experiment (E989) is being built with an integrated tracker system inside the vacuum chamber where typical conductive and convective heat transfer methods are not available. The placement and packing of mylar straws and electronics filled with an argon gas mixture are designed to maximize the resolution for tracking decaying orbits. Using the space and magnetic field constraints, simulations in heat transfer and gas flow are presented to demonstrate the feasibility of the design to maintain temperature of electronic circuits and uniformity of gas replenishment in the tracker straw tubes. Results will show that initial estimates of using argon gas for electronics cooling is insufficient therefore requiring concentric-tube liquid cooling. Additionally, the impedance paths of the gas through the straw end pieces is dependent on features of both the radial and axial orientation. Preliminary data of prototype performance during a Summer 2015 beam test experiment will also be reported. [Preview Abstract] |
Sunday, November 22, 2015 9:44AM - 9:57AM |
A14.00009: Massive separation around bluff bodies: comparisons among different cfd solvers and turbulence models Vincenzo Armenio, Ahmad Fakhari, Andrea Petronio, Roberta Padovan, Chiara Pittaluga, Giovanni Caprino Massive flow separation is ubiquitous in industrial applications, ruling drag and hydrodynamic noise. In spite of considerable efforts, its numerical prediction still represents a challenge for CFD models in use in engineering. Aside commercial software, over the latter years the opensource software OpenFOAM$^R$ (OF) has emerged as a valid tool for prediction of complex industrial flows. In the present work, we simulate two flows representative of a class of situations occurring in industrial problems: the flow around sphere and that around a wall-mounted square cylinder at $Re=10000$. We compare the performance two different tools, namely OF and ANSYS CFX 15.0 (CFX) using different unstructured grids and turbulence models. The grids have been generated using SNAPPYHEXMESH and ANSYS ICEM CFD 15.0 with different near wall resolutions. The codes have been run in a RANS mode using $k - \epsilon$ model (OF) and $SST-k-\omega$ (CFX) with and without wall-layer models. OF has been also used in LES, WMLES and DES mode. Regarding the sphere, RANS models were not able to catch separation, while good prediction of separation and distribution of stresses over the surface were obtained using LES, WMLES and DES. Results for the second test case are currently under analysis. [Preview Abstract] |
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