Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session G11: Jets: General and Supersonic |
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Chair: Antonio Sanchez, University of California Sand Diego Room: C120-121-122 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G11.00001: Counterflow laminar gas jets issuing from aligned planar nozzles Adam Weiss, Wilfried Coenen, Antonio L Sanchez The laminar flow resulting from the impingement of two gaseous jets issuing from aligned planar nozzles of semi-width $R$ separated a distance $2H$ is investigated by numerical and analytical methods, with specific consideration given to the high-Reynolds and low-Mach number conditions typically present in counterflow-flame experiments. The resulting flow, nearly inviscid and effectively incompressible, can be described by using a density-weighted stream-function/vorticity formulation that removes the need to consider specifically the boundary separating the two jet streams. Besides the geometric parameter $H/R$, the solution depends only on the shape of the velocity profiles in the feed streams and on the jet momentum-flux ratio $\Lambda$. While conformal mapping can be used to determine the potential solution corresponding to uniform feed-stream velocity profiles, numerical integration is required in general to compute vortical flows, including those arising with Poiseuille velocity profiles, with simplified solutions found in the limits $H/R \ll 1$ and $H/R \gg 1$. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G11.00002: On plane submerged laminar jets Wilfried Coenen, Antonio L Sanchez We address the laminar flow generated when a developed stream of liquid of kinematic viscosity $\nu$ flowing along channel of width $2h$ discharges into an open space bounded by two symmetric plane walls departing from the channel rim with an angle $\alpha \sim 1$. Attention is focused on values of the jet volume flux $2Q$ such that the associated Reynolds number $\textit{Re}=Qh/\nu$ is of order unity. The formulation requires specification of the boundary conditions far from the channel exit. If the flow is driven by the volume flux, then the far-field solution corresponds to Jeffery-Hamel self-similar flow. However, as noted by Fraenkel (1962), such solutions exist only for $\alpha < 129^{\rm o}$ in a limited range of Reynolds numbers $0 \le \textit{Re} \le \textit{Re}_c(\alpha)$ (e.g. $\textit{Re}_c \simeq 1.43$ for $\alpha=\pi/2$). It is reasoned that an alternative solution, driven by a fraction of the momentum flux of the feed stream, may also exist for all values of $\textit{Re}$ and $\alpha$, including a near-centerline Bickley jet, a surrounding Taylor potential flow driven by the jet entrainment, and a Falkner-Skan near-wall boundary layer. Numerical integrations of the Navier-Stokes equations are used to ascertain the existence of these different solutions. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G11.00003: PIV measurements of in-cylinder, large-scale structures in a water-analogue Diesel engine A. Kalpakli Vester, Y. Nishio, P.H. Alfredsson Swirl and tumble are large-scale structures that develop in an engine cylinder during the intake stroke. Their structure and strength depend on the design of the inlet ports and valves, but also on the valve lift history. Engine manufacturers make their design to obtain a specific flow structure that is assumed to give the best engine performance. Despite many efforts, there are still open questions, such as how swirl and tumble depend on the dynamics of the valves/piston as well as how cycle-to-cycle variations should be minimized. In collaboration with Swedish vehicle industry we perform PIV measurements of the flow dynamics during the intake stroke inside a cylinder of a water-analogue engine model having the same geometrical characteristics as a typical truck Diesel engine. Water can be used since during the intake stroke the flow is nearly incompressible. The flow from the valves moves radially outwards, hits the vertical walls of the cylinder, entrains surrounding fluid, moves along the cylinder walls and creates a central backflow, i.e. a tumble motion. Depending on the port and valve design and orientation none, low, or high swirl can be established. For the first time, the effect of the dynamic motion of the piston/valves on the large-scale structures is captured. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G11.00004: Large eddy simulations of the flow field of a radially lobed nozzle Noushin Amini, Aarthi Sekaran Lobed nozzles have been a studied over the past couple of decades due to their enhanced mixing capabilities. Despite experimental (Hu et al, 2000) and numerical studies (Cooper et al, 2005), the nature of the jet is yet to be fully understood. This numerical study intends to carry out a thorough analysis of the flow field within and downstream of a six lobed nozzle. The study aims to confirm vortical interaction mechanisms and establish the role of hydrodynamic instabilities in the mixing process. This was inspired by a prior study by the authors wherein the same flow was studied using hot-wire anemometry. Although this helped obtain a qualitative idea of the flow, the 2D data was incapable of visualizing streamwise structures and the flow within the nozzle. Previous numerical simulations have used RANS and to simulate a single lobe of the nozzle; these results show some deficiencies in predicting the potential core length. Previous simulations done by authors indicated that RANS models qualitatively capture the flow structures but do not accurately represent the values of key parameters in the flow field. The present study aims to perform a 3D LES study of the flow field within and downstream of the nozzle to follow the ensuing free jet and thus analyze various mechanisms. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G11.00005: Mathematical design of fluidic jets Adam Haque, Marcus Roper, Sarah Hakim, Kaitlyn Hood Recent experimental work has revealed the possibility of sculpting fluid jets by passing them through a sequence of fluid posts. Simplifying the transformation that occurs when a jet passes a post at finite Reynolds number, we ask: Are there rational ways to tailor the sequence of transformations to achieve a given jet shape? Studying these simplified transformations reveals fundamental constraints on what shape changes can be produced by single transformations, and suggests strategies for optimizing combinations of transformations to achieve desired jet shapes. [Preview Abstract] |
Monday, November 21, 2016 9:05AM - 9:18AM |
G11.00006: Multi-Measurement Correlations in the Near-Field of a Complex Supersonic Jet Using Time-Resolved Schlieren Imaging Andrew Tenney, Thomas Coleman, Jacques Lewalle, Mark Glauser, Sivaram Gogineni Supersonic flow from a three-stream non-axisymmetric jet is visualized using time resolved schlieren photography (up to 400,000 frames per second) while pressure on the aft deck plate of the nozzle is simultaneously sampled using kulites. Time series are constructed using the schlieren photographs and conditioned to reduce the effects of signal drift and clipping where necessary. The effect of this detrending and clipping reconstruction on signal statistics is examined. In addition, signals constructed from near field schlieren will be correlated with one another to visualize the propagation of information in the near field. The goal of utilizing space-time correlations is to assist in identifying and tracking the evolution of individual structures in the near field. The schlieren signals will also be correlated with the deck pressure traces to assist in unraveling the interaction of flow structures. [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G11.00007: Time-resolved schlieren POD and aft deck pressure correlations on a rectangular supersonic nozzle and sonic wall jet Matthew Berry, Andrew Magstadt, Cory Stack, Datta Gaitonde, Mark Glauser A multi-stream single expansion ramp nozzle (SERN) with aft deck, based on three-stream engine concepts, is currently undergoing experimental tests at Syracuse University’s Skytop Turbulence Laboratory. In the context of this study, we view this as an idealized representation consisting of two canonical flows; a supersonic convergent-divergent (CD) nozzle and a sonic wall jet (representing the 3$^{rd}$ stream). The jet operates at a bulk flow of $M_{j,1} = 1.6$ and wall jet $M_{j,3} = 1.0$. Proper orthogonal decomposition (POD) is then performed on the schlieren images and the time-dependent coefficients are related to the near-field deck pressure. Structures within the flow field are correlated to particular flow events and help track the downstream evolution of the jet. A multitude of scales are seen within the flow corresponding to a wide range of coherent structures. High fidelity LES is also performed on the same nozzle geometry and relations are made back to the experiments. [Preview Abstract] |
Monday, November 21, 2016 9:31AM - 9:44AM |
G11.00008: Dynamics of the Coherent Structures in a Supersonic Rectangular Jet of Aspect Ratio 2 Kamal Viswanath, Andrew Corrigan, Ryan Johnson, Kazhikathra Kailasanath, Ephraim Gutmark Asymmetric exhaust nozzle configurations, in particular rectangular, are likely to become more important in the future for both civilian and military aircraft. Various nozzle geometry features including the presence of sharp corners impact the evolution of the cross-sectional shape of the jet and its mixing features. Asymmetric nozzles potentially offer a passive way of affecting mixing for low aspect ratio jets through both large-scale entrainment due to coherent structures and fine scale mixing at the corners. Data is presented that show the dynamic evolution of the coherent structures for an ideally expanded rectangular nozzle of aspect ratio 2. The sense of the vortex pairs setup through the self-induction at the corners and stretching of the azimuthal vortex ring into streamwise vortices results in diagonal elongation of the time-averaged jet cross-section and contraction at the sides. The phase averaged velocity contours further clearly show the effect of mixing at the sharp corners and the deformation of the rectangular exit cross-section as it propagates downstream. It is observed that the dominant vortex pairs in this case work against axis-switching. [Preview Abstract] |
Monday, November 21, 2016 9:44AM - 9:57AM |
G11.00009: Flow and Noise Characteristics of Under- and Over-expanded Supersonic Rectangular Jets of Aspect Ratio 2 Ryan Johnson, Kamal Viswanath, Andrew Corrigan, kazhikathra kailasanath, Ephraim Gutmark Simulations of under- and over-expanded flow for two operating temperatures were con- ducted with a low aspect ratio, AR $=$ 2.0, rectangular nozzle. These cases are compared to the same nozzle at the design pressure ratio. The simulated acoustic data are validated against experimentally recorded sound pressure level (SPL) spectra. The axial flow structure is examined along parallel lines that originate at the center and nozzle walls in the direction of the core flow. The shock cell structure, jet core length, and the axial distributions of the flow are different in all observed planes for the over-, under-, and ideally-expanded jet flow cases. How these flow structures contribute to SPL and overall sound pressure levels (OASPL) is discussed. [Preview Abstract] |
Monday, November 21, 2016 9:57AM - 10:10AM |
G11.00010: Coherent structures in a supersonic complex nozzle Andrew Magstadt, Matthew Berry, Mark Glauser The jet flow from a complex supersonic nozzle is studied through experimental measurements. The nozzle’s geometry is motivated by future engine designs for high-performance civilian and military aircraft. This rectangular jet has a single plane of symmetry, an additional shear layer (referred to as a wall jet), and an aft deck representative of airframe integration. The core flow operates at a Mach number of $M_{j,c}=1.6$, and the wall jet is choked ($M_{j,w}=1.0$). This high Reynolds number jet flow is comprised of intense turbulence levels, an intricate shock structure, shear and boundary layers, and powerful corner vortices. In the present study, stereo PIV measurements are simultaneously sampled with high-speed pressure measurements, which are embedded in the aft deck, and far-field acoustics in the anechoic chamber at Syracuse University. Time-resolved schlieren measurements have indicated the existence of strong flow events at high frequencies, at a Strouhal number of $St=3.4$. These appear to result from von K\`{a}rm\`{a}n vortex shedding within the nozzle and pervade the entire flow and acoustic domain. Proper orthogonal decomposition is applied on the current data to identify coherent structures in the jet and study the influence of this vortex street. [Preview Abstract] |
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