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 A15: Jets in Crossflow |
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Chair: Ann Karagozian, UCLA Room: 310 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A15.00001: Asymmetric Excitation of Convectively Unstable Jets in Crossflow Andrea Besnard, Elijah Harris, Stephen Schein, Alexandra Dembry, David D. W. Ren, Ann Karagozian, Leonardo Alves This experimental study explores the influence of external asymmetric excitation on the dynamics, structure, and mixing characteristics of the gaseous jet in crossflow (JICF) with a jet-to-crossflow momentum flux ratio of J=61. In the absence of excitation, the jet’s upstream shear layer (USL) is convectively unstable with an asymmetric mean cross-section. Asymmetric forcing is applied via flush-mounted speakers about the jet exit periphery, allowing for controlled directional azimuthal forcing in counterclockwise or clockwise directions as well as localized sinusoidal excitation outside of the jet exit. For specific perturbation amplitudes, especially near the fundamental frequency, the jet’s USL locks-in to the forcing frequency, while other forcing conditions provide evidence of quasi-periodicity. Lock-in is typically required to affect both jet structure and mixing. Snapshot proper orthogonal decomposition (POD) analysis is applied to the JICF’s scalar field, quantified via acetone planar laser induced fluorescence (PLIF). For forcing cases known to produce a strongly locked-in USL, phase space mapping of the dominant POD mode coefficients show the emergence of coherent shapes resembling strange attractors, potentially suggesting a transition in the flow. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A15.00002: DNS, stability and sensitivity of the low-speed transverse jet Samantha Harel, Krishnan Mahesh DNS, tri-global stability and adjoint analysis are performed for a jet in cross-flow (JICF) using a novel capability developed on unstructured grids and parallel platforms. Linear stability analysis reveals that upstream shear-layer modes have frequencies that match simulation and experiment. The relative importance of upstream and downstream shear layer modes, as well as axisymmetric and non-axisymmetric modes is studied. Adjoint modes show that the upstream shear-layer is most sensitive along the upstream side of the jet nozzle. Lower frequency downstream modes are sensitive in the cross-flow boundary layer. The transverse jet has multiple pathways to instability; non-modal interactions are examined on their multiple time-scales. Helical actuations of the transverse jet is being studied; these results will be discussed. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A15.00003: The role of turbulent inflow on the development of a jet in cross-flow Graham Freedland, Greg Sakradse, Stephen Solovitz, Ra\'{u}l Bayo\'{a}n Cal Prediction of the development of jets in cross-flow has many useful applications in various fields such as chemical mixing and volcanic plume models. Most models used to predict the growth assume irrotational flow when both atmospheric and high Reynolds number flows are not. Simple laboratory experiments of air jets in crossflow downstream of an active grid system are used to simulate uniform turbulent inflows. A jet of air is injected orthogonally into a closed-loop wind tunnel with several cross-flow velocities and three active grid settings to simulate a range of turbulent conditions. Mean flow statistics and Reynolds stresses are computed using PIV data to identify key regions of interaction. The flow-fields are reoriented to provide components normal and tangential to the centerline of the jet and descriptions of the trajectory and shear layer expansion are quantified and compared. Analysis is then focused on the evaluation of the dissipation and eddy viscosity for the purpose of refining $k-\varepsilon$ modeling parameters. Identifying the differences turbulent cross-flow has on development of the jet and lee-side wake region provides more details on the important features necessary for accurate prediction of the spread and entrainment. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A15.00004: The spatial evolution of anisotropy along a jet in cross-flow Gregory Sakradse, Graham Freedland, Stephen Solovitz, Raul Bayoan Cal Volcanic plumes present a unique challenge in the realm of atmospheric flow modelling, and many current models rely on general parameters applied to a wide range of flows. Improvements in modelling can be made by tuning model parameters to specific flows with experimental data. In laboratory conditions a volcanic plume can be approximated as a buoyant jet interacting with a cross-flow. The present work examines a round jet emitted into a cross-flow. Stereo PIV is used to directly measure three components of velocity in the near to medium field of the jet on a plane parallel to the crossflow and on the central axis of the jet. Buoyant, neutrally buoyant and negatively buoyant cases are considered. The state of anisotropy is determined along lines parallel to the outer edges of the jet shear layers, and the progression of of the state of anisotropy is examined on an Anisotropy Invariant Map (AIM). The development in space of the state of anisotropy is used to refine coefficients in both linear and non-linear return to anisotropy models for the transport of the anisotropy tensor. These experimentally determined coefficients can be used to refine Reynolds-Stress models of atmospheric flows in the presence of a volcanic plume. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A15.00005: Flame Position-Shear Layer Offset Effects on Jet in Crossflow Dynamics Vedanth Nair, Vishal Acharya, Tim Lieuwen The dynamics and mixing behavior of Reacting Jet in Crossflow systems can be studied by considering the behavior of coherent structures and their formation and growth. This study aims to understand the influence of heat-release on the growth of shear layer vortices (SLV) for a non-premixed, reacting jet in crossflow (RJICF) configuration. Two reacting cases are~considered: pure methane jet into a crossflow of air (flame lies outside the jet shear layer) and a diluted methane jet into a crossflow of oxygen (flame lies inside), in order to gauge the influence of changing the location of heat release with respect to the shear layer. These two configurations lead to significant differences in the spatial orientation of shear-heat release interactions and how the vorticity interacts with regions on the other side of the jet.~The results demonstrate that the presence of heat release in the near field has a suppressive effect on shear layer growth as well as the development of the counter-rotating vortex pair (CVP) and this effect is amplified in the case where the flame is moved inside the shear layer. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A15.00006: Lagrangian Coherent Structures (LCS) in crossflow jets subject to very strong Favorable Pressure Gradient (FPG) German Saltar Rivera, Christian Lagares, Guillermo Araya Incompressible jets transversely issuing into a spatially-developing turbulent boundary layer is one of the most challenging types of three dimensional flows due to its thermal-fluid complexity and technological applications: film cooling of turbine blades, fuel injection, thrust vector control, chimney plumes, among others. Complex interactions between the jet and the crossflow create a variety of coherent structures which govern the flow's transport properties, most notably, the counter-rotating vortex pair (CVP). The CVP's influence in the thermal transport of a turbulent round jet in a crossflow with a strong FPG has been previously studied by Quinones \& Araya (2017). The FPG exhibited a damping effect on the CVP wake development and a wall-normal stretch on its geometry. To expand upon this work, we conduct Direct Numerical Simulation (DNS) at different jet velocity ratios (i.e., VR = 0.5, 1 and 2) and make use of the Finite-Time Lyapunov Exponent (FTLE) as well as the Finite-Space Lyapunov Exponent (FSLE) to detect and evaluate LCS. The main purpose is to shed light of the combined effect of crossflow-jet and strong FPG on passive scalar transport. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A15.00007: Favorable Pressure Gradient Effects on an Inclined Jet in Crossflow Clayton Pelzer, Ralph Volino, Ronald Warzoha Mixing of inclined jets in crossflow is of fundamental interest and significant for engineering applications including film cooling in gas-turbine engines. The effect of a pressure gradient on these jets is not fully understood. This study considers how a favorable pressure gradient affects the rate of spreading of a jet and its mixing with the main flow, utilizing heated jets injected into a boundary layer in a wind tunnel. The test section includes a flat test wall with jets inclined at 35 degrees to the surface and an adjustable opposite wall that is positioned to achieve the desired pressure gradients. A thermal camera is used to measure temperatures along the test wall, and hot-wire and cold-wire anemometry are used to measure velocity and temperature fields in the flow. These measurements will be used to determine cooling effectiveness on the surface and how the pressure gradient affects the jet mixing with the crossflow. [Preview Abstract] |
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