Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M29: Turbulent Mixing I |
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Chair: Luminita Danaila, CORIA, INSA de Rouen Room: Georgia World Congress Center B401 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M29.00001: Experimental investigation of multi-scalar mixing in a turbulent coaxial jet Alais Hewes, Laurent B Mydlarski The present experiments focus on the (concurrent) evolution of two passive scalars (temperature and helium concentration) and velocity in a turbulent coaxial jet. The latter is based on the work of Cai et al. (J. Fluid Mech., 2011) and consists of a vertically oriented central jet of helium and air, surrounded by an annular flow of (unheated) pure air, emanating into a slow co-flow of (pure) heated air. The two scalars and velocity are measured simultaneously using a 3-wire thermal-anemometry-based probe, which is composed of two hot-wires forming an interference (or Way-Libby) probe to measure velocity and helium concentration, as well as a cold-wire for measuring temperature. The downstream and cross-stream evolutions of single and multivariable/joint statistics, including scalar fluxes, the scalar covariance, JPDFs, and the conditional scalar diffusion, will be presented and validated against previous experimental and numerical studies of coaxial jets. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M29.00002: Statistics of homogeneous isotropic decaying turbulence with variable viscosity Luminita Danaila, Michael Gauding, Emilien Varea The decay of homogeneous isotropic turbulence in a variable viscosity fluid with a viscosity ratio up to 15 is analyzed by means of highly resolved direct numerical simulations (DNS). The question is how quantities such as the kinetic energy and the associated dissipation rate, as well as the inter-scale transport mechanism of turbulence are changed by local fluctuations of the viscosity. The comparison is performed with respect to the decaying homogeneous isotropic turbulence with constant viscosity (CV), equal to the mean value of the variable viscosity (VV). It is shown that VV leads to an enhanced level of small-scale intermittency with respect to CV flow, which results in the presence of smaller length scales. The effect of VV on the turbulent cascade is analyzed by a budget equation for the velocity second-order structure function. Viscosity gradients contribute to the inter-scale transport mechanism in the form of an inverse transport. The phenomenology is discussed in the context of closures of the transport term, based on a Lagrangian approach. The latter takes into account contributions from the variable-viscosity interfaces. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M29.00003: The effect of external intermittency on the scaling and self-similarity of structure functions in turbulent shear flows Michael Gauding, Luminita Danaila, Emilien Varea The edge of a free turbulent shear flow is characterized by a turbulent/non-turbulent interface (TNTI) which is a distinct and highly contorted layer that separates turbulent from irrotational flow regions. Transfers of mass, momentum and scalar quantities, such as species or heat, occur over the thickness of this layer, which renders its physical understanding crucial for a variety of engineering and environmental applications. Moreover, strong fluctuations are created in the vicinity of the TNTI and are transported by the mechanism of entrainment into the turbulent core of the flow. These fluctuations are known as external intermittency. In this study, we investigate the impact of external intermittency on velocity and scalar structure functions of different orders. It is shown that external intermittency breaks the self-similarity of structure functions and invalidates the classical scaling relations proposed by Kolmogorov. By conditioning structure functions on an intermittency parameter, we show that self-similarity of these structure functions can be recovered. The analysis is based on highly resolved direct numerical simulations of turbulent jet flows and mixing layers. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M29.00004: Blowing Ratio Effects on an Inclined Jet in Crossflow Ian E. Gunady, Andrew J. Banko, Christopher J. Elkins, John K. Eaton The inclined jet in crossflow is a canonical variant on the perpendicular jet in crossflow and is used extensively in gas turbine film cooling applications. Few studies have examined the turbulent scalar transport at blowing ratios (BR) greater than one, where jet lift-off can reduce the film cooling performance. This experimental work studies the effect of blowing ratio on a round jet pitched at 30° from horizontal, a jet Reynolds number nominally of O(5000), and boundary layer thickness to jet diameter ratio of 2. Magnetic Resonance Velocimetry (MRV) is used to obtain the 3D, 3-component mean velocity field on a Cartesian grid of approximately 2 million data points at BR = 1.5 and BR = 2.0. Magnetic Resonance Concentration (MRC) is used to measure the 3D mean concentration field at BR = 2.0. Jet trajectories, counter-rotating vortex pair (CVP) structures, and mean scalar fields are compared to data previously collected with MRV and MRC at BR = 1.0. Attention is given to turbulent mixing on the leeward side of the jet, which can be modulated by proximity to the wall and critically determines film cooling effectiveness. Blowing ratio affects the distortion of the jet streamtube by the CVP, especially on the bottom side of the jet. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M29.00005: Experimental investigation of turbulent mixing between liquids of disparate viscosity in a co-axial jet mixer Michael Cameron Reza Ahmad, Gokul Pathikonda, Irfan Khan, Cyrus K Aidun, Devesh Ranjan Industrial chemical processes often involve mixing of reactive fluids of different viscosities. These processes would involve a mixer that should efficiently mix reactants molecularly to prevent unwanted side products that decrease yield. To this end, the current work studies the physics of mixing to optimize mixing efficiency. A facility for study of coannular jet mixing was built that produces turbulent flows with high viscosity disparity between the liquids. To investigate the hydrodynamics of such mixing, highly resolved simultaneous PIV and PLIF data are acquired on confined co-flowing jet mixing configuration with refractive index matched binary mixtures of aqueous glycerol and calcium chloride solutions (viscosity ratio of 5). The PIV and PLIF data are used to extract mean and turbulent velocity and passive scalar statistics, and velocity-concentration cross-correlations from the flow fields, providing a statistical description of turbulent mixing and evolution of this confined coaxial jet flow. The observations in this study in concert with collaborative simulations enable the development of more physical models for turbulent mixing of fluids with disparate viscosities. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M29.00006: Scalar dispersion in a smooth wall turbulent boundary layer from a point source at the wall Claudia Nicolai, Mantas Gudaitis, Bharathram Ganapathisubramani, Christina M Vanderwel We present an experimental investigation on the dispersion of a passive scalar, released from a point source at the wall in a turbulent boundary layer naturally developing in a water tunnel. Simultaneous measurements of concentration and velocity fields are carried out by combining two planar techniques: quantitative planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) on a domain over a field of view of 3.5δ x 1.2δ (where δ is the boundary layer thickness), immediately downstream of the point source. These measurements provide physical insight into the scalar transport processes allowing for the assessment of the scalar fluxes u’c’ and v’c’, together with the momentum fluxes, which are critical parameters for dispersion models applied to weather modelling, pollution transport, and industrial mixing processes. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M29.00007: Large-scale experimental study of the turbulent flow over an effusion cooling plate Jeremy Basley, Kevin A Gouder, Yushi Murai, Cloe Fradin, Dan Glymond, Luc J M Vandeperre, Jonathan F Morrison Used in gas turbines, effusion cooling of the blades is an efficient way to alleviate the thermal and shear strain they sustain while increasing the temperature in the chamber. A large-scale low-velocity experiment is carried out in the 3 x 1.5 x 20m3 test section of our closed-loop 10x5 wind-tunnel facility – Department of Aeronautics, Imperial College London. The scaled-up effusion device consists of a coolant-supplied settling chamber located directly underneath a perforated thick plate replacing a portion of the floor of the wind-tunnel. The effusion plate is pierced by a staggered grid of inclined D=16mm-diameter holes with a pitch of 5D. This set-up is placed in a turbulent boundary layer, tripped and developing over 15meters. Three cases: a) no effusion, null flow rate coming out of the chamber; b) effusion without cooling, atmospheric air is supplied to the chamber; c) effusion cooling is supplied by a carbon dioxide cylinder; are investigated to let us identify independently the effects of holes-induced roughness (a), jet-injected momentum (b), and negative heat flux (c) on the flow dynamics. Hot-wire measurements provide velocity profiles at various locations throughout the effusion plate. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M29.00008: The sudden viscous dissipation mechanism for a multi-species turbulent flow Alejandro Campos, Brandon E Morgan Previous work carried out by Davidovits & Fisch [Phys. Rev.Lett. 116, 105004 (2016)] demonstrated a rapid and sudden viscous dissipation of turbulence when viscosity has a greater sensitivity on temperature. We extend on the previous work by conducting direct numerical simulations of this sudden viscous dissipation for a multi-species, rather than a single-species, fluid. This allows for the use of complex multi-component models for viscosity, conductivity, and diffusivity that are based on plasma transport theory for weakly and strongly coupled plasmas. Results obtained with these transport models are compared against simulations performed with the simpler fluid formulations based on constant Prandtl and Schmidt numbers. Among the quantities of interest to be described are the energy transfer between the turbulent kinetic energy and the internal energy, as well as statistics relevant to the mixing of the multiple species. Finally, the high-fidelity data is used to measure the ability of Reynolds-averaged Navier-Stokes models to predict the sudden viscous dissipation for multi-component flows. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M29.00009: Turbulent entrainment into a cylinder wake from a turbulent background Krishna Kankanwadi, Oliver Buxton The effect of free-stream turbulence (FST) on entrainment into a cylinder wake is investigated through simultaneous particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) experiments. Previous studies have indicated the individual importance of the turbulence intensity, length scale and dissipation rate on turbulent/turbulent entrainment (TTE), however a complete study considering all three parameters is lacking. Space filling fractal grids are used to generate FST and allow us to conduct a parametric study by independently varying all three parameters, whilst commenting on the influence of each. The wake behavior in both the near and far field is measured. It is found that the incoming FST inherently affects the shedding mechanism of the cylinder. There is an observed difference in the shedding Strouhal number when FST is introduced, with a marked increase in the vortex formation length. FST is also seen to promote increased spreading of the wake by encouraging vortex centers to drift further away from the centerline. Furthermore, phase hiccups in the vortex shedding, which are intermittent events that lead to a complete loss of wake structure, come into existence when FST is introduced. |
Tuesday, November 20, 2018 9:57AM - 10:10AM |
M29.00010: Simultaneous Turbulent Momentum and Mass Transport in Swirling Flow of a Macroscale Multi Inlet Vortex Reactor Emmanuel Hitimana, Michael Gary Olsen, James C Hill, Rodney Otis Fox The production of uniformly sized functional nanoparticles for applications including pharmaceuticals, pesticides, and cosmetics is a problem of great interest. The macroscale multi-inlet vortex reactor (macro-MIVR) was developed for nanoparticle manufacturing through nanoprecipitation due to its ability to achieve rapid mixing and high efficiency. In the presented work, the turbulent momentum and mass transport in the macro-MIVR were investigated using simultaneous stereoscopic particle image velocimetry and planar laser induced fluorescence to determine flow statistics including turbulent viscosity, turbulent diffusivity, and turbulent Schmidt number. Measurements were performed in three planes located at different levels from the reactor bottom (¼, ½, and ¾) for Reynolds numbers of 3250 and 8125 based on reactor inlet mean velocity and hydraulic diameter. The turbulent viscosity was found to be nearly axisymmetric about the center of the reactor, but both the turbulent diffusivity and turbulent Schmidt number varied with azimuthal position. For both Reynolds numbers, the turbulent viscosity and diffusivity are the highest in the vortex core near the reactor center. Finally, turbulent Schmidt number was found to vary between 0.02 and 0.7 throughout the reactor.
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