A. Lozano

Acetone: a tracer for concentration measurements in gaseous flows by planar laser-induced fluorescence

This paper explores the use of acetone as a suitable tracer in planar laser-induced fluorescence concentration measurements in gaseous flows. The photophysics and physical properties of acetone relevant to its use as a fluorescent marker are discussed and compared to those of alternative molecular tracers, particularly the biacetyl molecule. Finally, as a direct example, concentration images obtained in a turbulent air jet seeded alternatively with acetone and biacetyl are compared.

Quantitative imaging of concentration by planar laser-induced fluorescence

The planar laser-induced fluorescence (PLIF) technique is attractive for instantaneous and non-intrusive imaging of species concentration in gaseous flows. This paper provides a framework for determining the experimental resolution in PLIF experiments and gives error estimates for concentration measurements in turbulent jet mixing experiments using biacetyl as the molecular tracer. The procedures to correct for experimental artifacts in the PLIF images are outlined. Images of the instantaneous, average, rms, and dissipation of concentration in a turbulent jet are presented.

A combined OH/acetone planar laser-induced fluorescence imaging technique for visualizing combusting flows

A combined OH/acetone planar laser-induced fluorescence (PLIF) imaging technique that provides simultaneous visualizations of regions of unburned fuel and of combustion in a reacting flow is described. OH marks the location of chemical reaction and of combustion products, and acetone vapor, which is seeded into the fuel stream, marks unburned fuel. A single pulse from an ultraviolet laser is used to simultaneously excite both the OH and acetone, and the fluorescence from each is detected on separate cameras. Acetone spectroscopy and chemistry are reviewed to provide a basis for interpreting acetone fluorescence signals in high-temperature combusting environments. The imaging technique is applied to two nonpremixed turbulent reacting flows to assess the utility of the technique for visualizing the instantaneous flow structure and to illustrate the dependence of the interpretation of the acetone PLIF images on the flow conditions.

Large-scale dynamics in high Reynolds number jets and jet flames

The far-field large-scale dynamics of a momentum-driven Re = 2 × 108 non-reacting jet and a Re = 3 × 107 jet diffusion flame are presented and compared. The results are derived from computer graphic volume rendering of a set of sequential images of each flow. When compared to conventional display techniques, volume rendering, by allowing many frames of a movie sequence to be presented simultaneously, more clearly shows the detailed flow evolution. For the non-reacting jet we see the passage and growth of large-scale organized structures up through the jet column, the axial velocity decay of the structures, the fluid entrainment patterns, and occasional pairing events. A rendering of a non-sequential set of images shows no discernible organized component. Volume rendering of the reacting jet shows a similar pattern of burning large-scale organized structures which convert over considerable axial distances but without the corresponding velocity decay, similar to observations of laboratory flames. The images presented here are believed to be some of the most direct visual evidence to date for large-scale organized motions in the far-field of high Reynolds number, fully developed jets and jet flames. Since conditional sampling techniques are not used, we believe that the volume renderings seen here are likely to be representative of the natural development of jet flows.

Some observations of a large, burning jet in crossflow

Some results are presented on the temporal evolution of a large jet in crossflow consisting of the burning plume from an unabated oil well discharge. The volume rendering approach is used whereby several sequential x-y images of the jet are stacked in time, t, to produce an object in x-y-t space which can be used to conveniently examine the jet dynamics. Similar to earlier findings for free jets, the burning jet in crossflow is seen to consist of a series of large-scale organized structures which convect downstream leading to a quasiperiodic flame tip burnout. The wake region however is seen to be much less organized. Most surprising is the constant speed of the burning structures as they progress from the jet to crossflow direction. It therefore appears that an underlying organization exists in the jet in crossflow, in spite of its relatively complex, three-dimensional structure.

Sensitized phosphorescence: a gas phase molecular mixing diagnostic

The use of sensitized phosphorescence for visualization of gas phase fluid mixing and the requirements for quantitative imaging measurements are discussed. A model for estimating the molecular-mixing signals dependence on fluid composition is developed and candidate molecular reactants are considered within the framework of the model. Experiments based on sensitized phosphorescence from both an acetonebiacetyl system and a toluene-biacetyl system show good qualitative agreement with modeled results. It is concluded that quantitative measurements using sensitized phosphorescence are feasible.

Three-dimensional visualization of temporal flow sequences

Flow visualisation remains one of the most powerful methods of gaining insight into turbulent flow physics. Recently there have been several excellent reviews that describe some of the latest developments in the field. Also video sequences of flow visualisation images are used to study flow development. This note describes a method which uses three-dimensional frames of still pictures stacked to form a data volume composed of the downstream spatial, cross-stream spatial and time dimension. High-resolution volume rendering is used to extract constant property surfaces from this three-dimensional data volume.

Planar Laser-Induced Fluorescence Scalar Measurements in a Turbulent Jet

The planar laser-induced fluorescence (PLIF) technique has been used to measure the concentration of a passive molecular tracer (biacetyl) in a turbulent axisymmetric nitrogen jet. The emitted light was recorded using two low noise, high dynamic range CCD cameras. The acquired images were corrected for experimental artifacts and statistically analyzed. Results are presented for mean concentration, RMS concentration fluctuations, scalar dissipation, and cross-section centered means.

Computer rendering of planar fluorescence flowfield images

Imaging rechniques based on light scattering by particles or molecular species are becoming increasingly popular for visualizing flowfield structure and development. The planar laser-induced fluorescence (PLIF) technique can be used to non-intrusively and instantancously measure concentration, temperature, velocity, or pressure in an entire plane in a flow. Acquiring a sequence of images provides two spatial dimensions and a time dimension for observing flowfield development. If the laser sheet is swept through the flow while rapidly acquiring images, a three dimensional data set can be built up from multiple 2-D images. The large data sets produced by these techniques arc most readily reduced and interpreted using a variety of image processing and graphic projection techniques. Examples of 2-D images, sequences of images, and Ihrcc-dimensional data sets acquired by the PLIF technique arc presented. Processing and rendering techniques for these data scts are discussed. .--