Jonathan H. Frank

Bio: Jonathan H. Frank is an academic researcher from Sandia National Laboratories. The author has contributed to research in topics: Jet (fluid) & Rayleigh scattering. The author has an hindex of 33, co-authored 96 publications receiving 3846 citations. Previous affiliations of Jonathan H. Frank include University of Cambridge & Yale University.

Effects of turbulence on species mass fractions in methane/air jet flames

Abstract: It is important that combustion models capture the effects of turbulent mixing on reaction zone structure in non-premixed and partially premixed flames. A more complete understanding of the response of species mass fractions to turbulent mixing is needed to improve predictive capabilities, particularly with regard to combustion intermediates and minor species. Using the combination of Raman scattering. Rayleigh scattering, and laser-induced fluorescence, simultaneous measurements of CO, OH, H2, and NO are obtained along with the major species, temperature, and mixture fraction in a series of six piloted methane/air jet flames. Flame conditions vary from laminar to turbulent with significant localized extinction. Two-photon laser-induced fluorescence (TPLIF) is used to determine instantaneous CO concentrations, providing an improvement over Raman scattering measurements of CO in methane flames. Conditional probability density functions (cpdf's) of species mass fractions in the six flames are compared. Significant changes are observed in the mass fraction cpdf's of several species. Results for H2O, CO2, H2, and OH are consistent with the concept that turbulent transport becomes dominant over molecular diffusion within the range of Reynolds numbers and axial locations considered in these experiments. The cpdf's of CO mass fraction are broadened in the turbulent flames relative to the laminar flame. However, there is not an increase in the maximum conditional mean value of the CO mass fraction as suggested by some previously reported measurements in methane flames. The cpdf's of NO mass fraction at a given streamwise location in the turbulent flames show NO levels decreasing significantly as jet velocity increases.

Supercontinuum radiation for applications in chemical sensing and microscopy

Abstract: The advent of compact, high brightness supercontinuum radiation sources employing solid core photonic crystal fibres is beginning to make an impact across the field of applied spectroscopy research In this article we focus on the use of supercontinuum sources to construct novel instrumentation for chemical sensing A brief overview is given on the mechanisms of supercontinuum generation in solid core photonic crystal fibres, and then we review recent, and present new, results from our own research We present examples on gas phase sensing applications, permitting wide bandwidth molecular spectra to be gathered at ultrahigh speed Furthermore we demonstrate the design and construction of a wide bandwidth microscope for wavelength flexible hyperspectral confocal imaging We conclude with an outlook and a summary of where and how we think the field may develop over coming years

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

Fluorescence Lifetime Measurements and Biological Imaging

Abstract: When a molecule absorbs a photon of appropriate energy, a chain of photophysical events ensues, such as internal conversion or vibrational relaxation (loss of energy in the absence of light emission), fluorescence, intersystem crossing (from singlet state to a triplet state) and phosphorescence, as shown in the Jablonski diagram for organic molecules (Fig. 1). Each of the processes occurs with a certain probability, characterized by decay rate constants (k). It can be shown that the average length of time τ for the set of molecules to decay from one state to another is reciprocally proportional to the rate of decay: τ = 1/k. This average length of time is called the mean lifetime, or simply lifetime. It can also be shown that the lifetime of a photophysical process is the time required by a population of N electronically excited molecules to be reduced by a factor of e. Correspondingly, the fluorescence lifetime is the time required by a population of excited fluorophores to decrease exponentially to N/e via the loss of energy through fluorescence and other non-radiative processes. The lifetime of photophycal processes vary significantly from tens of femotoseconds for internal conversion1,2 to nanoseconds for fluorescence and microseconds or seconds for phosphorescence.1 Open in a separate window Figure 1 Jablonski diagram and a timescale of photophysical processes for organic molecules.

Optical gas sensing: a review

Abstract: The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

Atomization and Sprays

Abstract: Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

Large-eddy simulation of turbulent combustion

Abstract: Large-eddy simulation (LES) of turbulent combustion is a relatively new research field. Much research has been carried out over the past years, but to realize the full predictive potential of combustion LES, many fundamental questions still have to be addressed, and common practices of LES of nonreacting flows revisited. The focus of the present review is to highlight the fundamental differences between Reynolds-averaged Navier-Stokes (RANS) and LES combustion models for nonpremixed and premixed turbulent combustion, to identify some of the open questions and modeling issues for LES, and to provide future perspectives.