Advanced Laser Diagnostics for Turbulent, Multiphase, and Reacting Flows

Abstract

Turbulent, multiphase, and reactive flows underpin the operation of modern combustion systems, which account for the majority of the world’s energy usage and will continue to do so for the foreseeable future. Applications, which range from power generation to transportation, will rely on advancements in energy-conversion systems that simultaneously increase efficiency, decrease emissions, and offer increased fuel flexibility. However, such advancements are quite challenging due to the complex (and often dynamic) coupling of turbulent fluid dynamics and chemistry over a broad range of length and time scales. Over the last several decades, the use of non-intrusive laser diagnostics in experimental fluid and combustion research has evolved from a luxury to a near necessity in order to decipher the coupled and multi-scale processes underpinning turbulent combustion systems. Such measurement capabilities have played a critical role in providing new fundamental insight on processes include reactant mixing, flame stabilization, ignition and extinction, dynamic instabilities, and the identification of rare, but extremely important, events including engine misfire, flashback, and flame blowoff.

In this seminar, I will discuss the development and targeted application of quantitative laser-based measurements for examining and understanding flow turbulence, mixing, and turbulence-chemistry interaction in turbulent, multiphase, and reacting flow environments. First, I will describe our efforts in high-speed measurements for investigating temporally evolving flows and transient events. Our research involves the development and application of a unique high-energy pulse burst laser system (HEPBLS), which allows the generation of ultra-high pulse energies at repetition rates » 1 kHz. Such a system provides opportunities to utilize many combustion diagnostics traditionally limited to low acquisition rates for the investigation of turbulence and combustion dynamics. Specifically, I will focus on recent advancements in multi-kHz-rate Rayleigh/Raman scattering in turbulent flows and flames and the application to simple jets, jet flames, and more complex auto-ignition environments.

I will discuss new advancements in laser-based measurement approaches that have been the focus of our recent research. This includes the application of filtered Rayleigh scattering (FRS) for multi-dimensional temperature imaging in turbulent non-premixed flames in the presence of particles. Specifically, FRS allows both (i) simultaneous temperature and PIV-based velocity measurements in order to examine the relationship between flow field kinematic properties and scalar gradients and (ii) temperature measurements in sooting flames. FRS also is applied to spray flows for quantitative mixing measurements in the presence of liquid-phase droplets. Finally, I will describe a new high-resolution velocimetry technique using a wavelet-based optical flow methodology applied to both scalar and “seed particle” fields. The approach is shown to be accurate and yields a dense velocity vector field; that is, a velocity measurement at each camera pixel, which is in stark contrast to standard correlation-based methods (i.e., PIV).

JEFFREY A. SUTTON

Ohio State University