دانلود Detailed simulations of primary breakup of turbulent liquid jets in crossflow

Motivation and objectives

The problem of breakup of a liquid fuel in a crossflow finds relevance in applications such as lean premixed prevaporized (LPP) ducts, afterburners for gas turbines and combustors for ramjets and scramjets. Combustion efficiency and pollutant formation are directly determined by the efficient mixing of the fuel/air mixture, which is in turn controlled by the breakup of the fuel jet. Liquid jet breakup in a crossflow is a result of a complex process that includes development of instabilities along the liquid surface along with shedding of ligaments and drops from the sides of the injected liquid column. The breakup is amplified by the presence of various contributing factors: turbulence in the crossflow and liquid jet, cavitation in the injection nozzle, pressure fluctuations and aerodynamic sources. The subject of liquid jet in crossflow (LJCF) has been the focus of several experimental studies with the primary objective of understanding the phenomenon better and proposing physical models for liquid breakup. Various regimes of liquid breakup have been observed both for turbulent and non-turbulent round liquid jets in crossflow, and the effect of variation in physical variables that characterize both the liquid jet injection and crossflow has been investigated (Sallam et al. 2004; Lee et al. 2007). From the experimental datasets, phenomenological scaling laws for various statistics such as liquid jet penetration and trajectory, Sauter mean diameter of drops and wavelength of liquid surface instabilities have been proposed. These models have also been adapted into computational fluid dynamics (CFD) calculations of gas turbine combustors and spray flames (Madabhushi et al. 2004; Raju 2005). Yet, predictive models for primary breakup of turbulent liquid jets that can predict a drop size distribution for a given set of inlet and ambient conditions are still unavailable. Our understanding of the precursors of ligament shedding and drop formation from the surface of the liquid jet is still inadequate to enable us to propose such models. Although experiments have shed light on some of these aspects, further investigation is necessary. It is challenging to obtain detailed measurements in the near field region (close to the injector) and inside the liquid jet that are needed to accurately quantify these precursors. It is also challenging to perform parametric experimental studies that isolate the effect of density ratio, crossflow and liquid jet Reynolds number and other non-dimensional groups related to the LJCF. Using numerical simulations, on the other hand, one can ideally explore the entire parametric space that characterizes the LJCF. With the advent of novel robust and accurate numerical methods to simulate the complex interfacial structures observed during liquid breakup and the availability of large, high-performance computational resources, one is in a position to quantify and understand fundamental mechanisms associated with liquid primary breakup with unprecedented detai.