Numerical simulation of the fluid dynamic effects of laser energy deposition in air.pdf

J. Fluid Mech. (2008), vol. 605, pp. 329–354.
c 2008 Cambridge University Press 329
doi:********** Printed in the United Kingdom
Numerical simulation of the fluid dynamic effects
of laser energy deposition in air
SHANKAR GHOSH AND KRISHNAN MAHESH
Aerospace Engineering and Mechanics, University of Minnesota, MN 55455, USA
(Received 8 June 2006 and in revised form 6 March 2008)
Numerical simulations of laser energy deposition in air are conducted. Local
thermodynamic equilibrium conditions are assumed to apply. Variation of the
thermodynamic and transport properties with temperature and pressure are accounted
for. The flow field is classified into three phases: shock formation; shock propagation;
and subsequent collapse of the plasma core. Each phase is studied in detail. Vorticity
generation in the flow is described for short and long times. At short times, vorticity
is found to be generated by baroclinic means. At longer times, a reverse flow is found
to be generated along the plasma axis resulting in the rolling up of the flow field near
the plasma core and enhancement of the vorticity field. Scaling analysis is performed
for different amounts of laser energy deposited and different Reynolds numbers of
the flow. Simulations are conducted using three different models for air based on
different levels of plexity. The impact of these models on the evolution
of the flow field is discussed.
1. Introduction
The deposition of laser energy into air has been studied by a number of workers
(. Damon & Tomlinson 1963; Knight 2003; Maker, Terhune & Savage 1963;
Meyerand & Haught 1963; Root 1989), and finds application in localized flow
control of supersonic flows (Adelgren et al. 2003; Shneider et al. 2003), drag reduction
in supersonic and hypersonic flows (Riggins, Nelson & Johnson 1999), ignition of
combustion gases (Phuoc 2000) and provision of thrust to aerospace vehicles (Molina-
Morales et al. 2001; Wang et al. 2001). When a laser beam is fo