## SMALL-SCALE CHARACTERISTICS OF THE FLUCTUATING PASSIVE SCALAR FIELD IN A TURBULENT BOUNDARY LAYER
## ResumoThe objective is to study the effects of mean scalar
gradient on the structure functions and power
spectrum of the fluctuating scalar field. The scalar
field is created by a continuous iso-kinetic release of a
passive scalar ( Re = 1×l0^{4}). Measurements of the scalar field are
performed using the planar laser induced fluorescence
(PUF) technique at four distances downstream of the
source in a vertical plane through the plume
centerline. Scaling exponents in the inertial-convective
range, estimated from the second and
higher (even) order structure functions, show
dependence on the longitudinal scalar gradient. As
the mean longitudinal scalar gradient increases, the
longitudinal exponents decrease from the isotropic
expectation of n/3. Scaling behavior is also noted in the viscous-convective range of the variance
spectrum. The exponent for the dependence on the
wavenumber increases in proportion to the logarithm
of the mean longitudinal scalar gradient. Overall, the
scaling behavior appears to be dependent on the mean
field and agrees with isotropic expectations as the
mean scalar gradient tends toward zero. |

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