Experimental investigation on aero-optics of supersonic turbulent boundary layers

Abstract

Nanoparticle-based planar laser scattering was used to measure the density distribution of the supersonic (Ma=3.0) turbulent boundary layer and the optical path difference (OPD), which is quite crucial for aero-optics study. Results were obtained using ray tracing. The influences of different layers in the boundary layer, turbulence scales, and light incident angle on aero-optics were examined, and the underlying flow physics were analyzed. The inner layer plays a dominant role, followed by the outer layer. One hundred OPD of the outer layer at different times satisfy the normal distribution better than that of the inner layer. Aero-optics induced by the outer layer is sensitive to the filter scale. When induced by the inner layer, it is not sensitive to the filter scale. The vortices with scales less than the Kolmogorov scale (=46.0 μm) have little influence on the aero-optics and could be ignored; the validity of the smallest optically active scale (=88.1 μm) proposed by Mani is verified, and vortices with scales less than that are ignored, resulting in a 1.62% decay of aero-optics; the filter with a width of 16-grid spacing (=182.4 μm) decreases OPD by 7.04%. With the increase of the angle between the wall-normal direction and the light-incident direction, the aero-optics becomes more serious, and the difference between the distribution of the OPD and the normal distribution increases. The difficulty of aero-optics correction is increased. Light tilted toward downstream experiences more distortions than when tilted toward upstream at the same angle relative to the wall-normal direction.

A New Method for Analyzing Aero-Optical Effects with Transient Simulation

“…The directional dependence of aero-optical effects has been widely confirmed by experiments and simulations [10,20,28,29]. The method of constructing the density field presented in Section 3.2.1 is for the case of the normal incident beam in Figure 6b.…”

“…The relation between height H and freestream density ρ ∞ is described by an approximate atmospheric density model of ρ ∞ = 1.5373e −0.1462H , where the units for ρ ∞ and H are kg/m 3 and km, respectively. ρ ∞ affects the output of the TSAO through the calibration parameter κ in Equation (28). The density field is divided into five wall height layers, and each layer corresponds to a certain range of structure sizes.…”

Spiral Spectrum of a Laguerre-Gaussian Beam Propagating in Anisotropic Turbulent Plasma

“…Instead, in the field of computational electromagnetics, more attention is paid to the electron density [18][19][20] or collision frequency [21,22] of this medium. Theories and experiments also show that the hypersonic plasma sheath has turbulent characteristics [23,24]. Therefore, similar to the atmospheric turbulence, it also follows the statistical average theory.…”

“…We give the varying range of output OAM spectrum with different Δℓ in Table 1, in which the upper bounds are calculated by (24) and (25). For all Δℓ, its lower bounds is 0, as inf{ΩΔℓ(r)|rM}=limr→+∞ΩΔℓ(r)=0.…”

Validation case for supersonic boundary layer and turbulent aero-optical investigation in high-Reynolds-number freestream by WCNS-E-5

“…One solves the propagation equation dds(ndr→ds)=∇n for the light path after determining the density gradient field. 47 The other traces virtual light particles according to equation (13) based on the uniform flow assumption in each cell, 25,44 with refraction only occurring on the grid interface. The latter method is obviously easier to implement.…”