Time- and Length Scales of Combustion in Liquid Rocket Thrust Chambers

Correlation of optical emission and turbulent length scale in a coaxial jet diffusion flame

“…The integral length scales in the present simulation are defined as the distance at which the value of correlation function reaches 0.5. This definition of length scale is consistent with the procedure in the experiment by Ivancic and Mayer [7,8]. The length scale defined by this procedure is sufficiently accurate, and the difference between the obtained length scale and that defined by the usual definition (area under the curve) is very small, as stated in [7,8].…”

“…This definition of length scale is consistent with the procedure in the experiment by Ivancic and Mayer [7,8]. The length scale defined by this procedure is sufficiently accurate, and the difference between the obtained length scale and that defined by the usual definition (area under the curve) is very small, as stated in [7,8]. Furthermore, the cost of computing the exact integral length scale can be reduced drastically by this procedure.…”

“…In the procedure proposed by Ivancic and Mayer [7,8], the visible length scale of emission intensity structure is determined by the two point correlation of intensity signals on two neighboring pixels (pixels 1 and 2) as follows: The computation of the length scale by two point correlation is conducted using the intensities of pixels along the symmetry line because only at these pixels it is ensured that light passes through the flame perpendicular to the flame surface [7,8]. Note that the line "  Y 0" in emission image in In the present study, the refraction of light due to density gradient is ignored in the radiative transfer calculations.…”

“…Radiative transfer is then calculated from the LES flame data, and the emission intensity distribution is obtained numerically, giving a simulated emission image of the flame. The length scale is then estimated from the simulated emission images using the procedure proposed by Ivancic and Mayer [7,8]. This will be compared with integral length scales evaluated directly from the LES flowfield data to examine the validity of estimating length scale from emission images.…”

“…As an attempt to obtain quantitative data other than expansion angle, Ivancic and Mayer estimated length scales from spatially and temporary resolved OH* emission images using the two point correlation method [7,8]. They assumed that OH* emission structures are determined by the turbulent coherent structures of vortices, and computed length scales using the two-point correlations of OH* emission intensities.…”