Scalar dissipation rate measurements in a starting jet

Abstract

Measurements of the scalar dissipation rate are performed in an impulsively started gas jet, using planar laser induced fluorescence. The measurements are well resolved spatially. The deteriorating effect of experimental noise on this experiment is treated with a Wiener filter, which is shown to be applicable to this large-scale inhomogeneous flow. The accuracy of the scalar dissipation rate is within 20%, as determined from an explicit calculation of the filtering errors. The residual fields that remain after the filtering are analysed in detail and their statistical properties show that these resemble white noise to a good approximation. The level of corrections is minimal for the scalar field but it is of the order of 40% for the scalar dissipation rate. An examination of the filtering operation using modeled spectra and the measured spatial resolution shows that the Wiener filter produces errors in the estimate of the scalar dissipation rate ∼ 30%, for Taylorscale Reynolds number up to 1000. The implications of this modelling are discussed with respect to common experimental situations and point out the relative merits of improving the spatial resolution as compared to improvements in the signal to noise ratio.

The role of temperature, mixture fraction, and scalar dissipation rate on transient methane injection and auto-ignition in a jet in hot coflow burner

“…The jet penetration was found to scale linearly with time until the jet tip reaches a certain distance from the nozzle exit; afterwards, the jet penetration scales with the square root of time [33] . Soulopoulos et al [34] performed scalar dissipation rate measurements in a starting jet and found that high values of scalar dissipation rate were concentrated at the jet boundary as well as at random regions in the jet body.…”

Mixing and scalar dissipation rate statistics in a starting gas jet

“…More details on the experimental setup, the data processing and the error assessment are provided in Ref. 36.…”

Evaluation of the topological characteristics of the turbulent flow in a ‘box of turbulence’ through 2D time-resolved particle image velocimetry

“…In the current work, the PSF is represented by a Gaussian profile, which is expected for most of the optical systems without the presence of an image intensifier that alters the PSF with a longer tail. In the context of fluid mechanics, where the Wiener Filter is applied to the two-dimensional velocity vector field, the estimation of spectral density of noise and un-blurred noise-free 'image' is achieved via kinetic energy power spectrum following the approach of Soulopoulos et al (2014). The kinetic energy power spectrum of the turbulent flow condition, detailed in Table 1, is shown in Fig.…”

“…5. According to the procedure described by Soulopoulos et al (2014), power spectral density estimation is shown in Fig. 5.…”

“…The line spread function (LSF) is the PSF along a given direction and could be measured by the scanning edge-knife technique (Soulopoulos et al 2014) as the first order derivative of the edge spread function (ESF) or estimated according to a Gaussian profile when the image intensifier is not employed in the optical system. The Fourier transform of the line spread function is an important parameter in the process of digital filtering and is generally referred to as the modulation transfer function (MTF).…”