Investigation of dissipation elements in a fully developed turbulent channel flow by tomographic particle-image velocimetry

Abstract

A new method to describe statistical information from passive scalar fields has been proposed by Wang and Peters ͓"The length-scale distribution function of the distance between extremal points in passive scalar turbulence," J. Fluid Mech. 554, 457 ͑2006͔͒. They used direct numerical simulations ͑DNS͒ of homogeneous shear flow to introduce the innovative concept. This novel method determines the local minimum and maximum points of the fluctuating scalar field via gradient trajectories, starting from every grid point in the direction of the steepest ascending and descending scalar gradients. Relying on gradient trajectories, a dissipation element is defined as the region of all the grid points, the trajectories of which share the same pair of maximum and minimum points. The procedure has also been successfully applied to various DNS fields of homogeneous shear turbulence using the three velocity components and the kinetic energy as scalar fields ͓L. Wang and N. Peters, "Length-scale distribution functions and conditional means for various fields in turbulence," J. Fluid Mech. 608, 113 ͑2008͔͒. In this spirit, dissipation elements are, for the first time, determined from experimental data of a fully developed turbulent channel flow. The dissipation elements are deduced from the gradients of the instantaneous fluctuation of the three velocity components uЈ, vЈ, and wЈ and the instantaneous kinetic energy kЈ, respectively. The measurements are conducted at a Reynolds number of 1.7ϫ 10 4 based on the channel half-height ␦ and the bulk velocity U. The required three-dimensional velocity data are obtained investigating a 17.75ϫ 17.75ϫ 6 mm 3 ͑0.355␦ ϫ 0.355␦ ϫ 0.12␦͒ test volume using tomographic particle-image velocimetry. Detection and analysis of dissipation elements from the experimental velocity data are discussed in detail. The statistical results are compared to the DNS data from Wang and Peters ͓"The length-scale distribution function of the distance between extremal points in passive scalar turbulence," J. Fluid Mech. 554, 457 ͑2006͒; "Length-scale distribution functions and conditional means for various fields in turbulence," J. Fluid Mech. 608, 113 ͑2008͔͒. Similar characteristics have been found especially for the pdf's of the large dissipation element length regarding the exponential decay. In agreement with the DNS results, over 99% of the experimental dissipation elements possess a length that is smaller than three times the average element length.

Simultaneous Stereo PIV and MPS3 Wall-Shear Stress Measurements in Turbulent Channel Flow

“…Previous PIV and laser Doppler velocimetry measurements showed that the flow inside the measurement section is two-dimensional and fully turbulent. Tomographic PIV measurements have successfully been applied to investigate turbulent flow structures such as dissipation elements [31].…”

Dissipation Element Analysis of Turbulent Premixed Jet Flames

“…An important characteristic of the statistics of the separation length , is its invariance toward changes in Reynolds numbers when normalized with the mean length , Ã ¼ ,=, m Schaefer et al, 2011;Gampert et al, 2013a). The probability density functions (PDF) of the normalized separation length Pð,=, m Þ are shown in Figure 4 for all cases both in linear and linear logarithmic scale.…”

Stability of Dissipation Elements: A Case Study in Combustion

“…For example, dissipation elements were used to understand the scales of scalar structures in DNS of homogeneous shear turbulence [WP06, WP08], to measure the turbulence scales as a function of distance from a wall structure in a wall‐bounded fluid flow [AO11], to partition a DNS of temporally evolving shear layer into laminar, turbulence interface, and turbulent regions [MWP09], and to apply the same zonal partitioning and statistics to experimental data collected using high‐speed Laser‐Rayleigh scattering imaging [GSNP13]. Recently, Schaefer et al [SDKS11] computed dissipation elements for the first time on experimental data of a fully developed turbulent channel flow using tomographic particle‐imagery velocimetry. Schaefer et al [SGP12] have extended the concept of dissipation elements to velocity fields to study flow‐inherent properties.…”