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October 2009 - March 2013

## Publications

Publications (35)

We present a detailed experimental investigation of conditional statistics related to dissipation elements based on the scalar field θ and its scalar dissipation rate x. Based on high frequency two-dimensional measurements of the mass fraction of propane in a turbulent round jet discharging into surrounding air, we acquire data resolving the Kolmog...

Based on local extreme points of the absolute value u of the velocity field ui, streamlines are partitioned into segments as proposed by Wang (J. Fluid. Mech. 648:183–203, 2010). The temporal evolution of the arc length l of streamline segments is analyzed and associated with the motion of the isosurface defined by all points on which the gradient...

Based on a direct numerical simulation (DNS) of a temporally evolving mixing
layer, we present a detailed study of the turbulent/non-turbulent (T/NT) interface that
is deﬁned using the two most common procedures in the literature, namely either
a vorticity or a scalar criterion. The different detection approaches are examined
qualitatively and quan...

Streamlines constitute
natural geometries in turbulent flows. In this work streamlines are segmented based on local extrema of the field of the absolute value of the velocity along the streamline coordinate. Streamline segments are parameterized based on their arclength and a theoretical scaling of the mean length with the geometric mean of the Kol...

In this work, we perform an experimental investigation into statistics based on scalar gradient trajectories in a turbulent jet flow, which have been suggested as an alternative means to analyze turbulent flow fields by Wang and Peters (J Fluid Mech 554:457–475, 2006, 608:113–138, 2008). Although there are several numerical simulations and theoreti...

Streamlines recently received attention as natural geometries of
turbulent flow fields. Similar to dissipation elements in scalar fields,
streamlines are segmented into smaller subunits based on local extreme
points of the absolute value of the velocity field u along the
streamline coordinate s, i.e., points where the projected gradient in
streamli...

Using two-dimensional high-speed measurements of the mixture fraction in a turbulent round jet with nozzle-based Reynolds numbers between 3000 and 18 440, we investigate the scalar turbulent/non-turbulent (T/NT) interface of the flow. The mixture fraction steeply changes from to a final value which is typically larger than 0.1. Since combustion occ...

Based on four different direct numerical simulations of turbulent flows
with Taylor-based Reynolds numbers ranging from Reλ =
50 to 300 among which are two homogeneous isotropic decaying, one forced
and one homogeneous shear flow, streamlines are identified and the
obtained space curves are parameterized with the pseudo-time as well as
the arclengt...

Based on direct numerical simulations of homogeneous shear turbulence,
homogeneous isotropic decaying turbulence and a turbulent channel flow,
the scaling of the two-point velocity difference along gradient
trajectories <Δun|s> as well as between the
extreme points of the instantaneous turbulent kinetic energy field k is
studied. In the first step,...

Based on two large-eddy simulations (LES) of a non-reacting turbulent round jet with a nozzle based Reynolds number of 8,610 with the same configuration as the one that has recently been investigated experimentally (Gampert et al., 2012; J Fluid Mech, 2012; J Fluid Mech 724:337, 2013), we examine the scalar turbulent/non-turbulent (T/NT) interface...

We present a detailed experimental investigation of conditional statistics obtained from dissipation elements based on the passive scalar field θ and its instantaneous scalar dissipation rate χ. Using high-frequency planar Rayleigh scattering measurements of propane discharging as a round turbulent jet into coflowing carbon dioxide, we acquire with...

Based on planar high-speed Rayleigh scattering measurements of the mixture fraction Z of propane discharging from a turbulent round jet into co-flowing carbon dioxide at nozzle-based Reynolds numbers Re 0 = 3000–8600, we use scalar gradient trajectories to investigate the local structure of the turbulent scalar field with a focus on the scalar turb...

The geometrical properties of streamline segments (Wang, 2010 [1]) and their bounding surface (Schaefer et al., 2012 [2]) in direct numerical simulations (DNS) of different types of turbulent flows at different Reynolds numbers are reviewed. Particular attention is paid to the geometrical relation of the bounding surface and local and global extrem...

Based on the profile of the absolute value u of the velocity field ui along streamlines, the latter are partitioned into segments at their extreme points as proposed by Wang [J. Fluid Mech. 648, 183–203 (2010)]10.1017/S0022112009993041. It is found that the boundaries of all streamline segments, i.e., points where the gradient projected in streamli...

In the present work, we present a method to gather highly accurate three-dimensional measurements of a scalar field in order to experimentally validate the theory of dissipation elements as developped by Wang & Peters (2006, 2008). Combining a two-dimensional high-speed Rayleigh scattering technique with Taylor's hypothesis allows to resolve the co...

Based on direct numerical simulations of forced turbulence, shear turbulence, decaying turbulence, a turbulent channel flow as well as a Kolmogorov flow with Taylor based Reynolds numbers Reλ between 69 and 295, the normalized probability density function of the length distribution P̃(l̃) of dissipation elements, the conditional mean scalar differe...

Based on a coordinate transformation, similiar to the one used in the flamelet approach in non-premixed combustion, we introduce a coordinate locally tangent to streamlines and transform the Navier-Stokes equations to an equation for the variation of the absolute value of the velocity ui. Different from previous approaches, the unsteady term splits...

The mechanisms related to the secondary splitting of zero-gradient points of scalar fields are analyzed using the two-dimensional case of a scalar extreme point lying in a region of local strain. The velocity field is assumed to resemble a stagnation-point flow, cf. Gibson (Phys Fluids 11:2305–2315, 1968), which is approximated using a Taylor expan...

In decaying grid turbulence there is a transition from the initial state immediately behind the grid to the state of fully developed turbulence downstream, which is believed to be self-similar. This state is characterized by a power law decay of the turbulent kinetic energy with a time-independent decay exponent n. The value of this exponent, howev...

We compare the results of two large-eddy simulations (LES) of a Kolmogorov flow with 2563 and 1283 grid points respectively against the results of a direct numerical simulation (DNS) with 10243 grid points, which resolves the Kolmogorov scale, employing dissipation element analysis. This method is used to evaluate qualitatively the proper represent...

We present a method to gather highly accurate three-dimensional measurements of a scalar field θ, which in the present study is the concentration field in a turbulent round jet of gaseous propane discharging into air. Combining a two-dimensional high-speed Rayleigh scattering technique with Taylor's hypothesis allows to resolve the Kolmogorov scale...

Due to the liberalization of energy markets in the European Union, today's European utilities not only focus on electricity supply, but also offer exchange-traded “structured products” or portfolio management for unbundling financial and physical risk positions. Many utilities are only able to provide these services in their domestic markets. In a...

Based on direct numerical simulations of forced turbulence, shear turbulence, decaying turbulence, a turbulent channel flow as well as a Kolmogorov flow with Taylor-based Reynolds numbers Reλ between 69 and 295, the normalized probability density function of the length distribution of dissipation elements, the conditional mean scalar difference Δkl...

Gradient trajectories recently received attention in the context of dissipation elements, which are space-filling regions whose theoretical description has successfully been tested via Direct Numerical Simulations (DNS) of homogenous shear flows by Wang and Peters (J. Fluid Mech. 554: 457-475, 2006; J. Fluid Mech. 608: 113-138, 2008). In the presen...

Gradient trajectories recently received attention in the context of dissipation elements, which are space-filling regions whose theoretical description has successfully been tested via Direct Numerical Simulations (DNS) of homogenous shear flows by Wang and Peters (J. Fluid Mech. 554: 457-475, 2006; J. Fluid Mech. 608: 113-138, 2008). In the presen...

A new idea of analysing turbulent premixed flames was inspired by dissipation element analysis developed by Wang and Peters. Starting from every point on the flame surface in the direction of ascending and descending gradient of the underlaying curvature field, while not leaving the flame surface itself, one ends in a local maximum, respectively mi...

To analyze the geometrical properties of scalar turbulent fields, the concept of dissipation elements has been proposed by Peters and Wang (J. Fluid Mech. 2006, 2008). Starting from every grid point, trajectories can be traced in directions of ascending and descending gradient until a local extreme point is reached. Based on these trajectories, a d...

Direct Numerical Simulations (DNS) of Kolmogorov flows are performed at three different Reynolds numbers Re
λ
between 110 and 190 by imposing a mean velocity profile in y-direction of the form U(y) = F sin(y) in a periodic box of volume (2π)3. After a few integral times the turbulent flow turns out to be statistically steady. Profiles of mean quant...

Forschungszentrum ulich GmbH, ulich Supercomputing Centre (JSC), John von Neumann Institute for Computing (NIC), Schriften des Forschungszentrums ulich, IAS Series, Vol. 3, ISBN 978-3-89336-606-4, pp. 365-371. In order to extract small-scale statistical information on turblulent flows from passive scalar fields obtained by direct numerical simulati...

Today’s European utilities not only focus on electricity supply, but also offer exchange-traded “structured products” or portfolio management for unbundling financial and physical risk positions. Many utilities are only able to provide these services inside of their home markets, but in the globalized economy, the need for a centrally organized pan...

Gradient trajectories in scalar fields have recently received attention in the context of dissipation elements [1], [2] which
in turn are of interest for the flamelet concept in nonpremixed combustion [3]. Dissipation elements are space filling regions
in a scalar field defined such that gradient trajectories starting from any point within the elem...