73 research outputs found
Boundary-layer turbulence as a kangaroo process
A nonlocal mixing-length theory of turbulence transport by finite size eddies is developed by means of a novel evaluation of the Reynolds stress. The analysis involves the contruct of a sample path space and a stochastic closure hypothesis. The simplifying property of exhange (strong eddies) is satisfied by an analytical sampling rate model. A nonlinear scaling relation maps the path space onto the semi-infinite boundary layer. The underlying near-wall behavior of fluctuating velocities perfectly agrees with recent direct numerical simulations. The resulting integro-differential equation for the mixing of scalar densities represents fully developed boundary-layer turbulence as a nondiffusive (Kubo-Anderson or kangaroo) type of stochastic process. The model involves a scaling exponent (with → in the diffusion limit). For the (partly analytical) solution for the mean velocity profile, excellent agreement with the experimental data yields 0.58. © 1995 The American Physical Society
Simulation of wind gust structure in the atmospheric boundary layer with Lattice Boltzmann Method
Particle imaging velocimetry experiments and lattice-Boltzmann simulations on a single sphere settling under gravity
Inclusion of Preferential Diffusion in Simulations of Premixed Combustion of Hydrogen/Methane Mixtures with Flamelet Generated Manifolds
Investigation of Auto-Ignition of a Lifted Methane-Air Jet Flame in Hot Coflow with Progress Variable Approach
Post-processing method for predicting NO formation in one-dimensional and two-dimensional premixed methane- air flames Post-Processing Method for Predicting NO Formation in One- and Two-Dimensional Premixed Methane-Air Flames
Uncertainty Quantification with dependent inputs: wind and waves
A framework for performing uncertainty quantification is presented which is well-suited for systems with dependent inputs with unknown distributions. The multivariate input is given as a dataset whose variables can have strong, nonlinear dependencies. For each of the elements in the framework (dependency analysis, sample selection and sensitivity analysis), we recently developed new methods, which are here combined for the first time. The framework is tested on an example involving a wind farm simulation with offshore weather conditions as input
Towards Unsteady Simulation of Combustor-Turbine Interaction Using an Integrated Approach
In this paper a CFD solver with the ability of dealing with both
reacting and compressible flows is developed, so that an integrated
simulation of the whole. system “combustor and turbine” can be
performed. To its validation, the combustor turbine interaction in a jet
engine consisting of a Rolls-Royce combustor together with the first
high-pressure turbine stage NGV (Nozzle-Guide-Vane) is studied. The
unstructured CFD solver follows a pressure-based approach, using a PISO
algorithm (Pressure Implicit with Splitting of Operator) recently
extended for compressible flows. In order to allow acoustic waves to
leave the computational domain, nonreflecting boundary conditions based
on the NSCBC method (Navier-Stokes Characteristic Boundary Conditions)
have been implemented. The numerical methods have been coupled with the
Flamelet Generated Manifold combustion model (FGM) extended for
compressible flows.
After successfully verifying the NSCBC implementation, various numerical
results describing the combustor-turbine interactions of the jet engine
are analyzed and discussed in terms of temperature and total pressure
fields with and without NGV: It could be shown that the influence of the
NGV on the combustor flow is relatively limited. Differences in the
combustor flow field are mainly due to spatial and temporal averaging
used for the simulation without NGV to calculate the pressure field at
combustor outlet.
These numerical results demonstrate the ability of the developed
numerical model in its steady computation mode to well capture the
evolving flow properties in both combustor and turbine components
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