Flow, Turbulence and Combustion

https://link.springer.com/journal/10494

List of Papers (Total 132)

Statistics of Scalar Flux Transport of Major Species in Different Premixed Turbulent Combustion Regimes for H2-air Flames

The statistical behaviour of turbulent scalar flux and modelling of its transport have been analysed for both major reactants and products in the context of Reynolds Averaged Navier Stokes simulations using a detailed chemistry Direct Numerical Simulation (DNS) database of freely-propagating H2 −air flames (with an equivalence ratio of 0.7) spanning the corrugated flamelets, thin...

Blood Flow Simulations of the Renal Arteries - Effect of Segmentation and Stenosis Removal

Patient specific based simulation of blood flows in arteries has been proposed as a future approach for better diagnostics and treatment of arterial diseases. The outcome of theoretical simulations strongly depends on the accuracy in describing the problem (the geometry, material properties of the artery and of the blood, flow conditions and the boundary conditions). In this...

Flow Characteristics and Coherent Structures in a Centrifugal Blood Pump

Blood clot formation can be initiated by local flow conditions where regions of high shear and long residence time regions, such as flow separation and stagnation, have been identified as risk factors. This study highlights coherent structures, some of which not yet considered in the literature that may contribute to blood clot formation in the ECMO (Extra Corporeal Membrane...

Stretch Rate and Displacement Speed Correlations for Increasingly-Turbulent Premixed Flames

Probability density functions of the components of stretch rate are investigated using a previously-published Direct Numerical Simulation dataset spanning a range of turbulence intensities in the Thin Reaction Zones (TRZ) regime. The dataset was generated by varying the turbulence intensity across five different simulations while maintaining fixed the remaining physico-chemical...

Large Eddy Simulations for Indirect Combustion Noise Assessment in a Nozzle Guide Vane Passage

The combustion noise in aero-engines is known to originate from two different sources. First, the unsteady heat release in the combustion chamber generates the direct combustion noise. Second, hot and cold spots of air generated by the combustion process are convected and accelerated by the turbine stages and give rise to the so-called indirect combustion noise. The present work...

Large Eddy Simulation of a Bluff Body Stabilised Premixed Flame Using Flamelets

Large Eddy Simulations of an unconfined turbulent lean premixed flame, which is stabilised behind a bluff body, are conducted using unstrained flamelets as the sub-grid scale combustion closure. The statistics from the simulations are compared with the corresponding data obtained from the experiment and it is demonstrated that the experimental observations are well captured. The...

A Thickened Stochastic Fields Approach for Turbulent Combustion Simulation

The Stochastic Fields approach is an effective way to implement transported Probability Density Function modelling into Large Eddy Simulation of turbulent combustion. In premixed turbulent combustion however, thin flame-like structures arise in the solution of the Stochastic Fields equations that require grid spacing much finer than the filter scale used for the Large Eddy...

Resolution Requirements in Stochastic Field Simulation of Turbulent Premixed Flames

The spatial resolution requirements of the Stochastic Fields probability density function approach are investigated in the context of turbulent premixed combustion simulation. The Stochastic Fields approach is an attractive way to implement a transported Probability Density Function modelling framework into Large Eddy Simulations of turbulent combustion. In premixed combustion...

Pre-Chamber Ignition Mechanism: Simulations of Transient Autoignition in a Mixing Layer Between Reactants and Partially-Burnt Products

The structure of autoignition in a mixing layer between fully-burnt or partially-burnt combustion products from a methane-air flame at ϕ = 0.85 and a methane-air mixture of a leaner equivalence ratio has been studied with transient diffusion flamelet calculations. This configuration is relevant to scavenged pre-chamber natural-gas engines, where the turbulent jet ejected from the...

Numerical Evaluation of Combustion Regimes in a GDI Engine

There is significant interest in the gasoline direct-injection engine due to its potential for improvements in fuel consumption but it still remains an area of active research due to a number of challenges including the effect of cycle-by-cycle variations. The current paper presents the use of a 3D-CFD model using both the RANS and LES turbulence modelling approaches, and a...

Turbulent Drag Reduction Using Anisotropic Permeable Substrates

The behaviour of turbulent flow over anisotropic permeable substrates is studied using linear stability analysis and direct numerical simulations (DNS). The flow within the permeable substrate is modelled using the Brinkman equation, which is solved analytically to obtain the boundary conditions at the substrate-channel interface for both the DNS and the stability analysis. The...

Spectral Analysis of the Slip-Length Model for Turbulence over Textured Superhydrophobic Surfaces

We assess the applicability of slip-length models to represent textured superhydrophobic surfaces. From the results of direct numerical simulations, and by considering the slip length from a spectral perspective, we discriminate between the apparent boundary conditions experienced by different lengthscales in the overlying turbulent flow. In particular, we focus on the slip...

Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet

Self-activated feathers are used by almost all birds to adapt their wing characteristics to delay stall or to moderate its adverse effects (e.g., during landing or sudden increase in angle of attack due to gusts). Some of the feathers are believed to pop up as a consequence of flow separation and to interact with the flow and produce beneficial modifications of the unsteady...

Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface

In this work we study the turbulence modulation in a viscosity-stratified two-phase flow using Direct Numerical Simulation (DNS) of turbulence and the Phase Field Method (PFM) to simulate the interfacial phenomena. Specifically we consider the case of two immiscible fluid layers driven in a closed rectangular channel by an imposed mean pressure gradient. The present problem...

The Effect of Splitting Timing on Mixing in a Jet with Double Injections

We present large-eddy simulation (LES) of a high-pressure gas jet that is injecting into a quiescent inert environment. The injection is through a nozzle with a diameter of 1.35 mm. Four injection strategies are considered in which the results of a single continuous injection case are compared with those of double injection cases with different injection splitting timing. In all...

Direct Numerical Simulation of Head-On Quenching of Statistically Planar Turbulent Premixed Methane-Air Flames Using a Detailed Chemical Mechanism

A three-dimensional compressible Direct Numerical Simulation (DNS) analysis has been carried out for head-on quenching of a statistically planar stoichiometric methane-air flame by an isothermal inert wall. A multi-step chemical mechanism for methane-air combustion is used for the purpose of detailed chemistry DNS. For head-on quenching of stoichiometric methane-air flames, the...

Large-Eddy BreakUp Devices – a 40 Years Perspective from a Stockholm Horizon

In the beginning of the 1980’s Large Eddy BreakUp (LEBU) devices, thin plates or airfoils mounted in the outer part of turbulent boundary layers, were shown to be able to change the turbulent structure and intermittency as well as reduce turbulent skin friction. In some wind-tunnel studies it was also claimed that a net drag reduction was obtained, i.e. the reduction in skin...

Relaminarization by Steady Modification of the Streamwise Velocity Profile in a Pipe

We show that a rather simple, steady modification of the streamwise velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarizes. Two different devices, a stationary obstacle (inset) and a device which injects fluid through an annular gap close to the wall, are used to control the flow. Both devices modify the streamwise velocity...

Plasma Streamwise Vortex Generators for Flow Separation Control on Trucks

An experimental study of the effect of Dielectric Barrier Discharge plasma actuators on the flow separation on the A-pillar of a modern truck under cross-wind conditions has been carried out. The experiments were done in a wind tunnel with a 1:6 scale model of a tractor-trailer combination. The actuators were used as vortex generators positioned on the A-pillar on the leeward...