The flame pocket formation, including reactant pocket, product pocket, soot pocket, and fluid parcel, is a common phenomenon in turbulent combustion occurred as a response of the flame to flow straining and shearing. Understanding pocket behavior is vital to study the flames in such a regime. This work addresses the research need to experimentally measure and track multiple flame pockets in 3D. For

In free-field operation, many aerodynamic systems are confronted with changing turbulent inflow conditions. Wind turbines are a prominent example. Here, the rotation of the rotor blades causes incoming wind gusts to result in a local change in the angle of incidence for the blade segments, which changes the effective angle of attack and can lead to dynamic non-linear effects like dynamic stall. Dynamic

Prediction of differential molecular diffusion remains a great challenge for flamelet modeling of turbulent non-premixed combustion. This work addresses this challenge through a priori and a posteriori testing of flamelet models by using DNS databases to enable a detailed examination of the model capability and limitation for the prediction of differential molecular diffusion under different combustion

Scalar forcing in the context of turbulent stratified flame simulations aims to maintain the fuel-air inhomogeneity in the unburned gas. With scalar forcing, stratified flame simulations have the potential to reach a statistically stationary state with a prescribed mixture fraction distribution and root-mean-square value in the unburned gas, irrespective of the turbulence intensity. The applicability

The unsteady effects of buoyancy-induced instabilities on jet diffusion flames are investigated experimentally under normal gravity conditions. Methane and propane are used as test fuels that are lighter and heavier than ambient air, respectively. A similar Froude (Fr) and Reynolds (Re) number relationship is realized in both hydrocarbon fuels with different tube diameters ranging from 6 to 24.2 mm

The effects of varying turbulence intensity and turbulence length scale on premixed turbulent flame propagation are investigated using Direct Numerical Simulation (DNS). The DNS dataset contains the results of a set of turbulent flame simulations based on separate and systematic changes in either turbulence intensity or turbulence integral length scale while keeping all other parameters constant. All

This paper presents an experimental study on dynamic response of a forced low-swirl methane/air premixed flame with external acoustic excitation over a wide range of driving frequency. Global flame response in terms of gain and phase delay between flame intensity and incoming velocity perturbation is determined. Local flame response is investigated in detail at three typical frequencies: 55 Hz, 105 Hz

The physical mechanism leading to flame local extinction remains a key issue to be further understood. An analysis of large eddy simulation (LES) data with presumed probability density function (PDF) based closure (Chen et al., 2020, Combust. Flame, vol. 212, pp. 415) indicated the presence of localised breaks of the flame front along the stoichiometric line. These observations and their relation to

In this paper, a simple method to locally compute the model coefficient \(C_{DES}\) in Reddy et al. (Int J Heat Fluid Flow 50:103–113, 2014. https://doi.org/10.1016/j.ijheatfluidflow.2014.06.002) is presented. The formula for the coefficient is derived from the structural function \(B_{\beta }\) of Vreman (Phys Fluids 16(10):3670–3681, 2004. https://doi.org/10.1063/1.1785131). It, therefore, does not

The mean and instantaneous flow separation of two different three-dimensional asymmetric diffusers is analysed using the data of large-eddy simulations. The geometry of both diffusers under investigation is based on the experimental configuration of Cherry et al. (Int J Heat Fluid Flow 29(3):803–811, 2008). The two diffusers feature similar area ratios of \(\mathrm{AR}=4.8\) and \(\mathrm{AR}=4.5\)

The underlying mechanisms of three different flow-control strategies on drag reduction in a channel flow are investigated by direct numerical simulations at friction Reynolds numbers ranging from 65 to 85. These strategies include the addition of long-chain polymers, the incorporation of slip surfaces, and the application of an external body force. While it has been believed that such methods lead

The hydrodynamic instability characteristics of non-adiabatic N2-diluted n-butane/air flames generated on McKenna burner were investigated experimentally under atmosphere pressure. In order to capture the quantitative structure of cellular flames, planar laser induced fluorescence technology (OH-PLIF and CH2O-PLIF) was employed, as well as the chemiluminescence imaging was used to record flame morphology

An experiment-based closure framework for turbulent combustion modeling is further validated using the Sydney piloted turbulent partially premixed flames with inhomogeneous inlets. The flames are characterized by the presence of mixed mode combustion. The framework’s closure is “trained” on multi-scalar measurements to construct thermo-chemical scalar statistics parameterized in terms of principal

To understanding the initiating process in the pulse detonation curved-chamber and rotating detonation chamber, this article conducted an experimental study on the flame acceleration and the transition to detonation in the annular channel. With different equivalence ratios of acetylene-air and acetylene-oxygen as explosive mixtures, based on high-speed photography and shadow technology, the propagation

Hybrid RANS-LES methods are supposed to provide major contributions, in particular regarding the analysis and prediction of wall-bounded turbulent flows at high Reynolds numbers. Validation data are often unavailable under these conditions, this means we need reliable hybrid RANS-LES having a proven predictive power. The latter depends on the theoretical foundations of these methods. Inspired by a

A noise source characteristic of an unheated compressible jet is experimentally investigated for the jet with exit Mach number 0.8. Measurements of acoustic pressure fluctuations were performed in the near-field and far-field independently to identify noise source characteristics using the correlation technique. Near-field and far-field acoustic pressure fluctuations were also measured simultaneously

The exact placement of the laminar–turbulent transition has a significant effect on relevant characteristics of the boundary layer and aerodynamics, such as drag, heat transfer and flow separation on e.g. wings and turbine blades. Tripping, which fixes the transition position, has been a valuable aid to wind-tunnel testing during the past 70 years, because it makes the transition independent of the

A transitional hybrid RANS–LES model is devised to replicate the flow around a cyclist mannequin which is positioned at the high-drag position. The transitional model of Cakmakcioglu et al. (Proc Inst Mech Eng C J Mech Eng Sci 232(21):3915–3929, 2018) which is a modified Spalart–Allmaras model, is used to simulate the transitional flow with a coarse grid close to the solid walls, while the flow is

An amendment to this paper has been published and can be accessed via the original article.

The evolution of the capillary breakup of a liquid jet under large excitation amplitudes in a parameter regime relevant to inkjet printing is analysed using three-dimensional numerical simulations. The results exhibit a reversal of the breakup length of the jet occurring when the velocity scales associated with the excitation of the jet and surface tension are comparable, and an inversion of the breakup

In particle-laden flows, a turbulent field can be produced in the carrier phase by the movement of the particle/spray cloud. In this study, the intensity and the integral length scale of the particle-induced turbulence are studied using a simple mechanistic model with comparison to experimental data and numerical simulations for large-scale numerical applications. The experimental results of DynAsp

The predictive simulation of gas–liquid multiphase flows at industrial scales reveals the challenging task to consider turbulence and interfacial structures, which span a large range of length scales. For simulation of relevant applications, a hybrid model can be utilised, which combines the Euler–Euler model for the description of small interfacial structures with a volume-of-fluid model as a scale-resolving

The paper is devoted to an adjoint complement to the universal Law of the Wall (LoW) for fluid dynamic momentum boundary layers. The latter typically follows from a strongly simplified, unidirectional shear flow under a constant stress assumption. We first derive the adjoint companion of the simplified momentum equation, while distinguishing between two strategies. Using mixing-length arguments, we

The present study investigates the transient processes controlling ignition by a hot jet issued from a pre-chamber. Direct numerical simulations (DNS) have been performed to study the characteristics of the turbulent jet flow and of the associated flame during the whole ignition process, quantifying the relevant physicochemical interactions between pre-chamber and main chamber. Thanks to a detailed

A three-dimensional Direct Numerical Simulation (DNS) database of statistically planar \(H_{2} -\) air turbulent premixed flames with an equivalence ratio of 0.7 spanning a large range of Karlovitz number has been utilised to assess the performances of the extrapolation relations, which approximate the stretch rate and curvature dependences of density-weighted displacement speed \(S_{d}^{*}\). It has

The generation of initial or inflow synthetic turbulent velocity or scalar fields reproducing statistical characteristics of realistic turbulence is still a challenge. The synthetic eddy method, previously introduced in the context of inflow conditions for large eddy simulations, is based on the assumption that turbulence can be regarded as a superposition of coherent structures. In this paper, a new

In a cavitating water jet, cavity clouds emerge and collapse with an unsteady, but periodic tendency where the frequencies depend on the working conditions. The presented work aims at examining and analyze the dynamic behavior and properties of the clouds under different circumstances. Computer vision and image processing were introduced as tools to define the cavitation clouds based on the Contour

The local-correlation laminar-turbulent transition model of Langtry and Menter has seen use over a wide range of fluid dynamic flows. The model is often coupled to two-equation turbulence models via modification to the turbulent kinetic energy equation. A near-wall analysis of turbulent kinetic energy and specific dissipation shows that the coupling of the transition model introduces singular behavior

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is a promising technique to reduce pollutant emissions of combustion processes, especially nitrogen oxides. This combustion mode involves Turbulence-Chemistry Interaction (TCI), which constitutes a challenge in terms of numerical simulation since it must be properly captured. Up to now, the TCI has been modelled and the corresponding models

This work reports the development and validation of evaluation methods for measurements of 3D, instantaneous, local flame propagation speed on a turbulent methane jet diffusion flame. Despite its fundamental importance to turbulent flame research, the experimental measurements for 3D flame propagation speed are scarce due to the complexity of turbulent flame surfaces and the mathematical challenges

The unsteady air flow around a train and a noise barrier can be intensified due to the partially enclosed space when the train passes through the barrier. This may lead to the accidents, such as noise barrier failure. Therefore, in this study, the evolution of dynamic pressure loads, transient air velocities, and wake structures were investigated using an improved delayed detached eddy simulation (IDDES)

Aerodynamic resistance changes in the atmospheric surface layers (ASLs), such as coastal zones and rural–urban interface, complicate the transport processes. Their effect on ASL flows is investigated by the large-eddy simulation (LES) with the one-equation subgrid-scale model. The roughness elements at the bottom are explicitly resolved by sinusoidal wavy surfaces to examine the coupling between roughness

Gas turbines for power generation are optimised to run with fossil fuels but as a response to tighter pollutant regulations and to enable the use of renewable fuels there is a great interest in improving fuel flexibility. One interesting renewable fuel is syngas from biomass gasification but its properties vary depending on the feedstock and gasification principle, and are significantly different from

This work addresses a shortcoming of the beta distribution when applied to assumed probability density function (PDF) methods for reactive flow, such as the flamelet-progress variable method. Regardless of parameter values, the beta distribution contains the entire sample space of a conserved scalar, which can be shown to violate the strong maximum principle of partial differential equations. To remedy

Ultra-lean burn conditions (λ > 1.8) is seen as a way for improving efficiency and reducing emissions of spark-ignition engines. It raises fundamental issues in terms of combustion physics and its modeling, among which the significant reduction of the laminar flame speeds and increase of the laminar flame thickness, as well as an increased sensitivity to local fuel/air equivalence ratio variations

The Shannon entropy is a rigorous measure to evaluate the complexity in dynamical systems. Shannon entropy can be directly calculated from any set of experimental or numerical data and yields the uncertainty of a given dataset. Originating from information theory, the concept can be generalized from assessing the uncertainty in a message to any dynamical system. Following the concept of ergodicity

Jet fuels with various properties are desirable for different operational or environmental advantages, necessitating fuel-flexible technology. For example, JP-5 (A-3) and alternative jet-fuels with high flash points are favored for safe handling and other advantages. The study investigates the effects of fuel properties on the near-field spray characteristics of the relatively viscous A-3 and a more

Body forces such as buoyancy and externally imposed pressure gradients are expected to have a strong influence on turbulent premixed combustion due to the considerable changes in density between the unburned and fully burned gases. The present work utilises Direct Numerical Simulation data of three-dimensional statistically planar turbulent premixed flames to study the influence of body forces on the

Laminar flamelet decomposition (LFD) is a dynamic approach for modelling sub-filter scale turbulence-chemistry interactions in Large-Eddy Simulations using a stretched flamelet library. In this work, the performance of the LFD model – that was previously used only in non-premixed combustion—is investigated a priori for premixed combustion using positively-strained flamelets in the reactant-to-product

Three-feed combustion systems in which fuel gas, oxygen, and diluent (\(\hbox {CO}_{2}\)) are issued into a combustor are key components to realize an oxy-fuel type gas turbine in a zero-emission plant. Yet, simulations of such systems using mixture fraction-based models are difficult, since multiple mixture fractions are required to describe the system. In this study, large-eddy simulations (LES)

We present an experimental and numerical study of the turbulent boundary layer at \(1200< Re_{\theta} <3400\). We propose a combined approach that involves the use of a multi-hole pitot probe, hot-wire anemometry and direct numerical simulations, that allows to characterise the isotropy and the energy dissipation scalings of the flow in the outer layer, in the range \(0.4< y/\delta <0.75\), with y

A high-order low dissipative numerical framework is discussed to tackle simultaneously the modeling of unresolved sub-grid scale flow turbulence and the capturing of shock waves. The flows around two different airfoil profiles are simulated using a Spectral Difference discretisation scheme. First, a transitional, almost incompressible, low Reynolds number flow over a Selig-Donovan 7003 airfoil. Second

The isothermal mixing of a heavy and a light liquid of different physical properties is numerically investigated by means of Large Eddy Simulations. The validation is based on experimental data held in a system reproducing various components of a pressurized water nuclear reactor, during a scenario of cold water injection at a low Atwood number of 0.05. The flow has two distinct stages: first a buoyancy-driven

The partially integrated transport modeling (PITM) method first introduced in Refs. Schiestel and Dejoan (Theor Comput Fluid Dyn 18:443, 2005) and in Chaouat and Schiestel (Phys Fluids 17:065106, 2005) provides a continuous approach for hybrid RANS-LES simulations. Inspired from the multiple scale approach, the basis of the development of the method is the spectral space in quasi-homogeneous turbulence

A direct numerical simulation (DNS) of the incompressible flow around a rectangular cylinder with chord-to-thickness ratio 5:1 (also known as the BARC benchmark) is presented. The work replicates the first DNS of this kind recently presented by Cimarelli et al. (J Wind Eng Ind Aerodyn 174:39–495, 2018), and intends to contribute to a solid numerical benchmark, albeit at a relatively low value of the

Multiplication of hydroxyl and formaldehyde planar laser-induced fluorescence signals for turbulent hydrogen-enriched methane–air flames with compositionally inhomogeneous mixtures is investigated experimentally. Hydrogen-enriched methane–air flames with a global fuel–air equivalence ratio of 0.8 and hydrogen-enrichment percentage of 60% are examined. Two nozzles, each containing 4 fuel/air injection

Bluff-body flame instabilities are experimentally investigated under varying turbulence conditions during lean blowout. For all turbulence conditions, the blowout process is induced through a temporal reduction of the fuel flow rate to capture the flame-flow dynamics approaching blowout. Simultaneous high-speed particle image velocimetry (PIV), stereoscopic PIV, and C2*/CH* chemiluminescence imaging

Stratified propane air flames stabilized in the near wake region of a premixer/disk arrangement were investigated for a variety of inlet mixture compositions and preheating temperatures. The employed burner is capable of anchoring flames at very lean mixtures, expanding the lean flammability limits and promoting flame stabilization, at global equivalence ratio values of \(\Phi =0.13\) at 743 K. Particle

Hybrid RANS–LES approaches have aroused interest for years since they provide unsteady information at a reduced numerical cost compared to LES. In the hybrid context, the use of temporal filtering, to control the energy partition between resolved and modeled scales, ensures a consistent bridging between RANS and LES models. In this regard, a new formulation of Hybrid Temporal Large Eddy Simulation

The interaction of turbulent flows with the external structure of ground vehicles generates uncomfortable noise and a lot of attention is devoted to find new mechanisms for its suppression. The present work is concerned with open cavity flows, very often found in the automotive industry. A three-dimensional rectangular very wide open cavity with aspect ratio \(L/D=4\) at Reynolds number \(Re_D=5000\)

A method based on linear forcing is developed to generate realistic turbulent fluctuations at the inlet of a computational domain. The method uses a precursor computation of convected forced isotropic turbulence and variables are extracted from a plane to be imposed at the inlet of the main simulation. In the precursor computation, the turbulent fluctuations are generated and sustained using a synthetic

The paper focuses on a global instability phenomenon in counter-current round jets issuing from co-axial nozzles. Three different configurations that differ in a way of the counter flow generation are investigated. Besides typical configurations used in experimental and numerical research performed so far, in which suction applied in an annular nozzle is a driving force for the counterflow, a novel

The present paper deals with the large-eddy simulation (LES) of a zero-pressure-gradient smooth flat-plate boundary layer undergoing bypass transition due to the presence of freestream turbulence of intensity around \(3.0\%\). Transition has been achieved by the introduction of synthetic turbulence into the freestream in a manner designed to invoke a behaviour closely resembling that of the ERCOFTAC

The transition of thermo-acoustic oscillations in a turbulent bluff-body syngas combustor is analyzed experimentally in the present work. The analysis was carried out for three syngas compositions using simultaneous, unsteady pressure measurement and OH* chemiluminescence across the variation of Reynolds number, Re, over 2289–8009 range. It is observed that across the variation of controlled parameters

A trend towards the increasing use of Adaptive Mesh Refinement (AMR) algorithms to simulate combustion processes is observed in the recent literature. AMR is attractive as it enables the physical phenomena of interest to be tracked by the numerical mesh, reducing the computational cost drastically. It is particularly efficient for combustion as small computational cells are needed very locally to resolve

Combustion simulations with high fidelity turbulence models and detailed chemistry may suffer from high computational power requirements due to the combined cost of time-scale dissipation and small integration steps. Such a limitation can be avoided by employing a hybrid reaction mechanism reduction method called local self-similarity tabulation (LS2T). LS2T directly solves several dominant species

A computational investigation of three configurations of the Delft Spray in Hot-diluted Co-flow (DSHC) is presented. The selected burner comprises a hollow cone pressure swirl atomiser, injecting an ethanol spray, located in the centre of a hot co-flow generator, with the conditions studied corresponding to Moderate or Intense Low-oxygen Dilution (MILD) combustion. The simulations are performed in

In this study, experimental measurements are performed on a swirl-stabilized combustor to study the nonlinear combustor dynamic characteristics under acoustic excitations. The imposed acoustic disturbances with different frequencies and amplitudes generated by a loudspeaker are applied to the combustion system. The acoustic pressure oscillations and heat release rate fluctuations are measured using

Feedback-free internal impinging nozzle, which can generate fan-shape oscillating spray with constant pendulum angle, is well-suitable for flow control, as it has a wide range of operation frequency and does not require additional energy for moving parts. In this study, the spray characteristics of an internal impinging nozzle were investigated in an open atomization test bench by utilizing high-speed

This research deals with the oscillation frequency of a classical and simple flip-flop jet nozzle with one feed-back loop based on the measurements of pressure and velocity. From these measurements, the traces of pressure difference between both ends of a connecting tube are modeled by a triangular wave, and the flow velocities in the connecting tube are calculated numerically. The resulting accumulated