Han Wenhu

• Professor (Associate) at Beijing Institute of Technology

In recent years, boundary layer flame flashback (BLF) has re-emerged as a technological and operational issue due to the more widespread use of alternative fuels as a part of a global effort to promote carbon neutrality. While much understanding has been achieved in experiments and simulations of BLF in the past decades, the theoretical modeling of...

This work carries out simulations on the initiation and propagation of Aluminum (Al)-particle/C 2 H 2 /air detonations in a one-dimensional (1D) planar geometry, based on the Euler-Euler two-phase flow models and the 5 th -order weighted essentially non-oscillatory (WENO) scheme. The effect of Al particles on 1D detonation is studied by changing Al...

Inward-propagating cylindrical flames are studied numerically by high-resolution simulations using a one-step Arrhenius kinetics. Emphasis is placed on the effect of shock waves on the flame propagation by setting initial ignition conditions with and without shock wave. It is found that without initial shock wave, the inward-propagating flame propa...

In the field of explosion accidents and the combustion chamber of propulsion systems, gaseous mixtures are more likely to be highly non-uniform and a detonation usually propagates in a non-homogeneous medium. In this paper, one-dimensional (1D) pulsating detonations propagating in non-homogeneous medium with concentration gradient are studied by di...

Numerical simulations have been conducted to investigate the effects of ozone (O3) sensitization on pulsating and cellular instabilities of one- and two-dimensional (1-, 2D) detonations in hydrogen–oxygen–helium (H2/O2/He) mixture with and without O3 addition. The predictions have been analyzed to illustrate the different modes of 1D detonation in...

The study of detonation initiation under supersonic incoming flow is of significance for the supersonic air-breathing propulsion based on detonation waves. By high-resolution simulations based on the 5 th order weighted essentially non-oscillatory (WENO) and a two-step reaction model, this paper addresses the effect of incoming flow on re-initiatio...

This work numerically studies the propagation characteristics of detonation waves with multi-stage heat releases (MSHR) for stoichiometric dimethyl ether/oxygen (DME/O 2) mixtures with carbon dioxide (CO 2) addition. Results show that detonation with MSHR is intrinsically unstable and will develop to a new mode. It is found that in the mixtures wit...

Flame propagation in Hele-Shaw cells with a micro-sized gap was experimentally investigated. The evolution of flame front morphology was recorded via Schlieren photographs as the hydrogen-oxygen (H2–O2) mixture was ignited at ambient temperature and pressure. By varying gap size, two different regimes of flame propagation are identified: 1) the non...

One-dimensional, unsteady gaseous detonation propagation in a non-homogeneous medium is investigated numerically using the reactive, compressible Navier-Stokes equations with detailed chemistry. The effect of concentration inhomogeneity on the pulsating mode is modeled by a sinusoidal distribution of H 2 mole fraction in a H 2-O 2 mixture. The mixt...

Deflagration-to-detonation transition (DDT) in a macroscale tube is investigated experimentally for stoichiometric ethylene-oxygen with O 3 (ozone) addition. The effect of O 3 addition on the DDT process is studied, including its dependence on initial pressure. This kinetic effect of ozone addition was investigated by examining the influence of ozo...

This work studies numerically the spontaneous initiation and sustenance of a detonation wave from a hot spot with a nonuniform initial temperature embedded within an H2–O2 mixture with and without O3 addition. For the case with either no or just a small amount of O3 addition, a weak reaction wave is auto-ignited at the hot spot, accelerates and the...

A two-dimensional detonation in H 2 –O 2 system is simulated by a high-resolution code based on the fifth-order weighted essentially non-oscillatory (WENO) scheme in the spatial discretization and the 3th-order additive Runge–Kutta schemes in the time discretization, by using a detailed chemical model. The effect of a concentration gradient on cell...

The effects of cold, hot, and adiabatic walls on flame propagation and deflagration-to-detonation transition (DDT) in a microscale channel are investigated by high-resolution numerical simulation. Results show that the conducting, cold, and hot walls lower the flame acceleration rate, while DDT can occur and originate from local explosion near the...

Classical modes of one-dimensional (1D) detonation characterized by a simplified reaction model are reproduced by using a real chemical kinetics for the H2−O2 system with argon dilution. As Ar dilution is varied, the bifurcation points of pulsating instability are identified and a formed bifurcation diagram is compared with that obtained by the one...

Effects of tube diameter and equivalent ratio on flame propagation characteristics of lean ethylene–oxygen mixtures in millimeter-scale cylindrical tubes were experimentally investigated. Five different flame propagation modes—1) steady propagation mode (SPM), 2) jerky flame mode (JFM), 3) oscillating flame mode (OFM), 4) oscillating flame transiti...

The hot jet injection is utilized to actively control the oblique detonation wave, such as initiating and stabilizing an oblique detonation wave at a desired position that is shorter than the length of induction zone, and adjust the height of the oblique detonation wave at the exit of combustor when the oblique detonation wave engine is working on...

The effect of low-temperature chemistry (LTC) on flame acceleration and detonation onset has been investigated using high-resolution one-dimensional unsteady numerical simulations performed with detailed chemistry. A stoichiometry propane-oxygen mixture diluted with 85% by mole of CO2 was considered with initial pressure and temperature of 300 K an...

The coupled effect of wall heat loss and viscosity friction on flame propagation and deflagration to detonation transition (DDT) in micro-scale channel is investigated by high-resolution numerical simulations. The results show that when the heat loss at walls is considered, the oscillating flame presents a reciprocating motion of the flame front. T...

The numerical simulation of supersonic flow over a cone is carried out to investigate oblique detonation waves. A three-dimensional (3D) conical oblique detonation wave is studied by changing the heat release. It is found that the formation of a conical oblique detonation wave shifts from a moderate transition to an abrupt transition and the fronta...

The role of a transversal concentration gradient in detonation propagation in a two-dimensional channel filled with an $\text{H}_{2}{-}\text{O}_{2}$ mixture is examined by high-resolution simulation. Results show that, compared to propagation in homogeneous media, a concentration gradient reduces the average detonation velocity because of the delay...

The structure and propagation of the one-dimensional (1-D) detonation for the H2O2 system with argon dilution are calculated by solving the Euler and the diffusive NS equations. Classical detonation modes characterized by simplified reaction model are reproduced, including the highly unstable chaotic detonation, mildly unstable detonation with mult...

Premixed and partially premixed flames (PPFs) of H2/CO/air syngas are studied numerically to investigate the effect of pressure on syngas PPF structure. Chemical characteristics of the syngas flame at different pressures are investigated based on reaction limit analysis using a one-dimensional configuration. The results show that CO affects the syn...

Cylindrical detonations propagating in free space characterized by different activation energies were computationally studied. It is found that unstable detonations with the 2-D cellular structure have more velocity deficit than those without the cellular structure computed with the 1-D simulation. The weakening is due to lengthening of the detonat...

Cylindrical detonations propagating in free space characterized by different activation energies were computationally studied. It is found that unstable detonations with the 2-D cellular structure have more velocity deficit than those without the cellular structure computed with the 1-D simulation. The weakening is due to lengthening of the detonat...

Large eddy simulations (LES) for turbulent flames with detailed kinetic mechanisms have received growing interest. However, a direct implementation of detailed kinetic mechanisms in LES modelling of turbulent combustion remains a challenge due to the requirement of huge computational resources. An on-the-fly mechanism reduction method named correla...

In order to investigate the characteristics of correlated dynamic adaptive chemistry(CO-DAC)in turbulent combustion,a LES for nonpremixed jet flame Sandia Flame-D was conducted using GRI-Mech 3.0 detailed chemical mechanism with CO-DAC reduction method.The comparison between simulated results and experimental data demonstrates that using detailed c...

In the paper flame propagation in cylindrical confinement was simulated outwardly by high-resolution computing. It is first found that globally cylindrical flame acceleration contains three stages: exponential self-acceleration led by intrinsic instability, linear acceleration caused from gas compressibility, and ultrafast acceleration resulted fro...

The direct initiation of detonations in one-dimensional (1D) and two-dimensional (2D) cylindrical geometries is investigated through numerical simulations. In comparison of 1D and 2D simulations, it is found that cellular instability has a negative effect on the 2D initiation and makes it more difficult to initiate a sustaining 2D cylindrical deton...

The entire process of deflagration-to-detonation transition (DDT) is studied through direct numerical simulations in narrow channels. Calculations with adiabatic and heat-loss boundaries are conducted to investigate the effect of heat loss to walls on flame acceleration and DDT. The numerical results show that heat loss reduces the flame accelerati...

The integrated processes of flame acceleration, deflagration-to-detonation transition (DDT), and the resulting detonation propagation in micro- and macro-scale channels are simulated. It is found that the modes of flame acceleration and DDT in these two channels are different, being primarily controlled by viscosity and turbulent flame development,...

The role of the global curvature on the structure and propagation of cylindrical detonations is studied allowing and without allowing the development of cellular structures through two-dimensional (2-D) and 1-D simulations, respectively. It is shown that as the detonation transitions from being overdriven to the Chapman–Jouguet (CJ) state, its stru...

In numerical simulation of gaseous detonation, due to the complexity of the computational domain, negative density and pressure often emerge in high resolution numerical computing, which leads to blow-ups. The paper provides high order discontinuous Galerkin (DG) positivity-preserving scheme for two-dimensional (2D) Euler equations with two-step ch...

In this paper, by adopting a fifth-order weighted essentially non-oscillatory (WENO) scheme with a third-order TVD Runge–Kutta time stepping method for two-dimensional reactive Euler equations, a parallel code is developed, and reignition behavior after a self-sustaining detonation from the tube into free space filled with H2/O2 mixtures is investi...

The high order inverse Lax-Wendroff (ILW) procedure is extended to boundary treatment involving complex geometries on a Cartesian mesh. Our method ensures that the numerical resolution at the vicinity of the boundary and the inner domain keeps the fifth order accuracy for the system of the reactive Euler equations with the two-step reaction model....

The globally planar detonation in free space is numerically simulated, with particular interest to understand and quantify the emergence and evolution of the onedimensional pulsating instability and the two-dimensional cellular structure which is inherently also affected by pulsating instability. It is found that the pulsation includes three stages...

In numerical simulation of 3D gas detonation, due to the complexity of the computational domain in high resolution numerical computing negative density and pressure often emerge, which leads to blow-ups. In addition, a large number of grids resulting from relative mesh resolution and large-scale computing domain consume tremendous computing resourc...

In this paper a high-resolution, large-scale and parallel software is used to simulate methane explosion resulting from methane outburst in complicated laneway. Numerical results show that due to diffraction and reflection interaction in complicated laneway, the complicated wave structure can be formed. Explosion wave diffracts at the turning of la...

In this paper, we develop a three-dimensional parallel solver using the fifth order high-resolution weighted essentially non-oscillatory (WENO) finite difference scheme to perform extensive simulation for three-dimensional gaseous detonations. A careful study is conducted for the propagation modes of three-dimensional gaseous detonation wave-front...

The effect law of kinetics parameters was investigated extensively. The results show that the activation energy, heat release and overdrive factor have great influence on the characteristics of detonation propagation and the detonation cellular width. When the overdrive factor is 1.0, the detonation cellular width decreases with the increase in the...

In numerical simulation of three-dimensional gaseous detonation, a large number of grids resulting from relative mesh resolution and large-scale computing domain consume tremendous computing resources, which brings a great challenge for the numerical simulation. Based on MPI parallel mode, this paper uses 5-th order WENO scheme to discrete partial...

We investigate the evolution of cylindrical cellular detonation with different instabilities. The numerical results show that with decreasing initial temperature, detonation becomes more unstable and the cells of the cylindrical detonation tend to be irregular. For stable detonation, a divergence of cylindrical detonation cells is formed eventually...

In this paper we developed a parallel code, adopting a fifth-order weighted essentially non-oscillatory (WENO) scheme with a third-order TVD Runge-Kutta time stepping method for the two-dimensional reactive Euler equations, to investigate the propagation process of methane explosion in bend ducts. In the simulations, an inverse Lax–Wendroff procedu...