Large-eddy simulation(LES) is under its rapid development and is recognized as a possible second generation of CFD methods used in engineering.Large-eddy simulation of two-phase flows and combustion is particularly im...Large-eddy simulation(LES) is under its rapid development and is recognized as a possible second generation of CFD methods used in engineering.Large-eddy simulation of two-phase flows and combustion is particularly important for engineering applications.Some investigators,including the present authors,give their review on LES of spray combustion in gas-turbine combustors and internal combustion engines.However,up to now only a few papers are related to the state-of-the-art on LES of gas-particle flows and combustion.In this paper a review of the advances in LES of complex gas-particle flows and coal combustion is presented.Different sub-grid scale(SGS) stress models and combustion models are described,some of the main results are summarized,and some research needs are discussed.展开更多
A numerical study was conducted to seek an optimized dimension of jet chamber in the pulsating impinging flow.The flow and heat transfer effect of the pulsation flow through a jet chamber was investigated.The numerica...A numerical study was conducted to seek an optimized dimension of jet chamber in the pulsating impinging flow.The flow and heat transfer effect of the pulsation flow through a jet chamber was investigated.The numerical results indicate that heat transfer effective enhances near the stagnation region for the intermittent pulsed flow with jet chamber compared to that without jet chamber.Simulations of the flow through a jet chamber show that the heat transfer rate on the impingement surface is highly dependent on the velocity at the position which is really close to target surface.Examination of the velocity field suggests that the velocity exists a maximum value as the axis distance increases.In addition,the velocity at the jet hole is enlarged by the jet chamber due to the entrainment effect,and the velocity is amplified even greater as the size of the jet chamber becomes bigger.Nevertheless,the velocity declines quickly while the flow axis distance is more than a certain range,leading to poor heat transfer.Thus,intermittent pulsed flow with jet chamber is suggested as a method of improving heat transfer by employing larger dimensions of jet chamber for appropriate jet-to-surface spacing.展开更多
Lean premixed combustion,which allows for reducing the production of thermal NOx,is prone to combustion instabilities.There is an extensive research to develop a reduced physical model,which allows-without time-consum...Lean premixed combustion,which allows for reducing the production of thermal NOx,is prone to combustion instabilities.There is an extensive research to develop a reduced physical model,which allows-without time-consuming measurements-to calculate the resonance characteristics of a combustion system consisting of Helmholtz resonator type components (burner plenum,combustion chamber).For the formulation of this model numerical investigations by means of compressible Large Eddy Simulation (LES) were carried out.In these investigations the flow in the combustion chamber is isotherm,non-reacting and excited with a sinusoidal mass flow rate.Firstly a combustion chamber as a single resonator subsequently a coupled system of a burner plenum and a combustion chamber were investigated.In this paper the results of additional investigations of the single resonator are presented.The flow in the combustion chamber was investigated without excitation at the inlet.It was detected,that the mass flow rate at the outlet cross section is pulsating once the flow in the chamber is turbulent.The fast Fourier transform of the signal showed that the dominant mode is at the resonance frequency of the combustion chamber.This result sheds light on a very important source of self-excited combustion instabilities.Furthermore the LES can provide not only the damping ratio for the analytical model but the eigenfrequency of the resonator also.展开更多
Large eddy simulations(LESs)of cavity ignition processes were performed in a 2 D ethylene-fueled supersonic combustor with a single rear-wall-expansion cavity based on OpenFOAM.The ethylene combustion was modelled usi...Large eddy simulations(LESs)of cavity ignition processes were performed in a 2 D ethylene-fueled supersonic combustor with a single rear-wall-expansion cavity based on OpenFOAM.The ethylene combustion was modelled using a 35-step with 20-specie ethylene chemical mechanism,which had been validated by CHEMKIN calculations.The effect on the ignition process of different ignition sites inside the cavity was then studied.It was found that the rear region of the cavity floor is an optimized ignition site where successful ignitions will be achieved.According to different ignition behaviors,two flame extinguishing modes could be identified:blown-off extinguishing mode and flow dissipation extinguishing mode.Blown-off extinguishing mode mainly occurred after ignition near the cavity shear layer,in which the initial flame was blown off directly due to the high speed of the supersonic core flow.Flow dissipation extinguishing mode is likely to occur after ignition near the front and middle cavity floor as a result of severe turbulent dissipations and limited chemical reactions.The study indicates that the movement routine of the initial flame is important for the ignition process,including both moving towards a favorable flow field and forming a large heat release region along the movement.展开更多
基金Supported by the National Natural Science Foundation of China (50606026,50736006)the Foundation of State Key Laboratory of Engines,Tianjin University (K-2010-07)
文摘Large-eddy simulation(LES) is under its rapid development and is recognized as a possible second generation of CFD methods used in engineering.Large-eddy simulation of two-phase flows and combustion is particularly important for engineering applications.Some investigators,including the present authors,give their review on LES of spray combustion in gas-turbine combustors and internal combustion engines.However,up to now only a few papers are related to the state-of-the-art on LES of gas-particle flows and combustion.In this paper a review of the advances in LES of complex gas-particle flows and coal combustion is presented.Different sub-grid scale(SGS) stress models and combustion models are described,some of the main results are summarized,and some research needs are discussed.
基金Project(51306088)supported by the National Natural Science Foundation of ChinaProject(NJ20160039)supported by the Fundamental Research Funds for the Central Universities,China
文摘A numerical study was conducted to seek an optimized dimension of jet chamber in the pulsating impinging flow.The flow and heat transfer effect of the pulsation flow through a jet chamber was investigated.The numerical results indicate that heat transfer effective enhances near the stagnation region for the intermittent pulsed flow with jet chamber compared to that without jet chamber.Simulations of the flow through a jet chamber show that the heat transfer rate on the impingement surface is highly dependent on the velocity at the position which is really close to target surface.Examination of the velocity field suggests that the velocity exists a maximum value as the axis distance increases.In addition,the velocity at the jet hole is enlarged by the jet chamber due to the entrainment effect,and the velocity is amplified even greater as the size of the jet chamber becomes bigger.Nevertheless,the velocity declines quickly while the flow axis distance is more than a certain range,leading to poor heat transfer.Thus,intermittent pulsed flow with jet chamber is suggested as a method of improving heat transfer by employing larger dimensions of jet chamber for appropriate jet-to-surface spacing.
文摘Lean premixed combustion,which allows for reducing the production of thermal NOx,is prone to combustion instabilities.There is an extensive research to develop a reduced physical model,which allows-without time-consuming measurements-to calculate the resonance characteristics of a combustion system consisting of Helmholtz resonator type components (burner plenum,combustion chamber).For the formulation of this model numerical investigations by means of compressible Large Eddy Simulation (LES) were carried out.In these investigations the flow in the combustion chamber is isotherm,non-reacting and excited with a sinusoidal mass flow rate.Firstly a combustion chamber as a single resonator subsequently a coupled system of a burner plenum and a combustion chamber were investigated.In this paper the results of additional investigations of the single resonator are presented.The flow in the combustion chamber was investigated without excitation at the inlet.It was detected,that the mass flow rate at the outlet cross section is pulsating once the flow in the chamber is turbulent.The fast Fourier transform of the signal showed that the dominant mode is at the resonance frequency of the combustion chamber.This result sheds light on a very important source of self-excited combustion instabilities.Furthermore the LES can provide not only the damping ratio for the analytical model but the eigenfrequency of the resonator also.
基金Project supported by the National Natural Science Foundation of China(Nos.11902353 and 51706238)the Postdoctoral Innovation Talent Support Program of China(No.BX20190091)。
文摘Large eddy simulations(LESs)of cavity ignition processes were performed in a 2 D ethylene-fueled supersonic combustor with a single rear-wall-expansion cavity based on OpenFOAM.The ethylene combustion was modelled using a 35-step with 20-specie ethylene chemical mechanism,which had been validated by CHEMKIN calculations.The effect on the ignition process of different ignition sites inside the cavity was then studied.It was found that the rear region of the cavity floor is an optimized ignition site where successful ignitions will be achieved.According to different ignition behaviors,two flame extinguishing modes could be identified:blown-off extinguishing mode and flow dissipation extinguishing mode.Blown-off extinguishing mode mainly occurred after ignition near the cavity shear layer,in which the initial flame was blown off directly due to the high speed of the supersonic core flow.Flow dissipation extinguishing mode is likely to occur after ignition near the front and middle cavity floor as a result of severe turbulent dissipations and limited chemical reactions.The study indicates that the movement routine of the initial flame is important for the ignition process,including both moving towards a favorable flow field and forming a large heat release region along the movement.
