Rapid and effective ignition of pyrotechnic countermeasure decoy flares is vitally important to the safety of expensive military platforms such as aircraft. Qineti Q is conducting experimental and theoretical research...Rapid and effective ignition of pyrotechnic countermeasure decoy flares is vitally important to the safety of expensive military platforms such as aircraft. Qineti Q is conducting experimental and theoretical research into pyrotechnic countermeasure decoy flares. A key part of this work is the development and application of improved models to increase the understanding of the ignition processes occurring for these flares. These models have been implemented in a two-dimensional computational model and details are described in this paper. Previous work has conducted experiments and validated the computational model at ambient temperature and pressure. More recently the computational model has been validated at pressures down to that equivalent to 40,000 feet but at ambient temperature(~290 K).This paper describes further experimental work in which the ignition delays of the priming material in inert countermeasure decoy flares were determined for pressures down to 40,000 feet and at temperature extremes of -40℃ and 100℃ Also included in this paper is a comparison of the measured and predicted ignition delays at low pressures and temperature extremes. The agreement between the predicted and measured ignition delays is acceptable.展开更多
As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics （CFD）. A numerical study of one transitional flow in two-d...As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics （CFD）. A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation （RANS） in this paper. Turbulence model plays a significant role in the complex flows＇ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox （2006） k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition＇s behavior.展开更多
基金funded by the Defence Science and Technology Laboratory (Dstl), part of the UK MOD, under the Weapons Science and Technology Centre (WSTC)
文摘Rapid and effective ignition of pyrotechnic countermeasure decoy flares is vitally important to the safety of expensive military platforms such as aircraft. Qineti Q is conducting experimental and theoretical research into pyrotechnic countermeasure decoy flares. A key part of this work is the development and application of improved models to increase the understanding of the ignition processes occurring for these flares. These models have been implemented in a two-dimensional computational model and details are described in this paper. Previous work has conducted experiments and validated the computational model at ambient temperature and pressure. More recently the computational model has been validated at pressures down to that equivalent to 40,000 feet but at ambient temperature(~290 K).This paper describes further experimental work in which the ignition delays of the priming material in inert countermeasure decoy flares were determined for pressures down to 40,000 feet and at temperature extremes of -40℃ and 100℃ Also included in this paper is a comparison of the measured and predicted ignition delays at low pressures and temperature extremes. The agreement between the predicted and measured ignition delays is acceptable.
基金Foundation item： Supported by the National Natural Science Foundation of China （Nos. 51309040, 51379025）, and the Fundamental Research Funds for the Central Universities （Nos. 3132014224, 3132014318）.
文摘As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics （CFD）. A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation （RANS） in this paper. Turbulence model plays a significant role in the complex flows＇ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox （2006） k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition＇s behavior.
