Periodic Reporting for period 1 - TurbDDT (Predicting flame acceleration and deflagration to detonation transition in industrial scale explosions incorporating the turbulence effects)
Berichtszeitraum: 2019-08-27 bis 2021-08-26
What is the problem/issue being addressed?
The project aims to develop and validate computational fluid dynamics (CFD) based numerical models to facilitate the prediction of flame acceleration (FA) and Deflagration to Detonation Transition (DDT) in industrial scale explosions incorporating the turbulence effects.
Why is it important for society?
Despite increasingly stringent safety measures, explosions resulting from the accidental leaks of fuels continue to occur with higher frequency and consequences especially when DDT occurs. DDT involves transition from subsonic to supersonic flows. In practice, explosions resulting from accidental releases of flammable gases; e.g. congested chemical plants, nuclear installations or just gas leak in a residential building or underground pipelines, all involve non-uniform mixtures. The complex interaction between turbulent flame, obstacles and mixture concentration gradients all affect FA and DDT. These effects cannot be captured by the current provisions for explosion resistant design and explosion safety, which are based on the energy release mechanism of high-order explosives; they are insufficient to interpret the complex nature of vapour cloud explosions (VCE) and hence their use in facility siting and explosion protection design is problematic.
What are the overall objectives?
The objectives include:
⁃ To gain insight about the underlying physical mechanisms affecting FA and DDT in smooth channels/tubes with uniform mixtures and mixtures with concentration gradients using direct numerical simulations (DNS) with high order numerical schemes.
⁃ To repeat the above in channels/tubes with obstacles.
⁃ To assess the capability of the more efficient large eddy simulation (LES) approaches for medium scale simulations (order of several metres) and large scales (tens to hundreds of metres) to predict global safety parameters like flame speed, overpressure and onset of DDT.
⁃ To conduct large scale FA and DDT of practical scales and assess the resulting differences in the predicted likelihood of DDT and explosion impact on structures.
The project aims to develop and validate computational fluid dynamics (CFD) based numerical models to facilitate the prediction of flame acceleration (FA) and Deflagration to Detonation Transition (DDT) in industrial scale explosions incorporating the turbulence effects.
Why is it important for society?
Despite increasingly stringent safety measures, explosions resulting from the accidental leaks of fuels continue to occur with higher frequency and consequences especially when DDT occurs. DDT involves transition from subsonic to supersonic flows. In practice, explosions resulting from accidental releases of flammable gases; e.g. congested chemical plants, nuclear installations or just gas leak in a residential building or underground pipelines, all involve non-uniform mixtures. The complex interaction between turbulent flame, obstacles and mixture concentration gradients all affect FA and DDT. These effects cannot be captured by the current provisions for explosion resistant design and explosion safety, which are based on the energy release mechanism of high-order explosives; they are insufficient to interpret the complex nature of vapour cloud explosions (VCE) and hence their use in facility siting and explosion protection design is problematic.
What are the overall objectives?
The objectives include:
⁃ To gain insight about the underlying physical mechanisms affecting FA and DDT in smooth channels/tubes with uniform mixtures and mixtures with concentration gradients using direct numerical simulations (DNS) with high order numerical schemes.
⁃ To repeat the above in channels/tubes with obstacles.
⁃ To assess the capability of the more efficient large eddy simulation (LES) approaches for medium scale simulations (order of several metres) and large scales (tens to hundreds of metres) to predict global safety parameters like flame speed, overpressure and onset of DDT.
⁃ To conduct large scale FA and DDT of practical scales and assess the resulting differences in the predicted likelihood of DDT and explosion impact on structures.
Direct numerical simulations (DNS) have been conducted to investigate flame acceleration (FA) and Deflagration to Detonation Transition (DDT) in small-scale channels/tubes with uniform and non-homogeneous mixtures. Particular attention has been given to the influences of concentration gradients on flame propagation in the small-scale channel through high-resolution DNS.
For medium-scale application, the Linear Eddy Model (LEM) for subgrid-scale (SGS) turbulence treatment in large eddy simulations LES have been considered using the extended fully compressible formulations (CLEM-LES), which included special treatment of energy balance at SGS level to allow reaction rates to respond to strong shocks and rapid expansions in reactive and supersonic flow fields. The CLEM-LES has been implemented in the in-house high-resolution code as well as open source computational fluid dynamics (CFD) code OpenFOAM. Assessment have been conducted on its capability to capture turbulent flame effects and the impact on accuracy of the predictions for global safety parameters like flame speed, overpressure and onset of DDT by selectively repeating some of the above DNS calculations with LEM-LES.
For medium-scale application, the Linear Eddy Model (LEM) for subgrid-scale (SGS) turbulence treatment in large eddy simulations LES have been considered using the extended fully compressible formulations (CLEM-LES), which included special treatment of energy balance at SGS level to allow reaction rates to respond to strong shocks and rapid expansions in reactive and supersonic flow fields. The CLEM-LES has been implemented in the in-house high-resolution code as well as open source computational fluid dynamics (CFD) code OpenFOAM. Assessment have been conducted on its capability to capture turbulent flame effects and the impact on accuracy of the predictions for global safety parameters like flame speed, overpressure and onset of DDT by selectively repeating some of the above DNS calculations with LEM-LES.
The project objectives have been successfully achieved. The research has advanced the state of the art in the following key areas:
⁃ Advancing the understanding about the underlying physical mechanisms for FA and DDT in small scale and medium scale channels/tubes for both uniform and non-homogeneous mixtures.
⁃ The high resolution DNS predictions have identified turbulence combustion effects on DDT and are useful to conduct consequence analysis of large scale explosions.
⁃ Developed a robust LES approach based on CLEM-LES for applications to medium and large-scale applications.
⁃ Advancing the understanding about the underlying physical mechanisms for FA and DDT in small scale and medium scale channels/tubes for both uniform and non-homogeneous mixtures.
⁃ The high resolution DNS predictions have identified turbulence combustion effects on DDT and are useful to conduct consequence analysis of large scale explosions.
⁃ Developed a robust LES approach based on CLEM-LES for applications to medium and large-scale applications.
Verwandte Dokumente
- Figure 2 - Entire process of flame acceleration and DDT in av challenel with hot wall.png
- Figure 4 Flame evolution in the whole DDT process - enlarged view.png
- Figure 3 Flame evolution in the whole DDT process.png
- Figure 1 - Entire process of flame acceleration and DDT in av challenel with adiabatic wall.png