Evaluating long-duration blast loads on steel columns using computational fluid dynamics

Jack W Denny,Simon K Clubley

doi:10.1080/15732479.2019.1599966

Jack W Denny, Simon K Clubley

Open Access

https://doi.org/10.1080/15732479.2019.1599966

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Abstract

Long-duration blasts are typically defined by positive pressure durations exceeding 100 ms. Such blasts can generate dynamic pressures (blast winds) capable of exerting damaging drag loads on comparatively slender structural components such as columns. With limited drag coefficient availability for specific structural geometries, Computational Fluid Dynamics (CFD) can be the only satisfactory approach for analysing blast loading on user-specified, finite geometries. The ability to analyse long-duration blasts with commercially available CFD programmes is still not confidently offered, with no prior studies examining the accuracy of modelling interaction with relatively much smaller, finite geometries. This paper presents a comparative investigation between numerical and experimental results to assess the predictive capacity of inviscid Eulerian CFD as a method for calculating long-duration blast drag loading on finite cross-sectional geometries. Full-scale long-duration blast experiments successfully measured surface pressure–time histories on a steel I-section column aligned at four orientations. Calculated pressure–time histories on exposed geometry surfaces demonstrated good agreement although reduced accuracy and under-prediction occurred on shielded surfaces manifesting as overestimated net loading. This study provides new understanding and awareness of the numerical capability and limitations of using CFD to calculate long-duration blast loads on intricate geometries.

Highlights

Long-duration blast waves are typically defined by positive pressure durations over 100 ms, developing in later stages of shock wave propagation i.e. in the ‘far field’ from the source of detonation (Denny & Clubley, 2019; Johns & Clubley, 2016)
The Air Blast Tunnel (ABT) is capable of generating blast waves with long-duration characteristics; a peak overpressure of pi % 55 kPa and positive phase duration of tþ % 155 ms are attainable at maximum power in the 10.2 m section
Inviscid Eulerian Computational Fluid Dynamics (CFD) modelling was performed to calculate blast loading exerted on a rigid I-section geometry at varied angles of incidence corresponding to four long-duration blast experiments

Summary

Introduction

Long-duration blast waves are typically defined by positive pressure durations over 100 ms, developing in later stages of shock wave propagation i.e. in the ‘far field’ from the source of detonation (Denny & Clubley, 2019; Johns & Clubley, 2016). Proposed drag coefficients in literature demonstrate inconsistency and are typically single values lacking provision for different angles of incidence; it is unknown how to characterise drag loading for different orientations In such cases where simplified empirical methods are rendered unusable, Computational Fluid Dynamics (CFD) may be the only satisfactory approach available for calculating blast interaction and loading on user-specified geometries. This paper presents a comparative investigation between numerical simulations and experimental results to assess the capability of Eulerian CFD analysis to characterise long-duration blast drag loading on a relatively small I-section geometry from different angles of incidence. In the absence of verified drag coefficients for I-sections or provision for multi-axis interaction, Eulerian CFD analysis is evaluated as a potential tool for calculating long-duration blast drag loading on finite geometries

Experimental methodology

Incident blast environment

I-section blast interaction

Numerical methodology

Findings

Conclusions