Computational Modeling and Optimization of a Novel Shock Tube to Study Blast Induced Traumatic Brain Injury

Over the last decade, soldiers fighting in Iraq and Afghanistan are being exposed to blasts from powerful explosives with improvised detonation techniques. These blasts put them at high risk of closed head non-impact Blast-induced Traumatic Blast Injury (bTBI). bTBI is caused by interaction of shock-wave. It is a debilitating condition, but goes undiagnosed for several months. The pathology of bTBI is poorly understood making diagnosis, treatment, and prevention of bTBI difficult. One way to study it is to construct a shock tube that replicate blast profile. However, this method does not replicate blast conditions perfectly. The goal of this research is to improve shock tube as a research tool, for studying bTBI, by better replicating military ordnance.

Various 2D models to simulate the shock wave propagation in a shock tube to see the effects of varying shock tube geometry and working fluid on the blast profiles were developed. Ranges of different parameters evaluated are: tube length - 5ft to 25ft; tube diameter - 8? to 16?; working fluid - compressed air and helium; burst pressure- 20 to 55 psi. A total of 240 simulations were run to evaluate the effect of these factors on the pressure profile. Computations were carried out using commercial software, Star CCM+ (CD-adapco, NY, USA). Assumptions used to model the flow were unsteady, inviscid, compressible, axisymmetric flow with time-step of 1e-5s. Multiple regression was run on these parameters to establish empirical relationship with pressure profile. CFD model was validated using experimental data from Robbins-Moreno shock tube.

Results show that as the burst pressure increases, peak overpressure, positive phase duration, and impulse also increase. Increasing tube diameter decreases peak. Change in tube length does not have a significant effect on peak overpressure, positive phase duration, and impulse. Working fluid was most significant factor determining the magnitude of impulse and duration.

In conclusion, the empirical formulas developed using CFD model of the shock tube provide reasonable predictions about the key features of a pressure profile that and their dependence on the shock tube geometry, working fluid, and burst pressure. This knowledge will be used to improve shock tube to study bTBI.