Investigate the exhaust gas flow of a match rocket with schlieren photography

In this paper, the exhaust gas flow from a fixed match rocket is investigated with schlieren photography. The opening angle of the visualized exhaust gas flow is measured, deducing an opening angle varying between 23 degrees and 28 degrees. From applying a physics-based optical flow method on the schlieren photography images of the exhaust gas flow, the instantaneous velocity field is quantified. The spatially averaged and maximum velocities are calculated inside a trapezoidal region, revealing a continually weakening flow field. Moreover, the fluid acceleration is studied by calculating the material derivative of the instantaneous velocity field. The averaged fluid acceleration suggests that the exhaust gas decelerates under the shear stress/friction in the beginning close to the exit but accelerates later downstream. At a distance of 29 match rocket diameters from the exit, exhaust gas flow becomes fully decelerating, indicating that the local pressure balances the ambient pressure. Finally, the momentum equation is implemented on a designed control volume to estimate the reacting force applied on the rocket, deriving a maximum force of 31 mN.