A study of the impulse waves discharged from convergent and divergent ducts

The present study describes experimental and computational works to investigate impulse waves that are generated by discharge of a compression pulse from the exit of convergent and divergent ducts. The objective of the present study is to compare the impulse waves discharged from a straight duct with those discharged from convergent and divergent ducts. Computational analysis is performed using the axisymmetric, unsteady, inviscid, compressible, Euler equations. A second-order total variation diminishing finite difference scheme is used to solve the governing equation system. Experiment is carried out in a simple shock tube with an open end. Convergent and divergent ducts are connected to the open end of the shock tube. Initial compression pulses with different overpressures and wavelengths are made at the entrance of the convergent and divergent ducts. The present computational method predicts the measured impulse waves well. The results obtained show that for a given duct the magnitude of the impulse wave decreases as the wavelength of the initial compression pulse increases and it is a weakly increasing function of the overpressure of the initial compression pulse. Compared with a straight duct, a convergent duct leads to a weaker impulse wave, while a divergent duct causes a stronger impulse wave. It is therefore believed that the convergent duct can be a passive control device used to reduce the magnitude of the impulse wave.