Impulse Generation by an Open Shock Tube

Abstract

We perform experimental and numerical studies of a shock tube with an open end. The purpose is to investigate the impulse due to the exhaust of gases through the open end of the tube as a model for a partially filled detonation tube as used in pulse detonation engine testing. We study the effects of the pressure ratio (varied from 3 to 9.2) and the volume ratio (expressed as fill fractions) between the driver and driven section. Two different driver gases, helium and nitrogen, and fill fractions between 5 and 100% are studied; the driven section is filled with air. For both driver gases, increasing the pressure ratio leads to larger specific impulses. The specific impulse increases for a decreasing fill fraction for the helium driver, but the impulse is almost independent of the fill fraction for the nitrogen driver. Twodimensional (axisymmetric) numerical simulations are carried out for both driver gases. The simulation results show reasonable agreement with experimental measurements at high pressure ratios or small fill fractions, but there are substantial discrepancies for the smallest pressure ratios studied. Empirical models for the impulse in the limits of large and small fill fractions are also compared with the data. Reasonable agreement is found for the trends with fill fractions using the Gurney or Sato model at large fill fractions, but only Cooper's bubble model is able to predict the small fill fraction limit. Computations of acoustic impedance and numerical simulations of unsteady gas dynamics indicate that the interaction of waves with the driver-driven gas interface and the propagation of waves in the driven gas play an essential role in the partial-fill effect.

Optical and thrust measurement of a pulse detonation combustor with a coaxial rotary valve

“…Numerical analysis by Morris et al [23] and an experiment by Copper et al [33] showed that the expansion effect of by nozzle became dominant, like a steady flow, if the ambient pressure around a PDE was sufficiently low. Kasahara et al [34] showed the physical essence of the partial-fill effect in an experiment with a shock-tube-shaped ballistic pendulum and by numerical analysis. Not only the above-mentioned fundamental studies but also validations of PDE systems have been carried out as application studies.…”

Thrust Performance of Rotary-Valved Four-Cylinder Pulse Detonation Rocket Engine

“…This essence of the partial fill effect is explained by considering shock impedance. 16,25) If the shock impedance of the driven gas is higher than the detonation wave, the transmitted and reflected waves are both shock waves. The reflected shock wave undergoes repeated reflection between the contact surface and the closed end wall, and the impulse increases.…”

“…Kasahara et al 16) compared single-pulse experimental and numerical calculation results using an open shock tube and the bubble model (He and air, N 2 and air). When the fill fraction was small ( < 0:2), the analytical model predicted a maximum specific impulse.…”

“…The partial filling of the propellant in a detonation tube is the simplest way to increase the specific impulse. [11][12][13][14][15][16] In addition to the propellant in the detonation tube, purge gas, burned gas and air suctioned from the open end after the high-pressure burned gas has been blown down are compressed by a shock wave, and the specific impulse is increased by the compressed gases. In particular, the partial-fill effect is strongly dependent on the amount of suctioned air, because the air density of & air % 1:20 kg/m 3 at 1 atm and 300 K is higher than the burned gas density of & b % 0:104 kg/m 3 at 1atm.…”

Visualization study of ignition modes behind bifurcated-reflected shock waves

“…However, it is important to investigate the local ignitions behind shock waves under low temperature conditions, from the point of view of chemical kinetics in high-prssure (non-diluted test gases) shock tube experiments in which the non-uniformity of reflected shock waves tends to be greater because of increased viscous effects [23,24] and from the view of application systems (for example, pulse detonation engines (PDEs) [25][26][27][28][29][30][31][32][33][34][35] etc.). Therefore we focused on local ignitions induced by non-uniformity behind reflected shock waves under low-temperature conditions (Voevodsky and Soloukhin [17] : mild ignition, Gilbert and Strehlow [2] : hot spot initiation, Mayer and Oppenheim [18] : mild ignition) and investigated numerically and experimentally the local ignition position and the reason why local ignitions are located at a point distant from the reflecting wall.…”