The pulse jet engine, due to its simple structure, low weight, an‎d low production cost, has always attracted the attention of researchers in the field of aerial propulsion. In this study, parametric optimization of a thrust augmentor installed at the exhaust of a pulse jet engine was carried out. A transient, axisymmetric numerical simulation of a valved pulse jet engine operating under flight conditions was performed using ANSYS Fluent, employing the k–ω SST turbulence model an‎d modeling combustion as a volumetric energy source. A suitable cross-section downstream of the engine was selec‎ted for accurate calculation of net thrust using the momentum equation. Simulations were conducted over several successive cycles until the flow an‎d performance parameters reached a harmonic oscillatory pattern, after which thrust was time-averaged over the last three cycles. Assuming a cylindrical augmentor an‎d parameterizing its geometry, the effects of three key parameters—augmentor distance from the engine exit, augmentor diameter, an‎d augmentor length—on thrust enhancement were investigated, along with a detailed aerodynamic analysis of the engine with an‎d without the augmentor. Results showed that the optimized augmentor, by entraining ambient air an‎d enhancing exhaust momentum, increased thrust by 170% compared to the baseline engine. In the second part of the study, a coaxial twin-engine configuration comprising a central engine an‎d an annular engine was designed an‎d simulated. By equalizing combustion chamber volumes an‎d effective inlet areas, synchronized operation was achieved, an‎d through careful exhaust pipe design based on Helmholtz resonance, a half-cycle phase difference between the two engines was realized. Simulations indicated that this phase difference enhanced suction, increased inlet air mass flow, an‎d led to significant thrust improvement, while the spacing between exhausts played a key role in maximizing efficiency an‎d ensuring stable operation. The proposed configuration thus offers an effective approach for enhancing pulse jet propulsion performance. Despite advances in numerical modeling, experimental validation remained essential; therefore, the performance of the pulse jet engine without an augmentor was experimentally tested on a static stan‎d to provide a reliable baseline. The experiments showed that at an altitude of about 1600 meters above sea level an‎d an phi ratio of 0.7, the engine produced a thrust of 25.6 kgf, in close agreement with numerical predictions. The measured temperature distribution across engine sections also aligned well with simulation results. Based on the optimized geometry, a prototype augmentor was fabricated for future experimental testing to eva‎luate the engine’s performance under flight conditions.

مهدي نيلي احمدآبادي

فرهاد قدك

احمدرضا پيشه وراصفهاني , محسن دوازده امامي