Comparison of a Modeling Method and Helmholtz Resonator in Predicting the Frequency of a Valved Pulsejet Engine and Presentation of a Correction Factor

Hosseini, Seyed Mohammad; Doustdar, Mohammad Mehdi

doi:10.47176/MAJ.2025.1555

Comparison of a Modeling Method and Helmholtz Resonator in Predicting the Frequency of a Valved Pulsejet Engine and Presentation of a Correction Factor

Document Type : Propulsion and Heat Transfer

Authors

seyed mohammad Hosseini ¹

Mohammad Mehdi Doustdar ²

¹ Master's Degree, Imam Hossein Comprehensive University, Tehran, Iran

² Professor, Imam Hossein Comprehensive University, Tehran, Iran

10.47176/MAJ.2025.1555

Abstract

Accurate prediction of the operational frequency and thrust of valved pulsejet engines is vital for their design and optimization. Two common approaches for frequency estimation are using Helmholtz resonator models and modeling methods based on simulating the engine's operational cycle. This research was conducted to compare the results from a developed modeling method with those obtained from the nonlinear Helmholtz resonator relation. In the modeling method, the engine's operational cycle, including the intake, two-zone combustion (flame propagation), and exhaust stages, is simulated step-by-step. To perform the calculations of the modeling method, a Fortran code was developed to calculate the frequency for a wide range of engine geometries (combustion chamber diameter of 5 to 30 cm and combustion chamber length-to-diameter ratio of 1 to 2.25) using both methods. The results showed that both methods predict the general trend of decreasing frequency with increasing engine dimensions, but there are differences between them, especially at smaller diameters. To improve the consistency of the modeling method's results with the conventional Helmholtz method, a geometry-dependent correction factor (dependent on the diameter and the length-to-diameter ratio of the combustion chamber) was presented. This factor varied in the approximate range of 0.72 to 1.20. Using this correction factor demonstrates the difference between the modeling method and the Helmholtz method and allows for the use of more physical parameters of the modeling method while maintaining consistency with the Helmholtz results.

Graphical Abstract

Keywords

Pulsejet Engine

Operational Frequency

Cycle Modeling

Helmholtz Resonator

Flame Factor

Correction Factor

Subjects

Propulsion and heat transfer

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