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•To facilitate size scaling of RDREs, the relationships between geometric parameters, performance, and wave dynamics have been investigated utilizing gaseous methane-oxygen propellant.•Empirical relations have been derived between combustor geometry, feed conditions, and engine operation, as well as correlation to thermodynamic parameters calculated with chemical equilibrium codes.•The radius of curvature effects were explored through cylindrical combustor outer diameters of 25 mm, 51 mm, and 76 mm with a fixed gap width of 5 mm.•The injectors were scaled to have same oxidizer-to-fuel injector port diameter ratio, impingement distance, and injector-to-gap area ratio.•Larger engines were linked to higher wave counts during operation at a given mass flux and equivalence ratio.•Combustor axial pressures were found to be more dependent on propellant mass flux and equivalence ratio rather than geometry.•Mass flux combined with the inner-to-outer radius ratio provided boundary estimates for operating modes, and the ratio between the inner radius and detonation cell size provided insight for wave stability.

This paper presents advancement on one–dimensional (1–D) unsteady modelling of a ram accelerator (RAMAC) in the sub–detonative velocity regime by including real–gas equations of state (EoS) in order to account for the compressibility effects of the combustion products. Several equations of state based on generalised empirical and theoretical considerations are incorporated into a 1–D computer code TARAM. The objective of this work is to provide the best available formulations in order to improve the unsteady 1–D model and make the TARAM code a useful tool to predict the performance of the RAMAC in the sub–detonative velocity regime, without having to resort to more complicated 2–D or 3–D computational schemes. The calculations are validated against experimental data from 38–mm and 90–mm–bore facilities and good agreements have been achieved. Yet, the results demonstrate the need for further CFD studies involving the scale effect.

A one-dimensional performance analysis code has been developed at the Laboratoire de Combustion et de Detonique to predict the thrust in the thermally choked ram accelerator propulsion mode. This code includes the real gas effect in steady state calculations and incorporates the following equations of state: ideal gas, Boltzmann, Percus-Yevick (PY) and Becker-Kistiakowsky-Wilson (BKW). The code was validated against key experimental data from representative experiments at the University of Washington 38-mm-bore facility. The predicted thrust and velocity agree well with experimental measurements. The present paper provides details about the algorithm of the calculation in the thermally choked propulsion mode.