A SIMPLIFIED PREDICTION METHOD FOR THE STARTING PERFORMANCE OF CYLINDRICAL DIFFUSER IN HIGH-ALTITUDE SIMULATION TEST OF ROCKET ENGINES

Diffuser performance prediction plays a crucial role in high-altitude simulation test of rocket engines. This paper presents a study focused on calculating and applying the cylindrical diffuser’s starting performance, aiming to provide a straightforward and efficient approach for calculating the starting characteristic curve, which reveals the relationship between combustion chamber pressure ratio and vacuum chamber pressure ratio. The curve can be understood as representing three operational stages, consisting of 4 distinct feature points. To achieve this, a semi-empirical approach is proposed, which combines one-dimensional flow formulas with a fitting formula derived from the existing test data. By validating the starting characteristic curves for three different groups of engine nozzles and cylindrical diffusers, the computational results demonstrate good agreement with experimental results, with a margin of error of 7.1%, 12.9%, and 16.9%, respectively. For most common rocket engines with expansion ratios below 60, the starting characteristic curves of the cylindrical diffusers can be quickly obtained by using the proposed 4-point method.