Design and Initial Testing of a Wind Tunnel Platform for Studying Solid-Fuel Ramjet Combustion

The following contribution presents a novel wind tunnel design at Colorado State University (CSU) for the study of Solid Fuel Ramjet (SFRJ) combustion. This development represents an upgrade of the existing indraft supersonic wind tunnel at CSU’s Aerospace Propulsion and Diagnostics Laboratory, creating an optically accessible testbed for SFRJ research. The design, manufacturing, and validation of flow conditions are detailed. The setup is fitted with high-speed schlieren diagnostics for flow visualization and fast response pressure transducers for the study of combustion performance. Finally, a high-power CW laser (Pmax=330 Watts) is implemented within the tunnel for remote ignition of fuel grains. The results presented herein focused on cold flow testing and fuel grain ignition. Using static pressure measurements, we were able to confirm a Mach 0.54 flow inside the combustion chamber, in line with what was predicted by our 1-D isentropic flow model. Preliminary combustion testing of HTPB fuel grains demonstrated successful laser ignition and revealed a strong recirculation zone downstream of the backward facing cavity holder. Schlieren imaging confirmed the presence of a reattaching shear layer within the cavity, critical for flame holding. Ultimately, this modular testing facility will provide a reliable cost-effective testbed for future investigations into fuel regression, flame stability, and energetic additive optimization prior to full-scale SFRJ implementation.