Experimental Investigation on Laser Visualization of Flow Vortices

Current classical hybrid engines suffer from low solid fuel regression rate, low volumetric loading and relatively low combustion efficiency. The combustion occurs in a boundary layer flame zone, distributed along the length of the combustion chamber about the fuel surface. Portions of the propellant may pass through the chamber without reacting thus secondary combustion chamber are often employed. These chambers add length and mass and may serve as a potential source of combustion instability. These drawbacks can be avoided in Vortex Hybrid Rocket Engine (VHRE). This injection methods generates a bi-directional, co-axial vortex flow field in the combustion. The swirling high velocity rate enhances heat transfer to the fuel surface which in turn drives high regression rate. Vortices are a major component of turbulent flow. The dynamics of vortices depends majorly on the nozzle geometry which in turn drives the mixing properties. The stream wise vorticity drastically alters the mass entrainment of a jet, and the efficiency of this vorticity in entraining fluid increases as the jet evolves downstream. An attempt was made to study the effects of various orifice geometries under different operating flow velocities on characteristics of vortices created by smoke, using a laser visualization technique. The nozzle geometries studied include circular and noncircular (square, triangle). The characteristic features of non-circular ones include improved large and small scale mixing in low and high speed flows, and enhanced combustor performance by improving combustion efficiency, reducing combustion instabilities and undesired emissions. For square and triangular sections the effect of different angles were also observed. Further, straws and meshes were fixed inside the setup such that it ensured a uniform distribution of flow and reduced turbulence to avoid possible variation. Visualization of the flows was carried out in the vicinity of the orifice exit in order to identify flow regimes and to study coherence. The work can be utilized significantly in potential space applications of vortex dynamics in space debris removal system, injectors, HVAC (Heating, ventilation, and air conditioning), nozzles etc.