Turbojet
Turbojet
Led the mechanical design for the centrifugal compressor and its integration into the overall assembly of a 50-lbf microscale turbojet engine. Turbojet engines are the the simplest forms of gas-turbine engines where air is compressed, mixed with fuel and burned, expanded through the turbine to drive the compressor, and finally accelerated from the nozzle to produce thrust.
A bellmouth inlet is designed to capture and accelerate air into the IGV. The impeller then captures the incoming airflow from the IGV and imparts energy to it as it redirects the flow radially, resulting in a higher exit velocity and total pressure. To diffuse the flow after the impeller, a radial diffuser was chosen to match the radial outflow of the centrifugal compressor. A return channel redirects the diffuser discharge to the inlet of the combustor section.
Produce a pressure ratio of 3:1.
Provide Mach 0.1-0.3 airflow to the combustor.
Goal: The requirement for the IGV is to turn the flow from purely axial, 90° to 83.5°, which imparts a swirl to the flow.
How: Since no significant forces or thermal effects are acting on the component, assembly and manufacturing can be simplified by integrating the IGV into the inlet and fabricating the entire component using Formlabs Nylon 12 through selective laser sintering (SLS). The blade geometry and angles were generated using calculations derived from CFturbo, a commercial software package.
Goal: The impeller will be the primary component responsible for adding energy to the airflow in preparation for diffusion.
How: The tip diameter of the impeller was chosen after FEA iterations with Ansys Mechanical as a balance between efficient compression and required strength for bearing centrifugal stresses. The axial length of the impeller was determined from calculations using the flow coefficient and the component's dimensions. The contour was optimized to balance the necessary strength for centrifugal loads and weight reduction. The blade geometry and angles were generated using calculations derived from CFturbo. The impeller will ultimately be additively manufactured in Ti-6Al-4V, a material with an incredible strength-to-weight ratio and allows for acceptable margin of safety.
Goal: The diffuser will slow down the air exiting the impeller and increase its static pressure, in preparation for the combustor.
How: Parameters for the diffuser's size were determined using equations given the flow coefficient and the impeller outlet conditions. The blade profile thickness distribution for the diffuser blades follows an analytically specified distribution similar to that of a standard NACA 66-006 profile. Since the component is stationary and aerodynamic stresses are negligible, the diffuser can also be integrated with the subsequent stator and the impeller shroud to be fabricated through Stereolithography (SLA) in Formlabs High Temp Resin V2. The blade geometry and angles were generated using calculations derived from CFturbo.
Working on this project has taught me how to operate in a larger team environment, where I've needed to collaborate with members from other sub-teams, while also coordinating with members on my own sub team. Through various textbooks, I've learned how to derive parameters for sizing compressors, leading me to supplement these values with automatic calculations for complex geometries in CFturbo. I've learned how to work with assemblies and model various components in NX, a critical skill for modifying several features once preliminary sizing/geometries are determined. To ensure components won't yield, I've validated several designs through FEA simulations in Ansys Mechanical. Now that the design is complete for the compressor, I'm excited to learn more about manufacturing the engine!