Honors College Theses

Publication Date



Mechanical Engineering (B.S.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. Marcel Ilie


In the search for a Single-Stage-to-Orbit rocket, Altitude Compensating Nozzles concepts (ACNs) have been proposed since the 1950s, but research has stalled despite the modern analysis tools available. These nozzle concepts offer optimum performance at two or more altitude settings. This research chose three of these concepts, these being the Dual Bell, Expansion-Deflection, and Aerospike, which were designed and analyzed at various pressure ratios (NPR=10,15,30,36,30,45) using Computational Fluid Dynamics (CFD) software FLUENT. Simulations generated pressure distributions along the nozzle wall, which allowed to calculate data values such as thrust coefficients. Nozzle efficiency is calculated from this data and used to compare all nozzle concepts. The Aerospike nozzle showed the largest efficiencies, between 97-98%, for all NPRs. The Dual Bell showed efficiencies of 88-93% for low NPRs and then, during its transition to the operation on the second bell, the efficiencies lowered to 64-73%. For the Expansion-Deflection case, nozzle efficiencies were calculated between 75-82% for low NPRs, but they increased to 92% on high NPRs. While more simulations are necessary for a definite conclusion, these results suggest that the Aerospike possesses significantly superior altitude compensating capabilities over the Dual Bell and the Expansion-Deflection nozzles.