Date of Award

Fall 11-13-2025

Access Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Scott Montgomery Martin

Committee Chair Email

martis38@erau.edu

First Committee Member

William Engblom

First Committee Member Email

engbl7de@erau.edu

Second Committee Member

Mark Ricklick

Second Committee Member Email

ridlickm@erau.edu

College Dean

James W. Gregory

Abstract

The altitude compensating nozzle (ACN) is a type of rocket nozzle or engine that tries to minimize the negative effects of overexpansion at low altitudes. There are many forms of ACN's but most of them are heavier than traditional bell nozzles, alter the geometry of the nozzle, which requires extensive research into optimizing the new geometry, or require complex systems that can lead to structural, heating, or material problems. Out of the ACN's, the slot nozzle is a passive ACN that builds upon the bell nozzle and requires no additional weight or complex systems.

This slot nozzle is comprised of a bell nozzle with an annular slot taken out of the nozzle. This slot allows atmospheric air to flow into the nozzle at low altitudes. While this is physically impossible to manufacture, CFD analysis can be conducted to understand how a passive air-breathing engine operates under different conditions. The slot nozzle is a precursor to designing a permeable nozzle. Modeling or manufacturing a permeable nozzle is complex, so a slot nozzle is modeled to understand the common trends between the passive air-breathing engines.

This study focuses on how flight speed affects the nozzle’s performance and flow patterns at altitudes between 0-30 km. Results indicate that adding flight speed to the slot nozzle allows the slot nozzle to perform better than the traditional bell nozzles at altitudes ≥ 15km. The thrust can increase up to 5.3%. A small increase in flight speed can also increase performance by up to 0.4%. After 30km, the slot nozzle has diminishing performance benefits over the bell nozzle. Increasing the Mach number directly correlates to an increase in thrust performance. The slot nozzle also alters the flow pattern of the nozzle. The slot nozzle proves to be a promising method to understand passive air-breathing engines by showing performance gains and losses compared to a bell nozzle

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