Matching Items (2)
Description
This thesis examines how a recently proposed concept for a highly-truncated aerospike nozzle
can be expected to perform at altitudes corresponding to ambient pressures from sea-level to
full vacuum conditions, as would occur during second-stage ascent and during second-stage
descent and return to Earth. Of particular importance is how the base pressure varies with
ambient pressure, especially at low ambient pressures for which the resulting highly underexpanded flows exiting from discrete thrust chambers around the truncated aerospike merge to
create a closed (unventilated) base flow. The objective was to develop an approximate but
usefully accurate and technically rooted way of estimating conditions for which the jets issuing
from adjacent thrust chambers will merge before the end of the truncated aerospike is reached.
Three main factors that determine the merging distance are the chamber pressure, the altitude,
and the spacing between adjacent thrust chambers. The Prandtl-Meyer expansion angle was
used to approximate the initial expansion of the jet flow issuing from each thrust chamber.
From this an approximate criterion was developed for the downstream distance at which the
jet flows from adjacent thrust chambers merge. Variations in atmospheric gas composition,
specific heat ratio, temperature, and pressure with altitude from sea-level to 600 km were
accounted for. Results showed that with decreasing atmospheric pressure during vehicle
ascent, the merging distance decreases as the jet flows become increasingly under-expanded.
Increasing the number of thrust chambers decreases the merging distance exponentially, and
increasing chamber pressure results in a decrease of the merging distance as well.
ContributorsHerrington, Katie (Author) / Dahm, Werner (Thesis director) / Takahashi, Timothy (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Department of Physics (Contributor)
Created2024-05
Description
The aerospike nozzle belongs to the class of altitude compensating nozzles making it a strong candidate for Space Shuttle Main Engines. Owing to their higher efficiency compared to conventional bell nozzles, the aerospike nozzles are being studied extensively and are being used for many Single State to Orbit (SSTO) designs. A rocket engine nozzle with altitude compensation, such as the aerospike, consumes less fuel than a rocket engine with a bell nozzle. Aerospike nozzles are huge and are often difficult to construct and have to be truncated in order to make them feasible for application in a rocket propulsion system. Consequently, truncation of the aerospike leads to pressure loss under the base, which in-turn decreases the overall thrust produced by the rocket nozzle. To overcome this loss, a technique called base bleed is implemented in which a secondary jet is made to flow through the base of the truncated portion. This thesis uses dynamic pressure contour plots to find out the ideal base bleed mass flow rate to avoid base recirculation in 10 %, 20 % and 30 % truncated aerospike nozzles.
ContributorsNagarajan, Venkatraman (Author) / White, Daniel B (Thesis advisor) / Dahm, Werner (Thesis advisor) / Huang, Huei-Ping (Committee member) / Arizona State University (Publisher)
Created2017