Matching Items (36)
Description
This thesis aims to determine how finite wing aerodynamic loads change in proximity to the ground. In this study, the primary design tool is an inviscid panel method code, VORLAX.
The validation tool is a commercial volume grid CFD package, ANSYS FLUENT. I use VORLAX
to simulate wings with different incidences and aspect ratios to look at how ground effect
impacts spanwise loading and incipient flow separation. Then the results were compared to
widely published equations such as McCormick, Torenbeek, and Hoerner & Borst. Because I
found that these “famous” equations function best only for specific conditions, I propose a
new empirical equation to estimate ground effect lift as a function of aspect ratio and
incidence. Using Stratford’s method to predict signs of flow separation in the inviscid
solutions, I found that variations in the height above the ground were not significant enough
to change the stall angle of low aspect ratio wings. I did find early signs of flow separation
with increasing aspect ratio. I observe significant changes in spanwise loading when in
ground effect; as I narrow the gap, the transverse loading builds higher near the center of the
wing. These effects were more apparent in wings with smaller aspect ratio; higher aspect
ratio wings experience a higher loading gradient near the tips in proximity to the ground. I
found that high aspect ratio wings have a smaller stall angle compared to that of lower
aspect ratio wings; these trends are consistent between the potential flow solution and the
volume grid CFD viscous solution.
ContributorsValenzuela, Jose Vanir (Author) / Takahashi, Timothy (Thesis advisor) / Dahm, Werner (Committee member) / Huang, Huei-Ping (Committee member) / Arizona State University (Publisher)
Created2024
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
Micro/meso combustion has several advantages over regular combustion in terms of scale, efficiency, enhanced heat and mass transfer, quick startup and shutdown, fuel utilization and carbon footprint. This study aims to analyze the effect of temperature on critical sooting equivalence ratio and precursor formation in a micro-flow reactor. The effect of temperature on the critical sooting equivalence ratio of propane/air mixture at atmospheric pressure with temperatures ranging from 750-1250°C was investigated using a micro-flow reactor with a controlled temperature profile of diameter 2.3mm, equivalence ratios of 1-13 and inlet flow rates of 10 and 100sccm. The effect of inert gas dilution was studied by adding 90sccm of nitrogen to 10sccm of propane/air to make a total flow rate of 100sccm. The gas species were collected at the end of the reactor using a gas chromatograph for further analysis. Soot was indicated by visually examining the reactor before and after combustion for traces of soot particles on the inside of the reactor. At 1000-1250°C carbon deposition/soot formation was observed inside the reactor at critical sooting equivalence ratios. At 750-950°C, no soot formation was observed despite operating at much higher equivalence ratio, i.e., up to 100. Adding nitrogen resulted in an increase in the critical sooting equivalence ratio.
The wall temperature profiles were obtained with the help of a K-type thermocouple, to get an idea of the difference between the wall temperature provided with the resistive heater and the wall temperature with combustion inside the reactor. The temperature profiles were very similar in the case of 10sccm but markedly different in the other two cases for all the temperatures.
These results indicate a trend that is not well-known or understood for sooting flames, i.e., decreasing temperature decreases soot formation. The reactor capability to examine the effect of temperature on the critical sooting equivalence ratio at different flow rates was successfully demonstrated.
The wall temperature profiles were obtained with the help of a K-type thermocouple, to get an idea of the difference between the wall temperature provided with the resistive heater and the wall temperature with combustion inside the reactor. The temperature profiles were very similar in the case of 10sccm but markedly different in the other two cases for all the temperatures.
These results indicate a trend that is not well-known or understood for sooting flames, i.e., decreasing temperature decreases soot formation. The reactor capability to examine the effect of temperature on the critical sooting equivalence ratio at different flow rates was successfully demonstrated.
ContributorsKhalid, Abdul Hannan Hannan (Author) / Milcarek, Ryan (Thesis advisor) / Dahm, Werner (Committee member) / Kim, Jeonglae (Committee member) / Arizona State University (Publisher)
Created2019
Description
This thesis considers common definitions of uninstalled thrust, rigorous thrust derivations, and the significance of thrust definitions and derivations on air vehicle thrust-drag accounting methodology. This physics-based control volume approach to propulsive force accounting highlights differences in the application of control volume methods from different sources and summarizes common installation corrections. Certain combinations of thrust and installation corrections in practice lead to force accounting mistakes which can propagate in legacy aerodynamics and propulsion codes. The work concludes by proposing a simplified propulsive force accounting methodology applicable to many (not all) situations, a potential missing installation correction, and a procedural solution to the confusing and messy practice of aero-propulsive force accounting
ContributorsStauffer, Maxwell (Author) / Takahashi, Timothy (Thesis director) / Dahm, Werner (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2022-05
Description
This thesis addresses the issue of assessing longitudinal and lateral-directional trim capability during the conceptual design process. Modern high-performance aircraft are likely to feature complex flight control systems where the control system may independently command every control surface to develop necessary moments. However, to prove stability and controllability on such an aircraft requires a near-final set of control laws. This requirement is onerous at the conceptual design level, where engineering methods need to facilitate rapid, multidisciplinary design optimization trades. This work considers the differences in Attainable Moment Sets across a wide variety of airframes using a simplified “pre-mix” approach to controls as well as a model where the control systems have independent command authority over each control surface. This work indicates that the “independent-single-panel” model offers modest improvements in attainable moments over a “pre-mix” strategy. This suggests that a “pre-mix” approach used to assess basic combined trim problems will not lead to an overly conservative final design.
ContributorsHeinz, Joshua Holden (Author) / Takahashi, Timothy (Thesis advisor) / Dahm, Werner (Committee member) / Cotting, M. Christopher (Committee member) / Arizona State University (Publisher)
Created2023
Description
The objective of this study is to understand how to integrate conical spike external compression inlets with high bypass turbofan engines for application on future supersonic airliners. Many performance problems arise when inlets are matched with engines as inlets come with a plethora of limitations and losses that greatly affect an engine’s ability to operate. These limitations and losses include drag due to inlet spillage, bleed ducts, and bypass doors, as well as the maximum and minimum values of mass flow ratio at each Mach number that define when an engine can no longer function. A collection of tools was developed that allow one to calculate the raw propulsion data of an engine, match the propulsion data with an inlet, calculate the aerodynamic data of an aircraft, and combine the propulsion and aerodynamic data to calculate the installed performance of the entire propulsion system. Several trade studies were performed that tested how changing specific design parameters of the engine affected propulsion performance. These engine trade studies proved that high bypass turbofan engines could be developed with external compression inlets and retain effective supersonic performance. Several engines of efficient fuel consumption and differing bypass ratios were developed through the engine trade studies and used with the aerodynamic data of the Concorde to test the aircraft performance of a supersonic airliner using these engines. It was found that none of the engines that were tested came close to matching the supersonic performance that the Concorde could achieve with its own turbojet engines. It is possible to speculate from the results several different reasons why these turbofan engines were unable to function effectively with the Concorde. These speculations show that more tests and trade studies need to be performed in order to determine if high bypass turbofan engines can be developed for effective usage with supersonic airliners in any possible way.
ContributorsCleary, Spencer (Author) / Takahashi, Timothy (Thesis advisor) / White, Daniel (Committee member) / Dahm, Werner (Committee member) / Arizona State University (Publisher)
Created2018