The U.S. Army has recently developed cutting edge designs for gun barrels, projectiles, and propellants that require testing. This includes measuring the internal pressure during fire. There are concerns with the current method of drilling to mount pressure transducers near the breech and chamber of the gun barrel where pressure is highest. An alternative, non-intrusive strain measurement method is introduced and discussed in the present work. This focuses on determining the feasibility and accuracy of relating tangential strain along the sidewall of a gun barrel to the drastic internal pressure rise created during combustion. A transient structural, numerical modal was created using ANSYS of a 155 mm gun barrel. The pressure gradient was derived using a method outline in IBHVG2 (Interior Ballistics of High Velocity Guns, version 2), and the model was validated using published experimental tangential strain testing data from a gun of the same caliber. The model was used to demonstrate the ideal location for strain measurement along the sidewall of the chamber. Furthermore, three different pressure ranges were simulated in the model. The behavior of the tangential strain in each case indicates a similar trend to the internal pressure rise and has oscillation due to a dominant frequency of the barrel. A method to predict internal pressure from external tangential strain was developed. The internal pressure predicted is within 4% of the pressure applied in the model. A sensitivity study was performed to determine the primary factors affecting tangential strain. The study specifically looked at material properties and geometry of the gun barrel. The thickness and elastic modulus of the gun barrel were determined the most relevant. Overall, the present work helps to understand tangential strain behavior on the sidewall of a large caliber gun barrel and provides preliminary work to establish an accurate prediction of internal pressure from external tangential strain. / Master of Science / Innovative technology for large gun systems require testing to evaluate safety and performance. The most recent designs from the U.S. Army for long range artillery require higher pressures. Currently, large gun barrels are drilled to mount pressure transducers for internal pressure testing, but the new generation of weapons require a way to measure internal pressure of the gun without introducing these high stress locations. External strain offers a means to measure displacement of the barrel caused by the internal pressure change with minimal alteration to the gun barrel. The present work focuses on modelling a large gun barrel using finite elements to understand the behavior of strain on the external surface due to internal pressure during fire. Measurements were taken near the chamber of the gun barrel model. The strain behavior is comprised of two components, a linear change due to a pressure increase and vibrations introduced due to the sharp pressure increase over a short amount of time. Three cases were evaluated at different pressure ranges and a method was developed to predict internal pressure from the tangential strain with a maximum error of 4% for all cases studied. The model also indicates that the strain results are most sensitive to a change in thickness and the elastic modulus of the gun barrel material.

Increasingly stringent pollution and emission controls have caused a rise in the use of combustors operating under lean, premixed conditions. Operating lean (excess air) lowers the level of nitrous oxides (NOx) emitted to the environment. In addition, concerns over climate change due to increased carbon dioxide (CO2) emissions and the need for energy independence in the United States have spurred interest in developing combustors capable of operating with a wide range of fuel compositions. One method to decrease the carbon footprint of modern combustors is the use of high hydrogen content (HHC) fuels. The objective of this research is to develop tools to better understand the physics of turbulent flame propagation in highly stretch sensitive premixed flames in order to predict their behavior at conditions realistic to the environment of gas turbine combustors. This thesis presents the results of an experimental study into the flame propagation characteristics of highly stretch-sensitive, turbulent premixed flames generated in a low swirl burner (LSB). This study uses a scaling law, developed in an earlier thesis from leading point concepts for turbulent premixed flames, to collapse turbulent flame speed data over a wide range of conditions. The flow and flame structure are characterized using high speed particle image velocimetry (PIV) over a wide range of fuel compositions, mean flow velocities, and turbulence levels. The first part of this study looks at turbulent flame speeds for these mixtures and applies the previously developed leading points scaling model in order to test its validity in an alternate geometry. The model was found to collapse the turbulent flame speed data over a wide range of fuel compositions and turbulence levels, giving merit to the leading points model as a method that can produce meaningful results with different geometries and turbulent flame speed definitions. The second part of this thesis examines flame front topologies and stretch statistics of these highly stretch sensitive, turbulent premixed flames. Instantaneous flame front locations and local flow velocities are used to calculate flame curvatures and tangential strain rates. Statistics of these two quantities are calculated both over the entire flame surface and also conditioned at the leading points of the flames. Results presented do not support the arguments made in the development of the leading points model. Only minor effects of fuel composition are noted on curvature statistics, which are mostly dominated by the turbulence. There is a stronger sensitivity for tangential strain rate statistics, however, time-averaged values are still well below the values hypothesized from the leading points model. The results of this study emphasize the importance of local flame topology measurements towards the development of predictive models of the turbulent flame speed.

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