Earlier research has demonstrated that downstream of combustion in a rotating detonation engine, exhaust flow periodically reverses circumferential direction. For small periods, the circumferential flow reaches velocity magnitudes rivaling the bulk flow of exhaust, manifesting as a swirl. The minimization of this swirl is critical to maximizing thrust and engine performance for rocket propulsion. During this study, numerous nozzle contours were iteratively designed and analyzed for losses analytically. Once a nozzle was chosen, further losses were validated through computational fluid dynamics simulations and then tested experimentally. Three different configurations were run with the RDRE: no nozzle, a nozzle without a spike, and a nozzle with a spike. Images of the exhaust quality were recorded using OH* chemiluminescence in high-speed cameras. One camera was used to confirm the existence of a detonation and the frequency of detonation. The second camera is pointed perpendicular to the exhaust flow to capture the quality of exhaust. Quantitative results of the turbulent velocity fluctuations were obtained through particle image velocimetry of the side-imaging frames. All frames in each case were exported and converted to several time-averaged frames whereupon the time-averaged turbulent velocity fluctuation profiles could be compared between cases for swirl attenuation.

When studying pressure-gain combustion and wave rotor combustors, it is vital that any experimental model accurately reflect the real world conditions/applications being studied; this not only confirms previous computational and analytical work, but also provides new insights into how these concepts and devices work in real life. However, mixture stratification can have a noticeable effect on multiple combustion properties, including flame propagation, pressure, ignition time delay, and more, and this is especially true in constant-volume combustion chambers. Because it is beneficial to model wave rotor systems using constant-volume combustors such as what is employed in the IUPUI Combustion and Propulsion Research Laboratory, these stratification effects much be taken into account and reduced if possible. This study sought to find an effective method to reduce stratification in a rectangular constant-volume combustion chamber by means of manual recirculation pump. Spark-ignited flames were first produced in the chamber itself and studied using schlieren and color videography techniques as well as quantitative pressure histories. After determining the pump's effectiveness in reducing stratification, it was next employed when a hot jet of combustion products from a separate combustion chamber was used as an ignition source instead of the spark plug - a process typically employed in real wave rotor combustors. Lastly, the pump was used to study the leakage from the system for future test cases in order to offer further recommendations on how to effectively use the recirculation system. This process found that key properties significant to wave rotor development, such as time ignition delay, were affected by these stratification effects in past studies that did not account for this detail. As such, the pump has been permanently incorporated into the wave rotor model, as stratification is a vital. Additionally, significant fuel leakage is possible during rotational pre-chamber cases, and this should be address before proceeding with such experiments in the future. To combat this, the pump system has been reduced in volume, and suggestions have been provided on how to better seal the main rectangular chamber in the future.

<p>In rotating detonation engines the turbine inlet conditions may be transonic with unprecedented unsteady fluctuations, very different from those in conventional high-pressure turbines. To ensure an acceptable engine performance, the turbine passages must be unchoked at subsonic and started at supersonic conditions. Additionally, to maximize the aerodynamic performance potential, ad-hoc designs are required, suited for the oscillations in Mach number and flow angle. This manuscript focuses on designing and characterizing diffusive turbine vanes that can operate downstream of a transonic rotating detonation combustor.  </p> <p><br></p> <p>First, the phenomenon of unstarting is presented, concentrating on the effect of pressure loss on the accurate prediction of the starting limit. Afterward, a multi-objective optimization with steady Reynolds Averaged Navier Stokes simulations, including the endwall and 3D vane design, is performed. The results are discussed, highlighting the impact of the throat-to-inlet area ratio on the pressure loss and the geometric features of the top-performing designs. Compared to previous  research on stator passages with contoured endwalls, considerable reductions in pressure loss and stator-induced rotor forcing are obtained, with an extended operating range and preserving high turning.  </p> <p><br></p> <p>Subsequently, the influence of the inlet boundary layer thickness on the vane performance is evaluated, inducing remarkable increases in pressure loss and downstream pressure distortion. Employing an optimization with a thicker inlet boundary layer, specific endwall design recommendations are found, providing a notable improvement in both objective functions. The impact of the geometry variations on flow detachment is assessed as well.</p> <p><br></p> <p>Finally, the impact of the inlet flow angle on the vane design is studied through a multi-point, multi-objective optimization with different inlet angles. The effect of incidence on the flow field and vane performance is evaluated first. Then, by comparing the optimized geometries with those optimized for axial inflows, several design guidelines are identified </p>

<p dir="ltr">This study contributes to research involving wave rotor combustors by studying the</p><p dir="ltr">development of a hot jet issuing from a cylindrical pre-combustion chamber. The pre-chamber was</p><p dir="ltr">developed to provide a hot fuel-air mixture as an ignition source to a rectangular combustion</p><p dir="ltr">chamber, which models the properties of a wave rotor channel. The pre-combustion chamber in</p><p dir="ltr">this study was rebuilt for study and placed in a new housing so that buoyancy effects could be</p><p dir="ltr">studied in tandem with other characteristics. The effectiveness of this hot jet is estimated by using</p><p dir="ltr">devices and instrumentation to measure properties inside the pre-chamber under many different</p><p dir="ltr">conditions. The properties tracked in this study include maximum pressure, the pressure and time</p><p dir="ltr">at which an aluminum diaphragm ruptures, and the moment a developed flame reaches a precise</p><p dir="ltr">location within the chamber. The pressure is tracked through use of a high-frequency pressure</p><p dir="ltr">transducer, the diaphragm rupture moment is captured with a high-speed video camera, and the</p><p dir="ltr">flame within the pre-chamber is detected by a custom-built ionization probe. The experimental</p><p dir="ltr">apparatus was used in three configurations to study any potential buoyancy effects and utilized</p><p dir="ltr">three different gaseous fuels, including a 50%-50% methane-hydrogen blend, pure methane, and</p><p dir="ltr">pure hydrogen. Additionally, the equivalence ratio within the pre-chamber was varied from values</p><p dir="ltr">of 0.9 to 1.2, and the initial pressure was set to either 1.0, 1.5, or 1.75 atm. In all cases, combustion</p><p dir="ltr">was initiated from a spark plug, causing a flame to develop until the diaphragm breaks, releasing</p><p dir="ltr">a hot jet of fuel and air from the nozzle inserted into the pre-chamber. In the pressure transducer</p><p dir="ltr">tests, it was found that hydrogen produced the highest pressures and fastest rupture times, and</p><p dir="ltr">methane produced the lowest pressures and slowest rupture times. The methane-hydrogen blend</p><p dir="ltr">provided a middle ground between the two pure fuels. An equivalence ratio of 1.1 consistently</p><p dir="ltr">provided the highest pressure values and fastest rupture out of all tested values. It was also found</p><p dir="ltr">that the orientation has a noticeable impact on both the pressure development and rupture moment</p><p dir="ltr">as higher maximum pressures were achieved when the chamber was laid flat in the “vertical jet”</p><p dir="ltr">orientation as compared to when it was stood upright in the “horizontal jet” orientation.</p><p dir="ltr">Additionally, increasing the initial pressure strongly increased the maximum developed pressure</p><p dir="ltr">but had minimal impact on the rupture moment. The tests done with the ion probe demonstrated</p><p dir="ltr">that an equivalence ratio of 1.1 produces a flame that reaches the ion probe faster than an</p><p dir="ltr">equivalence ratio of 1.0 for the methane-hydrogen blend. In its current form, the ion probe setup</p><p>18</p><p dir="ltr">has significant limitations and should continue to be developed for future studies. The properties</p><p dir="ltr">analyzed in this study deepen the understanding of the processes that occur within the pre-chamber</p><p dir="ltr">and aid in understanding the conditions that may exist in the hot jet produced by it as the nozzle</p><p dir="ltr">ruptures. The knowledge gained in the study can also be applied to develop models that can predict</p><p dir="ltr">other parameters that are difficult to physically measure.</p>

No description available.

<p dir="ltr">Burst-mode lasers and burst-mode optical parametric oscillators (OPOs) are applied and developed for planar laser induced fluorescence (PLIF) measurements of key species for high-speed combustion measurements. OH-PLIF in the rotating detonation engine was performed for the first time at wave structure visualization in two different planes and was 10 times faster than any other burst mode OH-PLIF measurements at the time. The same system was used to perform another OH-PLIF experiment at 1 MHz for ~200 pulses to compare key features of the detonation wave structure with computational fluid dynamic simulations and a fundamental detonation tube experiment. The system was also used for seedless velocity measurements in the exhaust by tracking a pocket of OH with a technique called FLASH. A similar OPO was built, aligned, and tuned to perform 1 MHz NO PLIF in a Mach 10 hypersonic tunnel to visualize second mode instabilities and calculate the frequency in the boundary layer transition of a 7-degree cone. A high-efficiency OPO was developed and characterized utilizing the KTP crystal to provide narrow bandwidth pulses for the fluorescence of multiple species. The OPO was pumped at repetition rates up to 1 MHz and was calculated to have a 1.9% UV efficiency from the fundamental 1064 nm output. This is 3 – 5 times increase in efficiency from previous custom and commercial built OPOs. The OPO was applied to the RDC for OH PLIF in the combustor channel and NO PLIF for injector dynamics and response studies. Lastly, a burst-mode laser was used to perform LII on the post detonation blast flow field to measure explosively generated soot. The data was taken at 1 MHz and compared and corrected with a separate set of experiments and computational simulations.</p>