Doctor of Philosophy, The Ohio State University, 2023, Aero/Astro Engineering

The feasibility of an active flow control enabled variable area turbine was explored. Pressurized air was ejected from the nozzle guide vanes to reduce the effective choke area, and mass flow rate through, the turbine inlet. A set of experimental and computational studies were conducted with varying actuator types and parameters to determine their effectiveness and develop models of the flow physics. Preliminary results from a simple quasi-1D converging-diverging nozzle, with an injection flow slot upstream of the throat, showed a 2.2:1 ratio between throttled mass flow rate and injected mass flow rate at a constant nozzle pressure ratio. The penetration of the injection flow and corresponding reduction in the primary flow streamtube were successfully visualized using a shadowgraph technique. Building on this success, a representative single passage nozzle guide vane transonic flowpath was constructed to demonstrate feasibility beyond the quasi-1D converging-diverging nozzle. Both secondary slot blowing from the vane pressure surface and vane suction surface just upstream of the passage throat again successfully reduced primary flow. In addition, fluidic vortex generators were used on the adjacent suction surface to reduce total pressure loss along the midspan and further throttle the primary flow. Computational fluid dynamics simulations were used to explore the effects of a variety of parameters on the flow blockage and actuator effectiveness. Simplified models were developed to describe the relationships of various factors impacting flow blockage, turning angle, and total pressure loss. Finally, the active flow control systems were simulated at engine relevant pressures and temperatures and found to have only a minimal drop in total pressure recovery and effectiveness, which could be predicted by the simplified blockage model.

Committee: Jeffrey Bons (Advisor); Datta Gaitonde (Committee Member); Randall Mathison (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, The Ohio State University, 2020, Mechanical Engineering

Gas turbine is an integrated part of modern aviation and power generation industry. The thermal efficiency of a gas turbine strongly depends on the turbine inlet temperature (TIT), and the turbine designers are continuously pushing the TIT to a higher value. Due to the increased freedom in additive manufacturing, the complex internal and external geometries of the turbine blade can be leveraged to utilize innovative cooling designs to address some of the shortcomings of current cooling technologies. The sweeping jet film cooling has shown some promise to be an effective method of cooling where the coolant can be brought very close to the blade surface due to its sweeping nature. A series of experiments were performed using a row of fluidic oscillators on a flat plate. Adiabatic cooling effectiveness, convective heat transfer coefficient, thermal field, and discharge coefficient were measured over a range of blowing ratios and freestream turbulence. Results were compared with a conventional shaped hole (777-hole), and the sweeping jet hole shows improved cooling performance in the lateral direction. Numerical simulation also confirmed that the sweeping jet creates two alternating vortices that do not have mutual interaction in time. When the jet sweeps to one side of the hole exit, it acts as a vortex generator as it interacts with the mainstream ow. This prevents the formation of the counter-rotating vortex pair (CRVP) and allows the coolant to spread in the lateral direction. The results obtained from the low speed at plate tests were utilized to design the sweeping jet film cooling hole for more representative turbine vane geometry. Experiments were performed in a low-speed linear cascade facility. Results showed that the sweeping jet hole has higher cooling effectiveness in the near hole region compared to the shaped hole at high blowing ratios. Next, a detailed experimental investigation of sweeping jet film cooling on the suction surface of a near engine scale (open full item for complete abstract)

Committee: Jeffrey Bons (Advisor); James Gregory (Committee Member); Randall Mathison (Committee Member); Ali Ameri (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2019, Mechanical Engineering

Heat transfer and pressure drop experiments were conducted for two gas turbine nozzle guide vane trailing edge designs. A circular pin fin array with clearance and a center-body (PFC) was designed and denoted as additive manufacturing-enabled design. The PFC design has two near wall channels with partial-length pins attached to the vane walls. Partial length pins have a gap to channel height ratio (G/H) of 0.23. Thermal performance and pressure ratio of the PFC design were compared to a conventional circular pin fin (PF) design. Test articles were additively manufactured using Stereolithography (SLA) and have identical pin diameters (D) as well as identical streamwise (X/D=1) and spanwise (S/D=2) spacing. Steady state heat transfer experiments were performed in a low speed linear cascade at low (Tu=6.1%) and high (Tu=14.3%) freestream turbulence intensities relevant to gas turbines. Infrared (IR) thermography was used to measure the trailing edge suction side wall temperature and overall cooling effectiveness (Φ) was estimated. Four different coolant mass flow rates were studied with Re based on pin diameter and inlet channel cross section just upstream of the pins of 820-1915 and 262-612 for the PFC and PF designs, respectively. As expected, cooling effectiveness nonlinearly increased with higher coolant mass flow rates. The PFC design has more uniform Φ in the region with partial-length pins than in corresponding locations of the PF design; implying that the PFC design would lead to less thermal stress than the PF design. The PFC design has slightly better thermal performance (≤4%) than the PF design at low Tu, except for the highest coolant mass flow rate. At low Tu, for the PFC design, coolant mass flow rate dependency of Φ was not as strong as in the PF design due to the flow passing through the clearance in the PFC design. At high Tu, the two designs show comparable thermal performance. Higher freestream turbulence intensity case exhibited higher overall cool (open full item for complete abstract)

Committee: Jeffrey P. Bons Professor (Advisor); Randall Mathison Assistant Professor (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2018, Aero/Astro Engineering

Sweeping jet impingement cooling was investigated in a gas turbine nozzle guide vane design with an engine-relevant Biot number of 0.3. Sweeping jets were created with fluidic oscillators and were compared to steady jets produced by cylindrical orifices (with length-to-diameter ratio of 1), the current state-of-the-art in engine designs. Experiments were performed in a low speed linear cascade with additively manufactured test pieces. The impingement cooling geometries were examined at multiple coolant mass flow rates and freestream turbulence intensities. The overall effectiveness of each cooling geometry was calculated using thermocouple measurements of the freestream and coolant temperatures, and infrared thermography measurements of the vane external surface temperature. A computational thermal inertia technique was used to determine the internal Nusselt numbers. The heat transfer provided by steady impinging jets produced a higher overall effectiveness and Nusselt number in the leading edge geometry. The sweeping jets provided more uniform heat transfer, reducing thermal gradients near the stagnation point. Pressure drop across each jet geometry was measured at a range of applicable mass flow rates. Fluidic oscillators were shown to create similar pressure drop to circular orifice holes when additive manufacturing abilities were fully incorporated in the nozzle guide vane internal cooling designs.

Committee: Jeffrey Bons (Advisor); Ali Ameri (Committee Member); James Gregory (Committee Member) Subjects: Aerospace Engineering

Master of Science, The Ohio State University, 2012, Aero/Astro Engineering

An accelerated deposition test facility was used to study the relationship between film cooling, surface temperature, and particle temperature at impact on deposit formation. Tests were run at gas turbine representative inlet Mach numbers (0.1) and temperatures (1090°C). Deposits were created from lignite coal fly ash with median diameters of 1.3 and 8.8µm. Two CFM56-5B nozzle guide vane doublets, comprising three full passages and two half passages of flow, were utilized as the test articles. Tests were run with different levels of film cooling back flow margin and coolant temperature. Particle temperature upon impact with the vane surface was shown to be the leading factor in deposition. Since the particle must traverse the boundary layer of the cooled vane before impact, deposition is directly affected by the film and metal surface temperature as well. Film coolant jet strength showed only minor effect on deposit patterns on the leading edge. However, larger Stokes number (resulting in higher particle impact temperature) corresponded with increased deposit coverage area on the shower head region. Additionally, infrared measurements showed a strong correlation between regions of greater deposits and elevated surface temperature on the pressure surface. Thickness distribution measurements also highlighted the effect of film cooling by showing reduced deposition immediately downstream of cooling holes. A set of secondary tests were also conducted to briefly study the effect of Stokes number on leading edge deposition with no cooling, in order to support conclusions from the primary tests. It was found that larger Stokes number led to an increase in rate of deposition due to a greater number of particles being able to follow their inertial trajectories and impact the vane. Implications for engine operation in particulate-laden environments are discussed.

Committee: Jeffrey Bons PhD (Advisor); Micheal Dunn PhD (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering