Browsing by Subject "Wind tunnel"
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Item An Updated Procedure for Tare and Interference Wind Tunnel Testing of Strut-Mounted Models(2014-05-02) Kutz, Douglas MDespite advances in modern computing and simulation, wind tunnel testing remains the most trusted method for determining aerodynamic vehicle behavior. Corrections are applied to accurately obtain results representative of free-air performance due to the presence of wind tunnel walls. The standard correction procedure adjusts for the presence of these boundaries using approximations based on linear potential flow theory. Separately,tare and interference removal involves the linear subtraction of mounting strut effects, accomplished using mirrored mounting systems. Uncertainty in wind tunnel data is quantified throughout each step in the data analysis procedure. Additionally, an updated procedure for the analysis and correction of wind tunnel data for strut mounted models is recommended.Item Closed-loop control of shock location to prevent hypersonic inlet unstart(2014-08) Ashley, Jonathan Michael; Akella, Maruthi Ram, 1972-Hypersonic inlet unstart remains a major technical obstacle in the successful implementation of hypersonic air-breathing propulsion systems such as ramjets and scramjets. Unstart occurs when combustor-induced pressure fluctuations lead to rapid expulsion of the shock system from the isolator, and is associated with loss of thrust. The research presented here attempts to mitigate this behavior through the design and implementation of a closed-loop control scheme that regulates shock location within a Mach 1.8 wind tunnel isolator test section. To localize the position of the shock within the isolator, a set of high frequency Kulite pressure transducers are used to measure the static pressure at various points along the wind tunnel test section. A novel Kalman filter based approach is utilized, which fuses the estimates from two distinct shock localization algorithms running at 250 Hz to determine the location of the shock in real time. The primary shock localization algorithm is a geometrical shock detection scheme that can estimate the position of the shock system even when it is located between pressure transducers. The second algorithm utilizes a sum-of-pressures technique that can be calibrated by the geometrical algorithm in real time. The closed-loop controller generates commands every 100 ms to actuate a motorized flap downstream of the test section in an effort to regulate the shock to the desired location. The closed-loop control implementation utilized a simple logic-based controller as well as a Proportional-Integral (PI) and a Proportional-Derivative (PD) Controller. In addition to the implementation of control algorithms, the importance of various design criteria necessary to achieve satisfactory control performance is explored including parameters such as pressure transducer spacing, shock localization speed, flap-motor actuation speed and actuator resolution. Experimental results are presented for various test scenarios such as regulation of the shock location in the presence of stagnation pressure disturbances as well as tracking of time-varying step inputs. Performance and robustness properties of the tested control implementations are discussed. Further areas of improvement for the closed-loop control system in both hardware and software are discussed, and the need for reduced-order dynamics-based controllers is presented.Item Dynamic Pressure Improvements to Closed-Circuit Wind Tunnels with Flow Quality Analysis(2015-03-31) Herring, AlexanderTesting of aerodynamic loads on a sub-scale model has been the most accurate way to predict full-scale loads for many years. Even with modern advances in computing technology and computational fluid dynamics (CFD), each computer-aided model must be calibrated against a known standard, usually found through wind tunnel testing. Because wind tunnel testing is usually performed on sub-scale models, flow speeds that span the flight envelope are commonly tested. Traditionally the Texas A&M Engineering Experiment Station Low-Speed Wind Tunnel (LSWT) was limited through available power to a dynamic pressure of 120 psf. The addition of a higher power motor, construction of a new, smaller test section, diffuser liners to prevent flow separation, and increased structure to withstand higher static pressures allows for flow speeds up to 240 psf, nominally Mach 0.4. With proper design and construction, flow quality can be maintained to less than 1% deviation from mean flow velocity. Additionally, an accurate prediction of flow speed for a given test section geometry and power draw can be found.Item Experimental investigation of film cooling and thermal barrier coatings on a gas turbine vane with conjugate heat transfer effects(2013-05) Kistenmacher, David Alan; Bogard, David G.In the United States, natural gas turbine generators account for approximately 7% of the total primary energy consumed. A one percent increase in gas turbine efficiency could result in savings of approximately 30 million dollars for operators and, subsequently, electricity end-users. The efficiency of a gas turbine engine is tied directly to the temperature at which the products of combustion enter the first stage, high-pressure turbine. The maximum operating temperature of the turbine components’ materials is the major limiting factor in increasing the turbine inlet temperature. In fact, current turbine inlet temperatures regularly exceed the melting temperature of the turbine vanes through advanced vane cooling techniques. These cooling techniques include vane surface film cooling, internal vane cooling, and the addition of a thermal barrier coating (TBC) to the exterior of the turbine vane. Typically, the performance of vane cooling techniques is evaluated using the adiabatic film effectiveness. However, the adiabatic film effectiveness, by definition, does not consider conjugate heat transfer effects. In order to evaluate the performance of internal vane cooling and a TBC it is necessary to consider conjugate heat transfer effects. The goal of this study was to provide insight into the conjugate heat transfer behavior of actual turbine vanes and various vane cooling techniques through experimental and analytical modeling in the pursuit of higher turbine inlet temperatures resulting in higher overall turbine efficiencies. The primary focus of this study was to experimentally characterize the combined effects of a TBC and film cooling. Vane model experiments were performed using a 10x scaled first stage inlet guide vane model that was designed using the Matched Biot Method to properly scale both the geometrical and thermal properties of an actual turbine vane. Two different TBC thicknesses were evaluated in this study. Along with the TBCs, six different film cooling configurations were evaluated which included pressure side round holes with a showerhead, round holes only, craters, a novel trench design called the modified trench, an ideal trench, and a realistic trench that takes manufacturing abilities into account. These film cooling geometries were created within the TBC layer. Each of the vane configurations was evaluated by monitoring a variety of temperatures, including the temperature of the exterior vane wall and the exterior surface of the TBC. This study found that the presence of a TBC decreased the sensitivity of the thermal barrier coating and vane wall interface temperature to changes in film coolant flow rates and changes in film cooling geometry. Therefore, research into improved film cooling geometries may not be valuable when a TBC is incorporated. This study also developed an analytical model which was used to predict the performance of the TBCs as a design tool. The analytical prediction model provided reasonable agreement with experimental data when using baseline data from an experiment with another TBC. However, the analytical prediction model performed poorly when predicting a TBC’s performance using baseline data collected from an experiment without a TBC.Item Experimental investigation of the performance of a fully cooled gas turbine vane with and without mainstream flow and experimental analysis supporting the redesign of a wind tunnel test section(2013-12) Mosberg, Noah Avram; Bogard, David G.This study focused on experimentally determining the cooling performance of a fully cooled, scaled-up model of a C3X turbine vane. The primary objective was to determine the differences in overall effectiveness in the presence and absence of a hot mainstream flowing over the vane. Overall effectiveness was measured using a thermally scaled matched Biot number vane with an impingement plate providing the internal cooling. This is the first study focused on investigating the effect of removing the mainstream flow and comparing the contour and laterally-averaged effectiveness data in support of the development of an assembly line thermal testing method. It was found that the proposed method of factory floor testing of turbine component cooling performance did not provide comparable information to traditional overall effectiveness test methods. A second experiment was performed in which the effect of altering the angle of attack of a flow into a passive turbulence generator was investigated. Measurements in the approach flow were taken using a single wire hot-wire anemometer. This study was the first to investigate the effects such a setup would have on fluctuating flow quantitates such as turbulence intensity and integral length scale rather than simply the mean quantities. It was found that both the downstream turbulence intensity and the turbulence integral length scale increase monotonically with approach flow incidence angle at a specified distance downstream of the turbulence generator.Item Simulation of windborne debris trajectories(2005-08) Lin, Ning; Letchford, Christopher W.; Chen, XinzhongWindborne debris is possibly the major cause of building damage and destruction in strong wind events such as hurricanes and tornadoes. It has been long recognized that fast-flying debris can penetrate building envelopes, inducing internal pressurization and doubling the net loading on roofs, side walls, and leeward walls. Consequently, failed roofing structures, damaged wall cladding panels, and broken glass become debris sources, threatening downwind areas. Knowledge of debris aerodynamics is necessary for proper estimation of debris trajectory and for establishment of rational debris impact criteria. This research aims to investigate the aerodynamics of flying debris through simulating debris trajectories. Extensive wind-tunnel tests on 3D (compact-like), 2D (plate-like), and 1D (rod-like) debris are carried out in the Texas Tech University wind tunnel. The simulation procedure is introduced. Full-scale simulation is explored, employing a C-130 Hercules aircraft to generate strong winds. Three categories of parameters affecting debris trajectories are investigated: wind field, debris properties, and debris initial support. It is determined that although many parameters influence debris trajectory in the vertical direction, the Tachikawa parameter (1983) governs the horizontal trajectory of debris. Aerodynamic functions for debris horizontal trajectory are established based on both experimental data and theoretical equations of debris motion. These functions can be used to predict debris horizontal speed (at a given flight distance) and flight distance (for a given flight time). The application of these functions in debris impact criteria is discussed. The incorporation of these functions into debris risk analysis is recommended for the further research.Item Simulation of windborne debris trajectories(Texas Tech University, 2005-08) Lin, Ning; Letchford, Christopher W.; Chen, XinzhongWindborne debris is possibly the major cause of building damage and destruction in strong wind events such as hurricanes and tornadoes. It has been long recognized that fast-flying debris can penetrate building envelopes, inducing internal pressurization and doubling the net loading on roofs, side walls, and leeward walls. Consequently, failed roofing structures, damaged wall cladding panels, and broken glass become debris sources, threatening downwind areas. Knowledge of debris aerodynamics is necessary for proper estimation of debris trajectory and for establishment of rational debris impact criteria. This research aims to investigate the aerodynamics of flying debris through simulating debris trajectories. Extensive wind-tunnel tests on 3D (compact-like), 2D (plate-like), and 1D (rod-like) debris are carried out in the Texas Tech University wind tunnel. The simulation procedure is introduced. Full-scale simulation is explored, employing a C-130 Hercules aircraft to generate strong winds. Three categories of parameters affecting debris trajectories are investigated: wind field, debris properties, and debris initial support. It is determined that although many parameters influence debris trajectory in the vertical direction, the Tachikawa parameter (1983) governs the horizontal trajectory of debris. Aerodynamic functions for debris horizontal trajectory are established based on both experimental data and theoretical equations of debris motion. These functions can be used to predict debris horizontal speed (at a given flight distance) and flight distance (for a given flight time). The application of these functions in debris impact criteria is discussed. The incorporation of these functions into debris risk analysis is recommended for the further research.Item Superposition in the leading edge region of a film cooled gas turbine vane(2013-12) Anderson, Joshua Brian; Bogard, David G.The leading edge of a turbine vane is subject to some of the highest temperature loading within an engine, and an accurate understanding of leading edge film coolant behavior is essential to efficient engine design. Although there have been many investigations of the adiabatic effectiveness for showerhead film cooling within the leading edge region, there have been no previous studies in which individual rows of the showerhead were tested with the explicit intent of validating superposition models. For the current investigation, a series of adiabatic effectiveness experiments were performed with a five-row showerhead, wherein each row of holes was operated in isolation. This allowed evaluation of superposition on both the suction side of the vane, which was moderately convex, and the pressure side of the vane, which was mildly concave. Superposition was found to accurately predict performance on the suction side of the vane at lower momentum flux ratios, but not for higher momentum flux ratios. On the pressure side of the vane, the superposition predictions were consistently lower than measured values, with significant under-prediction of adiabatic effectiveness occurring at the higher mass flow rates. Possible reasons for the under-prediction of effectiveness by the superposition model are presented.