Thesis (M.S.)--University of North Texas, May, 2009. / Title from title page display. Includes bibliographical references.

Several flow control schemes were designed and tested to determine the most suitable method for reducing the momentum deficit in a rotor wake and thus attenuate rotor-stator interaction noise. A secondary concern of the project was to reduce the amount of blowing required air for wake filling and thus limit the efficiency penalty in an aircraft engine environment. Testing was performed in a linear blow down cascade wind tunnel, which produced an inlet Mach number of 0.345. The cascade consisted of five blades with the stagger angle, pitch, and airfoil cross-section representative of 90% span of the rotor geometry for NASA's Active Noise Control Fan (ANCF) test rig. The Reynolds number for the tests was based on inlet conditions and a chord length of 4 inches. Trailing edge jets, trailing edge slots, ejector pumps, and pressure/suction side jets were among the configurations tested for wake filling. A range of mass flow percentages were applied to each configuration and a pressure loss coefficient was determined for each. Considerable reduction in wake losses took place for discrete jet blowing techniques as well as pressure side and suction side jets. In the case of the pressure and suction side jets, near full wake filling occurred at 0.75% of the total mass flow. In terms of loss coefficients and calculated momentum coefficients, the suction/pressure surface jets were the most successful. Jets located upstream of the trailing edge helped to re-energize the momentum deficits in the wake region by using a flow pattern capable of mixing the region while also adding momentum to the wake. The slotted configuration was modeled after NASA's current blowing scheme and served as a baseline for comparison for all data. Digital particle image velocimetry was performed for flow visualizations as well as velocity analysis in the wake region. / Master of Science

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An aeroacoustic investigation was performed to assess the effects of adding mass flow at the trailing edges of four stators upstream of an aircraft engine simulator. By using trailing edge blowing to minimize the shed wakes of the stators, the flow into the rotor was made more uniform. In these experiments a reduced number of stators (four) was used in a 1/14 scale model inlet which was coupled to a 4.1 in (10.4 cm) turbofan engine simulator with 18 rotors and 26 downstream stators. This study is a preliminary step toward a more in depth investigation of using trailing edge blowing to reduce unsteady rotor-stator interaction. Steady-state measurements of the aerodynamic flow field and acoustic far field were made in order to evaluate the aeroacoustic performance at three simulator speeds: 40%, 60%, and 88% of the design speed. The lowest test speed of 40% design speed showed the most dramatic reduction in radiated noise. Noise reductions as large as 8.9 dB in the blade passing tone were recorded at 40% design speed, while a tone reduction of 5.5 dB was recorded at 60% design speed. At 88% design speed a maximum tone reduction of 2.6 dB was recorded. In addition, trailing edge blowing reduced the overall sound pressure level in every case. For both the 40% design speed and the 60% design speed, the fan face distortion was significantly reduced due to the trailing edge blowing. The addition of trailing edge blowing from the four upstream stators did not change the total pressure ratio, and the mass flow added by the blowing was approximately 1%. The results of these experiments clearly demonstrate that blowing from the trailing edges of the stators is effective in reducing unsteady rotor-stator interaction and the subsequent forward radiated noise. / Master of Science

Boundary layer characteristics at the trailing edge of a tiltrotor blade model were measured using a flattened pitot probe and a single hot wire. The blade was mounted in Virginia Tech Stability Wind tunnel stationary on a turntable on the wind tunnel's upper wall with the tip pointing down. The measurement point was located at 1 mm behind the trailing edge to make it possible to measure the flow near the blade surface and measure the boundary layer on both sides of the trailing edge in a same run. Mean velocity profiles were measured for a variety of Reynolds numbers and angles of attack. Turbulence intensity and spectral measurements were performed using a single hot wire at the highest Reynolds number. Conclusion was reached that both of the flattened pitot probe and single hot wire are good for boundary layer thickness measurements. Displacement thickness, which is important in trailing edge noise prediction, was calculated from the profile data and fit using an algebra expression against the tip angle of attack. Once the relationship between tip angle of attack and local effective angle of attack is obtained by lifting line theory, the results can be used in the trailing edge noise prediction code. / Master of Science

Detailed measurements were taken downstream of several modified trailing edge configurations designed to impart streamwise velocity into the flow behind a cascade of GE Rotor B fan blades. These measurements were conducted in the Virginia Tech Low Speed Linear Cascade wind tunnel. The trailing edge configurations tested utilized passive techniques for producing streamwise vorticity, which in turn causes downstream wake diffusion and increased mixing. A more diffuse wake, when it impinges on the downstream stator, will produce lower noise levels as a result of this rotor-stator interaction. Furthermore, increased mixing in the flow will reduce the levels of turbulence kinetic energy observed downstream of the blade trailing edge. Thus, this project seeks to identify which passive techniques of imparting streamwise vorticity are most effective at improving the flow characteristics responsible for some of the noise production in modern jet aircraft. The three trailing edge configurations tested in detail for this project showed significant ability to widen and stretch the downstream wake by utilizing vorticity generation techniques. The TE-8 configuration was the most effective at increasing the wake width downstream of the trailing edge. Additionally, each configuration was able to successfully reduce some of the turbulence kinetic energy levels observed downstream when compared to the baseline blade, the most effective configuration being TE-8. Finally, the momentum thickness of each configuration was measured. When compared to the baseline, the TE-1 configuration showed an increased momentum thickness, TE-8 showed little change, and TE-7 actually showed an improved momentum thickness value. / Master of Science

This research performs an experimental study of a trailing edge blowing system that can adapt to variations in flow parameters and reduce the unsteady stator-rotor interaction at all engine operating conditions. The fan rotor of a 1/14 scale turbofan propulsion simulator is subjected to spatially periodic, circumferential inlet flow distortions. The distortions are generated by four struts that support a centerbody in the inlet mounted onto the simulator. To reduce the unsteady effects of the strut wakes on the rotor blades, the wake is re-energized by injecting mass from the trailing edge of the strut. Each strut is provided with discrete blowing holes that open out through the strut trailing edge. Each blowing hole is connected to a MEMS based microvalve, which controls the blowing rate of the hole. The microvalve is actuated by a signal voltage, generated by a PID controller that accepts free stream and wake axial flow velocities as inputs and minimizes their difference. To quantify the effectiveness of trailing edge blowing the far-field noise is measured in an anechoic chamber. The experiments are performed for two simulator test speeds, 29,500 rpm and 40,000 rpm, with and without trailing edge blowing. The maximum reduction recorded at 29,500 rpm is 8.2 dB, and at 40,000 rpm is 7.3 dB. Reductions of 2.9 dB and greater are observed at the first five harmonics of the blade passing frequency. The sound power level at the blade passing frequency, calculated from measured far-field directivity, is reduced by 4.4 dB at 29,500 rpm and by 2.9 dB at 40,000 rpm. The feasibility and advantage of active control is demonstrated by the ability of the system to respond to a step change in the inlet flow velocity, and achieve optimum wake filling in approximately 8 seconds. / Master of Science

Dredging projects are expensive government funded projects that are contracted out and competitively bid upon. When planning a trailing suction hopper dredge project or bidding on the request for proposal for such a project, having an accurate cost prediction is essential. This thesis presents a method using fluid transport fundamentals and pump power characteristics to determine a production rate for hopper dredges. With a production rate established, a number of financial inputs are used to determine the cost and duration of a project. The estimating program is a Microsoft Excel spreadsheet provided with reasonable values for a wide arrange of hopper dredging projects. The spreadsheet allows easy customization for any user with specific knowledge to improve the accuracy of his estimate. Results from the spreadsheet were found to be satisfactory using the default values and inputs of 8 projects from 1998 to 2009,: The spreadsheet produced an estimate that was an average of a 15.9% difference from the actual contract cost, versus a 15.7% difference for government estimates of the same projects.

The purpose of this study was to create a proof-of-concept piezoelectric actuator system capable of meeting the performance requirements necessary for actuation of a trailing edge flap for a helicopter main rotor blade. Due to extremely small displacements produced by piezoelectric actuators, their output is amplified several times in order to produce the required displacement for this device. The amplification is accomplished in two stages. The first stage, mechanical amplification, uses differential length lever arms to increase the piezoelectric actuator output. The second stage, hydraulic amplification, is coupled to the first stage and uses differential area pistons to further amplify the output of the mechanical amplifier. The actuation systems force and displacement output is characterized based on frequency.

Dredging projects are expensive government funded projects that are contracted out and competitively bid upon. When planning a trailing suction hopper dredge project or bidding on the request for proposal for such a project, having an accurate cost prediction is essential. This thesis presents a method using fluid transport fundamentals and pump power characteristics to determine a production rate for hopper dredges. With a production rate established, a number of financial inputs are used to determine the cost and duration of a project. The estimating program is a Microsoft Excel spreadsheet provided with reasonable values for a wide arrange of hopper dredging projects. The spreadsheet allows easy customization for any user with specific knowledge to improve the accuracy of his estimate. Results from the spreadsheet were found to be satisfactory using the default values and inputs of 8 projects from 1998 to 2009,: The spreadsheet produced an estimate that was an average of a 15.9% difference from the actual contract cost, versus a 15.7% difference for government estimates of the same projects.