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Wake Filling Techniques for Reducing Rotor-Stator Interaction NoiseMinton, Christopher Mills 18 August 2005 (has links)
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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Reduction of Unsteady Rotor-Stator Interaction Using Trailing Edge BlowingLeitch, Thomas A. 16 January 1997 (has links)
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
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Boundary Layer Characteristics on a Tiltrotor Blade ModelWang, Hongwei 18 July 2001 (has links)
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
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Reduction of Unsteady Stator-Rotor Interaction by Trailing Edge Blowing Using MEMS Based MicrovalvesRao, Nikhil M. 30 April 1999 (has links)
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
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Developement of Piezo-Hydraulic Actuation Systems Technology for use on a Helicopter Trailing Edge FlapHerdic, Scott Lucas 28 November 2005 (has links)
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.
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An experimental investigation of turbine blade heat transfer and turbine blade trailing edge coolingChoi, Jungho 17 February 2005 (has links)
This experimental study contains two points; part1 turbine blade heat transfer
under low Reynolds number flow conditions, and part 2 trailing edge cooling and
heat transfer. The effect of unsteady wake and free stream turbulence on heat transfer
and pressure coefficients of a turbine blade was investigated in low Reynolds number
flows. The experiments were performed on a five blade linear cascade in a low speed
wind tunnel. A spoked wheel type wake generator and two different turbulence grids
were employed to generate different levels of the Strouhal number and turbulence
intensity, respectively. The cascade inlet Reynolds number based on blade chord
length was varied from 15,700 to 105,000, and the Strouhal number was varied from 0
to 2.96 by changing the rotating wake passing frequency (rod speed) and cascade inlet
velocity. A thin foil thermocouple instrumented blade was used to determine the
surface heat transfer coefficient.
A liquid crystal technique based on hue value detection was used to measure
the heat transfer coefficient on a trailing edge film cooling model and internal model of
a gas turbine blade. It was also used to determine the film effectiveness on the trailing
edge. For the internal model, Reynolds numbers based on the hydraulic diameter of
the exit slot and exit velocity were 5,000, 10,000, 20,000, and 30,000 and
corresponding coolant to mainstream velocity ratios were 0.3, 0.6, 1.2, and 1.8 for
the external models, respectively. The experiments were performed at two different
designs and each design has several different models such as staggered / inline exit,
straight / tapered entrance, and smooth / rib entrance. The compressed air was used in
coolant air. A circular turbulence grid was employed to upstream in the wind tunnel
and square ribs were employed in the inlet chamber to generate turbulence intensity
externally and internally, respectively.
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Determination of heat (mass) transfer from blockages with round and elongated holes in a wide rectangular channelRupakula, Venkata Panduranga Praveen 25 April 2007 (has links)
Mass transfer experiments were conducted to study the thermal performance
characteristics of blockages with round and elongated holes, positioned in a 12:1
rectangular channel. Naphthalene sublimation technique was adopted to conduct
experiments with four different blockage configurations, flow rates corresponding to
Reynolds numbers (based on channel hydraulic diameter) of 7,000 and 17,000, and at
three blockage locations. The hole area to channel area ratio for all four blockage
configurations was the same at 0.196. The hole width was half the channel height, and
the distance between consecutive blockages was twice the channel height. Average heat
transfer, local heat (mass) transfer and overall pressure drop results were obtained. The
thermal performance for a particular blockage configuration was measured in terms of
the heat transfer enhancement and the friction factor ratio. Heat transfer enhancement
was measured as a ratio of average Nusselt number on the blockage surface to the
Nusselt number for a thermally fully developed turbulent flow in a smooth channel.
Results indicate that this ratio ranged between 3.6 and 12.4, while the friction factor ratio
varied between 500-1700. The blockage configuration with round holes was found to
yield best thermal performance, while the configuration with largest hole elongation was
nearly equal in thermal performance. In order to compare different blockage
configurations, an average value of upstream and downstream side thermal performances
was used. A general downward trend in Nusselt number ratio with elongation of holes was
observed on the upstream side and a reverse trend was observed on the downstream side.
An upward trend in the Nusselt number ratio with blockage hole elongation on the
downstream side of a blockage was primarily due to jet reversal from the downstream
blockage and its impingement on the downstream surface of the upstream blockage.
Local experiments were performed to compare against the results from average
experiments and also to gain insights into the flow behaviour. There was good
agreement between the results from local and average mass transfer experiments. The
average variation in Nusselt number ratio between local and average mass transfer
experiments was about 5.06%.
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Enhancement of roll maneuverability using post-reversal designLi, Wei-En. January 2009 (has links)
Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Hodges, Dewey; Committee Member: Bauchau, Olivier; Committee Member: Goldsman, David; Committee Member: Prasad, J.V.R.; Committee Member: Smith, Marilyn. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Study on the Vortex Wake of an Airfoil Equipped with Flexible Trailing Edge FringesHe, Zhengkai 04 June 2014 (has links)
No description available.
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Bio-Inspired Control of Roughness and Trailing Edge NoiseClark, Ian Andrew 27 April 2017 (has links)
Noise from fluid flow over rough surfaces is an important consideration in the design and performance of certain vehicles with high surface-area-to-perimeter ratios. A new method of noise control based on the anatomy of owls is developed and consists of fabric or fibrous canopies suspended above the surface. The method is tested experimentally and is found to reduce the total far-field noise emitted by the surface. The treatment also is found to reduce the magnitude of pressure fluctuations felt by the underlying surface by up to three orders of magnitude. Experimental investigations into the effects of geometric parameters of the canopies lead to an optimized design which maximizes noise reduction.
The results obtained during the canopy experiment inspired a separate new device for the reduction of trailing edge noise. This type of noise is generated by flow past the wing of an aircraft or the blades of a wind turbine, and is a source of annoyance for those in surrounding communities. The newly developed treatment consists of small fins, or "finlets," placed near the trailing edge of an airfoil. The treatment is tested experimentally at near-full-scale conditions and is found to reduce the magnitude of far-field noise by up to 10 dB. Geometric parameters of the finlets are tested to determine the optimal size and spacing of the finlets to maximize noise reduction. Follow-up computational and experimental studies reveal the fluid mechanics behind the noise reduction by showing that the finlets produce a velocity deficit in the flow near the trailing edge and limit the magnitude and spanwise correlation lengthscale of turbulence near the trailing edge, factors which determine the magnitude of far-field noise.
In a final experiment, the finlets are applied to a marine propeller and are found to reduce not only trailing edge noise, but also noise caused by the bluntness of the trailing edge. The results of this experiment show the potential usefulness of finlets to reduce noise from rotating systems, such as fans or propellers, as well as from structures which feature blunt trailing edges. / Ph. D.
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