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Flow Past a Cylinder : = Development of a Surface-Mounted Flow Separation Sensor and Lock-in of Vortex Shedding from a Cylinder Undergoing Prescribed Motions.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Flow Past a Cylinder :/
Reminder of title:	Development of a Surface-Mounted Flow Separation Sensor and Lock-in of Vortex Shedding from a Cylinder Undergoing Prescribed Motions.
Author:	Aleman Chona, Maria Auxiliadora.
Description:	1 online resource (157 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-01, Section: A.
Contained By:	Dissertations Abstracts International85-01A.
Subject:	Pressure distribution. -
Online resource:	click for full text (PQDT)
ISBN:	9798379866686

Flow Past a Cylinder : = Development of a Surface-Mounted Flow Separation Sensor and Lock-in of Vortex Shedding from a Cylinder Undergoing Prescribed Motions.
Aleman Chona, Maria Auxiliadora.

Flow Past a Cylinder :Development of a Surface-Mounted Flow Separation Sensor and Lock-in of Vortex Shedding from a Cylinder Undergoing Prescribed Motions. - 1 online resource (157 pages)

Source: Dissertations Abstracts International, Volume: 85-01, Section: A.

Thesis (Ph.D.)--North Carolina State University, 2023.

Includes bibliographical references

The classical problem of one of the most basic shapes of bluff bodies, has been the motivation of numerous fluid dynamic studies over many decades. Countless researchers have investigated aerodynamic characteristics of a stationary cylinder, for instance, the surface pressure distribution, oscillatory lift and drag forces, and behaviors in the wake region of the cylinder (flow separation and vortex shedding). This work first utilizes the static cylinder pressure distribution to develop a novel surface-mounted flow separation sensor that is applied to detection of airfoil stall. The high and low-pressure regions on the cylinder are appealing for designing a low-cost approach to detect flow separation using two pressure measurements, one facing the incoming flow (forward-facing), similar to a Preston tube, and the other one pointed towards the direction of flow (backward-facing). It is shown that the pressure difference between the forward- and backward-facing ports drops from positive to negative as the surface flow over a cambered airfoil changes from attached to separated at the sensor location. This zero-crossing behavior is independent of the freestream dynamic pressure, avoiding the need for any calibration. The effectiveness of the sensor to detect airfoil flow separation and stall is evaluated in wind-tunnel experiments. The detected angle of attack for onset of separation at the chordwise location of the sensor is seen to agree well with results deduced from oil-flow visualization and pressure-distribution characteristics. The sensor effectiveness is also seen to be relatively insensitive to the shape of the sensor. Because it does not depend on any other measured information, the sensor holds the potential to be further developed in follow-on efforts into an entirely self-contained device for use in providing stall warning for wings and detection of flow reversal on aerodynamic devices.The second part of this work studies the vortex shedding behind a cylinder and the oscillatory lift and drag forces that originate from that. Specifically, the regime where the frequency of the vortex shedding behind a moving cylinder coalescence with the cylinder oscillation frequency. This regime is often referred to as lock-in, and the hydrodynamic forces acting on the moving cylinder intensify when lock-in exists. The hydrodynamic forces and flow-field measurements are obtained from free-surface water tunnel experiments where a cylinder undergoes 1000 cycles of prescribed one-degree-of-freedom (DoF) and 2-DoF motions in a steady uniform flow at Red= 10,000. The 1-DoF motions are in-line and transverse to the flow, and the 2-DoF motions are figure-eight patterns that are commonly observed in nature. Tests are performed for a wide range of frequency ratios, amplitudes, and phase differences between the in-line and transverse motions. The forces acting on the cylinder are measured using a 6-DoF load cell, and planar laser-induced fluorescence (PLIF) dye visualization and particle image velocimetry (PIV) are used to obtain qualitative and quantitative flow-field measurements, respectively. The lift coefficient spectra, the variation of the root-mean-square lift coefficient and mean drag coefficient, the time histories of the lift and drag fluctuations with respect to the cylinder displacement and velocity, the continuous wavelet transform (CWT) of the lift and drag coefficient traces, and the qualitative instantaneous vorticity patterns are employed to identify states of no-lock in, quasi-lock in, minor lock-in, and predominant lock-in.The 1-DoF transverse cases exhibit frequency coalescence but the 1-DoF in-line cases do not. This is because a single predominant frequency is not attained while in lock-in.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798379866686Subjects--Topical Terms:

1413590
Pressure distribution.
Index Terms--Genre/Form:

554714
Electronic books.

Flow Past a Cylinder : = Development of a Surface-Mounted Flow Separation Sensor and Lock-in of Vortex Shedding from a Cylinder Undergoing Prescribed Motions.
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245 1 0 $a Flow Past a Cylinder : $b Development of a Surface-Mounted Flow Separation Sensor and Lock-in of Vortex Shedding from a Cylinder Undergoing Prescribed Motions.
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500 $a Source: Dissertations Abstracts International, Volume: 85-01, Section: A.
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502 $a Thesis (Ph.D.)--North Carolina State University, 2023.
504 $a Includes bibliographical references
520 $a The classical problem of one of the most basic shapes of bluff bodies, has been the motivation of numerous fluid dynamic studies over many decades. Countless researchers have investigated aerodynamic characteristics of a stationary cylinder, for instance, the surface pressure distribution, oscillatory lift and drag forces, and behaviors in the wake region of the cylinder (flow separation and vortex shedding). This work first utilizes the static cylinder pressure distribution to develop a novel surface-mounted flow separation sensor that is applied to detection of airfoil stall. The high and low-pressure regions on the cylinder are appealing for designing a low-cost approach to detect flow separation using two pressure measurements, one facing the incoming flow (forward-facing), similar to a Preston tube, and the other one pointed towards the direction of flow (backward-facing). It is shown that the pressure difference between the forward- and backward-facing ports drops from positive to negative as the surface flow over a cambered airfoil changes from attached to separated at the sensor location. This zero-crossing behavior is independent of the freestream dynamic pressure, avoiding the need for any calibration. The effectiveness of the sensor to detect airfoil flow separation and stall is evaluated in wind-tunnel experiments. The detected angle of attack for onset of separation at the chordwise location of the sensor is seen to agree well with results deduced from oil-flow visualization and pressure-distribution characteristics. The sensor effectiveness is also seen to be relatively insensitive to the shape of the sensor. Because it does not depend on any other measured information, the sensor holds the potential to be further developed in follow-on efforts into an entirely self-contained device for use in providing stall warning for wings and detection of flow reversal on aerodynamic devices.The second part of this work studies the vortex shedding behind a cylinder and the oscillatory lift and drag forces that originate from that. Specifically, the regime where the frequency of the vortex shedding behind a moving cylinder coalescence with the cylinder oscillation frequency. This regime is often referred to as lock-in, and the hydrodynamic forces acting on the moving cylinder intensify when lock-in exists. The hydrodynamic forces and flow-field measurements are obtained from free-surface water tunnel experiments where a cylinder undergoes 1000 cycles of prescribed one-degree-of-freedom (DoF) and 2-DoF motions in a steady uniform flow at Red= 10,000. The 1-DoF motions are in-line and transverse to the flow, and the 2-DoF motions are figure-eight patterns that are commonly observed in nature. Tests are performed for a wide range of frequency ratios, amplitudes, and phase differences between the in-line and transverse motions. The forces acting on the cylinder are measured using a 6-DoF load cell, and planar laser-induced fluorescence (PLIF) dye visualization and particle image velocimetry (PIV) are used to obtain qualitative and quantitative flow-field measurements, respectively. The lift coefficient spectra, the variation of the root-mean-square lift coefficient and mean drag coefficient, the time histories of the lift and drag fluctuations with respect to the cylinder displacement and velocity, the continuous wavelet transform (CWT) of the lift and drag coefficient traces, and the qualitative instantaneous vorticity patterns are employed to identify states of no-lock in, quasi-lock in, minor lock-in, and predominant lock-in.The 1-DoF transverse cases exhibit frequency coalescence but the 1-DoF in-line cases do not. This is because a single predominant frequency is not attained while in lock-in.
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538 $a Mode of access: World Wide Web
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650 4 $a Vortices. $3 1413589
650 4 $a Fluid dynamics. $3 528074
650 4 $a Aerospace engineering. $3 686400
650 4 $a Fluid mechanics. $3 555551
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710 2 $a North Carolina State University. $3 845424
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