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Flow Separation over Baffle Blades and Its Effect on the Nonlinear Acoustic Damping Mechanism in Liquid Rocket Engines.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Flow Separation over Baffle Blades and Its Effect on the Nonlinear Acoustic Damping Mechanism in Liquid Rocket Engines./
Author:	Day, Joseph.
Description:	1 online resource (97 pages)
Notes:	Source: Masters Abstracts International, Volume: 85-02.
Contained By:	Masters Abstracts International85-02.
Subject:	Engineering. -
Online resource:	click for full text (PQDT)
ISBN:	9798380078160

Flow Separation over Baffle Blades and Its Effect on the Nonlinear Acoustic Damping Mechanism in Liquid Rocket Engines.
Day, Joseph.

Flow Separation over Baffle Blades and Its Effect on the Nonlinear Acoustic Damping Mechanism in Liquid Rocket Engines. - 1 online resource (97 pages)

Source: Masters Abstracts International, Volume: 85-02.

Thesis (M.S.)--University of Colorado Colorado Springs, 2023.

Includes bibliographical references

Acoustically coupled combustion instabilities, the feedback coupling of acoustic modes with unsteady heat release, have occurred in nearly every liquid rocket engine development program. One common device for stabilizing the engine is a hub and spoke baffle blade structure. Much of the research performed on baffle structures was done empirically during the Apollo program, and as a result, many of the details of how baffles damp the acoustic modes, preventing instability, remain unknown. In the current work, a test facility was constructed that simulates the local acoustic field near the tip of a single baffle blade. This rig was used to test three simple baffle blades: a thin, sharp tipped blade; a thick, square tipped blade; and a thick, round tipped blade. By measuring the high-acoustic-pressure oscillations at two locations in the rig, the complex reflection coefficient can be found where a magnitude less than 1.0 indicates damping caused by the baffle blade. Compared to the two thick blades, the thin blade showed significantly higher damping. Acoustic simulations showed that the two thick blades have similar acoustic velocities near the blade tip, while the thin, sharp blade's acoustic velocity was over three times higher. In other high-amplitude acoustic systems nonlinear damping due to flow separation (e.g., orifice in a duct) has been observed and this damping has been found to be proportional to the maximum acoustic velocity magnitude. The current observations suggest that the main source of damping from a baffle blade comes from flow separation causing acoustic energy to be lost to coherent vortical motion in the shear layer and eventually heat. To quantify the flow separation, an unsteady Gortler transform was used to predict the point just upstream ¨ of where the flow separates as it turns around the various baffles. The sooner the flow separates, the more acoustic energy there is to be lost to flow separation, thus increasing the amount of acoustic damping. This model shows the sharp baffle separation point does not appreciably change with phase changes, it is effective at causing separation for all pressure gradients. The model shows that the thick baffle blades are much more dependent on the pressure gradient than the thin baffle. Additionally, the shape of the tip on the thick baffles has an affect on the separation location, as the square tip indicates earlier separation than the case of the round tip, indicating a higher damping effect. The experimental and modeling work on baffle blades give the physical understanding to start building an engine specific damping model.

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

Mode of access: World Wide Web

ISBN: 9798380078160Subjects--Topical Terms:

561152
Engineering.
Subjects--Index Terms:

BaffleIndex Terms--Genre/Form:

554714
Electronic books.

Flow Separation over Baffle Blades and Its Effect on the Nonlinear Acoustic Damping Mechanism in Liquid Rocket Engines.
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504 $a Includes bibliographical references
520 $a Acoustically coupled combustion instabilities, the feedback coupling of acoustic modes with unsteady heat release, have occurred in nearly every liquid rocket engine development program. One common device for stabilizing the engine is a hub and spoke baffle blade structure. Much of the research performed on baffle structures was done empirically during the Apollo program, and as a result, many of the details of how baffles damp the acoustic modes, preventing instability, remain unknown. In the current work, a test facility was constructed that simulates the local acoustic field near the tip of a single baffle blade. This rig was used to test three simple baffle blades: a thin, sharp tipped blade; a thick, square tipped blade; and a thick, round tipped blade. By measuring the high-acoustic-pressure oscillations at two locations in the rig, the complex reflection coefficient can be found where a magnitude less than 1.0 indicates damping caused by the baffle blade. Compared to the two thick blades, the thin blade showed significantly higher damping. Acoustic simulations showed that the two thick blades have similar acoustic velocities near the blade tip, while the thin, sharp blade's acoustic velocity was over three times higher. In other high-amplitude acoustic systems nonlinear damping due to flow separation (e.g., orifice in a duct) has been observed and this damping has been found to be proportional to the maximum acoustic velocity magnitude. The current observations suggest that the main source of damping from a baffle blade comes from flow separation causing acoustic energy to be lost to coherent vortical motion in the shear layer and eventually heat. To quantify the flow separation, an unsteady Gortler transform was used to predict the point just upstream ¨ of where the flow separates as it turns around the various baffles. The sooner the flow separates, the more acoustic energy there is to be lost to flow separation, thus increasing the amount of acoustic damping. This model shows the sharp baffle separation point does not appreciably change with phase changes, it is effective at causing separation for all pressure gradients. The model shows that the thick baffle blades are much more dependent on the pressure gradient than the thin baffle. Additionally, the shape of the tip on the thick baffles has an affect on the separation location, as the square tip indicates earlier separation than the case of the round tip, indicating a higher damping effect. The experimental and modeling work on baffle blades give the physical understanding to start building an engine specific damping model.
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650 4 $a Acoustics. $3 670692
650 4 $a Aerospace engineering. $3 686400
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653 $a Combustion
653 $a Damping
653 $a Rocket
653 $a Separation
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710 2 $a University of Colorado Colorado Springs. $b College of Engineering and Applied Science-Mechanical Engineering. $3 1180387
773 0 $t Masters Abstracts International $g 85-02.
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