Measurements of cavity flow

• Main Author: Tan, Kyle Fergus.
• Other Authors: Chua Leok Poh
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering; DRNTU::Engineering::Mechanical engineering::Fluid mechanics; DRNTU::Engineering::Aeronautical engineering
• Online Access: http://hdl.handle.net/10356/50298
• Institution: Nanyang Technological University

Cavity flow is a phenomenon which occurs when air flows over a cavity. When this occurs, the shear layer of the flowing air impinges the cavity surfaces to cause drag, vibrations and acoustic tones. These occurrences are commonly experienced in landing gear wells, weapon bays and automobile windows. This problem has to be addressed since excessive drag leads to increase power demand, vibrations can lead to fatigue failure and excessive noise beats the benefits of stealth in military aircrafts. Therefore, the study of cavity modification to reduce and prevent these issues needs to be conducted. Hence, cavity modification modules need to be fabricated for use with the existing cavity test rig to better understand the benefits of the chosen modifications have on subsonic cavity flow. The exisiting base line cavity models were modified to study the effects of ramped trailing edge and partial cavity cover modifications. The trailing edge ramp models had heights of 10mm and 20mm with ramp angles of 30°, 45° and 60°. The partial covers covered the different aspect ratio cavities at 25%, 50% and 75%. The cavity modification modules have to facilitate easy installation on the existing test rig and different concepts from past research were considered before designing and fabricating the units. With the finalised design, the modules were built and installed onto the current test rig to allow experimental studies in the Fluid Mechanics Laboratory subsonic wind tunnel. Cavity surface pressure distribution and particle image velocimetry flow visualisation were two techniques used to study the effects of cavity modifications on cavity flow. For the ramped and partial cover modifications, cavity surface pressure distribution of four different length-to-depth aspect ratios were measured and compared with non-modified base line cavities. In addition, 3-D effects were also determined using pressure measurements. Particle image velocimetry was used to study the flow of cavities with aspect ratio two. Results from the studies showed that the use of ramped modifications influenced the airflow within the cavities and had positive effects on the pressure distribution magnitudes for low aspect ratio cavities experiencing open cavity flow. This phenomenon is especially significant for cavities with ramp height of 20mm and ramp angle 30° where cavity floor pressure fluctuations were reduced. Furthermore, increasing the percentage of cavity coverage greatly stabilized the pressure distribution across the whole range of aspect ratio tested. Finally, the presence of 3-D effect within cavities was validated.