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NACA-TN-3487
Acoustic radiation from two-dimensional rectangular cutouts in aerodynamic surfaces
Year: 1955
Abstract: Subsonic and supersonic flow of air past rectangular cavities cut into a flat surface were studied. The cavities were found to emit a strong acoustic radiation. These acoustic fields were investigated by means of schlieren observation, interferometry, and hot-wire anemometer.
The frequency of the sound, as measured by a hot-wire, at a fixed depth of the gap was found to be inversely proportional to the breadth. No simple relationship was noticed between the Mach number M∞ and a non dimensional frequency S based on the gas breadth and the free-stream velocity.
The intensity of the radiation was conveniently measured by means of an optical interferometer of the Mach-Zehnder type. At a Mach number of 0.8, a unit fringe shift was found to correspond to an intensity level of 160 decibels. Fringe shifts equal to and greater than 1 were observed for the radiations from these cavities, indicating that the acoustic fields were very intense.
The frequency of the sound, as measured by a hot-wire, at a fixed depth of the gap was found to be inversely proportional to the breadth. No simple relationship was noticed between the Mach number M∞ and a non dimensional frequency S based on the gas breadth and the free-stream velocity.
The intensity of the radiation was conveniently measured by means of an optical interferometer of the Mach-Zehnder type. At a Mach number of 0.8, a unit fringe shift was found to correspond to an intensity level of 160 decibels. Fringe shifts equal to and greater than 1 were observed for the radiations from these cavities, indicating that the acoustic fields were very intense.
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| contributor author | NASA - National Aeronautics and Space Administration (NASA) | |
| date accessioned | 2017-09-04T17:59:56Z | |
| date available | 2017-09-04T17:59:56Z | |
| date copyright | 01/01/1955 | |
| date issued | 1955 | |
| identifier other | FVNUYDAAAAAAAAAA.pdf | |
| identifier uri | http://yse.yabesh.ir/std;jsery=autho162s7D8308/handle/yse/183044 | |
| description abstract | Subsonic and supersonic flow of air past rectangular cavities cut into a flat surface were studied. The cavities were found to emit a strong acoustic radiation. These acoustic fields were investigated by means of schlieren observation, interferometry, and hot-wire anemometer. The frequency of the sound, as measured by a hot-wire, at a fixed depth of the gap was found to be inversely proportional to the breadth. No simple relationship was noticed between the Mach number M∞ and a non dimensional frequency S based on the gas breadth and the free-stream velocity. The intensity of the radiation was conveniently measured by means of an optical interferometer of the Mach-Zehnder type. At a Mach number of 0.8, a unit fringe shift was found to correspond to an intensity level of 160 decibels. Fringe shifts equal to and greater than 1 were observed for the radiations from these cavities, indicating that the acoustic fields were very intense. | |
| language | English | |
| title | NACA-TN-3487 | num |
| title | Acoustic radiation from two-dimensional rectangular cutouts in aerodynamic surfaces | en |
| type | standard | |
| page | 36 | |
| status | Active | |
| tree | NASA - National Aeronautics and Space Administration (NASA):;1955 | |
| contenttype | fulltext |