Microphone System for the Measurement of Boundary Layer Pressure Fluctuations
Abstract
This report presents a description of a condenser microphone system developed for use in the measurement of boundary layer pressure fluctuations. Prime consideration in the design of the transducer of the system was the requirement for operation in abnormal environments, with emphasis on high temperature. Calibrations are described in the report which show that the Western Electro-ACOUSTIC Laboratory A-6 condenser microphone can operate at diaphragm temperatures to 800 deg F. Measurements utilizing an electrical analog of the microphone thermal characteristics and flat plate boundary layer theory show that an 800 F upper limit for the transducer would satisfy nearly all conceivable uses of the system in practice. For example, for a 'flight' condition of Mach 4.2 at sea level, where the recovery temperature would be 1600 F, the diaphragm temperature would reach 800 deg F. This same speed at 40,000 ft. would result in a diaphragm temperature of 300 F. A speed of Mach 6.9 would be required to produce an 800 deg F diaphragm temperature at 40,000 ft. These flight conditions are extreme for present day vehicles, including re-entry vehicles, hence the transducer can be used over a very large range of altitudes and Mach numbers. This report presents the methods and results of calibration, as well as some of the shortcomings of the system.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1967
- Accession Number
- AD0812993
Entities
People
- Jose C. Ortega