The Measurement of the Acoustic Radiation Impedance of the open End of a Thick Walled Tube with Hot Flow

Prediction of the radiation impedance of the open end of a combustion chamber or flue is important for the determination of combustion system acoustic impedances. A knowledge of the latter is necessary in order to attempt to predict when a combustion system will enter a state of oscillation.

A standing-wave tube technique has been used to measure the reflection coefficient and phase change on reflection of acoustic signals at the open end of a thick-walled tube with hot flow. Gas temperatures in the range 20°C to 1000°C have been considered. The acoustic radiation impedance of the open end has been determined and the radiation resistance, radiation reactance and reflection coefficient have been shown to be not significantly dependent upon the temperature at constant frequency. The results are compared with theoretical predictions.