Experimental Study On The Thermoacoustic Instability And Passive Control Of Thermoacouxtic Instability In Swirl Combustor

With the improvement of environmental requirements, lean premixed combustion gas turbines has been widely used in industry. Meanwhile thermoacoustic instability frequently occurs in the gas turbines. Large-amplitude thermoacoustic instability not only reduce the performance of gas turbines, but also increase the NOx emissions. Evenly thermoacoustic instability could cause structure damage to gas turbines. A experimental study of thermoacoustic instability and passive control of thermoacoustic instability in a swirl combustor was described in this thesis.First we clarified the thermoacoustic phenomenon and thermoacoustic theory, meanwhile we review the study on control of thermoacoustic oscillation. Then introduce the mechanism of control of thermoacoustic oscillation. Through a simple mode we describe the methods of control of thermaxoustic oscillation.After we summarized the study on swirl combustion, we designed and built a swirl combustion thermacoustic instability experimental setup, including the swirl combustor , fuel control system, temperature measurement system and pressure measurement system.The characteristics of thermoacoustic instability in swirl combustion was studied on the setup. We measured the temperature and pressure of thermacoustic oscillation at different chemical rates and swirl intensity. And studied variety of temperature, pressure and frequency of thermoacoustic oscillation as the change of chemical rates or swirl intensity. We found that chemical rates and swirl intensity greatly affects the temperature in swirl combustor and the amplitude of thermoacoustic oscillation, also influences the first mode frequency of themaocoustic oscillation. While the second and the third mode frequency changed a little.We progressed a passive control of thermoacoustic instability in swirl combustor with a central jet. We found that central jet has great impacts on the dynamics of central recirculation zone in swirl combustion. When the volume of central jet rises to 15 percent of the total air volume, a clear decrease of the amplitudes of the thermoacoustic oscillation can be observed. The velocity of the central jet is an important parameter when the central jet is used to change the dynamics of central recirculation zone. Meanwhile we applied a second air jet to swirl combustor instead of the central jet as a comparative experiment. We make sure that it is the central jet which reduced the amplitude of thermoacoustic oscillation, not the decrease of the swirl intensity.