To grip control mechanism of plate structure radiation noise, a method to calculate radiation resistance was improved based on series approximation, by which the analytical solution of acoustic features were derived. And then the effects of the mutual-modal coupling were investigated in studying vibro-acoustic characteristics of a simply supported plate. Some conclusions have been given, such as the relationship between the radiated noise level and the space-time distributing, fundamental principles and measures of altering the space-time distributing, which supplied the academic and applied foundation for noise control.
Short seal (e.g. shroud seal) is a key component for the safe and reliable operation of a turbine unit. This paper sets up the three dimensional numerical model of a short labyrinth seal and analyzes its characteristics of the fluid-induced force. Results show that the tangential fluid-induced force increases almost linearly as the rotational speed increases. The sign of the radial fluid-induced force changes as the rotational speed increases. For higher inlet pressure, a more dramatic increase can be found for both the tangential and radial fluid-induced force. A transition speed range was found that the magnitude of the radial fluid-induced force at higher inlet pressure became less than that at lower inlet pressure. For each seal cavity, the peak pressure location had a shift away from the minimum clearance location as the rotational speed increased. This shift also existed in the axial direction. The effect of the rotational speed on the fluid-induced force became more remarkable for the longer seal with many cavities. Both the radial and tangential fluid-induced force increased with the increasing preswirl ratio. However, the two forces decreased with the increasing preswirl ratio when the inlet total pressure was kept as a constant value. In the end, the critical preswirl ratio which corresponds to zero tangential fluidinduced force was calculated, and results show that a smaller magnitude of the preswirl ratio will be needed to offset the effect of rotational speeds at higher inlet pressures. The inlet preswirl generated a majority of the tangential force for short seals.
Lean premixed low swirl combustion is an effective way to control NOx emission. In the present work a low swirl burner fitting with vane swirler has been used to investigate the flowfield characteristics. Two swirlers (65° and 40° setting angle) have been adopted for velocity measurement by using PIV technique. The results show that the critical swirl number when recirculation zone appears scarcely changed with the swirler setting angle and central jet velocity, and the demarcation between high and low swirl flow can be set as 0.48 in this work. Compared to swirler II, a wider low speed zone and a more divergent flow emerge downstream swirler I. Dimensionless axial velocity profiles along central axis decline linearly and approximately come to zero at x/D=1.37 for swirler II and x/D=1.56 for swirler I. For two-dimensional turbulent kinetic energy profiles, two peaks downstream of the swirl mean higher burning velocity than central jet. And turbulent kinetic energy downstream swirler II is observed higher.
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