首页|Unsteady flow characteristics in an over-under TBCC inlet during mode transition under unthrottled and throttled conditions
Unsteady flow characteristics in an over-under TBCC inlet during mode transition under unthrottled and throttled conditions
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The study presents an experimental exploration into the mode transition of an over-under TBCC(Turbine-Based Combined Cycle)inlet,with a specific emphasis on the flow charac-teristics at off-design transition Mach number.A systematic investigation was undertaken into the mode transition characteristics in both unthrottled and throttled conditions within a high-speed duct,employing high speed Schlieren and dynamic pressure acquisition systems.The results show that the high-speed duct faced flow oscillations primarily dictated by the separation bubble near the duct entrance during the downward rotation of splitter,leading to the duct's unstart under the unthrottled condition.During the splitter's reverse rotation,a notable hysteresis of unstart/restart of the high-speed duct was observed.Conversely,hysteresis vanishes when the initial flow-field nears the critical state owing to downstream throttling.Moreover,the oscillatory diversity,a distinctive characteristic of the high-speed duct,was firstly observed during the mode transition induced by throttling.The flow evolution was divided into four stages:an initial instability stage characterized by low-frequency oscillations below 255 Hz induced by shock train self-excitation oscillation and high-frequency oscillations around 1367 Hz caused by the movement of separation bubble.This stage is succeeded by the"big buzz"phase,comprised of pressure accumulation/re-lease within the overflow-free duct and shock motion outside the duct to retain dynamic flow bal-ance.The dominant frequency escalated with the increase of the internal contraction ratio in the range of 280 Hz to 400 Hz.This was followed by a high-frequency oscillation stage around 453 Hz dominated by a large internal contraction ratio with low pulsating energy,accompanied by a continuous supersonic overflow.Lastly,as the splitter gradually intersected the boundary layer of the first-stage compression surface,the capture area and the turbulence intensity of the incoming flow underwent a sudden shift,leading to a more diverse flow oscillation within the duct,manifested as various forms of mixed buzz.
Jiangsu Province Key Laboratory of Aerospace Power Systems,College of Energy and Power Engineering,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China
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