| The vehicle internal combustion engine is up against the greater challenge with the development of automobile industry, growing shortage of fossil fuel and worsening atmosphere environment. Turbocharging is widely applied in vehicle engine because of its advantages in fuel economy and the emission characteristic, especially, for the turbocharger equipped with variable radial turbine, of which is paid widely attention because it can achieve a good match between the turbocharger and engine in whole operating range. Currently, the researches on the internal flow of variable radial turbine focus on the clearance leakage flow of guide vane and the aerodynamic load acting on rotor blade surface, while few work pays attention to the interference effects of the guide vane wake, the clearance leakage flow and the shock, as well as these interferences with downstream flow field of the rotor. The related interference model is also not perfect. In addition, the investigation on the shock modulation of variable radial turbine has not been published in the literature. Therefore, it is worthy both in academic study and engineering application for understanding the unsteady flow interference pattern of radial turbine and weakening the shock of guide vane trailing edge.In this paper, the investigation of unsteady flow characteristic of the variable radial turbine is conducted with steady state inlet and pulsation inlet condition. Meanwhile, in order to modulate the intensity of guide vane trailing edge shock, several modification methods of guide vane are proposed, the main research results are presented as follow:(1) By studying the unsteady flow characteristic of turbine with different gap size of guide vane, the relation between the gap size of guide vane and the tip clearance leakage flow form of guide vane, the variation of the shock intensity, the interference between guide vane wake and leakage flow, the pressure fluctuation of rotor blade are obtained. The results show that: the leakage flow is divided to two different flow patterns when it departure from the guide vanes gap, one is leakage jet and the other is leakage vortex. The leakage flow meets and interferes with the mainstream and the leakage vortex generated, and it promotes the mainstream flow away from the suction surface of guide vane, so that the downstream leakage jet does not interfere with the mainstream. With the increase of guide vane gap, the range of leakage vortex reduces, while the scope of leakage jet increases. When the tip clearance leakage flow of guide vane interferes with the adjacent wakes, it will make the guide vane wake from "straight" to "C-type". The shock wave intensity of guide vane trailing edge is the trend of "increase firstly and decrease then" due to the effect of leakage vortex. The leakage flow of guide vane induce the drastic fluctuation at blade tip and root zone of leading edge of the rotor blade, and the shock will induce the high excitation area at the middle span of leading edge of rotor blade.(2) The effect of the opening of guide vane on the flow characteristic of turbine is obtained by comparing the unsteady flow field variation of variable turbine in 20% and 50% opening. This comparison expands the distribution theory of the leakage flow and the leakage loss. Meanwhile, the sensitivity of shock to the gap size of guide vane in different opening is compared. The results show that: the effect of gap size of guide vane on the efficiency of turbine in small opening is more obvious than that of the large opening. With the gap size of guide vane increases, the decline rate of turbine efficiency in 20% opening is larger than that of 50% opening. The tip leakage flows and the leakage losses of guide vane and rotor blade both increases linearly. For the same gap size of the guide vane and rotor blade, the leakage flow and leakage loss of guide vane in 20% opening is larger that of 50% opening, but in the rotor section, the leakage flow and leakage loss in 50% opening is greater than that of 20% opening. With the opening of guide vane increases, the shock strength weakens, and in 20% opening, the shock intensity is more sensitive to the change of the gap size of guide vanes.(3) By analyzing the flow field of turbine under pulsation inlet condition, the effects of pulsation pressure on the leakage flow and total loss pressure of guide vane, the shock strength of guide vane trailing edge, the blade load of leading edge of rotor blade are obtained. The results show that: the leakage flow of guide vane, total pressure loss and the shock all increase linearly with the increase of inlet pressure, every increase of 10 kPa pressure, the leakage flow rate increased by about 2.9%, the total pressure loss of guide vane increases about 2.7%, the shock enhances about 14%. The blade load of leading edge also increase linearly with the increase of pulsation inlet pressure, when the pulsation pressure increases 50 kPa, the blade load peak of leading edge increases by about 12.7%, the blade load peak of the middle span with the increase of about 24.9%.(4) For the purpose of modulating the shock intensity of guide vane trailing edge, one guide vane modification method is proposed and three guide vanes shape are designed. Two methods including groove the suction surface of guide vane and redesign the airfoil of guide vane are explored to evaluate their effects on the shock and the leakage flow of guide vane. The results show that: The arrange of groove at the shock position of the suction surface of guide vane, not only can reduce the intensity of shock, but also can reduce the affected area of shock, which can reduce the aerodynamic load of downstream rotor blade induced by the shock at the middle span of blade leading edge, and it is benefit to enhance the reliability of rotor blade. For the redesigned airfoil of guide vane, it changes the shape of the channel to reduce the air expand degree flow through the channel of guide vane, and to reach the purpose of weakening shock intensity of guide vane trailing edge. |
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