Unsteady Effects Of Manifold Flow On The Performance Of A Twin Scroll Turbine

The objective of this thesis is to understand the complex unsteady flow interaction between a 4-2 manifold connected to a twin scroll asymmetric turbocharger turbine and its sensitivity to typical inflow conditions at peak torque and peak power operating points.The 3D CFD results showed that the operation of the turbine under oscillating flow deviates strongly from the steady state assumption,causing the turbine to operate further away from the design point.Furthermore,the unsteady inflow from the coupled manifold domain introduces capacitive effects and Helmholtz type disturbances into the turbine volute region.Out of these,it was found that the narrowing flow channel in the volute dampened the effects of both manifold domains generated secondary flows and Helmholtz disturbances through superimposing locally generated flow features onto the incoming flow features.A cross-scroll leakage phenomenon was observed where unsteady pressure oscillations in the exhaust manifold increased twin scroll pressure difference,initiating leakage and causing up to 12% isentropic power loss.The manifold inlet pulse frequency and phase difference and manifold volume are key factors contributing to the pressure difference between the scrolls.A control method using a switchable valve is proposed to control the leakage flow.The device changes the exhaust flow path according to the exhaust pressure frequency.It improved system efficiency by 6.1% and cycle averaged power by 8.9%.