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CFD Provides Insight Into Pulse Turbocharging
Posted Fri July 25, 2003 @07:02AM
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Application Turbocharging is a method of increasing the power output from reciprocating engines by utilizing the waste energy in the exhaust gases. The exhaust gases drive a turbine, which provides power to a compressor pressurizing the air at engine inlet, allowing more fuel to be burned. The advantages of this are increased power, reduced specific fuel oil consumption and reduced thermal loading.

Automotive engines typically use the pulse turbocharging method in which the turbine inlet is closely coupled with the exhaust manifold. As a consequence, the turbine is subjected to a highly pulsating flow field caused by, and synchronized with, the opening and closing of the engine valves. However, there is a lack of understanding of the turbine aerodynamics under pulsating conditions. As a consequence of this, over the past decade the Thermofluids Section at Imperial College, London, has focused on researching the aerodynamics of turbocharger turbines under pulsating flow conditions.


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The problem lies with the difficulty in acquiring detailed experimental data for such a highly unsteady flow field and also because of the computational expense associated with predicting the full three-dimensional time-accurate flow within the volute-turbine system. As a result, turbocharger design methods rarely take into account the effect of the pulsating inlet conditions. Using computational fluid dynamics from the CD adapco Group, the engineers at Imperial have been able to get the answers they need. Their work has been predominantly experimental, but STAR-CD and advanced computing resources has made it possible to quickly investigate the turbine performance under pulsating conditions.

For the first time, CFD has enabled information to be gained which allows an assessment of the propagation of the pulse waveforms through the turbine passages and their interaction with the stationary as well as rotating components. Using STAR-CD's moving mesh capability, a mesh has been built enabling turbine rotation to be modeled and the effect of the pulse waves on turbine performance to be measured. The CFD results have been compared with experiment and proven to be good; the velocity field is particularly well resolved and the efficiency trace exhibits the same hysteresis type loop.

In summary, the work is testament to a successful collaboration between experimentation and computational studies using a commercially available CFD code. N. Karamanis, Imperial College, University of London says, “ Using STAR-CD, a much more detailed understanding of the highly unsteady nature of the flow in a turbocharger turbine has been achieved than would have been possible by experimental means alone”.

instantaneous pressure and mass flow
Experimental measurement data of pressure and mass flow variation at the turbine inlet.

pressure wave entering the turbine inlet
Simulation of a pressure wave entering the turbine inlet.

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Simulating the Flowfield Around Helicopters | CD adapco Group Becomes PERMAS Distributor  >

 

 
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