> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:flightgear-devel- > [EMAIL PROTECTED] On Behalf Of Arnt Karlsen > Sent: 23 April 2005 22:02 > To: FlightGear developers discussions > Subject: Re: [Flightgear-devel] YASim turbo/supercharger issues > > On Sat, 23 Apr 2005 20:02:48 +0100, Vivian wrote in message > <[EMAIL PROTECTED]>: > > > Arnt Karlsen wrote: > > > > > > > > > Andy Ross wrote > > > > > > > > > > > > > > Drew wrote: > > > > > > IMHO, it's best to use interpolation tables rather than > > > > > > equations if you're trying to curve fit empirical data. > > > > > > > > > > Not in this context. The data here isn't being used to model a > > > > > specific engine, but to provide sane parameters for all > > > > > (super/turbochared) engines. The performance and code size > > > > > advantages of an equation here are significant. > > > > > > > > At the moment we are looking at gear driven centrifugal > > > > compressors. Although I haven't researched it in any detail, the > > > > output of turbo-driven centrifugal compressors do not have a > > > > direct relationship with rpm (turbo lag), and the situation is > > > > complicated by the wastegate which operates on the turbo rather > > > > than the compressor. I suspect that this is another black art! > > > > Gear driven is easy in comparison. When someone comes up with a > > > > turbo we may have to have separate models. > > > > > > ..if your supercharger code takes shaft input (shaft speed, torque > > > or power), then it can be re-used in the turbocharger's compressor > > > code. > > > > It doesn't because a gear driven compressor has a fixed relationship > > to engine rpm, and I deal with 2 speed superchargers separately, but > > you are right: a centrifugal compressor neither knows nor cares if it > > is gear- or turbo-driven. > > > > > ..the turbocharger's compressor or turbo-compound engine's > > > crankshaft then only needs a turbine derivering shaft outnput (shaft > > > speed, torque or power) to the compressor or gear box. > > > > > > > Now, if we knew what the turbo rpm was for a given engine rpm, > > .._not_ gonna happen. Turbo rpm will always, always, always be a > function of the exhaust gas pressures piped in and out, and, the > turbines own shaft loads, temperature, mass, and time. > > ..just think of any water wheel, or power turbine, to do the power > turbine code part of the turbo. Then you can saw the gear box off the > supercharger shaft and weld that stub onto the power turbine to make > a turbocharger. ;o) > > > and I think we need throttle opening ... any guidance welcome. > > ..just like in the supercharger code. Now, keep in mind, the power > turbine _only_ sees exhaust gas pressures and temperatures piped > in and out and its own mass and inertia, time and the shaft and > bearing and lube film loads. > > ..the compressor on the _other_ end of that turbo shaft, will see the > _same_ as the supercharger, except for the power turbine replacing > the gear box. > > ..exhaust gas pressures and temperatures vary, think pulses, spikes, > waste gates and even exhaust throttles, if you wanna model a new > fancy way of blowing up a model engine in that spectacular way > I read about in some model magazine some 20 years back. ;o)
Or TFD - I'll think about it later (much later :-). Regards, Vivian _______________________________________________ Flightgear-devel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
