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) -- ..med vennlig hilsen = with Kind Regards from Arnt... ;o) ...with a number of polar bear hunters in his ancestry... Scenarios always come in sets of three: best case, worst case, and just in case. _______________________________________________ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
