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Post by hassanalawi on May 11, 2020 12:37:47 GMT -5
hey guys, how do i decide on the input parameters for jetspecs turbo analysis since i dont have any other than the wheels sizes
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Post by racket on May 11, 2020 16:48:10 GMT -5
Have you tried just putting in your compressor wheel diameters ??
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Post by hassanalawi on May 11, 2020 17:36:37 GMT -5
Have you tried just putting in your compressor wheel diameters ?? Yeah but i dont have the rest
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Post by hassanalawi on May 11, 2020 18:08:48 GMT -5
how do i know what pressure ratio suits my application
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Post by racket on May 11, 2020 18:52:26 GMT -5
They're assumptions you need to make , and/or take them from the relevant compressor map etc etc .
Jetspecs tries to cover the entire range of turbos which is an impossible job considering the thousands of configurations , its not a precise tool , its a very "blunt instrument" that will hopefully provide a "ballpark" outcome.
An outcome which could be 20-50 % from optimum because of the fact we are dealing with turbochargers that have been configured for a multitude of different engines and engine usages.
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Post by hassanalawi on May 11, 2020 19:01:19 GMT -5
exactly since i dont have the compressor map i cannot know what pressure ratio should i run and i dont have the experience to guestimate that too. 2.5 3 maybe more, maybe less ? recommendations? for efficiencies i thought of keeping them as they are in jet specs.
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Post by racket on May 11, 2020 20:49:13 GMT -5
Use the 2.5:1 pressure ratio I recommended back on 15 March, with efficiency of 72% for the comp and 70% for the turb to keep your numbers conservative to begin with , once the engine is operational and you start collecting data you may be able to revise those parameters
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Post by hassanalawi on May 12, 2020 14:06:26 GMT -5
i am wondering why jetspecs assume inlet air velocity to be 500ft/sec to calculate mass flow rate
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Post by racket on May 12, 2020 16:54:55 GMT -5
Because 500 ft/sec is a nice "round" number and roughly corresponds to reality.
Turbos come in a huge range of configurations , so some might only flow at 400 ft/sec whilst others at 600 ft/sec , all depends on the individul turbo , hence the "500" number
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Post by hassanalawi on May 13, 2020 18:09:50 GMT -5
do i assume to take this value as my inlet velocity/flight velocity? (for the sake of calculation)
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Post by racket on May 13, 2020 20:26:45 GMT -5
Considering the fact that you have a oversized turbine wheel and possibly stage , your compressor will most likely be flowing at an inlet velocity of >500 ft/sec .
But without knowledge of all the various aspects of the turbo and combustor its impossible to give you an answer
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