Is it possible to determine the mass flow rate for different power settings? Unfortunately I was unsuccessful in finding the engine specification for the PW2037 so I used the data from this source, which states that the mass flow rate at take-off for the PW2037 engine is 1210 lb/s. Given this flow rate, would it be possible to calculate the mass flow rate at idle setting? And therefore also the mass flow rate for 50% engine setting (or 25%, 75%, etc.)?

An answer in this question suggests using thermodynamic equations to approach this. However, I am not too sure on how to use these equations.


2 Answers 2


Yes, it can be done but you need a complicated model with information only the producer has access to. The data in your source are not enough.

You can play around with this a bit https://www.grc.nasa.gov/www/k-12/airplane/ngnsim.html but don't expect overly realistic answers. You have to use the Tunnel Test Mode for off-design performance after entering all the data you have available. And you should pick the "turbofan" engine type.

  • 1
    $\begingroup$ This should be a comment. $\endgroup$
    – Koyovis
    Dec 22, 2017 at 20:58
  • 1
    $\begingroup$ @Koyovis No, it's the correct answer. $\endgroup$
    – user7241
    Dec 22, 2017 at 21:01
  • $\begingroup$ It would be an answer if you would play around with the engine simulator, and would stipulate where the limitations and inacurracies are. Pointing out where to find methods is done in comments, not in answers. $\endgroup$
    – Koyovis
    Dec 22, 2017 at 21:43
  • $\begingroup$ The limitation is mentioned, though not in detail. It's the lack of accurate numerical values in a generic gas turbine performance model, such as (but not limited to) the data for the actual compressors and turbines as used in the PW2037 engine. But it is correct and does relate to and address the question raised. So it is actually an answer. It's just not as comprehensive as you might like. $\endgroup$
    – Penguin
    Dec 23, 2017 at 7:07
  • $\begingroup$ The problem here is that the applet does not account for bypass airflow, just core airflow. $\endgroup$
    – Zack
    Feb 13, 2018 at 18:40

Prediction of the mass flow, fuel flow and thrust can be given without detailed knowledge of the compressor and turbine maps, as the pdf in this link states, when we assume that the LP turbine is always choked because it operates in front of an exhaust nozzle.

The linked pdf gives an elaborate method for determining the off-design parameters for different turbofan engine configurations. The difficulty is that all parameters change relative to each other: mass flow, thrust, fuel flow, even the bypass ratio.

The paper matches the computed data with actual published data of two turbofan engines, neither of which unfortunately are from the PW2000 series. The closest one calculated is the RB211, which is a three-spool design but the twin spool simulation calculation works for the 3-spool as well according to the article:

The added assumption that the LP turbine is choked, makes the three-spool case exactly similar to a twin- spool engine. The design point calculations are nearly the same as those for the twin spool. So one can effectively use the same program for three-spool and twin- spool engines, with the only difference that the inter- turbine and inter-compressor temperatures and pressures calculated will be totally different from the actual values.

Meaning that the model will create good results for the overall parameters even though some of the internal parameters won't match. Figure 7. then gives the mass flow as a function of hot and cold thrust for the RB211 engine:

  • Thrust----Mass Flow

  • 100 % --- 100 %

  • 75 % --------87%
  • 50 % --------71%
  • 25 % --------51%
  • 8 % ---------30 % (idle)

enter image description here

So without going through the detailed procedures for the OP specific engine, above gives data for a comparable engine class.

  • $\begingroup$ I noticed this assumes an aircraft flying at 30,000 ft at Mach 0.80. Would these values be any different than say at rest at sea level? So would an engine at rest at sea level have a mass flow of 30%? $\endgroup$
    – Zack
    Feb 11, 2018 at 18:41
  • $\begingroup$ @Zack hard to tell without doing the actual calculations in the paper. Have seen a graph somewhere that seems to indicate an idle thrust flow of about 30% but cannot find it anymore. Sorry, am lacking the time to be of more help at the moment. $\endgroup$
    – Koyovis
    Feb 13, 2018 at 9:41

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