turbo compressor flow numbers 2

[Artsi]

Hello

I'd welcome a helping hand in converting unfamiliar turbocharger compressor air flow format. Please have a look here:

http://image51.webshots.com/51/9/41/79/2513941790085019242mApMkI_fs.jpg

I'd like to convert flow data into lbs/min, or kg/sec.

 

[Artsi]

Picture hosting is blocking that address. Let's try another one.

http://community.webshots.com/photo/2513941790085019242mApMkI

 

[j2bprometheus]

Artsi-
That is "normalized" compressor flow. Here's the formula that Holset used in the plot you mentioned:

normalized_flow_parameter = mass_flow_rate_kg_per_sec*[sqrt(inlet_Temperature_in_Kelvin)]/inlet_pressure_in_megapascals


SAE does almost the same thing with turbine maps.


Compressor / turbocharger manufacturers (ABB, Garrett, KBB, Holset, etc.) all normalize their compressor maps but they often use slightly different reference temperatures & pressures or methods to normalize the data.

This makes it more difficult to compare maps by different manufacturers.


j2bprometheus

 

[gtsim]

Compressor and turbines (radial and axial) are normally plotted on a Mach number basis because they are valid for all pressure and temperatures provided the flow is turbulent. The non-dimensional groups for flow are
W*((ZRT/k)^0.5)/AP and for speed ND/(ZkRT)^0.5 and know as non-dimensional mass flow and speed respectively.

W = Inlet mass flow rate kg/s
Z = Inlet compressibility factor
R = gas constant (kJ/kgK)
T = Inlet temperature (K)
P = Pressure (Pa or Bars)
k = cp/cv at inlet
D = rotor diameter (m)
A = Inlet area (m^2)

In fact these non-dimensional parameters are Mach numbers at inlet to the compressor or turbine. At normal working pressures and temperatures air and combustion products act as a perfect gas therefore ‘Z’ is unity. ‘R’, ‘k’, ‘D’ and ‘A’ is approximately constant and omitted from these non-dimensional groups. Thus the non-dimensional mass flow and speed reduce to W(T^0.5)/P and N/(T^0.5) respectively as shown in your compressor map. Strictly, we should at least include R and k as this allows us to analysis compressor and turbine performance due to humidity and fuel-air ratio changes.

Regards,
gtsim

 

[gtsim]

Sorry, forgot to answer how to convert these non-dimensional parameters to flows and speed.

Consider the inlet pressure and temperature at inlet to the compressor is 0.1013 megapascals and 288K. Select a compressor speed and for each point on this speed line multiply the value by 0.1013/(288^.5) and this will give you the mass flow in the corresponding units (e.g., kg/s). Similarly the non-dimensional speed is multiplied by (288^.5) to give RPM. Now repeat for all the points on a given speed and for all the speed lines. As stated earlier your compressor map is only valid for these inlet conditions. For different inlet conditions you should repeat the process for that condition.

gtsim

 

[Artsi]

Thank's.

 

[benkitcher]

Hi,
The T3 maps here

http://www.turbocharged.com/catalog/compmaps/fig1.html

almost suggest that the top line of the flow coeff is to the power 1/W. Is it not? It just appears that way? I guess it being a product of W and not a power would be make far more sense.

Ben Kitcher

 

[gtsim]

Normally we represent non-dimensional flow as I have described above and the coefficient 0.5 but we need to include ‘k’ and ‘R’ terms. Some manufacturers omit these terms and use a different index, which can vary from 0.45 to about 0.525 to allow of these terms. Some would use an index other than 1 for the pressure term.

gtsim