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Thread: Helmholtz resonator calculation q's

  1. #1
    I've been messing with intake calculations and am looking at the Helmholtz multi-cylinder calculation now. There's an example on This Page that is right out of the book I'm using.

    I'm a little confused about where to model the plenum in this equation: should it be modelled as part of the intake, or as part of the 'dead' volume of the other cylinders?

    Lehigh Formula SAE

    www.lehigh.edu/~insae/formula

  2. #2
    I've been messing with intake calculations and am looking at the Helmholtz multi-cylinder calculation now. There's an example on This Page that is right out of the book I'm using.

    I'm a little confused about where to model the plenum in this equation: should it be modelled as part of the intake, or as part of the 'dead' volume of the other cylinders?

    Lehigh Formula SAE

    www.lehigh.edu/~insae/formula
    Lehigh Formula SAE 1999-2004

  3. #3
    Check this website:
    http://www.grapeaperacing.com/GrapeA...ntaketerms.cfm

    I think it's clearer than the one you have.
    Hope it helps you,

    Alfonso Ochoa
    F-SAE USB, Venezuela.
    cabezota311@hotmail.com
    Alfonso Ochoa Vega
    cabezota311@hotmail.com
    F-SAE USB Team, Venezuela

  4. #4
    Angry Joe, I don't think that page has a correct formula. If the formula is correct, then the variable definitions are incorrect.

    The formula is supposed to output a value in Hertz, but none of the inputs are time dependant. I don't see how that is possible.

    Perhaps I am making incorrect assumptions:
    Vd=1 cylinders displacement
    Rc=Compression ratio
    and then the others as he's defined them.

    The terms L1=1/A1 and L2=1/A2 strike me as being wrong. However, I am not sure what they should actually be. Does anyone have the Haywood book (1988) that can verify this formula for us?

    -------------------------
    UVIC Formula SAE Team

    http://fsae.uvic.ca
    -------------------------
    UVIC Formula SAE Team
    http://members.shaw.ca/drax77/Formula%20UVic%20Sig.jpg
    http://uvic.fsae.ca

  5. #5
    This is a page that I referenced for a small thermo report on compressible flow, and have partially used for our new intake design.

    http://www.mecc.unipd.it/~cos/DINAMO...suonatore.html

    Kevin Hall
    University of Saskatchewan
    Engine Guy
    www.engr.usask.ca/~formula
    Kevin Hall
    University of Saskatchewan
    Engine Guy
    www.engr.usask.ca/~formula

  6. #6
    I ran and got the Heywood book, and found out the terms I thought weren't correct, weren't correct. They should be L/A not 1/A. The formula still isn't giving me any results that I can discern however.

    -------------------------
    UVIC Formula SAE Team

    http://fsae.uvic.ca
    -------------------------
    UVIC Formula SAE Team
    http://members.shaw.ca/drax77/Formula%20UVic%20Sig.jpg
    http://uvic.fsae.ca

  7. #7
    I actually used the Heywood formula, I just used that site for an example. I also could not get the formula to work. I went trough the units and it came out as 1/(2*pi*cm), and my numbers were not even close.

    Anybody know what's going on here?

    Lehigh Formula SAE

    www.lehigh.edu/~insae/formula
    Lehigh Formula SAE 1999-2004

  8. #8
    Here's what I have in my spreadsheet. I derived it from an equation in Winterbourne-Pearson and I don't remember the exact equation it came from.

    Oscillations in Hz = (Speed of Sound*SQRT(Pipe cross-sectional area/(Pipe length* Mean cyl volume)))/2pi

    Where mean cylinder volume is defined as 1/2 the displacement volume plus the entire clearance volume.

    -Charlie Ping
    Auburn University FSAE 1999-present
    -Charlie Ping

    Auburn FSAE Alum 00-04

  9. #9
    I have that one done as well... but I didn't see how both formula's could be correct, and the one you used charlie doesn't take the plenum volume into account at all...

    -------------------------
    UVIC Formula SAE Team

    http://uvic.fsae.ca
    -------------------------
    UVIC Formula SAE Team
    http://members.shaw.ca/drax77/Formula%20UVic%20Sig.jpg
    http://uvic.fsae.ca

  10. #10
    I wasn't aware that the Heimholtz Equation took plenum volume into account. I know the Ohata & Ishida Eq. does. However I've gotten mixed results because it include an inlet pipe frequency that I cannot match to a restrictor accurately (IMO). If anyone know how to do this I'm all ears.

    -Charlie Ping
    Auburn University FSAE 1999-present
    -Charlie Ping

    Auburn FSAE Alum 00-04

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