I need to convert some compressor curves into a 3-d equation for modelling
purposes, P = f(Q,V), where P is pressure, Q flow and V a vane position. For
fixed V, the P-Q relationship is well behaved, and monotonic (avoiding the
surge region) within the domain of interest, essentially a segment of a
parabola or cubic. As V varies, the curves shift, rescale and rotate
slightly.

I can generate a table of spot values of the variables, but the regression functions I've come across such as the Excel linest function, seems to be confined to linear functions. Can anyone suggest a tool that will faciliate deriving a polynomial (or other form) equation to model my datasets? The alternative is the very fiddly process of manually working out variable coefficients for the constant-V curves that model them as they shift around.

Being a real engineering problem, I'm hoping for a quick and easy solution, precision isn't essential. otoo +/- 10% would do. TIA

I can generate a table of spot values of the variables, but the regression functions I've come across such as the Excel linest function, seems to be confined to linear functions. Can anyone suggest a tool that will faciliate deriving a polynomial (or other form) equation to model my datasets? The alternative is the very fiddly process of manually working out variable coefficients for the constant-V curves that model them as they shift around.

Being a real engineering problem, I'm hoping for a quick and easy solution, precision isn't essential. otoo +/- 10% would do. TIA