# Aerodyn: Some input parameters for unsteady aerodynamic case

Hi,

I am using Aerodyn v15.02 to calculate a horizontal axis tidal turbine in two cases: steady and unsteady.

However, I encounter the requirements of providing some input parameters in unsteady aerodynamic case.

Specifically, they are:

1. C_nalpha: the slope of the 2D normal force coefficient curve in the linear region.

2. Cn1: the critical value of C0n at leading-edge separation for positive AoA and should be extracted from airfoil data at a given Reynold’s number and Mach number; Cn1 can be calculated from the static value of Cn at either the break in the pitching moment or the loss of chord force at the onset of stall; Cn1 is close to the condition of maximum lift of the airfoil at low Mach numbers.

3. Cn2: the critical value of C0n at leading-edge separation for negative AoA and should be extracted from airfoil data at a given Reynold’s number and Mach number; Cn2 can be calculated from the static value of Cn at either the break in the pitching moment or the loss of chord force at the onset of stall; Cn2 is close to the condition of maximum lift of the airfoil at low Mach numbers.

I do not know how to capture these parameters.

So, I will be very grateful if someone can show me how to capture them.

Thank you very much for this help.

I look forward to hearing from you.

Best regards,
Ngoc Ha Tran.

Dear Ngoc Ha Tran,

From their descriptions, all you need to calculate these constants are the static airfoil data in terms of normal (normal to chord) force, chord (tangential to chord) force, and pitching moment coefficient versus angle of attack. If you have the airfoil data in terms of lift force and drag force coefficients, you can convert these easily to normal force and chord force coefficient.

Best regards,

Sir,

Where could I get data for pitching moment coefficient (PMC)?

For instance, in the Unsteady report (Phase VI), there’s PMC data for Re > 750,000, as attached.
I’m wondering if there’s PMC data for Re < 750,000 (e.g. Re = 300k, 500k and 650k).

Kind regards,
Wesley

Dear Wesley,

The airfoil data I’m aware of for the NREL Phase VI rotor is available in Appendix A of the following report: wind.nrel.gov/airfoils/AirfoilData.html.

Best regards,