*BEM THEORY

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*BEM THEORY

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Purpose

To specify the blade element momentum (BEM) theory options.

Theory

Refer to AeroDyn Overview for further information.

Keyword Format

Six lines of data, defining blade element momentum theory parameters as follows:

SKEWMOD=Skewed-Wake Correction

SKEWMODFACTOR=Skewed-Wake Correction Factor

TIPLOSS=Tip Loss, HUBLOSS=Hub Loss

TANIND=Tangential Induction

AIDRAG=Axial-Induction Drag, TIDRAG=Tangential-Induction Drag

INDTOLER=Convergence Threshold

MAXITER=Maximum Iterations

 

Set Skewed-Wake Correction to 1 to use the uncoupled BEM solution technique without an additional skewed-wake correction, or 2 to include the Pitt/Peters correction model.

Skewed-Wake Correction Factor is used only when SkewMod = 1. Enter a scaling factor to use in the Pitt/Peters correction model, or enter DEFAULT to use the default value of 15 PI /32.

Set Tip Loss to 1 to include the Prandtl tip-loss model, or 0 to disable it. Likewise, set Hub Loss to 1 to include the Prandtl hub-loss model, or 0 to disable it.

Set Tangential Induction to 1 to include tangential induction (from the angular momentum balance) in the BEM solution, or 0 to neglect it. Set Axial-Induction Drag to 1 to include drag in the axial-induction calculation, or 0 to neglect it. If Tangential Induction = 1, set Tangential-Induction Drag to 1 to include drag in the tangential-induction calculation, or 0 to neglect it.

Convergence Threshold sets the convergence threshold for the iterative nonlinear solve of the BEM solution. Maximum Iterations determines the maximum number of iterations steps in the BEM solve.

Table Input

Input:

Description

Skewed-Wake Correction:

The option are Uncoupled (uncoupled BEM solution technique without an additional skewed-wake correction), or the Pitt/Peters correction model.

Skewed-Wake Correction Factor:

This factor is used only when Skewed-Wake Correction is set to Pitt/Peters. Enter a scaling factor to use in the Pitt/Peters correction model, or enter DEFAULT to use the default value of 15 PI /32.

Prandtl Tip-Loss:

This option allows you to include the Prandtl tip-loss model, or to disable it.

Prandtl Hub-Loss:

This option allows you to include the Prandtl hub-loss model, or to disable it.

Tangential Induction:

This option allows you to include tangential induction (from the angular momentum balance) in the BEM solution, or to neglect it.

Axial-Induction Drag:

This option allows you to include drag in the axial-induction calculation, or to neglect it.

Tangential-Induction Drag:

This option allows you to include drag in the tangential-induction calculation, assuming tangential induction itself is being included, or to neglect it.

Convergence Threshold:

The convergence threshold for the iterative nonlinear solve of the BEM solution. The nonlinear solve is in terms of the inflow angle, but the convergence threshold represents the tolerance of the nondimensional residual equation, with no physical association possible. ‘DEFAULT’ may be specified rather than a numerical value, allowing AeroDyn to select an appropriate default value as recommended by NREL.

Maximum Iterations:

The maximum number of iterations steps in the BEM solve. If the residual value of the BEM solve is not less than or equal to Convergence Threshold in Maximum Iterations, AeroDyn will exit the BEM solver and return an error message.