Creating input file for the aero_noise module#
The aim of this section is to explain how to generate the necessary input file for the aero_noise module (see Sections Sub command block – aero_noise, Data format for the trailing edge noise model (bldata) and Example of a trailing-edge noise model file (bldata)). This file is only required if using a trailing edge noise model.
In short, the trailing edge noise models implemented in the aero_noise module requires the knowledge of the turbulent boundary layer developing on the airfoil sections along the blade span. More precisely, the information about the turbulent quantities need to be extracted in the vicinity of the trailing edge, right before the flowfield passes over the trailing edge, both on the suction and pressure side of the airfoil. Typically, these quantities are extracted at a chordwise location between 97% and 98% of the airfoil length (getting closer to the trailing edge can become problematic, e.g. if the airfoil trailing edge is rounded). These quantities amount to:
\(U_{\textrm{edge}}\): The boundary layer edge velocity
\(C_{\textrm{f}}\): The wall friction coefficient
\(\partial P/\partial x\): The wall pressure gradient along the chord
\(\delta\): The boundary layer thickness
\(\delta^*\): The boundary layer displacement thickness
\(\theta\): The boundary layer momentum thickness
\(X_{\textrm{tr}}\): The transition location
\(X_{\textrm{sep}}\): The separation location (if separation occurs)
In addition, the following turbulent quantities across the boundary layer thickness (at the same chord position where the above quantities have been extracted) are required:
\(Y\): The distance from the wall (in the direction normal to the wall)
\(U(Y)\): The flow velocity in the direction parallel to the wall at each \(Y\) position
\(k_{\textrm{t}}(Y)\): The turbulent kinetic energy at each \(Y\) position
\(\varepsilon(Y)\): The turbulent dissipation rate at each \(Y\) position
The boundary layer thickness must therefore be discretized across its thickness in order to extract the above turbulent quantity profiles. Typically, 40 to 60 points equally distributed across the boundary layer are required.
Note that all the above data must be non-dimensionalized using the air density \(\rho\), the airfoil chord \(C\), the inflow velocity \(U_{\infty}\), and the air dynamic viscosity \(\mu\). If using a CFD code, this is achieved by running the simulation with a density, airfoil chord and inflow velocity equal to 1, and enforcing a dynamic viscosity equal to the inverse of the Reynolds number \(Re\), where:
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