Shia-Hui Peng, FOI/Chalmers
|Sponsors:||Clean Sky, Joint Technology Initiative for Aeronautics and Air Transport|
|Start of project:||Juni 2010|
|End of project:||May 2012|
In this project, aeroacoustic performances of three-dimensional wings that are slotted with the high-lift multi-elemental devices are assessed, which are termed as Config. 1, Config. 2 and Config. 4. The baseline configuration is set as Config. 1. It consists of a double slotted part-span flap. The wing has a trailing edge kink, and the high-lift system of the flap has separate elements inboard and outboard of the kink. There are cavities for all flaps. Config. 2 adopts a structure with a single slotted part-span flap. Config. 3 uses the same flap as the second one, except for the Krueger flap. A common fuselage body is employed to attach these wing configurations in computation. The free-stream flow conditions are Ma=0.2 and Re=1.7E7.
The instantaneous quantities of the flow are obtained using a hybrid method of RANS/LES. The computational domain is spherical with a radius of about 80 times the wing chord. Characteristic boundary conditions are used on the surface of the sphere. To reduce the computational cost, a symmetrical boundary condition is applied at the symmetry plane of the computational domain, which corresponds to the symmetry plane at the fuselage.
The analogy approaches adopted here includes: 1) the Kirchhoff method, 2) the FWH method of the permeable surface and 3) the Curle method. The first two methods are used to compute the noise generated by the core flow region where the energetic structures exist. The last method is adopted to predict the noise specifically from the pressure perturbation on the wall.
A new way to define the integral surface that encloses the major noise sources is proposed for the Kirchhoff method and FWH method. Considering complexity of the local properties of the flow around the multi-element object -- the actual wing with high-lift devices, a integral surface with regular shape is no longer applicable. Therefore, the surface is defined based on vorticity. A precursor RANS computation gives a rough estimation to vorticity. It is proved numerically that the energetic noise sources corresponding to dimensionless vorticity magnitudes larger than 2.7 is covered well by this surface.
The noise from the core flow region is studied on the basis of the dependent integral quantities on the integral surface, which are indicated by the Kirchhoff formulation and by the FWH formulation. In the Kirchhoff formulation, the dependent quantities are formulated in terms of the pressure perturbations, p', its normal gradient, dp'/dn, and its time derivative, dp'/dt. It is found that dp'/dn is dominant, which has approximately a monopole directivity. The noise from the pressure and time derivative present dipole directivities whose strong polar point upwards and downwards. According to the FWH formulation, the noise can be related to variations of the pressure, p', the flow momentum, ρuiuj, and the flow mass, ρuj. The flow mass is found to be the dominant term. It induces the noise with an approximate monopole directivity. The other two components follow dipole directivities, but they tend to be perpendicular to each other. The strong polar by the flow momentum points to the downstream and upstream, and is thus unimportant in practice.
The Curle method gives the numerical solution for the noise induced by the fluctuating pressure over wall components. Directivities of the noise is shown to be connected to the incidence angles of the wall components. The wall of the inboard flap is found to be a common dominant source for the configurations.
Because the FWH method takes into account more effects of the noise sources than the other two methods, it is preferred to evaluate acoustic performances for the three configurations. It is shown in the figure below that the total noise is reduced considerably by Config. 4.
This page, Aerodynamic loads on wind turbines, should be part of a frames system at www.tfd.chalmers.se/~lada/projects/proind.html