Post Processing

In this section is explained how to visualize the results and use the integrated post processing api for studying airfoils. All the results are saved in the folder /Results.

Using Integrated API

A specific module ReadAirfoilResults has been develop. While running an Airfoil simulation the code automatically saves the results - for pressure and velocity normal gradient - just for the nodes that are part of the airfoil boundary.

Use the ReadAirfoilResults module

using SegregatedVMSSolver
using SegregatedVMSSolver.ReadAirfoilResults

Specify the path where the .csv files with the results are stored. Specify also the geometrical and physical parameters

res_path = "Results/"
Re = 500_000
u0 = 1.0
c = 1.0
rho = 1.0
μ = u0*c*rho/Re
α = 1.0

Get the nodes and normals

nodes, normals = get_geometry_info(res_path;α=α)

You can get the average - in time and spanwise direction - of velocity and friction field. It is possible to specify the number of time-step that you want to skip at the beginning of the averaging using the keyword offset. It allows to avoid averaging also the initils time-steps where the solution is still evolving.

Ph = time_space_average_field(res_path, "ph", nodes)
Velocity = time_space_average_field(res_path, "uh", nodes)
Friction = time_space_average_field(res_path, "friction", nodes)

Writing the parameters of the simulation allows the code to get the local values for Cp and Cf splitting between top and bottom side.

cp_top, cp_bottom = extract_Cp(nodes, Ph; u0=u0, rho=rho)
friction_top, friction_bottom = extract_Cf(nodes, Friction, μ; u0=u0, rho=rho)

CL,CD = compute_CL_CD(nodes, cp_top, cp_bottom,
friction_top, friction_bottom; chord=1.0)

It is possible to plot the results. For example

using Plots
plot(nodes.top.x, cp_top, label = "VMS", color = :red, linewidth = 1.5)
plot!(nodes.bottom.x,cp_bottom, label = false, color = :red, linewidth = 1.5 )

Advanced Post Processing

There are also more powerful API to extract velocity fluctuations, TKE and spectra.

Time Averaging

In this example we compute the time-average of the velocity field in the volume "topairfoil". The user while creating the mesh has to add this tag to the volume to analyze

tagname="topairfoil"

topairfoil_nodes = get_nodes(res_path; tagname=tagname)

Vel_avg3D = compute_time_average(res_path; tagname=tagname)
Vel_avg2D = compute_time_span_average(res_path,Vel_avg3D; tagname=tagname)

It is possible to extract one of the components of the average velocity

ux_avg = Vel_avg2D[:,1]
uy_avg = Vel_avg2D[:,2]
uz_avg = Vel_avg2D[:,3]

And to plot it on the plane 0.1

xgrid,ygrid,velocity_dense = compute_scatter_interp(res_path, ux_avg, 0.1)

using Plots

#it can take a while
scatter(xgrid,ygrid .+ 0.0028;
zcolor=velocity_dense,markerstrokewidth=0, label="U_x average")

Fluctuations

It is possible to create a proble aligned with the z axis in the point xc,yc and get the fluctuations of that line.

xc,yc= 0.5,0.1 #it has to be a point of the domain
zprobe, Vel = read_fluctuations(res_path, [xc,yc]; offset=1_000,offend=5_000)

It is also possible to compute the Power Spectral Density (PSD)

dt = 0.001
nt=size(Vel)[1]-1 #Number of time-steps
tn = collect(0.0:dt:dt*nt)
PSD,freqs = compute_PSD(Vel, tn)

Computing the TKE in the plane 0.1

tke_xy = compute_plane_tke(res_path; zp =0.1)