Naslov
ANALYSIS AND IMPLEMENTATION OF THE HARMONIC BALANCE METHOD IN COMPUTATIONAL FLUID DYNAMICS

Autori
Cvijetić, Gregor

Vrsta, podvrsta i kategorija rada
Ocjenski radovi, diplomski rad, diplomski

Fakultet
Fakultet strojarstva i brodogradnje

Mjesto
Zagreb

Datum
17.07

Godina
2015

Stranica
90

Mentor
Jasak, Hrvoje

Ključne riječi
Harmonic Balance; CFD; OpenFOAM; Fourier series; harmonic; periodic; nonlinear; NACA; airfoil pitching

Sažetak
In this thesis the Harmonic Balance Method for non-linear periodic flows is presented. Assumption of a time-periodic flow allows us to formulate 2n + 1 coupled steady state problems. By solving 2n+1 steady state problems, a transient flow field is obtained. Fourier series expansion is the core of the Harmonic Balance Method, therefore the accuracy of the method depends on the number of harmonics specified, n. Accuracy of the method also depends on the periodic nature of the problem. The method was first derived for a passive scalar transport and implemented in OpenFOAM. Validation has been carried out on 4 test cases concerning forced periodic behaviour at the inlet of the rectangular 2D domain. The first test case was a sine wave, which was fully resolved with 1 harmonic. The second case was a linear combination of sine and cosine waves with different frequencies, resolved with 2 harmonics. After successful validation of harmonic waves, robustness and accuracy test was carried out on two square waves. Square waves are numerically more difficult and more demanding, which was also shown in the convergence study carried out using 3, 5, 7 and 10 harmonics. Harmonic Balance Method results were compared to transient simulation for all of the test cases. After validation of the passive scalar transport, pressure-velocity system for the Harmonic Balance Method was derived and implemented. Validation of NACA2412 pitching airfoil was presented together with performance comparison of transient solver and harmonic balance.

Izvorni jezik
Engleski

Znanstvena područja
Strojarstvo

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