نوع مقاله : پژوهشی
نویسندگان
دانشکدهی مهندسی عمران، دانشگاه خواجهنصیرالدین طوسی
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
The objective of this work is to perform aliased and de-aliased direct numerical simulation of a turbulent channel flow with a variable time-stepping algorithm. The time advancement is carried out by an implicit 3rd order
backward different scheme for linear terms, and explicit forward Euler for nonlinear terms (SBDF3), in T=300s (about 12000 time step). A $tau$ pseudo spectral method is employed on 128$times$65$times$128
computational grids in $Omega$=[0.4$pi$]$times$[-1.1]$times$[0.2$pi$].
The Fourier series in stream-wise and span-wise directions and Chebychev polynomial expansion in a
normal direction are employed. The friction Reynolds number is $Re_{tau}$=175 and initial viscosity is set to $nu$=1/4000. The effect of aliasing errors is examined in the NoDealiasing scheme. Also, the products aliasing errors are eliminated by truncating the Fourier coefficients of the velocity and the product, using the so-called 2/3 rule, in three schemes of: DealiasY ،DealiasXZ and DealiasXYZ. A comparison of turbulence intensities is made over the interval from $T_{0}=100$ to $T_{1}=300$.
The results of turbulence statistics, wall-shear velocity, standard deviation, overall CPU time and total normalized energy of instantaneous velocities have also been collected. Also, the results of the mean velocity profile are
compared to the scaling laws for viscous and inertial layers in all schemes.
The present results of turbulence strength show significant discrepancies between the results of NoDealiasing and DealiasY schemes and the DealiasXZ and DealiasXYZ schemes at the other side. Alsom there are no considerable differences between DealiasXZ and DealiasXYZ results. The differences between computed values of turbulent quantities vary from 96% in total normalized energy to 3% in dissipation. Compared to the NoDealiasing scheme, modified DealiasXYZ reduces the computational time around 33%. Therefore, from a practical standpoint, the choice between the costly, ordinary, and de-aliased rotational form reduces to the last one, if the final decision rests on economics.
کلیدواژهها [English]
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