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## Large Eddy Simulation of Turbulent Pulsating Jets Case Solution

Abstract

In this paper we showed the numerical method for “Large Eddy Simulation of Turbulent Jets” with software implementation Ansys fluent this paper designed to show the whole process of simulation of large eddy with the geometry designing.

There are four main parts of this paper, the first part is describes the brief introduction of the “Large Eddy Simulation of Turbulent Jets”, second part is the problem description of the for the large eddy simulation in this part is important to understand the main purpose of the paper, the third part showed the software implementation of the “Large Eddy Simulation of Turbulent Jets” there are different steps shown for the simulation with snaps, the fourth showed the results of the simulation where we can analyses the results of the large eddy simulation for the turbulent jet there is another sub part which concludes the obtained results from the large eddy simulation.

Introduction:

We are investigating the “Large Eddy Simulation of Turbulent Jets” it is basically a turbulence’s mathematical model which is used in computational fluid dynamics. The simulation of the turbulent flows by numerically solving with Navier-Strokes equations requires the very long length of scale with time and these all directly affect the field of flow. The resolution can be accomplished through the DNC direct numerical simulation it is expensive solution used for simulation of pumps, landing gear, turbulent jets.

For the feasible future turbulent flow can hardly be simulatedreliably via direct numerical simulation (DNS) because direct numericalsimulation requires resolution of all persistent eddies.  AssumingKolmogorov's description of turbulence valid, the smallest length scale isexpected to be

O (Re^ (-3/4)).

The physical problem:

The physical state of the turbulent jet is given as,

The size of the domain is represented by the Lx, Ly, Lz which are the (2x4x0.02) m. The planar jet issues vertically from the central region of the bottom side of the domain as shown in the figure 1 there some parameters for the jets which are jet velocity inflow boundary and the temperature is uniform in the computation domain. The z direction must be included in the simulation of the planar jets,  2 grid points to the model of “3D” planar jet with small distance in z direction, the grid resolution must be sufficient at least 80 grid. For the physical problem we would analyses the two cases one for pulsating inlet flow velocity which mathematically can be represent as,

Where  is the inlet velocity, A is pulsating amplitude,  is the pulsating frequency and the t is time for pulsating inlet velocity.

The second we would study the inflow velocity of the jet which mathematically can be represent as,

To analyses the above to cases we would perform the simulation in Ansys fluent with user define function UDF.

Simulation Parameters:

To simulate the large eddy simulation for turbulence jet we have the following simulation parameters.

• The domain size for jet is given as

Lx = 2m

Ly = 4m

Lz= 0.02m

Volume=0.16m3

• The jet width is 0.1m.
• The mean velocity of the jet at the inflow boundary is 10m/s and 0.
• Temperature is uniform.
• The pulsating frequency is 20Hz.
• For the non-zero mean velocity at the inflow amplitude of pulsating is A=0.3.
• The grid points are 200.
• Simulation time is tmax =2 seconds.
• Simulation step of time of delta tmax=0.01 seconds.

Results and Discussion:

• We designed the geometry of the turbulence jet in Ansys software with the given parameters Lx=2m, Ly=4m and Lz=0.02m. Figure number 2 is illustrating the geometry of turbulence jet the 200 grid points.

geomentory

The dimension of the turbulence jet geometry is showing in the figure 2b where D5 is the diameter of the nozzle H1 and H2 are x-axis parameters H=1+1=2m and V4 is the vertical axis 4m..........................................

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