CFD Analysis Process

There

are few main components of CFD design cycle. Below are the following important

steps:

1. Problem

statement

First, states the problem to be solved and identify

the flow problems. Notice the physical phenomenon need to be considered in this

analysis. Besides, create the geometry of the object (domain) and those

necessary operating conditions. After that, notice the internal obstacles,

internal-surface and free surface of the object. Identify the type of flow

whether it’s laminar, turbulent or it’s a steady or unsteady flow.

2. Mathematical

model

First, a proper flow model, good viewpoint and

reference frame are chosen. Identify the forces that influence the fluid

motion. Second, problem is set with the computational domain. Writes out all

the related formula for the conservation law of mass, momentum and energy.

Furthermore, equation is simplified for reducing the computational effort.

Lastly, specify those necessary boundary conditions.

3. Discretization

method

First, Partial differential equations system (PDE) is

transformed into a set of algebraic equations. Through this, it is created

become approximately, become discretized versions and because of those small

part element. It became more easily to be solved. In fact, there are many ways

to discretize the partial equations but in the end. The goal of all the methods

are the same, that is turn a calculus problem that human cannot solve into an

algebra problem which human can solve.

Below is some example of discretizing method:

·

Discretization of spatial

volumes through finite difference, finite element and finite volume.

·

Discretization of grid

topology through structured, unstructured cartesian and generalized

unstructured.

4. CFD

Simulation

First, once the object in 2D geometry such as

representative cross section is created. It is necessary to

familiar those parameters in the simulation.

Once simulate it, there are something that can obtained from this simulation.

For example, investigation of effect of fluid properties on the overall object,

what proper meshing and what appropriate boundary layer meshing to be used and

estimate the accuracy that expected from a 3D model. Furthermore, the quality

of simulation results based on some few factors such as assumptions made before

the simulation, mathematical model and quality, size of mesh and so on.

5. Post

processing

After CFD Simulation, the next step is to extract the

important information from the computed flow field. The important information

such as the calculation of derived quantities and integral parameters,

verification of CFD model and visualization of 1D, 2D and 3D value.

6. Error

and uncertainty

Results of CFD simulation is depends on the

accumulation of error and the level of variability. The source of causing

uncertainty is might be not enough of knowledge about CFD. Error might be cause

by other reasons. If comparing both of it. Error is more easily to find out compare

to uncertainty. This is because, error have many ways to determine, estimating

and solving them. But for uncertainty, there is no proper way to find it out

because it is because of lack of knowledge about CFD. So, it might remain the

problem that undiscovered ever and in the end. It might also cause other

different big problems. (Patel, 2013)

Advantages of CFD

Again,

Computational Fluid Dynamics (CFD) is a software or can be said as system to

predict the fluid flow, heat transfer, mass transfer, chemical reaction and so

on. Furthermore, there are a lot of benefits about it. First, development cost.

It is very expensive that using real or physical experiments and tests to get

some important engineering data for design purpose. Thus, this software is used

to get those important data and it is relatively inexpensive in cost. Data get

from CFD sometime is more accurate as it is using computer to calculate.

Second, execution time. CFD simulation can run or so call test in a short

period of time, this make engineering data introduced early before the design

process. Third, overall data. Experiments or tests can only get those data in

limited location and it is not so detailed, but CFD allows to get more precise

data and it is very comprehensive. Lastly, simulation under many conditions. In

real experiment, some fluid flow or heat transfer process cannot be easily

control or tested under different kind of conditions. But in CFD, it provides

this ability.

Disadvantages of CFD

Even

though there are a lot of advantages about CFD. However, there are also have

disadvantages of it. First, for an CFD investor, they have no power to vote or

say in an engineering company since CFD is not their underlying asset. Second,

for CFD system, it is very hard to get a perfect grid for a complex geometry,

sometimes it can but very time consuming. Besides, it is also very difficult to

get the accurate flow motion result over the whole thing in simulation. This is

because, those data required a good quality in grid session, perfect grid is

very hard to get for a complex geometry. Lastly, this system is not so friendly

to all people and it is quite complicated to be used as well. Thus, it has to

take a long time to keep one practice in how to use this software and how to

analyse the results.

Application of CFD

Computational

Fluid dynamic can be used in many ways for predicting the important data to

design something. Below are some examples of application of CFD:

·

Smoke control system

·

Classroom

·

Swimming pool ventilation

·

Aerospace

·

Automotive

·

Electronic

In

fact, there are still a lot of application about CFD but not necessary to show

all of it. Smoke control system is one of the most common usage of CFD

application. CFD has the capability to simulate the smoke flow in a space with

complex geometry. This idea is keeping the smoke away from the objects or to be

said as occupants for saving their life when accident happens. From here shows

that, why CFD is so important in simulation before designing the building for

safety issues. (Saeidi,

1998)

Figure 2 Figure

3

Figure

2 shows the smoke away from the building when accident happens. Figure 3 shows

it’s result of simulation in CFD.