top-rated free essay

Computional Fluid Dynamics Through a Pipe

By OmarOleimy1 Mar 21, 2013 1028 Words
Table of Contents
INTRODUCTION3
Method:3
Part 23
Part 33
Part 44
Part 54
RESULTS4
Part 14
Part 26
Part 36
Part 46
Part 5:6
DISCUSSION7
CONCLUSION7
REFERENCES7

INTRODUCTION
The main objective of this assignment is to simulate a 3-D air flow in a pipe using Ansys CFX. The pipe was simulated under specific conditions. These conditions are air temperature to be 25⁰C (degrees Celsius), one atmospheric reference pressure, no heat transfer and laminar flow. The results from the simulation of laminar flow in the pipe were compared with the theoretical ones. Also the mesh was refined in the simulation to see if it is possible to get more accurate results using grid convergence analysis. Method:

The pipe used in the simulation has dimensions of a 0.5m axial length and a radial diameter of 12mm. The air entering the pipe, inlet velocity, is set to 0.4 m/s at a temperature of 25⁰C and one atmospheric pressure. No slip condition was set on the pipe walls. The outlet of pipe was set to zero gauge average static pressure. In CFX a mesh was formed on the pipe with a default mesh spacing (element size) of 2mm. Figure (1) and (2) shows the setup of the model before simulation was preformed Figure 1: Mesh without Inflation

Figure 1: Mesh without Inflation

Figure 2: Mesh with Inflation

Part 2
Calculating the pressure drop Δp=fLDρ Ub22Equation (1) Calculating Reynolds number Re=UbD/μ Equation (2) Friction Factorf=64/ReEquation (3)

The results were calculated using excel, and plotted in Figure (3). Part 3
Estimating the entrance pipe length Le: Le/D=0.06ReEquation (4) Having Re=UbD/μEquation (3)
The simulated results of velocity vs. axial length were plotted in Figure (5). From the graph the Le (entrance pipe length) was determined by estimating the point in the x-axis where the curve is straight horizontal line. Part 4

Comparison of the radial distribution of the axial velocity in the fully developed region in the simulated model against the following analytical equation:
UUmax = 1-rr02 Equation (5)
The results were calculated using excel, and plotted in Figure (4). Part 5
The simulation was performed three times, each time with a different grid setting. The numbers of nodes were 121156,215875 and 312647 for the 1st, 2nd and 3rd simulation. RESULTS
Part 1
Figure 3: Pressure Distribution vs. Axial Length
Figure 3: Pressure Distribution vs. Axial Length

Figure 4: Axial Velocity vs. Radial Diameter

Figure 5: Velocity vs. Axial Distance
Part 2
Having: Dynamic viscosity μ = 1.835x10-5 kg/ms and Density ρ = 1.184 kg/m3 Reynolds Number Re=UbDμ== 261.58
Friction Factorf=64Re== 0.244667
Δp=0.965691 Pa
From the simulation the pressure estimated at the inlet is Δp=0.96562 Pa
(0.95295-0.965691)/0.965691*100 = 1.080 %
Part 3
Having Re=UbDμ=261.58
The entrance pipe length Le: Le=0.06Re*D = 0.188 m
From the graph in Figure (3) the Le is estimated to be ~ 0.166667 ((0.166667-0.188)/0.188)*100 = 11.73%
Part 4
From the graph in Figure 2 the theoretical velocity at the center of the pipe is estimated to be 0.8 m/s. From the simulation the velocity at the center of the pipe is estimated to be 0.660406 m/s. ((0.688179-0.8)/0.8)*100= 13.98%

Part 5:
Table 1: Percentage Error for Each Simulation
Number of Nodes| Axial Velocity % error (%)| Pressure % error (%) | 120000
Simulated I| 13.98| 1.31|
215000
Simulated II| 12.42| 2.24|
312000
Simulated III| 12.38| 2.28|

Figure 6: Percentage Error vs. Number of Nodes
Figure 6: Percentage Error vs. Number of Nodes

The percentage error for the axial velocity results from the 1st, 2nd and 3rd simulation were calculated and plotted in Figure (6), as well as the pressure result along the pipe. Table (1) shows the axial velocity and pressure percentage error for each simulation. DISCUSSION

After the simulation was successfully done on Ansys CFX and the simulated results were compared with theoretical results, it was found that the simulated results have slight deviation from theoretical ones. In PART 2, the pressure in the simulated result differed by the theoretical by a 1.080%, for 1st simulation. In PART 3, the simulated results for entrance pipe length, Le, differed from the theoretical results by 11.73%. In PART 4, Figure (4), the simulated velocity curve is less accurate than that of the theoretical. In PART 5, meshing refinements and inflation were done to the simulation in order to getting better results. Figures (6) show with more nodes and inflation the accuracy of the results increases. Increasing the nodes gradually was found to be an advantage where higher or more accurate results were obtained. This is noted in grid convergence graph, Figure (6), as the number of nodes increase the pressure percentage error is converging to 2% while for velocity percentage error is converging to 12%. On the other hand, the percentage error increased with the increase of the number of nodes while the velocity error decreased with the increase of number of nodes. In Part 2 the percentage error for pressure drop is 1.080%, for 1st simulation. But when trying to increase the accuracy of the simulated velocity result by refining the meshing and adding nodes the pressure drop percentage error increases, as shown in figure (6). This is due to that Darcy-Weisbach equation, equation (1), assumes constant developed flow all along the pipe where in the simulated results the flow is observed to become developed father down the pipe from the inlet. This is assumed to change the pressure distribution along the pipe. CONCLUSION

More nodes used in meshing will produce more accurate and precise results, as shown in Figure (6). Also the meshing plays a vital rule on the sensitivity of results in terms of the accuracy of these results. REFERENCES

[1]Fluid Mechanics Frank M. White Sixth edition. 2006

Cite This Document

Related Documents

  • Computational Fluid Dynamics

    ...compared to exact solution. In the next steps, the validation, stability and effects of changing boundary condition on our solution will be investigated. Finally, the results will be presented and completely discussed. Programming Assignment 2-Wave Equation 1. Introduction The wave equation is an important second-order linear partial d...

    Read More
  • Fluid Flow in a Smooth Pipe

    ...Experiment 1 Fluid Flow In A Smooth Pipe Abstract In this experiment, three variable flow meters are used to alter the flowrate. Changes in pressure drop due to the change in flowrate are then observed from the three pressure gauges that can measure pressure at different range and recorded. The shift from laminar flow to turbulent flow is see...

    Read More
  • Fluid

    ...Experiment 3: Fluid Flow Friction and Fitting Loss Objective To determine the pressure or head loss in different diameters pipes, joints and valves Theory Pipe flows belong to a broader class of flows, called internal flows, where the fluid is completely bounded by solid surfaces. In contrast, in external flows, such as flow over a flat ...

    Read More
  • Fluid Dynamics and Pressure

    ...Chapter 3: FLUID FLOW CHAPTER THREE FLUID FLOW 3.1 3.2 3.3 3.4 3.5 Fluid Flow Unit Pump Test Unit Hydraulics bench and accessories Flow Curve Determination for Non-Newtonian Fluids Fixed and Fluidized Bed Facts which at first seem improbable will, even in scant explanation, drop the cloak which has hidden them and stand forth in ...

    Read More
  • Pipe Report

    ... Introduction: In any pipe system there is going to be a loss of energy due to the effect of viscosity from a fluid acting upon the surface of the pipe, this is called Friction Loss. This type of lost depends on the shear stress due to the walls of the pipe and the fluid. It also depends in weather the fluid is laminar or turbulent. A major ...

    Read More
  • Fluid Dynamics: Flow in Closed Conduits

    ...Flow Smooth Pipe Law Rough Pipe Law Different Workers Results Application    Energy/ pressure loss problem Velocity/ flow rate problem Pipe Sizing Problem • Explicit Equation for Friction Factor CN2122 / CN2122E Main Topics    • • • Equivalent Diameter for Non- Circular Conduit Pressure Drop due to F...

    Read More
  • Fluid Dynamics and Wind Tunnels

    ...Definition of Aerodynamics: a branch of dynamics that deals with the motion of air and other gaseous fluids and with the forces acting on bodies in motion relative to such fluids http://www.merriam-webster.com/dictionary/aerodynamics Other: aerios, concerning the air, and dynamis, which means force. http://www.grc.nasa.gov/WWW/K-12/airp...

    Read More
  • computational fluid dynamics

    ...th th Proceedings of the 37th National & 4th International Conference on Fluid Mechanics and Fluid Power Proceedings of the 37 International &16-18, 2010, IIT Madras, Chennai, India. 4 National Conference on Fluid December Mechanics and Fluid Power FMFP10 - TM - 08 FMFP2010 December 16-18, 2010, IIT Madras, Chennai, India FMF...

    Read More

Discover the Best Free Essays on StudyMode

Conquer writer's block once and for all.

High Quality Essays

Our library contains thousands of carefully selected free research papers and essays.

Popular Topics

No matter the topic you're researching, chances are we have it covered.