comparison between three different cfd software and numerical simulation of an ambulance hall

66 Pages·2015·7.98 MB·English

by  Your User Name

COMPARISON BETWEEN THREE
DIFFERENT CFD SOFTWARE AND
NUMERICAL SIMULATION OF AN
AMBULANCE HALL

Ning Li

Master of Science Thesis
KTH School of Industrial Engineering and Management
Energy Technology EGI-2015-017MSC
Division of Energy Technology
SE-100 44 STOCKHOLM

I
Master of Science Thesis EGI 2015: 017MSC

Comparison between three different CFD
software and numerical simulation of an
ambulance hall

Ning Li
Approved Examiner Supervisor
2015-03-05 Joachim Claesson Joachim Claesson
Commissioner Contact person
SWECO Systems AB David Burman
Liu Ting
Abstract
Ambulance hall is a significant station during emergency treatment. Patients need to be transferred from
ambulance cars to the hospital’s building in the hall. Eligible performance of ventilation system to supply
satisfied thermal comfort and healthy indoor air quality is very important. Computational fluid dynamic
(CFD) simulation as a broadly applied technology for predicting fluid flow distribution has been
implemented in this project.
There has two objectives for the project. The first objective is to make comparison between the three
CFD software which consists of ANSYS Fluent, Star-CCM+ and IESVE Mcroflo according to CFD
modeling of the baseline model. And the second objective is to build CFD modeling for cases with
difference boundary conditions to verify the designed ventilation system performance of the ambulance
hall.
In terms of simulation results from the three baseline models, ANSYS Fluent is conclusively
recommended for CFD modeling of complicated indoor fluid environment compared with Star-CCM+
and IESVE Microflo. Regarding to the second objective, simulation results of case 2 and case 3 have
shown the designed ventilation system for the ambulance hall satisfied thermal comfort level which
regulated by ASHRAE standard with closed gates. Nevertheless, threshold limit value of the contaminants
concentration which regulated by ASHRAE IAQ Standard cannot be achieved. From simulation results of
case 4.1 to 4.3 shown that the designed ventilation system cannot satisfy indoor thermal comfort level
when the gates of the ambulance hall opened in winter. In conclusion, measures for decreasing
contaminants concentration and increasing indoor air temperature demanded to be considered in further
design.

-II-
Table of Contents
Abstract .......................................................................................................................................................................... II
Acknowledgements ...................................................................................................................................................... V
List of Figures ............................................................................................................................................................. VI
List of Tables ............................................................................................................................................................ VIII
Nomenclature.............................................................................................................................................................. IX
1 Introduction .......................................................................................................................................................... 1
1.1 Background .................................................................................................................................................. 1
1.2 Objectives ..................................................................................................................................................... 2
1.3 Method .......................................................................................................................................................... 3
2 Numerical principle of simulation ..................................................................................................................... 4
2.1 Governing Equations ................................................................................................................................. 4
2.1.1 Conservation laws of fluid flow. ...................................................................................................... 4
2.1.2 Thermal equations of wall boundary condition. ........................................................................... 4
2.2 Turbulence modeling .................................................................................................................................. 5
2.2.1 Different choice of k-ε Model ......................................................................................................... 5
2.2.2 Near – Wall functions ....................................................................................................................... 7
2.3 Meshing ........................................................................................................................................................ 8
2.3.1 Shapes of Cell ..................................................................................................................................... 8
2.3.2 Classification of Grids ....................................................................................................................... 8
2.3.3 Mesh Quality ....................................................................................................................................... 9
2.4 Solver...........................................................................................................................................................10
2.4.1 Finite Volume Method ....................................................................................................................10
2.4.2 Upwind scheme ................................................................................................................................11
2.4.3 SIMPLE Scheme ..............................................................................................................................11
3 Baseline model and Comparison between Software ....................................................................................13
3.1 Data of ventilation system for baseline model. ....................................................................................13
3.1.1 Design Concept ................................................................................................................................13
3.1.2 Parameter of supply air diffuser ....................................................................................................13
3.1.3 Parameter of Exhaust Grilles .........................................................................................................13
3.2 Geometry ....................................................................................................................................................14
3.3 Meshing ......................................................................................................................................................15
3.3.1 Meshing Independency ...................................................................................................................15
3.3.2 Meshing Method ..............................................................................................................................17
3.4 Numerical Setup ........................................................................................................................................19
3.4.1 Selection of simulation models ......................................................................................................19
3.4.2 Boundary conditions .......................................................................................................................19
-III-
3.4.3 Solution Control ...............................................................................................................................21
3.5 Simulation results ......................................................................................................................................23
3.5.1 Assessment of thermal comfort in an arbitrary point. ...............................................................23
3.5.2 Velocity Distribution .......................................................................................................................24
3.5.3 Temperature Distribution ...............................................................................................................28
4 Ventilation Performance in Different Situations ..........................................................................................33
4.1 Geometry ....................................................................................................................................................33
4.1.1 Case 2: Improved ventilation system. ...........................................................................................33
4.1.2 Case 3: Polluted emission from tailpipes of the ambulance cars. ............................................34
4.1.3 Case 4.1-4.3: With opened gates and installed air curtains. .......................................................34
4.2 Meshing ......................................................................................................................................................36
4.3 Boundary Conditions Setup ....................................................................................................................36
4.3.1 Case 2: Improved ventilation system. ...........................................................................................36
4.3.2 Case 3: Polluted emission from tailpipes of the ambulance cars. ............................................36
4.3.3 Case 4.1-4.3: With opened gates and installed air curtains. .......................................................37
4.4 Simulation Results and Analysis. ............................................................................................................38
4.4.1 Case 2: Improved ventilation system. ...........................................................................................38
4.4.2 Case 3: Polluted emission from tailpipes of the ambulance cars. ............................................40
4.4.3 Case 4.1-4.3: With opened gates and installed air curtains. .......................................................43
4.5 Optimized approaches for improving thermal comfort. ....................................................................48
4.5.1 One more supply air diffuser on the specified wall. ...................................................................48
4.5.2 Exhaust extraction system. .............................................................................................................49
4.5.3 Supplement of heat in winter. ........................................................................................................49
5 Conclusion and future improvement ..............................................................................................................51
6 Bibliography ........................................................................................................................................................52
Appendix A: Data sheet/Dimension of Jet Nozzle Diffuser ..............................................................................54
Appendix B: Data and Dimension of Exhaust Grilles ..........................................................................................55
Appendix C: Data and Type of Air curtain. ............................................................................................................56
Appendix D: CO Level vs. Condition&Health Effects. .......................................................................................57

-IV-
Acknowledgements
Foremost I would like to express my fully gratitude to Will Sibia from SWECO systems AB, Stockholm
Sweden for giving me the opportunity to do my master thesis within such interesting and cutting edge
field by a practical project.
Specially, I would like to extend my deepest thanks to Liu Ting, who is my thesis supervisor from
SWECO in the field of CFD simulation. Encouragements, professional and theoretical supports from her
were very beneficial and helpful for me to complete the project.
Sincerely, I would also very thankful to David Berman, who is my thesis supervisor from SWECO in the
field of energy technology and ventilation systems design. Professional advices and positive feedbacks
from him supervised me done the project in the right way.
Moreover, I would like to express my grate gratitude to my supervisor, Associate Professor Joachim
Claesson, at the Royal Institute of Technology (KTH) for your fully helpful supports, responsible
feedback and all the fantastic knowledge were taught from you during the graduate study.
Finally, I am deep appreciate to my parents, my friends for their love and supports.

-V-
List of Figures
Figure 1, 3D layout of SÖS ambulance hall. ..................................................................................................................... 1
Figure 2, Project Outline .................................................................................................................................................... 2
Figure 3, Velocity distribution near a wall (Versteeg & Malalasekera, 2007) ............................................................... 7
Figure 4, Typical 2D control volume (Versteeg & Malalasekera, 2007). ....................................................................... 8
Figure 5, Block-structured mesh (left) and Unstructured mesh (right) of aerofoil (Versteeg & Malalasekera, 2007) ........ 8
Figure 6, Comparison between coarse, medium and fine hybrid grid. .................................................................................... 9
Figure 7, Misalignment of midpoints for skewed grid. ......................................................................................................... 9
Figure 8, Conservation of general flow variable within finite volume method (Versteeg & Malalasekera, 2007).............10
Figure 9, Evaluation of face value according to Upwind Scheme (Cho, et al., 2010). ......................................................11
Figure 10, Calculation process of SIMPLE Scheme (Versteeg & Malalasekera, 2007)...............................................12
Figure 11, Air motion of Group A outlets (ASHRAE, 1997). ......................................................................................13
Figure 12, Geometry of the ambulance hall .......................................................................................................................14
Figure 13， Face sizing for air inlet (Left: Element size is 0.05m; Right: Element size is 0.03m) ..................................15
Figure 14, Face sizing for air outlet (Left: Element size is 0.1m; Right: Element size is 0.05m) ......................................16
Figure 15, Velocity distribution for the two different meshing cases. ...................................................................................16
Figure 16, Generated mesh of the ambulance hall in IESVE Microflo. ...........................................................................17
Figure 17, Generated mesh of the ambulance hall in ANSYS mesh. ................................................................................17
Figure 18, Section plane of (a) Air Inlet; (b) Air Outlet; (c) Exterior Wall; (d) Internal space ........................................18
Figure 19, Mesh metrics control of ANSYS mesh (Left: Skewness; Right: Aspect Ratio) ................................................18
Figure 20, Cell Monitor of point in Case 1.3. ..................................................................................................................23
Figure 21, PPD as a function of PMV (ISO, 1994). ....................................................................................................23
Figure 22, Thermal comfort zone display in Psychronmetric chart. ....................................................................................24
Figure 23, Vector of velocity distribution (h=3m) of case 1.1. ..........................................................................................25
Figure 24, Velocity Magnitude (h=3m) of case 1.1. (Left: 0 to 5.02m/s, Right: 0 to 1 m/s) ..........................................25
Figure 25, Vector of Velocity distribution (h=1m) of case 1.1. ........................................................................................25
Figure 26, Zoomed-in views of velocity distribution at plant (h=1m).s ..............................................................................26
Figure 27, Vector of velocity distribution (h=3m) of case 1.2. ..........................................................................................26
Figure 28, Vector of velocity distribution (h=1m) of case 1.2. ..........................................................................................27
Figure 29, Vector and contour of velocity distribution (h=3m and h=1m) of case 1.3. ......................................................27
Figure 30, Local mean age of air (h=1m) of case 1.3. ......................................................................................................28
Figure 31, Temperature distribution (h=1m, local temperature). .......................................................................................29
Figure 32, Temperature distribution (h=1m, specified temperature). .................................................................................29
Figure 33, Temperature distribution (h=1m, global temperature) with isosurface. ..............................................................30
Figure 34, Temperature distribution (Left: x=3.6m, 11m and 18.3m; Right: y=10.3m, 15.5m and 21m). ...................30
Figure 35, Temperature distribution on envelop of ambulance hall.....................................................................................30
Figure 36, Temperature distribution of case 1.2. ...............................................................................................................31
Figure 37, Temperature distribution of case 1.3. ...............................................................................................................32
Figure 38, Geometry of case 2 with 4 exhaust grilles. .......................................................................................................33
Figure 39, Geometry of case 3 with tailpipe emission (Left: whole room; Right: zoomed-in to the tailpipe) .........................34
Figure 40, Configuration of air curtain which installed in case 4.1-4.3. ............................................................................34
Figure 41, Geometry of case 4.1 - 4.3. .............................................................................................................................35
Figure 42, Zoomed-in views of geometry for case 4.1-4.3. ..................................................................................................35
Figure 43, Meshing of case 4.1-4.3 (Left: Global: Right: Section cut view). ......................................................................36
Figure 44, Velocity distribution at h=3m over the ground (Local Velocity). .....................................................................38
Figure 45, Velocity distribution at h=1m (Local Velocity). .............................................................................................38
Figure 46, Zoomed-in views to figure 45. ..........................................................................................................................39
Figure 47, Temperature distribution of case 2 at h=1m (Left: local temperature, Right: Specified temperature). ................39
Figure 48, Temperature distribution of case 2 (Left: h=0.1m, isosurface=18C; Right: Room Envelope). .........................40
Figure 49, Velocity distribution of case 3 (Left: h=3m; Right: h=0.4m) .........................................................................40
-VI-
Figure 50, Velocity distribution of case 3 (h=1m). ...........................................................................................................41
Figure 51, Temperature distribution of case 3 h=0.4m (Left: Local temperature; Right: specified temperature) .................41
Figure 52, Temperature distribution of case 3 at h=1m (Specified Temperature). ..............................................................42
Figure 53, CO concentration distribution of case 3 (h=1.5m). ..........................................................................................42
Figure 54, CO2 concentration distribution of case 3 (h=1.5m). .......................................................................................43
Figure 55, Velocity distribution of case 4.1 (h=1m) .........................................................................................................44
Figure 56, Specified velocity of case 4.1 at h=1m (Left: Velocity 0m/s - 0.2m/s; Right: Velocity 0m/s - 1m/s). ...........44
Figure 57, Velocity distribution of case 4.1 around the opened gates. ................................................................................45
Figure 58, Temperature distribution of case 4.1 (Left=3m; Right=1m). ..........................................................................45
Figure 59, Temperature distribution of case 4.1 (Transection view at gate). .......................................................................46
Figure 60, Pressure distribution at h=1m of case 4.2(Left) and case 4.3 (Right). .............................................................46
Figure 61, Pressure change along the line of case 4.2(red line) and case 4.3 (blue line). ......................................................46
Figure 62, Velocity distribution at h=1m of case 4.2(Left) and case 4.3 (Right). .............................................................47
Figure 63，Zoomed-in Velocity distribution at h=1m of case 4.2(Left) and case 4.3 (Right). .........................................47
Figure 64, Temperature distribution at h=1m of case 4.2(Left) and case 4.3 (Right). ......................................................48
Figure 65, Install position of the additional supply air diffuser. .........................................................................................48
Figure 66, Conventional exhaust extraction system (Left) and "in ground" exhaust extraction system (Right). ..................49
Figure 67, Working principle of "in ground" exhaust extraction system (Nenerman, 2014). .........................................49

-VII-
List of Tables
Table 1, Cade name of different cases.................................................................................................................................. 2
Table 2, Skewness range and cell quality (Fluent, 2006). ...............................................................................................10
Table 3, Input dimensions of geometry of the ambulance hall. ............................................................................................14
Table 4, Performance of 3D modeling for different tools. ...................................................................................................15
Table 5, Comparison of Mass flow rate and Total heat transfer rate between the two meshing cases .........16
Table 6, Statistics of mesh which generated from ANSYS mesh and IES VE – CFD Grid. .........................................18
Table 7, Performance of meshing for the three software. .....................................................................................................18
Table 8, Boundary Conditions set up in ANSYS Fluent and Star - CCM+. .................................................................20
Table 9, Solution control for the three software. .................................................................................................................22
Table 10, Performance of numerical setup for the three software. ........................................................................................22
Table 11, Thermal sensation scale for PMV Method. ......................................................................................................23
Table 12, Simulation results of the three software. ............................................................................................................32
Table 13, Different between the two types of exhaust grilles in two cases. ...........................................................................33
Table 14, Additional parameters of geometry for case 4.1 to 4.3. ......................................................................................34
Table 15, Input parameters for boundary conditions of tailpipes. .......................................................................................37
Table 16, Air curtain boundary conditions of case 4.1-4.3. ..............................................................................................37

-VIII-
Nomenclature
Symbols
A area
Cp specific heat
C contaminant concentration
i
C k-epsilon model constant
u
g gravitational constant
h external heat transfer coefficient
ext
h heat transfer coefficient of the fluid side
f
I tensor of unit
k thermal conductivity
P pressure
Q heat transfer rate
S source of mass
m
T Temperature
t time
u velocity
V volumetric flow rate
y+ dimensionless wall distance
 dissipation rate of k
 emissivity
ext
k turbulence kinetic energy
 Stefan-Boltzmann constant
 laminar Prandtl number
T,l
 turbulent Prandtl number
T,t
Φ flow variable
 under-relaxation factor
 near-wall temperature equation constant
ρ density
Ω rate-of-rotation tensor
ij
 local mean age of air
i
stress tensor

 viscosity of molecular
Abbreviations
CFD Computational Fluid Dynamic
FVM Finite Volume Method
LMA Local Mean Age
PMV Predicted Mean Vote
PPD Percentage of Dissatisfied
RNG Re-Normalization Group
SIMPLE Semi-Implicit Method for Pressure-Linked Equations

-IX-
1 Introduction
1.1 Background
Numerical visualization is a platform provides a simpler way to analysis of large, complex and muti-
dimensional information. Computational fluid dynamic, also called CFD, has combined fluid mechanic
with this platform to simulate both compressible and incompressible fluid flow behavior. Distribution of
temperature, velocity, pressure, contaminant concentration and other fluid properties can be calculated
and displayed from results of CFD simulation (Stamou, et al., 2007). Output results help engineers to
improve and consummate their design quickly and effectively.
In this project, three different CFD commercial software have been employed by the author to evaluate
indoor thermal comfort of an ambulance hall which is belong to SÖS hospital renovation project from
SWECO, in Stockholm, Sweden. As defined by international standard ISO 7730, thermal comfort as
“condition of mind which expresses satisfaction of thermal environment” has explained that comfort level
need to be determined by subject method (ISO, 1994). According to the criteria ISO 7730, metabolic rate
(MET) and thermal insulation of clothing index (CLO) will be introduced for obtain thermal comfort
indexes which are predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) (ISO, 1994).
The three different CFD commercial software consist of ANSYS - Fluent, IES VE – Microflo and Star –
CCM+. Internal analyses of the ambulance hall were established by the three tools for baseline case.
Thereafter, three additional modeling cases which include improvement of ventilation system, hall with
tailpipe emissions and opened gates with natural ventilation were implemented by ANSYS – Fluent
independently.

Figure 1, 3D layout of SÖS ambulance hall.
Ambulance hall is a significant station during emergency treatment. Patients need to be transferred from
ambulance cars to the hospital’s building in the hall. High performance of ventilation system which supply
fresh and comfortable indoor environment is required to achieve.
As shown in Figure 1, during peak operation condition there has 8 ambulance cars parking in the hall.
Consider walls of the ambulance hall, 2 exterior wall are exposed directly to ambient environment and 2
interior walls are connected to internal corridors. For sake of simplifying the model and emphasize
performance of fluid flow within the main hall, interior rooms and internal corridors will be removed in
further 3D modeling.

1