CFD analysis of external aerodynamic and

entry into to the air conditioning system

on the roof of a bus

Samuel Diaz – ESSS Argentina

Samuel.diaz@esss.com.ar

PRESENTATION TOPICS

• Company Overview;

• Problem Description;

• Goals;

• Methodology;

• Conclusion.

COMPANY OVERVIEW

THE ANSYS CHANNEL PARTNER FOR SOUTH AMERICA

ANSYS GLOBAL PRESENCE

• 1.600 employees

• 60+ sales offices on 3 continents

• Network of sales channel partners in 40 countries

COMPANY OVERVIEW

Brazil • Florianópolis

• São Paulo

• Rio de Janeiro

• Caxias do Sul

Argentina • Córdoba

Colombia • Bogota

Peru • Lima

USA • Houston

an ESSS and EnginSoft Partnership

Chile • Santiago

19 YEARS OF EXPERIENCE Since 1995 providing the most comprehensive

simulation solutions to the market

WHAT WE DO? • Reduce product development time

• Optimize processes

• Improve product performance

TEAM PROFILE High-quality services and support to customers

LOCATIONS

COMPANY OVERVIEW

TECHNICAL SUPPORT • Phone

• E-mail

• Online

• On-site

CONSULTING SERVICES • Modeling activities (R&D)

• Troubleshooting

• Integration of technologies

• Value-added services

CUSTOM DEVELOPMENT • Design of new applications

• Multiplatform GUI

• Numerical methods

• Parallel processing

• Scientific visualization

ACADEMIC PROGRAM • Student / Academic & Research

• Affordable prices

• Great flexibility

• Partnership program

TRAINING • 60+ training courses

• Postgraduate courses

• Online courses

• 900+ attendees per year

SOFTWARE • ANSYS

• modeFRONTIER

• EnSight

• VCollab

• KRAKEN

• Chimera

PROBLEM DESCRIPTION

In order to get a good air conditioning

condenser performance is very important to

have a proper flow pattern and a slow air in the

condenser inlet region. Furthermore, the hot

gases from exhaust system don’t have to be

absorbed by the air conditioner.

CFD analyses have been done in order to

compare the air flow over the region near the

air conditioning condenser for two different

configurations of the roof and for two

different bus velocities.

GOALS

• Air flow analysis over the roof of the Bus;

• Investigate the air flow over the region near the air

conditioning condenser;

• Compare two different configurations of the roof near

the opening on the rear;

• Study the behavior of the exhaust gases near the

condenser.

CASES

4 (four) steady state simulations:

• Case 1: The original geometry of the bus

into a stream of air of 100 km/h.

• Case 2: The same conditions of the Case

1 but with a geometry of the roof modified.

• Case 3 & 4: Simulation of the rear of the roof with exhaust gases and bus

stopped for both geometries.

METHODOLOGY

Original Geometry

Simplified Geometry

• The geometry has been simplified in any parts

where the shape will not affect the results of the

analysis. The shape of the roof has remained

exactly the same geometry.

METHODOLOGY

Original Geometry

Internal Flow

Simplified Geometry

The radiator is modeled as a porous zone with a

heat source and the fans with rotating domains.

Radiator Fans

Porous Zone

Fan’s

Rotating

Domains

METHODOLOGY

ANSYS TGrid Wrapper Surface Mesh

ANSYS ICEM-CFD Volumetric Mesh

Boundary Layer

ANSYS Meshing for both Surface and

Volumetric Mesh

METHODOLOGY

METHODOLOGY

Condenser Inlet

Inlet:

Velocity = 100 km/h (case 1 & 2)

Velocity = 0 km/h (case 3 & 4)

Bus Walls (No-slip condition):

Adiabatic walls

Operation Conditions:

Pressure = 1 atm

Temperature = 43 ºC

Floor (Free slip condition)

Outlet (all other zones):

Pressure outlet Gauge Pressure = 0 Pa

Exhaust (Hot Air):

Case 1 & 2:

Flow: 12,8 kg/min

Temp.: 600 ºC

Case 3 & 4:

Flow: 3,8 kg/min

Temp.: 350 ºC

METHODOLOGY

Condenser Inlet

(grille modeled like a pressure drop)

Condenser Outlet

(grille modeled like

a pressure drop)

Radiator (Porous Zone):

Heat Source: 108000 BTU/hr

Fans (Rotating Domains):

Speed: 1920 rpm

RESULTS

Recirculation

CASE 1:

RESULTS

CASE 2:

Strong

recirculation

RESULTS

Condenser Inlet

RESULTS

180ºC Iso-surface 120ºC Iso-surface 60ºC Iso-surface

180ºC Iso-surface 120ºC Iso-surface 60ºC Iso-surface

CASE 3:

CASE 4:

RESULTS

Condenser Inlet

The combustion gases

absorbed by the condenser

generate higher temperatures

in this corner

CONCLUSION

• Case 1 & 2 (both 100 kph)

Air flow at the rear of the bus roof was resolved in detail.

Significant flow pattern differences were observed as the roof

fairing defined the velocity field near the condenser inlet.

Condenser volumetric flow for Case 1 (with fairing) is 52%

higher in comparison with Case 2 (without fairing).

The roof fairing in Case 1 reduces the air speed in the

condenser inlet region, creating a favorable stagnation region

allowing the condenser fans to work properly.

• Case 3 & 4 (both bus stopped)

In the roof without fairing, the condenser absorbs part of the hot

combustion gases, increasing the temperature in condenser

inlet and decreasing its performance. This problem is not

observed in the roof fairing because the plume generated by

exhaust does not interact with the condenser.

Condenser volumetric flow for both cases are similar, the

difference between them is less than 5%.

CONCLUSION

Thank you for your attention !!

Questions?

Ing. Samuel Diaz CAE Division – CFD Specialist

samuel.diaz@esss.com.ar