My thesis project was undertaken in

collaboration with Reynard Racing Cars for

the development of the Reynard Inverter, a

trackday race car designed by André Brown

and Adrian Reynard. Following a significant

modification to the bodywork, consisting

of the relocation of the radiator from the

sidepods to the nosecone, a CFD analysis

was requested. This would evaluate the

effectiveness of the new configuration, and

would identify any issues that may have

emerged as a result of these modifications.

It would also highlight any investigation

routes that could lead to a further

improvement of the cooling performance

of the radiator.

LIMITATIONS

As is the case with every engineering

problem, before commencing the proposal

of possible solutions or investigation routes

(for the design of the radiator duct in this

case), we must acknowledge the

limitations imposed (in this case due to

the positioning of the race car’s crush

structure in the nosecone). As such, it was

thought that a possible alteration to the

design of the intake might incur a

deterioration in the crush performance of

the Inverter. Given that the safety of the

driver is of greater importance than the

reliable operation of the engine unit, it

was decided not to investigate

modifications to the intake (despite its

considerable importance for the cooling

flow) but rather focus all modifications on

the duct exit, which in any case is a well-

established method of influencing the

cooling flow through the radiator core.

SIMULATIONS

The steps that were taken for each CFD

simulation were pretty much standard; they

started with the modification of the design

in a CAD package, continued with the

meshing of the flow domain in an

appropriate package (Gambit), the import

and solution of the flow in a CFD solver

(Fluent) and finally the visualisation and the

quantification of the cooling flow in a CFD

post-processor (FieldView).

The inherent symmetry of the race car was

taken advantage of in the CFD simulations,

as only the half-car was used for the

requirements of the analysis. Doing this

reduced the computational time

significantly, while at the same time the

accuracy of the solution was not expected

to be significantly influenced.

The comparison between the various

design modifications was made in terms of

the cooling flow (air mass flow) that is

drawn through the radiator duct at a

reference speed of 30 m.s-1. FieldView offers

the opportunity to create your own

equations in order to define magnitudes

AT THE MENTION of motorsport,

we tend to think of race cars

equipped with powerful engines

and a number of elaborately designed

aerodynamic elements. However, these on

their own would not allow a driver to win a

race unless reliability issues that are related

to their operation are dealt with.

The reliable operation of an engine unit

is intimately connected to the efficiency

of the radiator unit, which ensures the

dissipation of heat from the engine

coolant through a heat transfer process

with ambient air. The potential of a

radiator to dissipate heat is largely

determined by the air mass flow through

the radiator duct. Knowledge about the

cooling flow through the radiator is of

paramount importance, as a radiator that

fails to sufficiently reduce the

temperature of the coolant will result in

engine overheating.

June 201172 www.racetechmag.com

CASE STUDY RADIATOR EFFICIENCYwww.racetechmag.com

72

When Reynard Racing Cars relocated the radiator

of its Inverter from the sidepods to the nosecone, it

offered Cranfield motorsport MSc student Andrew

Raptis the ideal chance to study radiator efficiency

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A COOLSOLUTION

ABOVE The crush structure in theInverter's nosecone was a limitingfactor in the relocation of the radiator

CASE STUDYwww.racetechmag.com

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73

that are dependent on more than one parameter. This allowed us

to obtain a direct comparison of the cooling flow that is channeled

through the duct for each design.

DESIGN IMPROVEMENTS

One of the main objectives of the study was to increase the cooling

flow that was drawn through the radiator duct. As mentioned, it was

decided not to make any changes to the duct intake, but rather the

modifications would focus on the alteration of the duct exit. The fact

that the duct exit may affect the amount of air that is drawn through

the intake may seem a paradox, however, we must not overlook the

fact that the conservation of mass dictates that the air mass that exits

the duct is equal to the mass entering it. Thus, by identifying ways of

improving the exit of the flow from the duct, we can expect to gain

an increase of mass flow at the intake, and as such through the

radiator. In order to achieve this goal it was vital to conduct an initial

CFD simulation of the current design of the radiator duct and try to

determine whether there are any weak points in it.

The current design of the radiator duct comprises a single region

behind the radiator core, through which the flow is channeled to the

upper region of the Inverter’s bodywork. Following a CFD simulation

of this configuration, it became evident that there was scope for

improvement as the angle between the normal vector to the duct exit

and the flow velocity at the exit is large. As such the effective duct

exit area that is “visible” to the flow is small, which means that the

amount of air that can exit the duct is small. Based on the

conservation of mass in the duct we concluded that this results in a

low cooling flow at the duct intake.

The solution therefore needed to essentially increase the “visible”

to the flow area, which we aimed to achieve through the use of a

secondary face in the nozzle which would collect the flow

departing the radiator core and guide it towards the exit at a

more favourable angle. It was obvious that the incorporation of an

additional solid element in the flow would deprive the flow of

momentum, but we anticipated that the gains made would more

than compensate.

Further to the secondary face, this design presents two

deflectors intended at shielding the two channels of the cooling

flow from each other and from the external air flow, as can be

seen in the cross-section of the radiator duct design. This image

also depicts the streamlines at the exit of the duct.

Our results offered a considerable increase in the cooling flow, as is

evident in the above images from a face at the duct intake.

An equation defined in FieldView (“mass flow per area unit

function”) is used in the top

image and the considerably

deeper colour of the face at

the duct intake for the

proposed modification (above)

is indicative of the cooling

flow increase. By probing the

values of the function at the

points of a 5x5 grid at the

presented face, the simulation

indicates that the proposed

modification produces an

BELOW A cross-section of theInverter’s radiator duct design

BELOW The proposeddesign modification

ABOVE & BELOW Mass flowper area unit at the duct intakefor the current design (above)and the proposed modification

BELOW The cross-sectionof the proposed design

June 201174 www.racetechmag.com

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increase in the cooling flow by 31.18%,

which will assist the reliable operation of the

engine in warmer environments and

provides scope for a possible incorporation

of a larger engine unit than the one currently

installed on the Inverter.

DUCT INTAKE RESTRICTION

A further result of the research was a

proposal for the radiator duct exit aimed at

reducing the cooling flow through the duct.

Based on our previous rationale, where by

increasing the effective area that is visible to

the flow we increased the cooling flow, we

then looked into ways of reducing the duct

exit area, while diverting the majority of the

cooling flow away from the engine intake

(which is located aft of the radiator duct).

The proposed solution, according to the

CFD simulations undertaken, allows a

similar amount of cooling flow through the

duct as in the case of a 10 mm duct-tape

strip blocking the duct intake, while at the

same time ensures a more efficient

performance of the radiator from an

aerodynamic point of view.

Never visible, but crucial to the

performance of the race car, the cooling

system ensures that the engine neither

overheats (a situation that could result in

reliability issues) nor runs cold (in which

case it will be inefficient). It is therefore vital

to tailor the cooling flow through the

radiator both to the environmental

conditions and to the heat that has to be

dissipated from the engine. As was

demonstrated, a very elegant and cost-

effective way of doing this and of

investigating further development routes is

through the use of CFD, which offers

enormous potential to amateur and

professional motorsport devotees alike.

• The supervision of this project was

undertaken by Dr James Njuguna,

programme director for the MSc Motorsport

Engineering and Management course at

Cranfield University, and André Brown,

technical director at Reynard Racing Cars.

RT

BELOW Flow recirculationbehind the duct-tape

BELOW The proposed design forthe restriction of the cooling flow