The Cooling Airflow of Heavy Trucks - a Parametric Study Thomas Hällqvist, Scania CV AB Company Logo

2 Introduction  Study of the influence on the cooling airflow from various installation parameters on a Heavy duty truck.  Analysis performed by means of 3D CFD.  The focus of the paper is on the system pressure loss, flow distribution and cooling capacity

3 Physical Model  Complete 2-axle tractor.  Air enters in the front via mesh screens.  Cooling package includes:  Condensor  Oil cooler  EGR cooler  CAC cooler  Radiator Pictures show the surface mesh

4 Physical Model  Fan diameter of 750 mm (default).  Fan placement depends on engine type.  Both V8 and inline six engines are considered.  High level of details in the engine compartment. Pictures show the surface mesh

5 Simulation Technique  3D isothermal CFD simulation.  LBM solver by EXA corp.  Coupling to 2D heat exchanger calculation.  Fan modeled via MRF.  Heat exchangers and mesh screens modeled as porous media

6 Model Size and Accuracy  Statistical convergence within <1 %.  Absolute accuracy within 6 % for massflow (rel. MP).  40-50·10 6 volume elements.  Simulated on 128 cpu’s Linux cluster.  Total runtime of approx h data sampling interval MP: Micro Probe measurements

7 General Boundary Conditions  Virtual windtunnel with moving ground.  Windspeed of 30 km/h.  Ambient temperature of 25°C.  Fan speed of 1700 rpm. inlet outlet L = 170 m W = 60 m H = 45 m

8 Parameter Variations  Front opening area.  Fan-to-radiator spacing.  Fan-to-engine spacing.  Width of cooling module.  Fan diameter.  Fan projection into shroud.

9 Results  Study of the impact from various parameter settings on:  the flow character,  the total pressure loss,  the flow distribution through the radiator,  the cooling capacity

10 Results: general flow character  The underhood includes different subsystems.  Subsystems installed in serial or in parallel.  The fan shroud has large influence on the pressure loss.  All subsystems, but the HX’s, must be optimized w.r.t dP.  A HX with large dP generally comes with large heat transfer capacity. Fan shroud Cooling pacakge RAD

11 Results: general flow character  Airflow enters via the front.  Static pressure decreases until the fan, where the pressure is build up to P amb + dP rear underhood.  Three main flow directions below the cab.  Flow also underneath the engine.

12 Results: general flow character  V8: fan in high position  S6: fan in low position  Fan placement and engine type influences the flow distribution.  V8: Fan on top of crossmember.  S6: Fan in front of crossmember.  Strong influence on dP below the engine. V8 setup Inline-six setup (S6) V8 setup Inline-six setup

13 Results: fan-to-radiator spacing V8 setup Inline-six setup  Fan shrouds with different depths tested.  Default setup V8 has a deeper shroud.  dx more critical for S6-cases.  At same depth the V8 setup features higher dP tot than S6. Case REF*

14 Results: fan-to-radiator spacing  dx also influences the flow distribution.  So also the shape of the shroud.  Bad uniformity for RAD  higher dP RAD. V8 setup

15 Results: fan diameter / width of RAD  The geometrical shape of the fan shroud influences the flow distribution.  A wide cooler gives low flow rates in the outer regions.  A larger fan improves the uniformity.  A larger fan can geometrically be compared to a deeper fan shroud. V8 default case setup 20 % wider cooling package 20 % larger fan uniformity = 0.87 (Case NF) uniformity = 0.88 uniformity = 0.91

16 Results: fan projection into shroud  FPiS determines the flow direction behind the fan.  FPiS should be tuned for each specific installation.  Large FPiS  axial fan behavior, high dP for large engine silhouette.  Small FPiS  radial fan behavior, high rates of leak flows.  The smaller fan-tip to fan-ring spacing the smaller FPiS is possible. axial fan behavior leak flows

17 Results: cooling performance (1/CC) Influence from flow uniformity Influence from massflow  The flow uniformity has some effect on the cooling performance.  The character of the flow distribution is also relevant.  Within the present interval the cooling performance has a linear relation to the massflow.  The non-uniform and the uniform flow show the same trends. non-uniform flow uniform flow

18 Conclusions  The underhood involves several subsystems.  The design of the fan shroud is crucial.  The flow distribution is important w.r.t. to dP.  For the cooling performance the massflow is of main importance, uniformity of less.

19 Future Work  Additional parameter settings.  Extend the study w.r.t. fan configuration.  Study the effect from fan modeling.  Extend the thermodynamic analysis.