1. Mark Claywell & Donald Horkheimer University of Minnesota
Improvement of Intake Restrictor Performance for a Formula SAE Race Car through 1D & Coupled 1D/3D Analysis Methods
Mark Claywell & Donald Horkheimer University of Minnesota

2. Agenda Background 1D Simulation Setup & Results
Coupled 1D/3D Simulation Setup & Results
Volumetric Efficiency
Flow measurements- Mach Number, Turbulent Kinetic Energy, & Total Pressure
Acoustic Filtering for Volumetric Efficiency
Flow Control
Conclusions

3. Background Overall Goal: Reduce the impact of the restrictor on VE
Achieve a better understanding of flow in different restrictors
Look for areas to reduce flow losses
Ricardo WAVE 1D model used with acoustic quality mesh in intake manifold
Multiple iterations quickly solved
Poor modeling of flow losses in diffuser section
Tuning impact of restrictor
Ricardo WAVE coupled with Ricardo VECTIS (CFD) to model full intake
More accurate losses in diffuser
No need for end corrections at runner to plenum junctions
Very long run times = fewer design iterations

4. Description of Intake Manifold Geometry
Diffuser
Half-Angle
Diffuser
Volume
Plenum
Total Volume =
Plenum + Diffuser Volume
Total
Height
Plenum Height
Diffuser Height
Diffuser Exit
Diameter

5. Case 1: Same Plenum Used
Difficult to get a clear trend of how diffuser angle affects tuning
Large changes in tuning across the rev range
Both total length and total volume are changing

6. Standing Waves - Case 1 14,000 RPM 11,000 RPM 4° 2nd Order 4th Order7°

7. Case 2: Equal Diffuser Lengths
NOTES:
1. dx=5mm for tubes, volume mesh = 15mm.
Diffuser length had large impact on tuning
Total volume had little impact on tuning
VE did not increase with increasing total volume

8. WAVE-VECTIS Setup Assumptions
WAVE-VECTIS junctions placed near 1D flow areas
No throttle body
No fuel spray particles in CFD domain
k-ε turbulence model
Full intake modeled for each diffuser change
Iterations in WAVE-VECTIS same as Case1 – Same Plenum Used
Inlet Box

9. VECTIS – Mesh Details
3.5mm
1.75mm
~ 600,000+ cells

10. Theoretical Maximum Volumetric Efficiency Through a Restrictor Orifice
Implicit Assumptions:
Steady state flow
Restrictor throat is choked 100% of the cycle
Flow through restrictor equals flow through the intake valves.
No pulse tuning effects
Engine Air Flow Demand
Maximum Isentropic Flow Through an Orifice Area
Maximum Theoretical Volumetric Efficiency
(Limited by Restrictor)

11. Volumetric Efficiency Predictions (CASE 1)
Typically defined as the “choke point” of the restrictor

12. Volumetric Efficiency Comparison – 1D vs. 1D/3D vs. Theoretical Maximum

13. CFD Results - Mach Number, Time Averaged

14. CFD Results – Mach, Time Avg.- 14,000 RPM3°
5.5° 4° 7°

15. Velocity over one cycle – 14,000 RPM7° 4°
Movies frames are at 5° CAD resolution
Scale peak at 347m/s

16. Mach Number – Over One Cycle (1D/3D), 14,000 RPM7° 4°

17. Mach Number – Over One Cycle (1D/3D), 10,000 RPM7° 4°
4° achieves supersonic velocities yet outperforms 7°

18. Flow Uniformity of Mach Number

19. Turbulent Kinetic Energy (TKE) – Time Averaged
14,000 RPM – clear trend
10,000 RPM – 4 degree tapers off, yet 7 degree never drops TKE values.
- 4 degree has higher TKE at lower area ratios due to higher velocities

20. T.K.E. – One Cycle at 14,000 RPM 7° 4°
5.5° 3°

21. TKE vs. Mach 4° at 14,000 RPM Peak TKE Minimum TKE Rising Mach #
Falling Mach #

22. Turbulent Kinetic Energy Over One Cycle7° 4°

23. Total Pressure – Time Averaged
Total Pressure at diffuser did not agree well with VE
Total Pressure loss vs. TKE shows good agreement

24. Total Pressure – Time Averaged7° 4°
5.5° 3°

25. Total Pressure Over One Cycle, 4° at 14,000 RPM

26. Total Pressure Over One Cycle 4° at 14,000 RPM
7deg peak Mach around 300 CAD

27. Acoustic Filtering (WAVE Only)
Reduce unsteady flow through use of acoustic filtering
Pressure pulse frequency given by:
Helmholtz resonator used to attenuate desired frequency
Plenum volume used mesh with 15mm cell size

28. Acoustic Filtering
Helmholtz Resonator A tuned for 442 Hz or 13,260 RPM (1st E.O.)
Vol. = liters
Helmholtz Resonator B tuned for 416 Hz or 12,480 RPM (1st E.O.)
Vol. = liters
Mesh held constant between different cases

29. Flow Effects of Adding Helmholtz Resonator A at 13,750 RPM
Pressure & Velocity variation decreased
% cycle choked increased
Can not ascertain possible influence on separation with WAVE

30. Flow Control – Swirl Vanes
Reduce onset of separation after throat by increasing dynamic radial pressure component
Flow separation reduction found in SAE
Impart radial momentum through use of swirl vanes.
Used with 7 Degree Restrictor
Run at 14,000 RPM
VE within 0.1%

31. Swirl Vanes vs. No Swirl Vanes – 14,000 RPM
With Swirl Vanes
No Swirl Vanes

32. Conclusions
Length of the intake plays an important role in VE curve; not just volume
Lower diffuser angles provided:
Lower TKE values
Higher percentage of cycle achieving choked flow through the throat
Better flow uniformity at 10,000 & 14,000 RPM
Volumetric Efficiency closer to that predicted by WAVE
Increased time averaged total pressure at the diffuser exit
3° & 4° restrictors achieved VE numbers greater than steady state based Theoretical Maximum VE
Peak TKE values occurred during falling Mach numbers, due to adverse pressure gradient.
Flow separation occurred for all diffuser angles and occurred at approximately the same area ratio
Acoustic filtering provided encouraging results in increasing VE, albeit in a narrow rpm range
Swirl vane flow control devices
Intangible benefit to Volumetric Efficiency
Reduced TKE values, but also Total Pressure
Possible Benefits at lower RPM or with more fine tuning?

33. ACKNOWLEDGEMENTS Minnesota Supercomputer Institute
Ricardo – Patrick Niven & Karl John
Univ. of Minnesota – Mechanical Engineering
Dr. Patrick Starr
Dr. David Kittleson
Dr. William Durfee
Kim Lyons – Daimler-Chrysler
Minnesota State University Mankato
– Dr. Bruce Jones

34. QUESTIONS ?

35. Static Pressure – Time Averaged