Unerwünschtes strömungsinduziertes Pfeifen von Ladeluft-Resonatoren von der Theorie über die Messung und Simulation zur Lösung Dr. Ralf Buck 18.10.2017 Simcenter Symposium zur Fahrzeugentwicklung Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 1 Unrestricted
UMFOTEC Founded in 1992 Products: resonators & wire meshes 200 employees Tier I and Tier II automobile industry ISO TS 16949 ISO 14001 Turnover 2016: 34 Mio. Global market leader for resonators on the charged air side Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 2 2
Mesh wires for structure-borne noise & vibrations reduction at high temperatures Mesh wires needed for flexible bearings in order to reduce structural born noise or prevent systems or components from vibrations. Only for high temperature applications. Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 3
Resonators for noise reduction: Umfotec offers resonators out of all materials Stainless Steel Resonators are needed for the reduction of disturbing noise propagating with the flow Typical applications: Resonators on the charged air side of combustion engines Air conditioning Plastic (injection moulding) Aluminium Material selection (steel, plastic, aluminum) depends on operating temperature, available installation space, volume and customer preferences Combination of different materials E.g. outer shell out of stainless steel or aluminum Inner part out of plastic Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 4
Mozart and the Flutes The magic flute Mozart (1756-1791) Pictures: Google Marine Mersenne (1588-1648) Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 5
Sound impressions of flow induced noise of a current series solution and an optimized Umfotec solution Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 6
What are resonators? Resonators positioned between turbo charger and charge air cooler Resonator Engine Cylinder Charge Air Cooler Turbocharger Air intake Exhaust Gas Exhaust Gas Source: Powerline Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 7
Properties of charged air resonators? Resonators based on the Helmholtz principle Typical frequency range of charged air resonators: 1,500 4,500 Hz Noise reduction level between 20 to 40 db Resonator are typically built up concentrically around the charged air duct with two to six or even more chambers The interaction with the noise in the tubes happens through holes or slots Equation of HELMHOLTZ c = Speed of sound S 0 = Area of the slots/holes V 0 = Volume of the chambers L = Depth of the slots/holes Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 8
Acoustic wave propagation: Tube at 2,000 Hz Simulation/Visibility of a sound wave propagation at 2,000 Hz only tube with diffusor Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 9
Acoustic wave propagation: Tube with resonator at 2,000 Hz Simulation/Visibility of a sound wave propagation at 2,000 Hz Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 10
Acoustic wave propagation: Tube with Resonator at 4,000 Hz Simulation/Visibility of a sound wave propagation at 4,000 Hz Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 11
Reaction of the resonator when a flow impact is simulated Simulation/Visibility of flow induced noise Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 12
Flow induced noise can be produced via flow test stand measurements Near field microphone Resonator Properties of flow induced noise Stage like behavior Double stages detectable Flow induced noise frequencies increases with the flow rate Highly dependent on the flow conditions Tonal disturbing sound Dependence on Helmholtz frequency Interacts with structural resonances Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 13
Three theories about flow induced noise are regarded. Do these theories fit to the measurement results? Keep things simple. Through understanding of the theories and simple FEA calculation a derivation of solutions becomes possible. Using existing theories for a better understanding of the underlying phenomena Deriving solutions out of the equations Carrying out of simple test stand measurements Using FEA calculations carried out with a concentric single chamber model to work out the best solutions Three theories for flow induced noise all of them seem to be valid and help to understand detected phenomena better. The Rossiter or Rockwell effect The flow induced Helmholtz effect The flute effect Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 14
With Rossiter Effect the stage like behavior can be described Only valid for Mach numbers > 0,4 Calculated frequencies do not fit to measurement results (too high) Dependency on flow rates can be explained Stage like behavior of flow induced noise can be described Smaller slots or holes lead to less tendencies for flow induced noise Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 15
Helmholtz-excited flow induced noise -> Describes the dependency on the Helmholtz resonance In the boundary layer turbulent flow is always existing. Turbulent layer can be regarded as broad band noise source which excites the resonator. Reason why even small holes or slots of the resonator produce flow induced noise at close to the Helmholtz resonance Modulations between flow induced noise and Helmholtz (double stages) The more effective a resonator is the more it shows the tendency to flow induced noise Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 16
Flute effect -> Describes the dependency on the chamber dimensions The old and simple equation of Mersenne (1588 1648) can be used for a rough calculation for flow induced noise of resonators. The flute effect describes the dependency on the chamber design of the Resonator Describes the reduced tendency on flow induced noise when the slots or holes are positioned at the end of the chamber (in flow direction) Flow direction Possible oscillation directions in the chamber Scheme of flute pipe (Reimer 2011) c = speed of sound l = chamber dimensions Oscillation of flow Equation of Mersenne (Reimer 2011) Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 17
Summarizing the theories and deriving solutions to prevent flow induced noise Rossiter effect -> the feedback mechanism has to be prevented possible through smaller slots Helmholtz excited flow induced noise: Only one solution exists with which the conflict of goal can be solved remaining a good transmission loss behavior while preventing flow induced noise Flute effect -> the oscillation of the flow can be prevented or reduced by moving the slot/holes to the end of the chamber but this influences the transmission loss through smaller slots or holes Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 18
Solutions for resonators to reduce flow induced noise significantly Solution with wire meshes on the inside of the chamber: No influence on main flow No influence on transmission loss No tendency to flow induced noise Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 19
Summary and Outlook The need to reduce flow induced noise is demonstrated via sound examples. Aim of this study/investigation was to find solution for a complex mechanism via simple theories. With the help of validated FEA simulations solutions to prevent flow induced noise were worked out. OUTLOOK: Air conditioning applications The very sensitive area of climate applications needs also this knowledge of Umfotec. Proofed Umfotec solutions for climate applications already exist. Climate channel resonators of Umfotec Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 20
Thank you for your attention. Dr. Ralf Buck r.buck@umfotec.de Tel.: +49 171 2261 058 Oktober 2017 Simcenter Symposium 2017 - Umfotec acoustic solutions - Dr. Ralf Buck 21