1. THERMOACOUSTICS
Optimisation of the Feedback Loop of the Thermoacoustic Travelling wave Engine
David Wee Shuon Tzern
Yousif Abdalla Abakr
David Hann
Paul Riley

2. The Simplest form of a Travelling Wave Thermoacoustic Engine
Regenerator
Linear Alternator
Tuning Stub
Feed Back Loop
Limiting amplitude occurs when the amplification of the regenerator is equivalent to the power absorbed by the system
Total Power Absorbed = Power absorbed by Linear Alternator + System Losses

3. Thermoacoustic Engine
SCORE -StoveTM
Thermoacoustic Engine
REQUIREMENT
Efficiency
Compact
INFLUENCING PARAMETER
Elbow Bends
An understanding of the Acoustic Transmission through bends is required in order to optimise the system

4. MICROPHONE Decomposition Method Decomposition Transfer Function
Scattering Matrix Technique

5. MICROPHONE Experimental Setup
Optimum Travelling wave Load

6. MICROPHONE Experimental Setup
Investigated Bends

7. Reynolds Number vs. Transmission Loss [%]
Legend
r = hydraulic cross sectional
radius (m)
R = Radius of curvature
of elbow(m)
u = RMS particle velocity (ms-1)
c = Speed of sound (ms-1)
ω = angular frequency (s-1)
ν = kinematic viscousity (m2s-1)
Legend
r = hydraulic radius (m)
R = radius of curvature
of elbow(m)
u = RMS particle velocity (ms-1)
c = speed of sound (ms-1)
ω = angular frequency (s-1)
ρ = density (kg/m3)
ν = kinematic viscousity (m2s-1)

8. Dean Number vs. Transmission Power Loss [%]
Linear Loss Region
Non-Linear Loss Region

9. PIV Experimental Setup
PIV=Particle Image Velocimetry

10. PIV Experimental Setup

11. PIV Experimental Setup

12. Dean Number vs. Transmission Power Loss [%]
Linear Loss Region
Non-Linear Loss Region

13. Dean Number vs. Transmission Power Loss [%]
Linear Loss Region
Non-Linear Loss Region
At Higher operating Amplitude such as that of the Engine, Losses may go up to 10% or more

14. CONCLUSIONS
A monotonic relationship has been found between the Percentage Acoustic Transmission Loss and the Acoustic Dean Number. A critical Dean Number (≈1) above which the transmission losses increase significantly has been identified.
Particle Image Velocimetry is being used to investigate the transition to nonlinearity by consideration of the flow field.
Once verified this would prove an important breakthrough in the design of future feedback resonator loop for thermoacoustic systems by providing new information about
the additional losses at the elbow bends.

15. THANK YOU