# IMPEDANCE TUBE DESIGN FROM VARIOUS PAPERS (Acoustic Liner) --- ## *acoustic performance of bias flow liners in gas turbine combustors* ---  - circular aluminium tube used and its diameter (Φ) = **140mm** - two symmetrical sections each **1200mm** long - loudspeakers installed at **x=1041mm** * 12 microphones used - distance between farthest microphones in section = **531mm** - minimum distance between inner microphones = **60mm** - distance from liner to nearest microphone = **200mm** - distance from liner to farthest microphone = **731mm** - frequency range = **204Hz- 1377Hz** - anechoic termination at both ends - microphones used - 1/4 inch G.R.A.S type 40BP condenser microphones [^1] [^1]: Lahiri C., 2014, “Acoustic Performance of Bias Flow Liners in Gas Turbine Combustors,” Ph.D. dissertation, Technical University of Berlin, Berlin, Germany. --- ## *liner impedance under grazing flow conditions* ---   - microphones used - B&K 1/4 inch condenser microphone * six microphones used - minimum spacing between two microphones = **25mm** - distance between loudspeaker to first microphone = **759mm** - distance between liner to nearest microphone = **216mm** - frequency range - not mentioned - anechoic termination not used [^2] [^2]: Kabral R. et al.,"Determination of Liner Impedance under High Temperature and Grazing Flow Conditions "AIAA 2014-2956, 20th AIAA/CEAS Aeroacoustics Conference, Atlanta, GA, 16-20 June 2014. --- ## *experimental investigation of liners with bias flow* ---  - rectangular cross section = **100mmx100mm** - cross section of cavity = **120mmx120mm** - cut off frequency = **1700Hz** - SPL of impedance tube = **90-125dB** - frequency range = **300Hz-1400Hz** - anechoic termination not used [^3] [^3]:X. Jing & X. Sun, "Experimental investigations of perforated liners with bias flow", J. Acoust. Soc. Am. 106, 2436 (1999). --- ## *design of acoustic liner in small gas turbine combustor using 1D-impedance model* ---  - frequency range = **200Hz-1000Hz** - same as lahiri claus impedance tube - anechoic termination is used [^4] [^4]:Kim, D., Jung, S., and Park, H. (August 20, 2018). "Design of Acoustic Liner in Small Gas Turbine Combustor Using One-Dimensional Impedance Models." ASME. J. Eng. Gas Turbines Power. December 2018; 140(12): 121505. --- ## *impedance eduction methods using different methods and test rigs* ---   - rectangular cross section = **25mmx70mm** - at each end sound source and anechoic termination is used * 12 microphones used - 4 microphones mounted each side of sample, 4 mounted in the lined section - microphones used 1/4 inch B&K condenser microphones - frequency range = **200Hz-2600Hz** - flow profile measured through pitot tube at number of positions at **M=0.1,0.2** - distance between microphones mentioned in figure [^5] [^5]:Zhou L. et al.,"Comparison of impedance eduction results using different methods and test rigs" 20th AIAA/CEAS Aeroacoustics Conference June 2014 --- ## *investigation on noise attenuation by acoustic liner using helmholtz resonators* ---  - dimensions of square cross section = **50mmx50mm** - cuboidal cavity = **300mm(L)X50mm(W)x20mm(H)** it is used to measure test sample * 13 microphones used - up stream there are 2 microphones at distance **30mm** - down stream there are 2 microphones at distance **50mm** - there are 9 microphones placed opposite to test sample equally spaced at distance **30mm** - microphones used 1/4 inch G.R.A.S 46B.D - frequency range = **700Hz-1000Hz** - anechoic termination is used in one end [^6] [^6]: Jingwen Guo, Yi Fang, Ziyan Jiang, and Xin Zhang, "An investigation on noise attenuation by acoustic liner constructed by Helmholtz resonators with extended necks", The Journal of the Acoustical Society of America 149, 70-81 (2021). --- ## *impedance eduction based on microphone measurements of liners under grazing flow conditions* ---  - cross section = **80mm x 80mm** - flow mach number **M=0.3** - length of sample = **220mm** * 32 microphones used (B&K 4136) - 5 microphones up stream 5 microphones down stream - 10 microphones placed opposite to sample - 6 microphones placed around the circumference in middle of each duct section - test rig used - German Aerospace Center (DLR) engine acoustic maintains a special flow tube, named **DUCT** - length of tube = **2 x length of duct sections + length of liner** = **2 x 975mm + 220mm** = **2170mm** - frequency range = **210Hz - 2110Hz** - duct is made of transparent acrylic glass, since it is used for investigation with optical measurement techniques [^7] [^7]: Stefan Busse-Gerstengarbe et al.,"Impedance Eduction Based on Microphone Measurements of Liners Under Grazing Flow Conditions", AIAA Journal 2012 50:4, 867-879. --- ## *Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects* ---  - length of tube = **8m** - two symmetrical sections - rectangular cross section = **60mm x 80mm** - radial compressor used upstream providing maximum **M = 0.3** * 10 microphones used - 5 upstream & 5 downstream - frequency range = **204 Hz - 2091 Hz** - overal SPL = **130dB** - anechoic termination used [^8] [^8]: Dannemann, Martin, Michael Kucher, Eckart Kunze, Niels Modler, Karsten Knobloch, Lars Enghardt, Ennes Sarradj, and Klaus Höschler. 2018. "Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects" Applied Sciences 8, no. 10: 1923. https://doi.org/10.3390/app8101923 --- ## *comparitive study of impedance eduction methods, DLR tests and methodology* ---  - DUCT-R used for measuring liner impedance - 106 microphones used - the experimental set up as the above mentioned paper **Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects** - frequency range not mentioned - anechoic termination is used [^9] [^9]: Stefan Busse-Gerstengarbe, Friedrich Bake, Lars Enghardt and Michael G. Jones. "Comparative Study of Impedance Eduction Methods, Part 1: DLR Tests and Methodology," AIAA 2013-2124. 19th AIAA/CEAS Aeroacoustics Conference. May 2013. --- ## *German Aerospace Center ,Institute of Propulsion Technology, Engine Acoustics, Berlin* ---   * Circular cross-section (DUCT-C) - Aluminum-walled pipe with an inner diameter of 140 mm - Cut-on frequency of the first higher-order mode 1400 Hz - Mach number of the mean flow up to 0.1 - Injection of secondary flow up to 600 kg/h air mass flow - Microphone mounting at 10 rings in axial direction and at 8 positions arround the circumference - Test object mounting for different cylindrical liner configurations * Square cross-section (DUCT-S) - Acrylic glass test rig with square cross-section (80mmx80mm) - Cut-on frequency of the first higher-order mode 2200 Hz - Mach number of the mean flow up to 0.27 - 5 axial microphone locations for each microphone section - 10 additional microphone locations face to face with the liner - Optical access * Rectangular cross-section (DUCT-R) - Aluminum-walled duct with rectangular cross-section (60mmx80mm) - Cut-on frequency of the first higher-order mode 2200 Hz - Mach number of the mean flow up to 0.28 - Microphone mounting at 8 axial positions with 6 positions arround the circumference for each section, upstream and downstream of the test object. Also additional single microphone mountings, altogether 106 microphone locations. - Up to 8 loudspeaker mountings available (4 upstream, 4 downstream) - Modular test object holder for liner lengths up to 800 mm, which can be applied at each duct wall [^10] [^10]: https://www.dlr.de/at/en/desktopdefault.aspx/tabid-9019/15997_read-38541/ --- ## *Influence of Hole-to-Hole Interaction on the Acoustic Behavior of Multi-Orifice Perforated Plates* ---  - circular cross section tube and cavity **Φ 92mm** - sample - perforated plates * 6 microphones used - distance between the perforated plate & closest microphone = 215mm - frequency range = 200 Hz - 700 Hz - no anechoic termination [^11] [^11]: Javareshkian, A, Dancelme, A, Chen, H, & Sattelmayer, T. "Influence of Hole-to-Hole Interaction on the Acoustic Behavior of Multi-Orifice Perforated Plates." Proceedings of the ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. Volume 3A: Combustion, Fuels, and Emissions. Virtual, Online. June 7–11, 2021. V03AT04A006. ASME. --- ## *Investigation of straightforward impedance eduction method on single-degree-of-freedom acoustic liners* ---   - dimensions of liner used are shown in above figure - length of tube = **466mm+25mm+180mm+408mm+255mm+620mm**=**1954mm** - length of liner section = **424mm** * 22 microphones used - 18 opposite to test liner, 2 upstream & 2 downstream - distance between microphones which are opposite to test liner = **24mm** - distance between microphones which are there upstream and downstream = **25mm** - distance from liner to upstream microphone = **180mm** - distance from liner to down stream microphone = **80mm** - microphone used 1/4 inch GRAS type 40BH - cross section of tube = **51mm x 51mm** - anechoic termination used at one end - 4 loudspeakers used : BMS 4592 [^12] [^12]: Xianghai QIU, Bo XIN, Long WU, Yang MENG, Xiaodong JING, "Investigation of straightforward impedance eduction method on single-degree-of-freedom acoustic liners", Chinese Journal of Aeronautics, Volume 31, Issue 12, 2018,Pages 2221-2233,ISSN 1000-9361, https://doi.org/10.1016/j.cja.2018.08.014.