Experimental investigation of acoustic liners to suppress screech in hydrogen-oxygen rockets
Evaluation of acoustic linears for suppression of screech in hydrogen oxygen rockets
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Tuned optimization of extended reacting acoustic liners
A finite element Galerkin formulation was employed to study the optimum attenuation and reflection characteristics of acoustic waves propagating in tw0 dimensional straight ducts with extended reacting absorbing walls without a mean flow. The reflection and transmission of acoustic energy at the entrance and the exit of the duct were determined by coupling the finite element solutions in the absorbing portion of the duct to the eigenfunctions of an infinite, uniform, hard wall duct. In the frequency range where the duct height and acoustic wave length are nearly equal, power attenuation contours were examined to determine conditions for minimizing acoustic transmission through the duct. The extended reacting liners were found to significantly minimize the reflective characteristics of the duct rather than to increase absorption in the liner. Thus, extended reacting wall liner properties can be theoretically chosen to yield large impedance mismatches in an open straight duct.
Baumeister, Kenneth J.↗
Acoustic liner optimum impedance for spinning modes with mode cut-off ratio as the design criterion
The theoretical optimum acoustic impedance for higher order spinning modes was studied in cylindrical ducts with a boundary layer at the outer edge of a uniform flow. All of the propagating modes were considered from highly propagating to nearly cut-off. It was observed that the mode cut-off ratio uniquely determined the optimum wall impedance and maximum possible attenuation for a given boundary layer thickness, Mach number and frequency. The implications of this phenomenon are quite important in noise suppressor design. Instead of the acoustic power distribution among all of the propagating modes, only the power distribution as a function of cut-off ratio needs to be known. Also, the far field radiation pattern is a function of modal cut-off ratio, and much needed information for liner design can be obtained from these more easily obtained data.
Rice, E. J.↗
Optimization of duct acoustic liners of finite length
Lining design procedures generally ignore the effects of discontinuous impedance changes on reflection and modal redistribution of incident energy. The present study involves identification of the mechanisms of optimal suppression by segmented liners, including impedance discontinuity effects. The mathematical model involves rectangular ducts in the absence of mean flow. Segmented acoustic fields are represented by duct eigenfunction expansions, and mode matching is used to ensure continuity of the total field. Extensive parameter studies were used to identify attenuation mechanisms and to define preliminary liner configurations. These are used as starting values in conjugate-gradient optimization studies. Optimal segmented liners are presented and it is shown that, if the sound source is sufficiently well-defined, conventional infinite duct optimum attenuation rates can be improved upon by taking advantage of wall impedance discontinuities. Finally, follow-on work which will involve experimental verification and extension to the case with mean flow in the duct is described.
Beckemeyer, R. J.↗
Development of an analytical technique for the optimization of jet engine and duct acoustic liners
A special integral representation of the external solutions of the Helmholtz equation is described. The analytical technique developed for the generation of the optimum acoustic admittance for an arbitrary axisymmetric body is also presented along with some numerical procedures and some preliminary results for a straight duct.
Zinn, B. T.↗
Advanced Technology Development for Active Acoustic Liners
Objectives include: (1) Develop electro-mechanical/acoustic models of a Helmholtz resonator possessing a compliant diaphragm coupled to a piezoelectric device; (2) Design and fabricate the energy reclamation module and active Helmholtz resonator; (3) Develop and build appropriate energy reclamation/storage circuit; (4) Develop and fabricate appropriate piezoelectric shunt circuit to tune the compliance of the active Helmholtz resonator via a variable capacitor; (5) Quantify energy reclamation module efficiency in a grazing-flow plane wave tube possessing known acoustic energy input; and (6) Quantify actively tuned Helmholtz resonator performance in grazing-flow plane wave tube for a white-noise input
Sheplak, Mark↗
Feasibility Study for Low Drag Acoustic Liners Final Report
This report documents the design and structural analysis as a final deliverable for the Phase 1 contract activity. Also included is a community noise test plan, which is a key deliverable for Phase 2. Finally, a high-level estimate (Phase 3 deliverable) is provided for the work statement of Phases 2-4, which covers the build of two inlet test articles, planning and execution of a flight test with the test inlets, as well as data analysis and final documentation. The two test inlets will be compared to the production baseline inlet configuration. There is also a plan to test one of the inlets "hardwalled" using speed tape or some other similar tape to block the acoustic perforations.
Riedel, Brian↗
On the design of acoustic liners for rocket engines - Helmholtz resonators evaluated with a rocket combustor
Helmholtz resonators with variable cavity depths tested with unstable rocket combustor
Hannum, N. P.↗
The nonlinearity of acoustic liners with flow effects
Helmholtz resonator associated flow field analysis in nonlinear regime, considering external pressure, mean flow, velocity fluctuations and orifice flow
Sirignano, W. A.↗
Acoustic liner feasibility program, design guide
Guidelines for designing combustion stability control devices
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Combustion instability with partial length acoustic liners
The development of analytical techniques and numerical methods for the prediction of the stability behavior of liquid propellant rocket combustors is discussed. The studies involved nonlinear wave propagation effects and nonlinear combustion zone, liner, and nozzle responses. A second primary extension of the basic theory was directed at the inclusion of the effects of injector face baffles. Attention was restricted to the linear (small amplitude) problem, finite Mach numbers, three dimensional oscillations, and distributed combustion effects.
Mitchell, C. E.↗
Coupling of Helmholtz resonators to improve acoustic liners for turbofan engines at low frequency
An analytical and test program was conducted to evaluate means for increasing the effectiveness of low frequency sound absorbing liners for aircraft turbine engines. Three schemes for coupling low frequency absorber elements were considered. These schemes were analytically modeled and their impedance was predicted over a frequency range of 50 to 1,000 Hz. An optimum and two off-optimum designs of the most promising, a parallel coupled scheme, were fabricated and tested in a flow duct facility. Impedance measurements were in good agreement with predicted values and validated the procedure used to transform modeled parameters to hardware designs. Measurements of attenuation for panels of coupled resonators were consistent with predictions based on measured impedance. All coupled resonator panels tested showed an increase in peak attenuation of about 50% and an increase in attenuation bandwidth of one one-third octave band over that measured for an uncoupled panel. These attenuation characteristics equate to about 35% greater reduction in source perceived noise level (PNL), relative to the uncoupled panel, or a reduction in treatment length of about 24% for constant PNL reduction. The increased effectiveness of the coupled resonator concept for attenuation of low frequency broad spectrum noise is demonstrated.
Dean, L. W.↗
Increase in effectiveness of low frequency acoustic liners by use of coupled Helmholtz resonators
Coupling of Helmholtz resonators in a low-frequency absorber array was studied as a means for increasing the effectiveness for absorbing low-frequency core engine noise. The equations for the impedance of the coupled-resonator systems were developed in terms of uncoupled-resonator parameters, and the predicted impedance for a parallel-coupled scheme is shown to compare favorably with measurements from a test model. In addition, attenuation measurements made in a flow duct on test coupled-resonator panels are shown to compare favorably with predicted values. Finally, the parallel-coupled concept is shown to give significantly more attenuation than that of a typical uncoupled resonator array of the same total volume.
Dean, L. W.↗
Optimized multisectioned acoustic liners
New calculations show that segmenting is most efficient at high frequencies with relatively long duct lengths where the attenuation is low for both uniform and segmented liners. Statistical considerations indicate little advantage in using optimized liners with more than two segments while the bandwidth of an optimized two-segment liner is shown to be nearly equal to that of a uniform liner. Multielement liner calculations show a large degradation in performance due to changes in assumed input modal structure. Computer programs are used to generate theoretical attenuations for a number of liner configurations for liners in a rectangular duct with no mean flow. Overall, the use of optimized multisectioned liners fails to offer sufficient advantage over a uniform liner to warrant their use except in low frequency single mode application.
Baumeister, K. J.↗
Development of an analytical technique for the optimization of jet engine and duct acoustic liners
A new method was developed for the calculation of optimum constant admittance solutions for the minimization of the sound radiated from an arbitrary axisymmetric body. This method utilizes both the integral equation technique used in the calculation of the optimum non-constant admittance liners and the independent solution generated as a by product of these calculations. The results generated by both these methods are presented for three duct geometries: (1) a straight duct; (2) the QCSEE inlet; and (3) the QCSEE inlet less its centerbody.
Zinn, B. T.↗
Design and flight test of a Kevlar acoustic liner
Previously cited in issue 10, p. 1378, Accession no. A83-25963
Lester, H. C.↗
High Temperature Acoustic Liner Technology
This paper describes work currently in progress at Langley on liner concepts that employ structures that may be suitable for broadband exhaust noise attenuation in high speed flow environments and at elevated temperatures characteristic of HSCT applications. Because such liners will need to provide about 10 dB suppression over a 2 to 3 octave frequency range, conventional single-degree-of-freedom resonant structures will not suffice. Bulk absorbers have the needed broadband absorption characteristic; however, at lower frequencies they tend to be inefficient.
Parrott, Tony L.↗
An Investigation of the Flow Physics of Acoustic Liners by Direct Numerical Simulation
This report concentrates on reporting the effort and status of work done on three dimensional (3-D) simulation of a multi-hole resonator in an impedance tube. This work is coordinated with a parallel experimental effort to be carried out at the NASA Langley Research Center. The outline of this report is as follows : 1. Preliminary consideration. 2. Computation model. 3. Mesh design and parallel computing. 4. Visualization. 5. Status of computer code development. 1. Preliminary Consideration.
Watson, Willie R.↗