A

Specific Acoustic Impedance Equation

Zc cavity acoustic impedance Rc + iXc ZA aperture acoustic impedance RA + iXA Rc cavity acoustic resistance Xc cavity acoustic reactance Ra aperture acoustic resistance XA aperture acoustic reactance The impedance of a simple resonator cavity alone (region Vc in fig. A-l) is purely reactive (i.e., Rc 0) and is given by the well-known expression Figure A-1. Sketch illustrating parameters involved in calculation of acoustic impedance (adapted from ref. 1). 7( ratio of specific heats of gas in the...

Design Pressure Amplitude

Some uncertainty and confusion exists concerning the amplitude of the oscillatory pressure for which an absorber should be designed. Because of impedance nonlinearities, predicted damping varies with amplitude. Most early liner calculations were made with an arbitrarily assumed incident amplitude of 190 decibels. The incident amplitude was assumed to be half the local amplitude thus, the 190-decibel level corresponds to a local amplitude of 56 psi (386 kN m2) peak-to-peak. It is unreasonable to...

Design Confirmation And Rating

In new design situations where the confidence in the analysis or empiricism on which the design is based is very low, it is possible to develop an effective baffle design by extensive hot-firing stability-rating tests. Ideally, the test series would be structured to determine sequentially l minimum effective baffle length, 2 maximum transverse dimension for which this minimum is effective, and 3 subsequent rate of increase of minimum effective length with increases in transverse dimension...

Material Selection

The selection of the baffle material has depended to a great extent on the required baffle lifetime, the operating conditions, the rate of heat transfer to the baffles, and the individual test duration. Generally, the design procedure and philosophy depend very strongly on the required baffle lifetime, both total firing duration and number of starts of the engine. For very short firings, baffles are not exposed to hot combustion gases for a very long time, so the material may be selected...

Calculation Of Acoustic Impedance

The acoustic impedance of a surface is given by where, as before, i 1 and Z acoustic impedance Y acoustic admittance R acoustic resistance X acoustic reactance P oscillatory pressure u oscillatory velocity outwardly directed unit normal vector An alternate definition of Z is used by Tonon ref. 1, p. 408 . Generally, the acoustic impedance is a function of both position and frequency. For simplicity, however, it is often assumed to be constant over some region of space. At high amplitudes, the...

Thrust Vector Control

The combustion gas flow in the wakes of baffles may carry appreciable transverse nonuniformities in composition and temperature all the way through the rocket exhaust nozzle. It has been shown ref. 44 that injection of a thrust vector control jet into a baffle wake may produce substantially lower side thrust than does injection into neighboring nonwake gases. Therefore, the baffle design and TVC injection site design are coordinated to avoid the effects of baffle wake. Although acoustic...

Slots Or Acoustic Cavities

Liquid Rocket

An acoustic-slot type of absorber usually consists of a partitioned annular cavity oriented either perpendicular or parallel to the injector face. Most recent test and development work has been done with the cavity configurations shown in figure 23. The acoustic absorber Figure 21. - Chamber liner acoustic absorber assembly for test and development ref. 48 . Figure 21. - Chamber liner acoustic absorber assembly for test and development ref. 48 . Figure 22. Acoustic liner design for F-1 engine...

Appendix B Glossary

A with subscript cross-sectional area Cf empirical flow coefficient for steady flow Cp specific heat at constant pressure LMA, LMAE lunar module ascent engine J4 effective aperture length, e 5 Mp Mach number of the steady flow past the orifice m angular index of the mode excited in the main chamber N number of radial baffles or baffle black's Nt f- number of cylindrical baffle cans n unit noriral vector directed outward from surface o f oxidi er to-fuel weight ratio Ra U - 0 acoustic resistance...

Cooling Methods Regenerative and Dump Cooling

Baffles Injectors Liquid Rocket Engine

Baffles usually are cooled with the rocket fuel, although oxidizer and bipropellant cooling occasionally have been used. A typical design, showing coolant passages used on the F- qualification injector, is presented in figure 15. Coolant flowrate through regenerative or dump-cooled baffles is established to satisfy two requirements 1 The total heat absorbed by the coolant must be equal to the integrated gas-side heat flux, and if the coolant is liquid this heat must be absorbed without...

References

H., eds. Liquid Propellant Rocket Combustion Instability. NASA SP-194,1972. 2. Oberg, C. L. Wong, T. L. and Schmeltzer, R. A. Analysis of the Acoustic Behavior of Baffled Combustion Chambers. NASA CR-72625, Rocketdyne Div., North American Rockwell Corp., January 1970. 3. Oberg, C. L. Evers, W. H. Jr. and Wong, T. L. Analysis of the Wave Motion in Baffled Combustion Chambers. NASA CR-72879, Rocketdyne Div., North American Rockwell Corp., October 1971. 4. Oberg,...

Ablative Baffles

Liquid Rocket Injection

For applications that have relatively short lifetime and few restarts, an alternative to an uncooled baffle i.e., conduction cooled is a baffle made of ablative materials. Ablative materials for baffles have been limited to fiber-glass-reinforced phenolics, but other ablatives such as carbon-cloth phenolics or nonreinforced materials such as nylon or Teflon could be used equally well, especially if the thrust chamber wall is made of these materials. Occasionally, baffles have been fabricated...