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Oberg, C. L.

Publications and source records attributed to Oberg, C. L..

16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Further analysis of the effects of baffles on combustion instability

A computerized analytical model, developed to predict the effects of baffles on combustion instability, was modified in an effort to improve the ability to properly predict stability effects. The model was modified: (1) to replace a single spatially-averaged response factor by separate values for each baffle compartment; (2) to calculate the axial component of the acoustic energy flux, and (3) to permit analysis of traveling waves in a thin annular chamber. Allowance for separate average response factors in each baffle compartment was found to significantly affect the predicted results. With this modification, an optimum baffle length was predicted which gave maximum stability.

Oberg, C. L.↗
NASA NTRS1974

Space shuttle maneuvering engine reusable thrust chamber program. Task 11: Stability analyses and acoustic model testing data dump

The combustion stability characteristics of engines applicable to the Space Shuttle Orbit Maneuvering System and the adequacy of acoustic cavities as a means of assuring stability in these engines were investigated. The study comprised full-scale stability rating tests, bench-scale acoustic model tests and analysis. Two series of stability rating tests were made. Acoustic model tests were made to determine the resonance characteristics and effects of acoustic cavities. Analytical studies were done to aid design of the cavity configurations to be tested and, also, to aid evaluation of the effectiveness of acoustic cavities from available test results.

Oberg, C. L.↗
NASA NTRS1974

Advanced acoustic cavity technology

A series of rocket motor firings was performed in a modified linear aerospike thrust chamber with the H2/O2 propellant combination to allow determination of the physical properties of the combustion gases in acoustic cavities located in the chamber side walls. A preliminary analytical study was first conducted to define theoretically both the appropriate cavity dimensions and the combustion gas flow field adjacent to the cavity openings. During the subsequent motor firings, cavity gas temperature profiles were measured and gas samples were withdrawn from the bottom of the cavities for compositional analysis by measurement of pressure/temperature variation and gas chromatography. Data were obtained with both radially and axially oriented cavities and with and without hydrogen bleed flow through the cavities. A simplified procedure was developed for predicting gas cavity and acoustic velocity for use in acoustic cavity design analyses.

Hines, W. S.↗
NASA NTRS1974

Analysis of combustion instability in liquid propellant engines with or without acoustic cavities

Analytical studies have been made of the relative combustion stability of various propellant combinations when used with hardware configurations representative of current design practices and with or without acoustic cavities. Two combustion instability models, a Priem-type model and a modification of the Northern Research and Engineering (NREC) instability model, were used to predict the variation in engine stability with changes in operating conditions, hardware characteristics or propellant combination, exclusive of acoustic cavity effects. The NREC model was developed for turbojet engines but is applicable to liquid propellant engines. A steady-state combustion model was used to predict the needed input for the instability models. In addition, preliminary development was completed on a new model to predict the influence of an acoustic cavity with specific allowance for the effects the nozzle, steady flow and combustion.

Oberg, C. L.↗
NASA NTRS1974

Analysis of the effects of baffles on combustion instability

An analytical model has been developed for predicting the effects of baffles on combustion instability. This model has been developed by coupling an acoustic analysis of the wave motion within baffled chambers with a model for the oscillatory combustion response of a propellant droplet developed by Heidmann. A computer program was developed for numerical solution of the resultant coupled equations. Diagnostic calculations were made to determine the reasons for the improper prediction. These calculations showed that the chosen method of representing the combustion response was a very poor approximation. At the end of the program, attempts were made to minimize this effect but the model still improperly predicts the stability trends. Therefore, it is recommended that additional analysis be done with an improved approximation.

Oberg, C. L.↗
NASA NTRS1974

High-temperature earth-storable propellant acoustic cavity technology

Design criteria, methods and data, were developed to permit effective design of acoustic cavities for use in regeneratively cooled OME-type engines. This information was developed experimentally from two series of motor firings with high-temperature fuel during which the engine stability was evaluated under various conditions and with various cavity configurations. Supplementary analyses and acoustic model testing were used to aid cavity design and interpretation of results. Results from this program clearly indicate that dynamic stability in regeneratively cooled OME-type engines can be ensured through the use of acoustic cavities. Moreover, multiple modes of instability were successfully suppressed with the cavity.

Oberg, C. L.↗
NASA NTRS1972

Evaluation of acoustic cavities for combustion stabilization.

The stabilizing influence of acoustic cavities (quarterwave acoustic resonators) on acoustic modes of combustion instability has been studied. The ability to analytically predict cavity damping was improved. Relatively good agreement between predicted damping and measured stability was demonstrated. Full-scale motor firings were made to evaluate the influence of several parameters on stability. Results from these firings showed that stability was changed, but not dramatically, by changes in the engine operating conditions. Variations in the film-coolant flowrate do not significantly affect cavity stabilization. The ability to stabilize an engine with unconventional cavity configurations was demonstrated.

Oberg, C. L.↗
NASA NTRS1971

Combustion stabilization with acoustic cavities.

An experimental and analytical study has been performed to develop the technology necessary for effective use of acoustic cavities to suppress acoustic modes of combustion instability. An unbaffled variation of the LM ascent engine has been made dynamically stable with acoustic cavities only; five different cavity configurations were found sufficient to produce dynamic stability. An analytical model was developed to calculate the damping contributed by the cavity. Further, subscale tests were made to determine the nonlinear acoustic impedance of these cavities.

Oberg, C. L.↗
NASA NTRS1970

Analysis of the F-1 Acoustic Liner

An analytical study was performed to re-evaluate data obtained during the F-1 Acoustic Absorber program. The acoustic liner had failed to produce substantial improvements in stability. Oscillatory-pressure, temperature and gas sampling data obtained from liner firings were employed to calculate the damping produced by the liner and the potential for increasing the damping by varying the liner dimensions. The results indicate the damping can be substantially increased. The liner damping was predicted by calculating temporal damping-coefficient contributions due to the liner.

Oberg, C. L.↗