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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Flow visualization techniques in the Airborne Laser Laboratory program

A turret/fairing assembly for laser applications was designed and tested. Wind tunnel testing was conducted using flow visualization techniques. The techniques used have included the methods of tufting, encapsulated liquid crystals, oil flow, sublimation and schlieren and shadowgraph photography. The results were directly applied to the design of fairing shapes for minimum drag and reduced turret buffet. In addition, the results are of primary importance to the study of light propagation paths in the near flow field of the turret cavity. Results indicate that the flow in the vicinity of the turret is an important factor for consideration in the design of suitable turret/fairing or aero-optic assemblies.

Walterick, R. E.↗
NASA NTRS1979

Measurement of vortex frequencies in a lean, premixed prevaporized combustor

A modified laser schlieren and fast Fourier transform analysis system has been developed and applied to the study of vortex frequencies in a lean, premixed prevaporized combustor. The system is sensitive to the passage of vortex structures which dominate the flow in the combustor studied. The frequency spectra of the passage of vortices show distinct frequency peaks which are postulated to be characteristic of the processes triggering the vortex shedding. The method provides additional information which should aid in the characterization and understanding of shear flows.

Parker, L. J.↗
NASA NTRS1979

Holographic flow visualization at NASA Langley

Holographic flow visualization systems at two NASA Langley facilities, a hypersonic blow-down tunnel using CF4 gas and an expansion tube with very short test time, are described. A pulsed ruby laser is used at a CF4 tunnel for single pulse holography, double pulse with several minutes between exposures, and dual plate holographic interferometry. Shadowgraph, schlieren, and interferograms are reconstructed from the holograms in a separate reconstruction lab. At the expansion tube the short run time of 200 microseconds requires precise triggering of its double pulsed ruby laser. With double pulse capability of 20 to 1200 microseconds pulse separation, one pulse can occur before and one later after flow is established to obtain fringe free background interferograms (perfect infinite fringe) or both pulses can occur during flow in order to study flow instabilities. Holograms are reconstructed at the expansion tube with an in-place setup which makes use of a high power CW Argon laser and common optics for both recording and reconstructing the holograms. The holographic systems at the CF4 tunnel and expansion tube are operated routinely for flow visualization by tunnel technicians. Typical flow visualization photographs from both facilities are presented.

Burner, A. W.↗
NASA NTRS1979

Convection phenomena during the growth of sodium chlorate crystals from solution

The paper examines convection phenomena during the growth of sodium chlorate crystals from solution. Schlieren observations of sodium chlorate crystals suspended in supersaturated solutions showed that with increase in supersaturation or crystal size, the boundary layer on the side faces was stable while the top boundary layer and emerging plume changed from stable to partially oscillatory. The transition was a function of the Grashof number, Gr sub top, and the crystal height. Gr sub top correlated with plume width, number of streamlines, eddy density, and plume velocity, but the oscillation period correlated with the weight increase growth rate. The mass transfer rate, the linear growth rate, and growth of vertical and horizontal faces are discussed, and an estimate of boundary layer flow vs growth rate for near-critical stable convection indicated that growth of side faces depleted over half of the excess solute in the boundary layer. Impulse energies greatly in excess of the threshold value caused transient separation of the boundary layer on the top face, and plume wavering due to background-induced fluid motion was observed only at the lowest supersaturations.

Chen, P. S.↗
NASA NTRS1979

Free convection about a rectangular prismatic crystal growing from a solution

Sodium chlorate crystals growing from unstirred aqueous solutions were observed by Schlieren techniques. Growth rate data were best correlated by a Sherwood number with finite interface kinetics and a characteristic length equal to the crystal height plus the inverse reciprocal sum of the horizontal dimensions. The growth rate was slightly higher when the plume was laminar than when it was irregular. The horizontal growth rate was greater than the vertical growth rate, with the ratio tending to decrease with increasing plume instability. The threshold Grashof number for plume instability was greatly decreased with decreasing height for crystals with the same horizontal dimensions. The velocity of the eddies approached a constant value with increasing distance above the crystal surface, the terminal value being roughly proportional to the ratio of the square root of the Rayleigh number to the crystal characteristic length.

Chen, P.-S.↗
NASA NTRS1979

Geophysical fluid flow experiment

The essential fluid flow processes associated with the solar and Jovian atmospheres will be examined in a laboratory experiment scheduled for performance on Spacelab Missions One and Three. The experimental instrumentation required to generate and to record convective fluid flow is described. Details of the optical system configuration, the lens design, and the optical coatings are described. Measurement of thermal gradient fields by schlieren techniques and measurement of fluid flow velocity fields by photochromic dye tracers is achieved with a common optical system which utilizes photographic film for data recording. Generation of the photochromic dye tracers is described, and data annotation of experimental parameters on the film record is discussed.

Broome, B. G.↗
NASA NTRS1980

Test section configuration for aerodynamic testing in shock tubes

This paper presents results of a study of the test section configuration required to minimize or alleviate interference effects on model flow produced by the presence of test section walls in the aerodynamic testing of two dimensional transonic airfoils in a shock tube. Tests at a nominal Mach number of 0.85 and a chord Reynolds number of 2,000,000 were carried out by means of schlieren photography and pressure measurements for several symmetric airfoil profiles using shock tube test sections with unmodified straight walls, contoured walls, and slotted walls with adjacent chambers. Results were compared with corresponding results from conventional wind tunnel tests of the airfoils. Results for the straight wall tests show major airfoil flow distortions. Results from contoured wall tests and those performed using a slotted wall test section developed in this study exhibit essential agreement with wind tunnel results. The collective results show that test sections for aerodynamic testing can be designed for shock tubes that will alleviate wall interference effects.

Cook, W. J.↗
NASA NTRS1980

Application of optical methods to the study of jet noise and turbulence

Optical methods are generally applied in fluid mechanics for either visualization or measurement. The use of a laser anemometer to study flow velocity in a jet and its relaton to the sound radiated is described. The same acoustic emission phenomenon is also measued by combining the signals from four Schlieren systems with that from an interferometer. The use of an optical Fourier transformation approach with real time analysis to determine the spatio-temporal structure of a field of mass volume such as a waveguide or free jet is also examined.

Sava, P. G.↗
NASA NTRS1981

Holographic flow visualization at the Langley Expansion Tube

A holographic system used for flow visualization at the Langley Expansion Tube is described. A ruby laser which can be singly or doubly pulsed during the short run time of less than 300 microns is used as the light source. With holography, sensitivity adjustments can be optimized after a run instead of before a run as with conventional flow visualization techniques. This results in an increased reliability of the flow visualization available for the study of real-gas effects on flow about models. Holographic techniques such as single-plate schlieren and shadowgraph, two plate interferometry, double pulse interferometry for perfect infinite-fringe interferograms, and double-pulse interferometry used to examine changes in the flow over a short time period are described and examples presented.

Goad, W. K.↗
NASA NTRS1981

An experimental study of combustion: The turbulent structure of a reacting shear layer formed at a rearward-facing step

A premixed propane-air flame is stabilized in a turbulent free shear layer formed at a rearward-facing step. The mean and rms averages of the turbulent velocity flow field were determined by LDV for both reacting and non-reacting flows. The reaching flow was visualized by high speed schlieren photography. Large scale structures dominate the reacting shear layer. The growth of the large scale structures is tied to the propagation of the flame. The linear growth rate of the reacting shear layer defined by the mean velocity profiles is unchanged by combustion but the virtual origin is shifted downstream. The reacting shear layer based on the mean velocity profiles is shifted toward the recirculation zone and the reattachments lengths are shortened by 30%.

Pitz, R. W.↗
NASA NTRS1981

Experimental study of combustion in a turbulent free shear layer formed at a rearward facing step

A premixed propane-air flame is stabilized in a turbulent free shear layer formed at a rearward facing step. The mean and rms averages of the turbulent velocity flow field are determined by LDV for both reacting (equivalence ratio 0.57) and nonreacting flows (Reynolds number 15,000-37,000 based on step height). The effect of combustion is to shift the layer toward the recirculation zone and reduce the flame spread. For reacting flow, the growth rate is unchanged except very near the step. The probability density function of the velocity is bimodial near the origin of the reacting layer and single-peaked but often skewed elsewhere. Large-scale structures dominate the reacting shear layer. Measurements of their passing frequency from LDV are consistent with high-speed Schlieren movies of the reacting layer and indicate that the coalescence rate of the eddies in the shear layer is reduced by combustion.

Pitz, R. W.↗
NASA NTRS1981

Mechanism of instabilities in turbulent combustion leading to flashback

High-speed schlieren cinematography, combined with synchronized pressure transducer records, was used to investigate the mechanism of combustion instabilities leading to flashback. The combustion chamber had an oblong rectangular cross-section to model the essential features of planar flow, and was provided with a rearward facing step acting as a flameholder. As the rich limit was approached, three instability modes were observed: (1) humming - a significant increase in the amplitude of the vortex pattern; (2) buzzing - a large-scale oscillation of the flame; and (3) chucking - a cyclic reformation of the flame, which results in flashback. The mechanism of these phenomena is ascribed to the action of vortices in the recirculation zone and their interactions with the trailing vortex pattern of the turbulent mixing layer behind the step.

Keller, J. O.↗
NASA NTRS1980

Optical measurements and tests performed in a low-gravity environment

Shadowgraph and schlieren techniques have been used on board the NASA KC-135 low-gravity simulation aircraft to measure gravity-related fluid flow occurring in various experimental configurations. These configurations included cooled and solidified ammonium chloride and water, electrodeposited cobalt in CoSO4 solution, and immiscible and crystal melt solutions. Hardware tests have also been performed for such critical optical system components as lasers and spatial filters to determine their performance and operation under low-gravity conditions. These test results will be used in the design of the various future Shuttle experiments which will utilize advanced optical measurement techniques. The design and configuration of the optical systems used to make these measurements and tests are presented, and the performance and operation of these systems and their components under low-gravity conditions are discussed. Some preliminary results are included.

Owen, R. B.↗
NASA NTRS1980

Holography on the NASA Space Shuttle

The SL-3 flight on the Space Shuttle will carry a 25 mW He-Ne laser holographic recorder for recording the solution growth of triglycine sulfate (TGS) crystals under low-zero gravity conditions. Three hundred holograms (two orthogonal views) will be taken (on SO-253 film) of each growth experiment. Processing and analysis (i.e., reconstructed imagery, holographic schlieren, reverse reference beam microscopy, and stored beam interferometry) of the holographic records will be done at NASA/MSFC. Other uses of the recorder on the Shuttle have been proposed.

Wuerker, R. F.↗
NASA NTRS1981

Numerical simulation of transonic flows in diffusers

Numerical simulations were made of two-dimensional transonic flows in diffusers, including flow separation induced by a shock or adverse pressure gradient. The mass-averaged, time-dependent, compressible Navier-Stokes equations, simplified by the thin-layer approximation, were solved using MacCormack's hybrid method. The eddy-viscosity formulation was described by the Wilcox-Rubesin's two-equation, k-omega model. Detailed comparison of the computed results with measurements showed good agreement in all cases, including one with massive separation induced by a strong shock. The computation correctly predicted the details of a distinct lambda shock pattern, closely duplicating the configuration observed experimentally in spark-schlieren photographs.

Liou, M.-S.↗
NASA NTRS1981

Acoustic power dissipation on radiation through duct terminations - Experiments

An acoustic impulse technique is used to study the acoustic transmission characteristics of ducts, nozzles, orifices, and perforated plates. High intensity pulses were generated by discharging a capacitor across a spark gap for both heated and unheated flows, with and without simulated flights. The effect of a termination geometry on power absorption for high acoustic intensities was observed, showing the existence of power absorption at low frequencies for the duct, nozzles, orifice plates, and perforated plates at a no flow condition; the amount of power absorption was controlled primarily by the open area at the exit. Power conservation with flow was similar to that for no flow: Power absorption initially increased for the duct and conical nozzles and then decreased with increasing Mach number. Power absorption results for the suppressor nozzle were similar to those for the conical nozzle, and the nonlinear effect was found to be insignificant in the presence of flow. A power imbalance was noted for heated jets, with a greater power loss at low frequencies than for unheated jets. Low frequency power absorption increased with the simulated flight, and a small amount of low frequency power absorption was found even for low intensity sound. A typical schlieren photograph of vortex formation (Whiffen and Ahuja, 1981) helped to confirm that sound energy can be converted into vortical energy and may account for low frequency power losses.

Salikuddin, M.↗
NASA NTRS1981

Shock-associated noise reduction from inverted-velocity-profile coannular jets

The reduction of shock-associated noise in inverted velocity profile coannular jets is investigated and quantified by making optical and acoustic measurements as a function of outer and inner stream pressure ratio combinations and interpreting noise results with the aid of new theoretical models. Schlieren photographs are obtained in three series of test conditions with a varying primary stream pressure ratio, and acoustic experiments are conducted on a polar arc radius of 3.05 m over a frequency range of 200 Hz to 80 kHz. A constant-thrust comparison is made, and data are plotted and discussed with emphasis on the variation of jet noise levels with primary stream Mach number and equivalent single jets on an absolute basis. It is shown that shock noise from the outer stream is almost eliminated when the inner stream is operated at a Mach number above unity at inverted and normal velocity profile conditions, and optical measurements indicate that for a fixed supercritical fan stream pressure ratio, the repetitive shock structure in the outer stream is minimized when the primary stream ratio becomes supercritical.

Tanna, H. K.↗
NASA NTRS1981

An experimental study of massive blowing from a nosetip during Jovian entry

The fluid dynamic structure and stability of the boundary layer and shock layer ahead of a highly blowing heat shield in an environment simulating entry into the Jovian atmosphere were investigated. The experimental studies were conducted in the Calspan 96 in shock tunnel with a freestream of a H2/He mixture at Mach numbers above 10. Measurements of heat transfer and pressure were made on the porous model surface, and high-speed schlieren photography was used to examine the structure and stability of the shock layer. Results are presented which show how the heat transfer and shock layer stability vary for gases of different molecular weights for a range of Reynolds numbers and mass-addition rates.

Holden, M. S.↗