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At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRS1924

A Method for the Instantaneous Determination of the Velocity and Direction of the Wind

The laboratory instruments, which we often constructed with makeshift means, gave encouraging results and showed that they could satisfactorily meet the required conditions. By limiting ourselves to the employment of hot wires of 0.05 mm (0.002 in.) diameter, we obtained instruments which faithfully followed all the wind fluctuations of over 0.1 second and even much more rapid variations without any very great error.

INSTRUMENTS - ANEMOMETERS↗

NASA NTRS1942

An Experimental Investigation of Flow Across Tube Banks

Flow across tube banks was investigated by surveys of total dynamic and static pressure by visualization of the flow through the use of titanium tetrachloride smoke, by thermocouple surveys of heated tubes, and by hot-wire surveys of both heated and unheated tubes. It was found that turbulence increased as the depth of the bank increased and that the broad wake behind each tube affected flow over the succeeding tubes.

AIR FLOW, TURBULENT-MEASUREMENT, HOT-WIRE↗

NASA NTRS2024

Background Turbulence Characterization of the Curved Duct Test Rig

Interest in applying acoustic treatment to nontraditional locations of turbofan engines has led to recent testing of acoustically treated airfoils in the NASA Langley Curved Duct Test Rig. Current testing focuses only on sound attenuation by the sample when exposed to an incident sound field driven by a loudspeaker array. However, there may be much to gain from an aeroacoustic study of the interaction of turbulence with treated airfoils, especially in the case of acoustically treated outlet guide vane designs. Thus, the intent of this study is to take the first step in assessing the aeroacoustic quality of the NASA Langley Curved Duct Test Rig (typically only used for grazing flow studies) by examining the flow quality. The background turbulence levels are measured using hot-wire anemometry just upstream of the test section. Measurements indicate that the turbulence intensity is less than 0.3% in the core region of the flow. The autospectral densities show cavity tones and weak vortex shedding present in the core. The vortex shedding is determined to be from the upstream total pressure probe used to determine flow speed. The cavity tones are found to be the fundamental and harmonic frequencies of a porous ceramic tubular acoustic liner sample that separates the acoustic drivers from the flow region. Recommendations for improving the aeroacoustic quality of the tunnel are provided, such as removing the upstream probe and redesigning the ceramic tubular liner. Future acoustic characterization of the background levels is also recommended to further understand the feasibility of aeroacoustic studies in CDTR.

Wind Tunnel Characterization↗

NASA NTRS1998

Experimental Study of Boundary Layer Behavior in a Simulated Low Pressure Turbine

A detailed investigation of the flow physics occurring on the suction side of a simulated Low Pressure Turbine (LPT) blade was performed. A contoured upper wall was designed to simulate the pressure distribution of an actual LPT blade onto a flat plate. The experiments were carried out at Reynolds numbers of 100,000 and 250,000 with three levels of freestream turbulence. Freestream turbulence levels ranging from 0.8% to 3% was used in this experiment. Smoke-wire flow visualization data was used to confirm that the boundary layer was separated and formed a bubble. Hot-wires (single and x-wire) and surface mounted hot-film gases and static pressure taps were used to map the flowfield. The transition process over the separated flow region is observed to be similar to a laminar free shear layer flow with the formation of a large coherent eddy structure. For each condition, the locations defining the separation bubble were determined by careful examination of pressure and mean velocity profile data. Transition onset location and length determined from intermittency profiles decrease as freestream turbulence levels increase. Additionally, the length and height of the laminar separation bubbles were observed to be inversely proportional to the levels of freestream turbulence.

Shyne, Rickey J.↗

NASA NTRS1992

Hot wire/film behavior in low-temperature gases

Commercially available hot wires/films were used to measure the velocities of evaporated hydrogen or helium gas during cryogenic mixing experiments. Hot wires were found to be too delicate to use in this harsh environment. Hot films were rugged enough to use at cryogenic temperatures even though they failed after a number of thermal cycles. Since the hot films have small aspect ratios, 13.4 and 20, they are quite sensitive to the thermal loading, Tw/Tg, even with a correction for the conduction end loss. In general, although the increase of the Nusselt number with Reynolds number at low temperatures was similar to that at room temperature, there was also a pronounced variation with Tw/Tg over the large range of 1.2 to 12 investigated.

Kwack, E. Y.↗

NASA NTRS1986

A summary of Reynolds number effects on some recent tests in the Langley 0.3-meter transonic cryogenic tunnel

Reynolds number effects noted from selected test programs conducted in the Langley 0.3-Meter Transonic Cryogenic Tunnel (0.3-m TCT) are discussed. The tests, which cover a unit Reynolds number range from about 2.0 to 80.0 million per foot, summarize effects of Reynolds number on: (1) aerodynamic data from a supercritical airfoil, (2) results from several wall interference correction techniques, and (3) results obtained from advanced, cryogenic tests techniques. The test techniques include: (1) use of a cryogenic sidewall boundary layer removal system, (2) detailed pressure and hot wire measurements to determine test section flow quality, and (3) use of a new hot film system suitable for transition detection in a cryogenic wind tunnel. The results indicate that Reynolds number effects appear most significant when boundary layer transition effects are present and at high lift conditions when boundary layer separation exists on both the model and the tunnel sidewall.

Johnson, C. B.↗

NASA NTRS2008

Microstructural Evaluation and Comparison of Solder Samples Processed Aboard the International Space Station

Samples from the In-Space Soldering Investigation (ISSI), conducted aboard the International Space Station (ISS), are being examined for post-solidification microstructural development and porosity distribution. In this preliminary study, the internal structures of two ISSI processed samples are compared. In one case 10cm of rosin-core solder was wrapped around a coupon wire and melted by conduction, whereas, in the other a comparable length of solder was melted directly onto the hot wire; in both cases the molten solder formed ellipsoidal blobs, a shape that was maintained during subsequent solidification. In the former case, there is clear evidence of porosity throughout the sample, and an accumulation of larger pores near the hot end that implies thermocapillary induced migration and eventual coalescence of the flux vapor bubbles. In the second context, when solder was fed onto the wire. a part of the flux constituting the solder core is introduced into and remains within the liquid solder ball, becoming entombed upon solidification. In both cases the consequential porosity, particularly at a solder/contact interface, is very undesirable. In addition to compromising the desired electrical and thermal conductivity, it promotes mechanical failure.

Grugel, R. N.↗

NASA NTRS1999

Effect of Wall Temperature on Roughness Induced Attachment-Line Transition

An experiment on a cooled swept cylinder in a low-disturbance Mach 1.6 wind tunnel is described. The flow attachment line is disturbed by trip wires of varying size and the laminar/turbulent state of the downstream boundary layer is determined with a hot wire. The results demonstrate that although cooling the wall increases the stability of the boundary layer, it promotes roughness induced transition. Analysis of the data suggests that the attachment- line Reynolds number can account for the effect of wall cooling if the viscosity is evaluated at a particular reference temperature.

Dietz, Anthony↗

NASA NTRS1983

Turbulence Characteristics of Swirling Flowfields

Combustor design phenomena; recirculating flows research; single-wire, six-orientation, eddy dissipation rate, and turbulence modeling measurement; directional sensitivity (DS); calibration equipment, confined jet facility, and hot-wire instrumentation; effects of swirl, strong contraction nozzle, and expansion ratio; and turbulence parameters; uncertain; and DS in laminar jets; turbulent nonswirling jets, and turbulent swirling jets are discussed.

Jackson, T. W.↗

NASA NTRS1991

Applications of hot-film anemometers in hypersonic shear layers

A wind tunnel test was conducted on a flat plate at zero angle of attack with a rearward facing 2D cooling film injector nozzle. The freestream Mach number was 8 and the injector Mach number was 3. The freestream Reynolds number varied from 0.43 to 3.3 million per ft during the test, and the injector flow rate was such that the jet exit and freestream static pressures were matched. The analysis reported herein will focus on data obtained at a freestream Reynolds number of 0.85 million per ft. The data consists of heat-transfer measurements obtained upstream and downstream of the injector nozzle and flowfield surveys obtained downstream of the injector nozzle with a pitot, total temperature, hot-film anemometer and hot-wire anemometer probes. The flowfield surveys were made at stations 0.1 to 9 in. downstream of the injector nozzle from near the model surface to approximately 2 in above the model surface. The hot-film anemometer was used to define the fluctuations in the shear layer separating the flows. The hot-film results are integrated with conventional measurement techniques to obtain a more complete description of the complicated shear layer separating hypersonic and supersonic flows.

Grubb, J. P.↗

NASA NTRS1980

Experimental investigation of a three dimensional turbulent boundary layer with a non disappearing pressure gradient

The results of measuring profiles of temporally determined velocities and Reynolds tension, wall shear stresses and pressure distribution in a three dimensional, turbulent boundary layer with pressure gradients in both tangential directions are reported. For determining the velocities X wire probes were used whose cooling was gauged according to magnitude and direction of the flow and was described with an effective cooling speed. In the evaluation consideration is given to the directional sensitivity of the hot wire. The ratio of the turbulence viscosities is calculated for both tangential directions and is found to be approximately N equals 1.2. Further, the profiles of the mixing path lengths for the flow direction are found to vary only slightly with increasing X-coordinates, while the boundary layer thickness increases substantially. The relationships of turbulent shear stress to turbulent, kinetic fluctuation energy is approximately constant over a large part of the boundary layer.

Mueller, U.↗

NASA NTRS1986

Resistance heating of Fe and W in diamond-anvil cells

A new method for internally heating a diamond-anvil cell is described. Fine wires of iron or tungsten are resistively heated in a gasketed cell, thus providing a uniformly distributed pressure that can be measured in situ by employing the ruby scale. Temperatures of several thousand degrees have been measured by fitting a black body radiation function to the spectrum of the hot wire taken with an optical multichannel analyzer. Temperatures as high as the melting temperature of tungsten have been achieved. The alpha-gamma and alpha-epsilon phase transitions of iron have been studied, and the results show excellent agreement with previous data obtained with piston-cylinder or externally-heated diamond cells.

Boehler, R.↗

NASA NTRS1992

Heat transfer from cylinders in subsonic slip flows

The heat transfer in heated wires was measured using a constant temperature anemometer over a Mach number range from 0.05 to 0.4 and pressures from 0.5 to 8.0 atmospheres. The total temperature ranged from 80 to 120 F and the wire diameters were 0.00015, 0.00032, and 0.00050 inch. The heat transfer data is presented in the form of a corrected Nusselt number. Based on suggested criteria, much of the data was obtained in the slip flow regime. Therefore, the data is compared with data having comparable flow conditions. The possible application of the heat transfer data to hot wire anemometry is discussed. To this end, the sensitivity of the wires to velocity, density, and total temperature is computed and compared using two different types of correlations.

Nagabushana, K. A.↗

NASA NTRS1956

Some Effects of Small-scale Flow Disturbance on Nozzle-burner Flames

Laminar-like and brush-like propane-air flames were obtained when wire grids were used as turbulence generators in a 1/2-inch nozzle burner. The laminar-like flames for grid-disturbed flow had a slightly higher burning velocity than "true" laminar flames (no grid used). The brush-like flames were similar to those obtained with pipe turbulent flow. Their burning-velocity dependence on a "flow disturbance" Reynolds number compared favorably with that obtained for pipe turbulent flames. Hot-wire-anemometer equipment was used to measure the flow disturbance intensity in the cold flow with and without the grids in place.

COMBUSTION, TURBULENT-FLOW↗

DOE OSTI2022

The Toughness of High-Strength Steel Weld Metals

Low-temperature phase transformation (LTPT) welding consumables are a new class of welding wires developed to mitigate hydrogen-induced cracking in the welding of high-strength steels without preheating or postweld heat treatment. LTPT weld metals have a high strength, but their toughness needs further investigation. LTPT weld metals predominately contain a martensite microstructure, which is necessary to achieve high strength; however, martensitic weld metals containing oxide inclusions have relatively poor toughness. For this study, three welding processes — gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and hot wire GTAW — were investigated. Optical microscopy, scanning electron microscopes, and transmission electron microscopes were employed for characterization. The role of the shielding gas in the formation of oxide inclusions in LTPT weld metals was investigated. The formation of oxide inclusions in the weld metals was related to the CO 2 in the shielding gas. When 100% Ar or a pure inert shielding gas mixture was used for all three welding processes, oxide inclusions were greatly reduced, and the weld metal toughness improved considerably, matching the base metal toughness. The mechanism by which inclusions promote fracture propagation in the weld metal was proposed.

36 MATERIALS SCIENCE↗

NASA NTRS1960

Investigation by Schlieren Technique of Methods of Fixing Fully Turbulent Flow on Models at Supersonic Speeds

An investigation has been made of the effectiveness of two-dimensional wire and three-dimensional grandular-type roughnesses for fixing transition on a 27 deg cone at a free-stream Mach number of 2.20. One height of each type of roughness was investigated over a free-stream Reynolds number per foot range of about 1.0 x 10 (exp 6) to 7.0 x 10 (exp 6). The tests were made at an angle of attack of 0 deg and with essentially zero heat transfer. The results indicate that, within the Reynolds number per foot range investigated, both two-dimensional wire and three-dimensional granular types of roughness caused large forward movements of transition at constant Reynolds number per foot; however, the forward movement with increase in Reynolds number per foot was very slow for the two-dimensional wire roughness and transition never reached the roughness location as it did with the three-dimensional granular roughness. An extrapolated value of the roughness Reynolds number (based on roughness height and flow conditions at the outer edge of the roughness) for the first appearance of forward movement from the smooth-cone case for the three-dimensional granular roughness was in good agreement with the value of about 600 for the first appearance of turbulent bursts obtained on a similar cone by the hot-wire technique. The range of values of roughness Reynolds number for which a fully turbulent boundary layer existed in the vicinity of the roughness element was about 4,500 to 6,500.

Jackson, Mary W.↗

DOE OSTI2021

IoT Devices and Applications for Wire-Based Hybrid Manufacturing Machine Tools

Hybrid manufacturing machine tools have the potential to be a disruptive technology as they can leverage the benefits of both additive and subtractive manufacturing by incorporating both processes on the same machine while limiting the downsides of the individual processes. Since these machines use two very disparate manufacturing processes and hybrid manufacturing is an emerging technology, it will be useful to monitor data coming from the machine and apply it to improve the manufacturing process, the operation of the machine, and to integrate the machine into the larger digital framework of Industrial Internet of Things (IoT). The present work discusses IoT devices that would be beneficial to add to a hybrid machine tool as well as applications for those devices. The proposed methods discussed in this work have not been experimentally implemented on a hybrid machine tool and so there are no performance data available yet. The hybrid machine tool used as a basis to generate these IoT applications is the Mazak VC-500A/5x AM Hot Wire Deposition, which is a 5-axis machine tool incorporated with a wire feedstock 4kW laser deposition system. Methodologies and applications will be outlined for machine health and process monitoring. Other areas covered include process benchmarking, secure networking options for the proposed IoT framework, and hybrid process improvement. Limitations of these methods and future work for new sensor devices and application areas is also discussed.

Thien, Austen↗

NASA NTRS1987

Flowfield measurements in a separated and reattached flat plate turbulent boundary layer

The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.

Patrick, William P.↗