Engineering topics

Sandborn, V. A.

Publications and source records attributed to Sandborn, V. A..

At least 19 records

NASA NTRS1991

Evaluation of high Reynolds number flow in a 180 degree turn-around-duct

Mean and turbulent velocities were measured for the flow in a 180 degree turn-around-duct over a Reynolds number range from 600,000 to greater than 900,000. The measurements were made in water using a forward scattering laser velocimeter. A duct of 100 x 10 cm constant cross-section, with a mean radius of curvature (centerline) of 10 cm was employed for the study. The measurements are in agreement with previous studies in that the use of local bulk velocity to nondimensionalize the mean and turbulent velocities reduce the Reynolds number variations. The basic phenomenon of relaminarization along the inner surface at the exit of the turn are similar to the flow observed at low Reynolds numbers. The separation bubble region shows a systematic variation with Reynolds number, however the Reynolds number effect may be of second order in the calculation of the overall flow. Large tangential, radial, and lateral turbulent velocities are measured along the outer surface of the turn.

Sandborn, V. A.↗

NASA NTRS1986

Computational and experimental study of turbulent flows in 180 degree bends

A theoretical and experimental investigation of turbulent flows inside a 180-deg strongly curved channel is included in the present study. A 10 by 100 centimeter water channel with a 10 centimeter radius turn was employed for the experimental study. Data measured are velocity profiles and distributions of longitudinal turbulence intensity. Numerical investigations are performed by solving the incompressible Navier-Stokes equations and turbulence models using a finite difference flow solver in generalized curvilinear coordinate systems. A widely used two-equation turbulence model and its modified version, which includes the effect of strong curvature on the turbulence length scale through a relation of algebraic Reynolds stress model, are employed to predict the turbulence quantities inside the flow field. Improvements on the predictions are obtained using the present approach.

Chen, Y. S.↗

NASA NTRS1979

Evaluation of the time dependent surface shear stress in turbulent flows

The time dependent surface shear stress has been evaluated using surface heat transfer measurements. For fully developed turbulent pipe and open channel water flows, and incompressible and compressible turbulent boundary layer air flows the measurements indicate the absolute magnitude of the surface shear stress fluctuations will be greater than two times the mean values. The root-mean-square shear stress fluctuations were of the order of 0.2 to 0.4 times the mean surface shear values. Due to these large surface shear stress fluctuations and the nonlinear relation between heat transfer and shear stress, a special technique has been developed to evaluate the measurements. It was found that the non-linear averaging errors for a hot film-surface shear stress gauge in a fully developed pipe flow was of the order of 10 percent at low velocities. A hot wire-surface shear stress gauge was employed for measurements of turbulent boundary layers in air.

Sandborn, V. A.↗

NASA NTRS1979

Particle dynamics associated with the space environment

A major factor in dust dynamics in a microgravity environment is the absence of settling; hence, Spacelab air will contain larger particles than a comparable laboratory on earth. In addition, the presence of low level acceleration fluctuations (thruster firings, crew motions, etc.) could inhibit dust removal by surface scavenging. Because of the presence of larger particles, aerosol dynamics at larger Reynolds numbers must be considered. An accurate drag coefficient for spherical particles was developed for the higher Reynolds number phenomena. A general graphic correlation for the drag coefficient as a function of Reynolds and Knudsen numbers was developed based on currently available drag data for spheres. The general equations that govern dust dynamics were reviewed.

Sandborn, V. A.↗

NASA NTRS1977

Boundary layer shear stress in subsonic and supersonic flow

A wide range of shear stress distributions for turbulent boundary layers is examined. A solution for the shear stress in terms of the mean flow is obtained for the limiting case of large Reynolds numbers. Attention is given to turbulent boundary layer shear stress, zero pressure gradient flow, increasing pressure gradient flow, and decreasing pressure gradient flow.

Sandborn, V. A.↗

NASA NTRS1976

Evaluation of mean and turbulent velocity measurements in subsonic accelerated boundary layers

Exploratory measurements of the mean and turbulent flow in the wall boundary layer of a 15.2- by 10.2-cm channel were obtained as part of an instrumentation development program for measurements in compressible flow. Mean surface and flow field surveys were obtained at channel Mach numbers ranging from 0.2 to 0.9. The mean velocity distributions were obtained with total pressure probes and a laser velocimeter. At a channel Mach number of 0.2, several types of hot-wire probes were used to obtain both velocity fluctuations and Reynolds shear-stress results.

Sandborn, V. A.↗

NASA NTRS1976

Outer flow and turbulence in boundary layers

Results presented in report indicate that perturbations travel through boundary layer and give rise to turbulence production process which occurs near viscous sublayer. Part of turbulence produced near wall, in turn, moves outward and eventually produces convoluting outer edge of boundary layer to reproduce and sustain itself.

Cliff, W. C.↗

NASA NTRS1976

Evaluation of mean and turbulent velocity measurements in subsonic accelerated boundary layers

Exploratory measurements of the mean and turbulent flow in the wall boundary layer of a 15.5- by 10.2-cm channel were obtained as part of an instrumentation development program for measurements in compressible flow. Mean surface and flow-field surveys were obtained at channel Mach numbers ranging from 0.2 to 0.9. The mean velocity distributions were obtained with total pressure probes and a laser velocimeter. At a channel Mach number of 0.2, several types of hot-wire probes were used to obtain both velocity fluctuations and Reynolds shear-stress results.

Sandborn, V. A.↗

NASA NTRS1976

Effect of velocity gradients on measurements of turbulent shear stress

Experiments were carried out to evaluate the effects of normal velocity gradients on hot wire measurements in a subsonic boundary layer of the same size as the flow investigated by Johnson and Rose (1975). Both hot wire and film anemometers were used to measure the turbulent properties of the boundary layer. A special X-wire probe with one wire vertical and the other at an angle of about 40 deg to the flow was used to demonstrate the gradient effects. The results indicate that major errors are encountered when mean and turbulent velocity gradients exist along the length of hot wire sensors, the problem being more pronounced at high speeds. Although the split film sensor results show a significant improvement over the X-wire sensor, further reduction in the space resolution of sensors by roughly an order of magnitude would appear to be necessary to reduce the error to acceptable values near the wall.

Sandborn, V. A.↗

NASA NTRS1975

Correlation between the outer flow and the turbulent production in a boundary layer

Space-time velocity correlation measurements between fluctuations occurring in the convoluting outer edge of a flat boundary layer with fluctuations occurring near the viscous subregion were made. The correlations indicate that information is propagated from the outer region to the inner region. The migration of turbulence away from the wall was previously studied in the open literature. The results presented here along with the migration results lend support to the limit cycle model for turbulence production.

Cliff, W. C.↗

NASA NTRS1974

Cross beam weather watch study

An optical cross beam correlation method has been proposed as a remote measuring system for atmospheric studies. Atmospheric measurements are limited due to the difficulty of placing measuring instruments at the desired location. Although meteorological towers and balloon flights are able to obtain wind data, they are greatly limited in their location. Thus, a real need exists for remote-sensing instrumentation in atmospheric measurements. Previous methods proposed to remotely sense atmospheric conditions include several types of microwave units, acoustic sounders, infrared sensors, optical sensors, and related laser techniques. The evaluation of a simple visible optical technique as a possible remote measuring system is discussed. A feasibility study of field tests of the instrumentation at meteorological sites is reported.

Sandborn, V. A.↗

NASA NTRS1974

Experimental probability density distributions for optical and infrared cross-beam units

A series of cross beam experiments for measuring meteorological parameters was conducted. Both optical and infrared sensors were tested for comparison. The test configuration and experiment identification are provided. A data report is presented for an approximate analysis of the probability density distributions of the signals from both the optical and the infared units. Two runs representing each of the two types of cross-beam units were selected for analysis. Probability density functions are also presented for the instantaneous product of the signals for each of the runs.

Huff, L. L.↗

NASA NTRS1974

Preliminary analysis of cross beam data from the Gun Barrel Hill site

Preliminary evaluation of cross beam data taken at the Gun Barrell Hill test site of ESSA is presented. The evaluation is made using the analog Princeton Time Correlator. A study of the frequency band width limitations of the Princeton Time Correlator is made. Based on the band width limitations, it is possible to demonstrate that nearly identical correlation is obtained for frequencies from .01 to 3.9 hertz. Difficulty is encountered in that maximums in the correlation curves do not occur at zero time lag for zero beam separations.

Sandborn, V. A.↗

NASA NTRS1974

Check out of rebuilt optical cross-beam units

Preliminary evaluations of limited cross beam data taken with the rebuilt optical cross beam units at the Gun Barrel Hill Test Site of ESSA are presented. The evaluations were made using the analogue Princeton Time Correlator. A study of these evaluations indicates that the rebuilt units are performing satisfactorily. However, there are indications that, in order to obtain useful information from the cross-correlations, it is essential to make judicious choices of computation time and frequency band pass filtering for the analysis of the data.

Huff, L. L.↗

NASA NTRS1974

Optical cross beam field tests at ESSA Haswell Field site, October 1969

A series of tests with both the visible and IR optical cross beam systems was made at the Haswell, Colorado, Field Site of ESSA. This memorandum covers only the details of the test setup and runs. A joint field test program was undertaken by ESSA at a 164 meter (500 foot) meteorological tower. The tower was instrumented with wind sensors, temperature sensors, temperature sensors, fluctuating wind and temperature sensors and humidity sensors. The sensors were located at three elevations: 42, 192 and 162 meters. A movable elevator was also instrumented and could be positioned at any desired location along the tower height. The main object of the cross beam studies was to compare the visible and IR systems. The instruments were also arranged so that direct comparison with the sensors on the tower can be made.

Sandborn, V. A.↗

NASA NTRS1974

Analysis of cross beam runs taken at Haswell Field site, October 1969

A series of cross beam experiments was conducted at the ESSA field site at Haswell, Colorado. Both the optical visual and infrared units were operated on a comparison basis. A data report of the initial auto- and cross-correlation evaluation of these tests is presented. The original test data from the Haswell tests were recorded on F M magnetic tape. A copy of the original tapes was made and employed for the present analysis. The tapes were played back at 60 inches per second for analysis. Some of the infrared units runs (Run Nos. 8,25,40,41,42,43,44,45) were played back at 30 inches per second in order to gain sufficient averaging time. The averaging time was nominally 3200 seconds real time at 60 inches per second and 1600 seconds real time at 30 inches per second. These averaging times correspond to 100 seconds of averaging time of the correlator.

Huff, L. L.↗

NASA NTRS1974

A review of turbulence measurements in compressible flow

A survey of turbulence measurements in compressible flows is presented. The majority of turbulence measurements at super- and hypersonic speeds were made for the zero pressure gradient, turbulent boundary layer. It was found that the nondimensional turbulent stress terms for the zero pressure gradient flow appear to agree closely with equivalent incompressible measurements in the outer part of the boundary layer. The stress terms were nondimensionalized by the wall value of shear stress and plotted versus the distance from the wall, nondimensionalized by the boundary-layer thickness. Indirect evaluation of the total shear stress distribution from mean velocity measurements for both super- and hypersonic flows (zero pressure gradient, two-dimensional flows) indicate a near universal distribution. These total shear stress curves also agree very closely with measured incompressible shear stress distributions. Recent laser anemometer measurements of the turbulent Reynolds shear stress (puv), reported by Johnson and Rose for a Mach number 2.9 flow, are in reasonable agreement with the expected total shear stress curve over the outer 60% of the boundary layer.

Sandborn, V. A.↗

NASA NTRS1974

Boundary layer separation and reattachment

A review of developments in a new model for boundary-layer separation is presented. The separation model encompasses timevarying as well as steady-flow conditions. Engineering criteria in terms of calculable pressure gradients are obtained for both laminar and turbulent boundary-layer separation. These criteria, together with limited information on time-dependent separations, should be of value in predicting flows in turbomachinery. The reattachment of boundary layers is also shown to fit within the separation model.

Sandborn, V. A.↗