Engineering topics

Gartrell, Luther R.

Publications and source records attributed to Gartrell, Luther R..

6 records

NASA NTRS1995

Velocity Fields of Axisymmetric Hydrogen-Air Counterflow Diffusion Flames from LDV, PIV, and Numerical Computation

Laminar fuel-air counterflow diffusion flames (CFDFs) were studied using axisymmetric convergent-nozzle and straight-tube opposed jet burners (OJBs). The subject diagnostics were used to probe a systematic set of H2/N2-air CFDFs over wide ranges of fuel input (22 to 100% Ha), and input axial strain rate (130 to 1700 Us) just upstream of the airside edge, for both plug-flow and parabolic input velocity profiles. Laser Doppler Velocimetry (LDV) was applied along the centerline of seeded air flows from a convergent nozzle OJB (7.2 mm i.d.), and Particle Imaging Velocimetry (PIV) was applied on the entire airside of both nozzle and tube OJBs (7 and 5 mm i.d.) to characterize global velocity structure. Data are compared to numerical results from a one-dimensional (1-D) CFDF code based on a stream function solution for a potential flow input boundary condition. Axial strain rate inputs at the airside edge of nozzle-OJB flows, using LDV and PIV, were consistent with 1-D impingement theory, and supported earlier diagnostic studies. The LDV results also characterized a heat-release hump. Radial strain rates in the flame substantially exceeded 1-D numerical predictions. Whereas the 1-D model closely predicted the max I min axial velocity ratio in the hot layer, it overpredicted its thickness. The results also support previously measured effects of plug-flow and parabolic input strain rates on CFDF extinction limits. Finally, the submillimeter-scale LDV and PIV diagnostics were tested under severe conditions, which reinforced their use with subcentimeter OJB tools to assess effects of aerodynamic strain, and fueVair composition, on laminar CFDF properties, including extinction.

Pellett, Gerald L.↗

NASA NTRS1994

Correcting For Seed-Particle Lag In LV Measurements

Two experiments conducted to evaluate effects of sizes of seed particles on errors in LV measurements of mean flows. Both theoretical and conventional experimental methods used to evaluate errors. First experiment focused on measurement of decelerating stagnation streamline of low-speed flow around circular cylinder with two-dimensional afterbody. Second performed in transonic flow and involved measurement of decelerating stagnation streamline of hemisphere with cylindrical afterbody. Concluded, mean-quantity LV measurements subject to large errors directly attributable to sizes of particles. Predictions of particle-response theory showed good agreement with experimental results, indicating velocity-error-correction technique used in study viable for increasing accuracy of laser velocimetry measurements. Technique simple and useful in any research facility in which flow velocities measured.

Jones, Gregory S.↗

NASA NTRS1993

Application of laser Doppler velocimeter to chemical vapor laser system

A laser Doppler velocimeter (LDV) system was used to measure iodide vapor flow fields inside two different-sized tubes. Typical velocity profiles across the laser tubes were obtained with an estimated +/-1 percent bias and +/-0.3 to 0.5 percent random uncertainty in the mean values and +/-2.5 percent random uncertainty in the turbulence-intensity values. Centerline velocities and turbulence intensities for various longitudinal locations ranged from 13 to 17.5 m/sec and 6 to 20 percent, respectively. In view of these findings, the effects of turbulence should be considered for flow field modeling. The LDV system provided calibration data for pressure and mass flow systems used routinely to monitor the research laser gas flow velocity.

Gartrell, Luther R.↗

NASA NTRS1991

Comparison of laser transit anemometry data analysis techniques

Two techniques for the extraction of two-dimensional flow information from laser transit anemometry (LTA) data sets are presented and compared via a simulation study and experimental investigation. The methods are a probability density function (PDF) estimation technique and a marginal distribution analysis technique. The simulation study builds on the results of previous work and provides a quantification of the accuracy of both techniques for various LTA data acquisition scenarios. The experimental comparison consists of using an LTA system to survey the flow downstream of a turbulence generator in a small low-speed wind tunnel. The collected data sets are analyzed and compared.

Humphreys, William M., Jr.↗

NASA NTRS1990

An investigation of the effects of seeding in laser velocimeter systems

Errors in laser velocimeter measurements associated with the lag of seeding particles in subsonic and transonic flows were investigated experimentally and theoretically. In a low-speed flow, errors exceeding 5 percent were measured for particle diameters greater than 5 microns. In transonic flows, errors up to 60 percent were measured for particles with 2-3-micron diameters and up to 30 percent for 1-2-micron particles. A three-dimensional method was developed to determine the magnitude of errors due to the lag in seeding particle response based on a simplified particle force balance model and an empirical coefficient of drag model for spherical bodies. A one-dimensional version of this model was shown to be successful in correcting velocity measurements in both the subsonic and transonic flow regions.

Jones, Gregory S.↗

NASA NTRS1987

Basic aerodynamic research facility for comparative studies of flow diagnostic techniques

Current flow diagnostic research efforts are focusing on higher order flow field data bases, such as those generated by laser velocimetry (LV), hot-wire anemometry, and multi-hole pressure probes. Recent low-speed comparisons of results obtained with LV and hot wires have revealed strengths and weaknesses of each instrument. A seeding study will be initiated to determine particulate tracking ability.

Jones, Gregory S.↗