Daryl J. Monson

Bio: Daryl J. Monson is an academic researcher from Ames Research Center. The author has contributed to research in topics: Wind tunnel & Boundary layer. The author has an hindex of 8, co-authored 14 publications receiving 356 citations.

Boundary-layer transition and global skin friction measurement with an oil-fringe imaging technique

Abstract: A new oil-fringe imaging fkin friction (FISF) technique to measure skin friction on wind tunnel models is presented In the method used to demonstrate the technique, lines of oil are applied on surfaces that connect the intended sets of measurement points, and then a wind tunnel is run so that the oil thins and forms interference fringes that are spaced proportional to local skin friction After a run the fringe spacings are imaged with a CCD-array digital camera and measured on a computer Skin friction and transition measurements on a two-dimensional wing are presented and compared with computational predictions

Boundary-layer transition and global skin friction measurement with an oil-fringe imaging technique

Abstract: A new oil-fringe imaging fkin friction (FISF) technique to measure skin friction on wind tunnel models is presented. In the method used to demonstrate the technique, lines of oil are applied on surfaces that connect the intended sets of measurement points, and then a wind tunnel is run so that the oil thins and forms interference fringes that are spaced proportional to local skin friction. After a run the fringe spacings are imaged with a CCD-array digital camera and measured on a computer. Skin friction and transition measurements on a two-dimensional wing are presented and compared with computational predictions.

Skin-friction measurements and calculations on a lifting airfoil

Abstract: A new technique for measuring skin friction was employed to help document the flow on an airfoil at angles of attack from -0.5 to 11.5 deg. Surface pressures were also measured on both the wing and wind-tunnel walls. The experiment was conducted at a freestream Mach number of 0.2 and Reynolds numbers of 0.6, 2, and 6 x 10 6 . The objective of the study was to provide data and boundary condition information sufficient for the validation of numerical simulations. Such a simulation of the experiment was conducted using the INS2D Navier-Stokes code with the shear-stress-transport turbulence model. The computations provide a good description of both laminar and turbulent shear levels, except for turbulent flow on the top surface of the wing at the higher angles of attack.

Skin Friction Measurements by a Dual-Laser-Beam Interferometer Technique

Abstract: A portable dual-laser-beam interferometer that nonintrusively measures skin friction by monitoring the thickness change of an oil film subject to shear stress is described. The method is an advance over past versions in that the troublesome and error-introducing need to measure the distance to the oil leading edge and the starting time for the oil flow has been eliminated. The validity of the method was verified by measuring oil viscosity in the laboratory, and then using those results to measure skin friction beneath the turbulent boundary layer in a low speed wind tunnel. The dual-laser-beam skin friction measurements are compared with Preston tube measurements, with mean velocity profile data in a "law-of-the-well" coordinate system, and with computations based on turbulent boundary-layer theory. Excellent agreement is found in all cases. (This validation and the aforementioned improvements appear to make the present form of the instrument usable to measure skin friction reliably and nonintrusively in a wide range of flow situations in which previous methods are not practical.)

Experiments with a CO2 gas-dynamic laser

Abstract: Carbon dioxide gas dynamic layer in shock tube facility, measuring shape, time, output energy, beam diameter, etc

Features of a reattaching turbulent shear layer in divergent channel flow

Abstract: Experimental data have been obtained in an incompressible turbulent flow over a rearward-facing step in a diverging channel flow. Mean velocities, Reynolds stresses, and triple products that were measured by a laser Doppler velocimeter are presented for two cases of tunnel wall divergence. Eddy viscosities, production, convection, turbulent diffusion, and dissipation (balance of kinetic energy equation) terms are extracted from the data. These data are compared with various eddy-viscosity turbulence models. Numerical calculations incorporating the k-epsilon and algebraic-stress turbulence models are compared with the data. When determining quantities of engineering interest, the modified algebraic-stress model (ASM) is a significant improvement over the unmodified ASM and the unmodified k-epsilon model; however, like the others, it dramatically overpredicts the experimentally determined dissipation rate.

Reynolds number effect on the skin friction in separated flows behind a backward-facing step

Abstract: Results from the present study show that the skin-friction coefficient decreases as the Reynolds number,Re h , increases in the following manner, C f ,min=−019Re h −1/2 The -1/2 power relationship deduced from the correlationC f,min vsRe h indicates laminar like behavior which is consistent with the findings of Adams et al (1984) Clauser's method, which is frequently used for the determination of the wall shear stress, leads to erroneous results when applied to the velocity measurements obtained in the near field of reattaching flows (and many other wall-bounded nonequilibrium flows) Direct measurements of theC f using the LOI technique give higher values than those obtained by the classical techniques The normalized mean velocity on the wall coordinates violates the universal law-of-the-wall in the near field of reattaching flows

An experimental study of a three-dimensional pressure-driven turbulent boundary layer

Abstract: A three-dimensional, pressure-driven turbulent boundary layer created by an idealized wing-body junction flow was studied experimentally. The data presented include time-mean static pressure and directly measured skin-friction magnitude on the wall. The mean velocity and all Reynolds stresses from a three-velocity-component fibre-optic laser-Doppler anemometer are presented at several stations along a line determined by the mean velocity vector component parallel to the wall in the layer where the u 2 kinematic normal stress is maximum (normal-stress coordinate system). This line was selected by intuitively reasoning that overlap of the near-wall flow and outer-region flow occurs at the location where u 2 is maximum. Along this line the flow is subjected to a strong crossflow pressure gradient, which changes sign for the downstream stations. The shear-stress vector direction in the flow lags behind the flow gradient vector direction. The flow studied here differs from many other experimentally examined three-dimensional flows in that the mean flow variables depend on three spatial axes rather than two axes, such as flows in which the three-dimensionality of the flow has been generated either by a rotating cylinder or by a pressure gradient in one direction only throughout the flow.

Review of CW high-power CO 2 lasers

Abstract: Various forms of CO 2 lasers have achieved CW powers in the 60-kW range, operating efficiencies approaching 30 percent, pulse energies of approximately 2000 J, pulsewidths less than 1 ns, peak pulse powers in excess of 109W, a frequency stability of a few parts in 1012, and sealed-off tube lifetimes of many thousands of hours. In addition, the laser can be easily Q-switched as well as gain-switched and has been electrically, optically, gas-dynamically, and chemically pumped. In addition to all these attributes, the CO 2 laser output wavelength lies within one of the best atmospheric windows. It should be no surprise then that during the last eight years, the CO 2 laser has firmly established itself as a candidate for recognition as the most important among the numerous laser devices presently known. Depending on the gas pressure, gas flow rate, pumping mechanisms, gas mixture, etc., CO 2 lasers can exhibit a wide range of noise, bandwidth, gain, and power saturation characteristics. This flexibility enables a designer to optimize the performance of CO 2 laser stable-frequency master oscillators; power oscillators; low-noise high-gain preamplifiers; intermediate-power or high-power amplifiers. As a result, CO 2 laser oscillator-amplifier chains can be designed utilizing guidelines similar to those which have been extensively applied in the design of transmitters in the RF and microwave region of the electromagnetic spectrum.