scispace - formally typeset
Search or ask a question

Showing papers on "Freestream published in 1987"


Journal ArticleDOI
Chul Park1
TL;DR: In this paper, a two-temperatur e chemical-kinet ic model for air is assessed by comparing theoretical results with existing experimental data obtained in shock tubes, ballistic ranges, and flight experiments.
Abstract: A two-temperatur e chemical-kinet ic model for air is assessed by comparing theoretical results with existing experimental data obtained in shock tubes, ballistic ranges, and flight experiments. In the model, one temperature (T) is assumed to characterize the heavy-particle translational and molecular rotational energies, and another temperature (Tv) the molecular vibrational, electron translational, and electronic excitation energies. The theoretical results for nonequilibrium flow in shock tubes are obtained using the computer code STRAP (shock-tube radiation program) and for flow along the stagnation streamline in the shock layer over spherical bodies using the newly developed code SPRAP (stagnation-point radiation program). Substantial agreement is shown between the theoretical and experimental results for relaxation times and radiative heat fluxes. At very high temperatures, the spectral calculations need further improvement. The present agreement provides strong evidence that the two-temperature model characterizes principal features of nonequilibriu m airflow. New theoretical results using the model are presented for the radiative heat fluxes at the stagnation point of 6 m radius sphere, representing an aeroassisted orbital transfer vehicle, over a range of freestream conditions. Assumptions, approximations, and limitations of the model are discussed. Nomenclature = average molecular speed ^/$kT/nm, cm s ~ ! = pre-exponential factor in reaction rate coefficient, cm3mole~ 1 s~ * - average vibrational energy per particle, erg = average vibrational energy per particle under equilibrium, erg = reaction energy, erg

690 citations



Journal ArticleDOI
TL;DR: In this article, a numerical solution for the unsteady flow over a three-dimensional cavity at a freestream Mach number of 1.5 and Reynolds number 1.09 x 10 6.
Abstract: A numerical solution is presented for the unsteady flow over a three-dimensio nal cavity at a freestream Mach number of 1.5 and Reynolds number of 1.09 x 10 6. The self-sustained oscillatory motion within the cavity is generated numerically by integration of the time-dependent compressible three-dimensional Reynolds averaged Navier-Stokes equations. Effects of fine-scale turbulence are simulated via a simple algebraic closure model. Details of the flowfield structure are elucidated, and it is verified that the fundamental behavior of the unsteady phenomena is two dimensional. Comparison with experimental data is made in terms of the mean static pressure and overall acoustic sound pressure levels within the cavity, as well as with the acoustic frequency spectra of the oscillation along the cavity floor and rear bulkhead.

155 citations


Journal ArticleDOI
TL;DR: In this article, the results of wind-tunnel studies of dynamic stall for an NACA 0015 airfoil pitching about the midchord at a constant rate were reported.
Abstract: This paper reports the results of wind-tunnel studies of dynamic stall for an NACA 0015 airfoil pitching about the midchord at a constant rate. Time-varying pressure readings from 16 locations on the airfoil were collected and used to determine the lift, pressure-drag, and moment coefficients as functions of angle of attack for 100 test cases, covering 20 dynamic airspeed/pitch rate combinations. The dynamic-stall effects of the change (from steady flow) in the angle of attack at which separation occurs at the quarter chord and the change in the angle of attack at which stall occurs were extracted from these data and found to collapse onto a nondimensional pitch rate given by the chord times the pitch rate divided by two times the freestream velocity. The results showed that relatively slow pitch rates had dramatic effects on both the delay of stall and the magnitude of the maximum lift coefficient. The nondimensional rate is a measure of the speed of the leading edge divided by the speed of the freestream; it was found that nondimensional rates of less than 0.03 more than doubled the maximum coefficient of lift. The reduced data also clearly indicate that quarter-chord separation is systematically linked to dynamic stall.

105 citations


Journal ArticleDOI
TL;DR: In this article, the Nusselt number within and just downstream of a region of flow separation displays a maximum whose location, relative to the point of reattachment of the flow, was investigated.

90 citations


Journal ArticleDOI
TL;DR: In this paper, three indirect methods for characterizing the drag of an arbitrarily rough surface on a flat plate are derived or rederived from the similarity laws of turbulent shear flows.
Abstract: Three indirect methods for characterizing the drag of an arbitrarily rough surface on a flat plate are derived or rederived from the similarity laws of turbulent shear flows These are: (1) the well- known procedure using displacement thickness; (2) the probably not- so-well-known procedure using total drag; and (3) a proposed new procedure using only the freestream velocity and a local shear stress The classical indirect procedure for pipe flow is also derived to show a commonality with the flat-plate methods

87 citations


Journal ArticleDOI
TL;DR: In this article, data and correlations for transition from laminar to turbulent flow on 45 and 60-deg swept cylinders are presented, and the results show that end plates or large trips near the upstream end of the cylinders cause turbulent flow along the entire attachment line of the models over the freestream test Reynolds number range (based on cylinder diameter) of approximately 1.6 x 10.
Abstract: Data and correlations for transition from laminar to turbulent flow on 45and 60-deg swept cylinders are presented. The data were obtained at Mach 3.5 in the Pilot Low-Disturbance Wind Tunnel at NASA Langley. Freestream noise levels were varied during the test program from extremely low values that were essentially in the instrument noise range to much higher values approaching those in conventional wind tunnels. The results show that end plates or large trips near the upstream end of the cylinders cause turbulent flow along the entire attachment line of the models over the freestream test Reynolds number range (based on cylinder diameter) of approximately 1.0 X10

54 citations


Proceedings ArticleDOI
01 Jun 1987
TL;DR: In this article, the role of compressible linear stability theory in prediction of boundary layer transition at supersonic and hypersonic speeds is investigated, and it is shown that the first oblique Tollmien-Schlichting mode is responsible for transition at adiabatic wall conditions for freestream Mach numbers up to 7.
Abstract: In this paper, the role of compressible linear stability theory in prediction of boundary layer transition at supersonic and hypersonic speeds is investigated. Computations for sharp cones, using the e exp N method with N = 10, show that the first oblique Tollmien-Schlichting mode is responsible for transition at adiabatic wall conditions for freestream Mach numbers up to 7. For cold walls, the two-dimensional second mode dominates the transition process at lower hypersonic Mach numbers due to the well-known destabilizing effect of cooling on the second mode. It is shown that pressure gradient and suction may be used to stabilize this mode. Some results on the real gas effects on hypersonic boundary-layer stability are presented.

44 citations


Journal ArticleDOI
TL;DR: The relative importance of convection by secondary flows and diffusion by turbulence as mechanisms responsible for mixing in multistage axial-flow compressors has been investigated by using the ethylene tracer-gas technique and hot-wire anemometry as discussed by the authors.
Abstract: The relative importance of convection by secondary flows and diffusion by turbulence as mechanisms responsible for mixing in multistage, axial-flow compressors has been investigated by using the ethylene tracer-gas technique and hot-wire anemometry. The tests were conducted at two loading levels in a large, low-speed, four-stage compressor. The experimental results show that considerable cross-passage and spanwise fluid motion can occur and that both secondary flow and turbulent diffusion can play important roles in the mixing process, depending upon location in the compressor and loading level. In the so-called freestream region, turbulent diffusion appeared to be the dominant mixing mechanism. However, near the endwalls and along airfoil surfaces at both loading levels, the convective effects from secondary flow were of the same order of magnitude as, and in some cases greater than, the diffusive effects from turbulence. Calculations of the secondary flowfield and mixing coefficients support the experimental findings.

41 citations


Journal ArticleDOI
TL;DR: In this paper, the authors define des distributions de pression and visualisation de l'ecoulement of le bulles de decollement, and propose a method to find the bulles of decolllement.
Abstract: Etude du comportement des bulles de decollement. Determination des distributions de pression et visualisation de l'ecoulement

34 citations


Proceedings ArticleDOI
01 Jun 1987
TL;DR: In this paper, a numerical study using the direct simulation Monte Carlo (DSMC) method is presented for the hypersonic flow about an elliptically blunted cone, where the authors highlight the thermal and chemical nonequilibrium nature of the flowfield and the impact of these effects on the surface heating and body drag.
Abstract: Results of a numerical study using the direct simulation Monte Carlo (DSMC) method are presented for the hypersonic flow about an elliptically blunted cone. The flow conditions are those for a proposed Aeroassist Flight Experiment (AFE) vehicle. The altitude range considered is that from 130 to 90 km which encompasses most of the transitional flow regime for the AFE vehicle, that is, the region bounded by free molecular and continuum flow. Freestream velocities of 9.9 to 7.5 km/sec are considered. The numerical simulations show that noncontinuum effects are evident for all cases considered. The onset of chemical dissociation occurs at a simulated altitude of about 130 km. Results presented highlight the thermal and chemical nonequilibrium nature of the flowfield and the impact of these effects on the surface heating and body drag. A calculation which included the additional effects of ionization and thermal radiation demonstrates that the inclusion of such efects would not significantly alter the surface quantities calculated in the present study. The radiative heating is negligible when compared with the convective heating, and the same would be true for the other conditions considered.

Journal ArticleDOI
TL;DR: In this paper, the effects of blockage and freestream turbulence on streamwise surface pressures in a separation bubble were studied and the importance of minimizing wind tunnel blockage when measuring fluctuating pressures on building models was demonstrated.

Journal ArticleDOI
TL;DR: In this paper, a transition-promoting effect of freestream turbulence was examined for vortex unsteadiness on slender bodies at high incidence, and it was found that, for the high laminar Reynolds numbers at which the tests have been performed, a likely source of the transient vortex behavior is the transition-enhanced effect of free-stream turbulence.
Abstract: Existing experimental evidence of vortex unsteadiness on slender bodies at high incidence is examined. It is found that, for the high laminar Reynolds numbers at which the tests have been performed, a likely source of the transient vortex behavior is the transition-promoting effect of freestream turbulence. By considering the similar effects on transition of Reynolds number, freestream turbulence, and surface roughness, the transitionpromoting flow phenomenon provides a consistent explanation also for the observed large effects of roll angle on the vortex-induced asymmetric loads. The experimental results of vortex unsteadiness reinforce earlier established evidence of the existing coupling between body motion and asymmetric vortex shedding, raising concern about rigid and elastic response of long slender bodies.

Proceedings ArticleDOI
06 Apr 1987
TL;DR: In this article, a transonic unsteady aerodynamic and aeroelasticity code is developed for application to realistic aircraft configurations, which is called CAP-TSD which is an acronym for Computational Aero-Elasticity Program - Transonic Small Disturbance.
Abstract: A transonic unsteady aerodynamic and aeroelasticity code has been developed for application to realistic aircraft configurations. The new code is called CAP-TSD which is an acronym for Computational Aeroelasticity Program - Transonic Small Disturbance. The CAP-TSD code uses a time-accurate approximate factorization algorithm for solution of the unsteady transonic small-disturbance equation that is efficient for solution of steady and unsteady transonic flow problems including supersonic freestream flows. The new code can treat complete aircraft geometries with multiple lifting surfaces and bodies. Applications to wings in supersonic freestream flow are presented. Comparisons with selected exact solutions from linear theory are presented showing generally favorable results. Calculations for both steady and oscillatory cases for the F-5 and RAE tailplane models are compared with experimental data and also show good overall agreement. Selected steady calculations are further compared with a steady flow Euler code.

01 Jan 1987
TL;DR: In this paper, the turbulent boundary layer under a freestream velocity that varies sinusoidally in time around a zero mean is considered, and a theory for the velocity and stress profiles at high Reynolds number is formulated.
Abstract: The turbulent boundary layer under a freestream velocity that varies sinusoidally in time around a zero mean is considered. The flow has a rich variety of behaviors including strong pressure gradients, inflection points in the velocity profile, and reversal of the shear stress. A theory for the velocity- and stress profiles at high Reynolds number is formulated. Well-resolved direct Navier-Stokes simulations are conducted over a narrow range of Reynolds numbers. The flow is also computed over a wider range of Reynolds numbers using a new algebraic turbulence model. The results produced by the three approaches and by experiments are compared. Detailed phase-averaged statistical results from the direct simulations are provided to assist turbulence-model development.

Journal ArticleDOI
TL;DR: In this article, the results of a numerical study of low-density hypersonic flow about cylindrically blunted wedges with body half-angles of 0, 5, and 10 deg are presented.
Abstract: The results of a numerical study of low-density hypersonic flow about cylindrically blunted wedges with body half-angles of 0, 5, and 10 deg are presented. Most of the transitional flow regime encountered during entry between the free molecule and continuum regimes is simulated for a re-entry velocity of 7.5 km/s by including freestream conditions of 70 to 100 km. The bodies are at zero angle of incidence and have diffuse and finite catalytic surfaces. Translational, thermodynamic, and chemical nonequilibrium effects are considered in the numerical simulation by utilizing the direct simulation Monte Carlo (DSMC) method. The numerical simulations show that noncontinuum effects such as surface temperature jump and velocity slip are evident for all cases considered. The onset of chemical dissociation occurs at a simulated altitude of 96 km for the configurations considered.

Journal ArticleDOI
TL;DR: In this article, the effects of convex curvature and freestream turbulence on boundary layer momentum and heat transfer during natural transition provided a two-dimensional boundary layer flow on a uniformly heated curved surface, with bending to various curvature radii.
Abstract: The test section of the present experiment to ascertain the effects of convex curvature and freestream turbulence on boundary layer momentum and heat transfer during natural transition provided a two-dimensional boundary layer flow on a uniformly heated curved surface, with bending to various curvature radii, R. Attention is given to results for the cases of R = infinity, 180 cm, and 90 cm, each with two freestream turbulence intensity levels. While the mild convex curvature of R = 180 cm delays transition, further bending to R = 90 cm leads to no signifucant further delay of transition. Cases with both curvature and higher freestream disturbance effects exhibit the latter's pronounced dominance. These data are pertinent to the development of transition prediction models for gas turbine blade design.

Journal ArticleDOI
TL;DR: In this paper, the effect of yaw on both staggered and in-line tube tanks was investigated, and it was found that the yaw effect was well correlated for the staggered array, but not so well for the inline array because of the aforementioned flow field modifications.

Journal ArticleDOI
TL;DR: In this article, the authors describe disturbance amplitude disturbance amplitude in freestream initial disturbance amplitude amplitude in boundary layer reference initial disturbance magnitude in the boundary layer at 1.3m.
Abstract: p Re 5 t At U x z a a. ot0 A e 6 A v £ p \l/ co, co Nomenclature disturbance amplitude disturbance amplitude in freestream initial disturbance amplitude in boundary layer reference initial disturbance amplitude in boundary layer at Mr(= 1.3) airfoil chord mean aerodynamic chord drag, coefficient CD = D/(p00Ux>/2)S frequency proportionality constant, Eq. (1) lift, coefficient CL = L /(p^ Ul/2)S sectional lift, coefficient cl = l/(p00(/i/2)c Mach number mass flow injected calculated mass flow in boundary layer just upstream of air holes sectional pitching moment, coefficient cm-mp/

Proceedings ArticleDOI
01 Jan 1987
TL;DR: In this article, a Lambda = 75 deg delta wing in a supersonic freestream under two conditions which lead to leading-edge vortices is analyzed, and it appears that this is due to truncation error of the convective derivatives.
Abstract: Computations are presented for a Lambda = 75 deg delta wing in a supersonic freestream under two conditions which lead to leading-edge vortices. For one condition, analysis of the computed vortical flow reveals a closed streamline in the core. From varying computational parameters, it appears that this is due to truncation error of the convective derivatives. For the other condition, comparisons are made with wind-tunnel data, and good agreement is noted for pitot pressure distributions, flow angles on the symmetry plane, and the position of an embedded shock. Many of the aerodynamic parameters are shown to be insensitive to grid spacing.

Book ChapterDOI
01 Jan 1987
TL;DR: In this paper, the Stokes boundary layer produced by fluid oscillating parallel to a flat plate is studied by hydrogen bubble visualization and a theoretical model consistent with these observations is proposed.
Abstract: The Stokes boundary layer produced by fluid oscillating parallel to a flat plate is studied by hydrogen bubble visualization. No significant departure from the laminar velocity profiles is found up to a Reynolds number, based on boundary layer thickness and freestream velocity amplitude, of about 600, The first visible finite amplitude disturbances appear shortly before and around flow reversal at the edge of the boundary layer. A theoretical model consistent with these observations is proposed. It is based on a quasisteady approach, valid for large Reynolds numbers, and involves nonlinear interaction between modes which possibly leads to a net disturbance growth over one freestream cycle.

Proceedings ArticleDOI
01 Jan 1987
TL;DR: In this article, a hybrid method was developed for the numerical prediction of turbulent mixing in a spatially-developing, free shear layer, which incorporated the effects of large-scale structures, Schmidt number and Reynolds number on mixing.
Abstract: A hybrid method has been developed for the numerical prediction of turbulent mixing in a spatially-developing, free shear layer. Most significantly, the computation incorporates the effects of large-scale structures, Schmidt number and Reynolds number on mixing, which have been overlooked in the past. In flow field prediction, large-eddy simulation was conducted by a modified 2-D vortex method with subgrid-scale modeling. The predicted mean velocities, shear layer growth rates, Reynolds stresses, and the RMS of longitudinal velocity fluctuations were found to be in good agreement with experiments, although the lateral velocity fluctuations were overpredicted. In scalar transport, the Monte Carlo method was extended to the simulation of the time-dependent pdf transport equation. For the first time, the mixing frequency in Curl's coalescence/dispersion model was estimated by using Broadwell and Breidenthal's theory of micromixing, which involves Schmidt number, Reynolds number and the local vorticity. Numerical tests were performed for a gaseous case and an aqueous case. Evidence that pure freestream fluids are entrained into the layer by large-scale motions was found in the predicted pdf. Mean concentration profiles were found to be insensitive to Schmidt number, while the unmixedness was higher for higher Schmidt number. Applications were made to mixing layers with isothermal, fast reactions. The predicted difference in product thickness of the two cases was in reasonable quantitative agreement with experimental measurements.

Journal ArticleDOI
TL;DR: In this paper, the characteristics of vortex formed behind a circular cylinder placed in a laminar boundary layer have been investigated experimentally by flow visualization and analysis on fluctuating velocity signals, and the following new results were obtained: within the range of Re=70∼613, separated shear layers from both sides and the free-edge of the cylinder were linked to form an arch-type vortex for h/d up to 4.
Abstract: Characteristics of vortex formed behind a circular cylinder placed in a laminar boundary layer have been investigated experimentally by flow visualization and analysis on fluctuating velocity signals. Three nondimensional paramerers of Re = U0d/v(U0 : freestream velocity, d : cylinder diameter, v : kinematic viscosity), h/δ(h : cylinder height, δ : boundary layer thickness) and h/d govern the flow field. In the present study, h/δ is kept constant to unity, and h/d and Re were varied. The following new results were obtained: (i) Within the range of Re=70∼613, separated shear layers from both sides and the free-edge of the cylinder were linked to form an arch-type vortex for h/d up to 4. (ii) At h/d=3 where an arch-type vortex is formed, the Strouhal number St(=fd/U0) against Re can be classified into three regions based on different time rates of intermittent vortex shedding. (iii) Simiraly, at h/d=6 where Karman-type vortex is formed, St against Re can be classified into two regions.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the effect of the buoyancy* parameter on the local Nusselt number of a moving sheet in a parallel freestream with a uniform wall temperature and uniform surface heat flux.
Abstract: Laminar mixed convection adjacent to vertical and inclined moving sheets in a parallel freestream is analyzed for both the uniform wall temperature and the uniform surface heat flux cases. The analysis covers the entire mixed convection regime, from pure forced convection to pure free convection. Numerical results are reported for different combinations of the velocities of the moving sheet us and the freestream u^ for Prandtl numbers of 0.7 and 7. Local Nusselt numbers as well as velocity and temperature distributions are presented for a wide range of the buoyancy* parameter. It is found that the local Nusselt number increases as the value of the buoyancy parameter increases. For the same dimensionless velocity difference \US— t£J, the local Nusselt number is larger for Us> U^ than it is for U^U^. Significant velocity overshoots occur within the boundary layer as the buoyancy parameter increases, with the low Prandtl number fluid exhibiting a more pronounced buoyancy effect than the high Prandtl number fluid. Simple correlations for evaluating local and average mixed convection Nusselt numbers are also presented and very good agreement is found between the computed results and the proposed simple correlations.

Proceedings ArticleDOI
01 Jan 1987
TL;DR: In this article, the development of Goertler vortices in a laminar boundary layer on a 1.83 m chord airfoil model was visualized using a sublimating chemical technique.
Abstract: Laser velocimetry (LV) was used to study the development of Goertler vortices in a laminar boundary layer on a 1.83 m chord airfoil model. The vortex pattern was visualized using a sublimating chemical technique. A fixed, essentially uniform vortex spacing was observed throughout the test region for any given freestream velocity but the vortex wavelength varied significantly with change in freestream velocity. An appreciable, abrupt decrease in streak contrast indicated vortex damping in the convex region and was confirmed by disturbance functions determined from LV measurements. Moderate variation in suction levels did not alter the vortex spacing but appreciably modified the vortex strength. The experimental results on the growth of Goertler vortices along the concave surface and the effect of suction are compared with results from linear stability theory.


Proceedings ArticleDOI
01 Aug 1987
TL;DR: In this paper, surface pressure coefficient measurements for a hemisphere-cylinder-flare model in a low supersonic flow (freestream M = 1.2) at various angles of attack (0 deg to 27.5 deg), have been analyzed.
Abstract: Detailed experimental surface pressure coefficient measurements, obtained for a hemisphere-cylinder-flare model in a low supersonic flow (freestream M = 1.2) at various angles of attack (0 deg to 27.5 deg), have been analyzed. The pressure values for each angle of attack were smoothed and checked against their respective oil-flow photographs. The smoothed results were then used to validate a theory which relates the number and type of singular points observed in the oil-flow patterns with local surface-pressure extrema.

Proceedings ArticleDOI
01 Jun 1987
TL;DR: In this paper, LDA, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3, and the reported results are believed to accurately define the flow physics of each case and may be used as benchmark data to verify three dimensional computer codes.
Abstract: Nonintrusive, three-dimensional, measurements have been made of a normal shock wave-turbulent boundary layer interaction. The measurements were made in the corner of the test section of a continuous supersonic wind tunnel in which a normal shock wave had been stabilized. LDA, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The reported results are believed to accurately define the flow physics of each case and may be used as benchmark data to verify three-dimensional computer codes.

Proceedings ArticleDOI
01 Jan 1987
TL;DR: In this paper, direct simulation Monte Carlo (DSMC) is applied to simulate one-dimensional flow along the stagnation streamline for different specified shock locations at a given altitude, and the effect of shock location on the stagnation-point gas composition and heat transfer is analyzed for specific altitude.
Abstract: The direct simulation Monte Carlo (DSMC) method is applied to simulate one-dimensional flow along the stagnation streamline. The freestream conditions considered are those encountered by the nose region of the Space Shuttle Orbiter during the hypersonic reentry. The range of altitudes (75 to 92 km) considered in the present calculations covers continuum to the less rarefied portion of the transition flow regime. The calculations account for thermal as well as the chemical nonequilibrium effects. The attention is focused on the flow structure along the stagnation streamline for different specified shock locations at a given altitude. The effect of shock location on the stagnation-point gas composition and heat transfer is analyzed for specific altitude; consequently, these results are appropriate for hemispherical bodies with different nose radii. Finally, comparison is made between the present DSMC results and the viscous shock-layer calculations, which show good agreement at the lowest altitude.

DissertationDOI
01 May 1987
TL;DR: In this paper, the authors used underwater holography to observe microbubbles and particulates, including microplankton in oceanic waters of Los Angeles Harbor, San Pedro Channel and near Catalina Island.
Abstract: Cavitation scale effects can be grouped into two major categories: susceptibility of the water to cavitation, i.e., the amount, size, and type of microbubbles or microparticulates in the water acting as inception nuclei, and flow field effects due to such factors as velocity and pressure distributions, body size and shape, viscous effects, and turbulent phenomena. Experimental investigations into these two aspects of scale effects were performed in the present study. Field investigations of marine nuclei populations were made using underwater holography to observe microbubbles and particulates, including microplankton in oceanic waters of Los Angeles Harbor, San Pedro Channel and near Santa Catalina Island. Holographic detection was shown to be a reliable method of measuring the nuclei number concentration density distributions. Overall, very high concentrations of the various types of potential cavitation nuclei were observed at all of the test sites and depths examined, although the statistical significance of these results is strong only in the smaller size ranges (less than 50 μm), where a significant number of counts were made. Relatively high bubble concentrations during calm sea conditions, and their population inversion below the thermocline where organism activity was high, indicate a possible biological source of bubble production rather than the usual surface mechanisms of breaking waves and whitecaps. The measured population of particulates is somewhat higher than comparable data in the ocean or in cavitation test facilities, and the number density distribution of particulates decreases approximately as the fourth power of the particle size, as often reported in the literature. An increase in particle concentration near the bottom of the thermocline in clear coastal waters is observed. The total concentration of particles and bubbles in a liquid provides an upper bound on the number of potentially active cavitation nuclei. The measured bubble sizes can be used to indicate that the average tensile strength of the ocean waters examined in this study should be on the order of via few thousand Pascals, with a minimum expected value of about one hundred Pascals. The present results support the recommendation of Billet (1985), that a concentration of at least 3 bubbles per cm^3 in the 5 to 20 μm radius range is needed in test facility water in order to model marine conditions. Experimental studies were also made on the inception processes in a large turbulent free shear layer generated by a sharp edged plate in a water tunnel at Reynolds numbers up to 2 X 10^6. Two distinct types of vortex motion were evident in the shear layer, the primary span wise and the secondary longitudinal vortices. Cavitation inception occurs consistently in the secondary shear layer vortices and more fully developed cavitation is visible in both structures, with the streamwise cavities primarily confined to the braid regions between adjacent spanwise vortices. A Rankine vortex model indicates that the secondary vortex strength is always less than 10% of that of the primary structure. Measurements of fluctuating pressures in the turbulent shear layer are made by holographically monitoring the size of air bubbles injected into the non-cavitating flow, showing that pressure fluctuations were much stronger than previously reported, with positive and negative pressure peaks as high as 3 times the freestream dynamic pressure, sufficient to explain the occurrence of cavitation inception at high values of the inception index. Cavitation inception indices display a strong dependence on the dissolved air content and thus on the availability of freestream bubble cavitation nuclei. The present inception data do not display a clear dependence on freestream velocity (or Reynolds number) but do fall into the overall range of data of previous bluff body investigations. The occurrence of inception in the secondary vortices of the shear layer, and previous reports of velocity dependence of these cores (Bernal 1981) may provide the key to explaining the commonly observed Reynolds number scaling of the inception index in shear flows.