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Lift, drag, and pitching moments of airfoils with leading-edge sinusoidal protuberances were measured in a water tunnel and compared with those of a baseline [63.sub.4]-021 airfoil. The amplitude of the leading-edge protuberances ranged from 2.5 to 12% of the mean chord length; the spanwise wavelengths were 25 and 50% of the mean chord length. These ranges correspond to the morphology found on the leading edge of humpback whales' flippers. Flow visualization using tufts was also performed to examine the separation characteristics of the airfoils. For angles of attack less than the baseline stall angle, lift reduction and drag increase were observed for the modified foils. Above this angle, lift of the modified foils was up to 50% greater than the baseline foil with little or no drag penalty. The amplitude of the protuberances had a distinct effect on the performance of the airfoils, whereas the wavelength had little. Flow visualization indicated separated flow originating primarily from the troughs and attached flow on the peaks of the protuberances at angles beyond the stall angle of the baseline foil.

The evolution of a pulsed vortex generator jet embedded in a turbulent boundary layer was examined experimentally. The jet, which was pitched 45 deg and skewed 90 deg, had a velocity three times greater than the freestream. The velocity field in planes normal to the freestream was measured by the particle-image-velocimetry method at four stations downstream of the jet exit. The pulsed jet created a starting vortex ring followed by a pair of counter-rotating streamwise vortices, one of them being markedly stronger. Phase-averaged data indicate that the maximum circulation and peak vorticity of the stronger vortex are approximately 30% greater than the average values for a steady jet with the same velocity. However, circulation averaged over the entire pulse was less than that for a steady jet at the same location. The core of the primary streamwise vortex penetrates approximately 50% farther into the boundary layer than a steady jet with the same velocity. The larger penetration takes place during the initial portion of the pulse and is caused by the jet starting vortex ring.

The parameters affecting the inflation of solid-cloth, flat circular parachute canopies were investigated. A primary dimensionless parameter in addition to mass ratio, Froude number, and permeability is a stiffness index. Comparison of sub- and full-scale C9 parachutes, along with small-scale wind- and water-tunnel models has revealed that a relative stiffness index is able to correlate the filling and opening times of various sized canopies. The filling and opening times can be expressed as the relative stiffness index raised to power -0.064, with a proportionality factor of 1.3 for the filling time. The proportionality factor that correlates opening times is 0.86 for mass ratios in the range of 0.1-0.2, and it approaches 1.3 as mass ratio becomes very large. The index has utility in correlating peak forces as well.

Pulsed, turbulent jet diffusion flames in an air coflow of variable strength were examined experimentally. In all cases, the flames were fully modulated, that is, the fuel flow was completely shut off between pulses. Isolated puffs of unheated ethylene fuel were injected using a 2-mm-diam-nozzle into a combustor with an air coflow at 1-atm pressure. For short injection times ([tau]< 50 ms), compact, pufflike structures were generated. The mean flame length of these puffs was at least 51% less than that of a steady-state, that is, nonpulsed, flame for the same injection Reynolds number. More elongated flame structures, with a flame length closer to that of steady-state flames, occurred for longer injection times of up to 300 ms. The addition of coflow generally causes an increase in the mean flame length. For short injection times ([tau]< 50 ms), this resulted in an increase in flame length of up to 27% for a coflow strength of [U.sub.cof]/[U.sub.jet] = 0.02. The fractional increase in the flame length due to coflow of pulsed flames with longer injection times, as well as steady flames, was significantly less. The mean flame length for the flame with the coflow duct generally exceeded that of the corresponding free flame, even for the case of zero coflow. The amount of coflow required to achieve a given increase in mean flame length is quantitatively consistent with a scaling argument developed as part of this investigation.

The computation of the impulsively started flow around a rigid parachute canopy is described.

The role of duty cycle and injection time on the penetration and mixing of fully-modulated, incompressible and turbulent transverse jets have been studied in a water tunnel. The jet flow was modulated by operating an in-line solenoid valve which cuts off jet supply during a portion of the cycle. Results indicate that complete modulation resulted in a modification of the jet flow as well as its penetration depth, dilution and mixing to various degrees. Long injection times led to the formation of axially elongated turbulent puffs that resembled a segment of the steady jet.

A new ultrasound method has been formulated for measuring the circulation of delta-wing primary vortices. It is also used in investigating the variation of circulation with angle of attack and chordwise location for wing sweep angles of 60 and 70 degrees. These angles have been selected because they represent the behavior of high- and low-sweep-angle delta wings. The strength of the vortex can be determined by measuring the circulation around a closed path which contains the vortex. Hot-wire or laser Doppler anemometry can be utilized for quantifying velocity vectors in a flowfield.

A study was conducted on the starting vortex of impulsively started jet diffusion flames using a special device to measure the volumetric flow under steady conditions. The device consists of a contoured nozzle, a solenoid valve and a sharp-edged orifice plate section. Results show that the height at which the starting vortex totally burned off was almost equal to the mean flame length of the stationary flow. Moreover, the timescale for complete burnoff of the starting vortex at its mean flame height seems to be about half of the vortex rotation time at the same location.

The starting vortex motion and jet penetration of round, incompressible and impulsively turbulent jets were analyzed based on a series of experiments in a water tank utilizing inert and chemically reactive markers. The starting vortex of the impulsively started turbulent jet separated from the rest in the near field after a brief period. Furthermore, the series of chemically reactive experiments indicated faster mixing of the jet tip with the ambient compared to the rest of the jet.

Pulsed blowing is a more efficient method for delaying vortex breakdown during ramp-pitching than steady blowing. Pulsing increases the vertical flow over the delta wing and delays breakdown. A hysteresis effect occurs during ramp-pitching, which is proportional to pitching rates. However, at higher pitching rates, the burst location is more substantially influenced by pitching parameters than blowing. The vortex manipulation is achieved using a recessed angle spanwise blowing technique.

Recessed angled spanwise blowing, a newly developed technique, is used for vortex control of beveled 60 deg delta wing in a water tunnel. A 22 deg attack angle and blowing coefficient of 0.05 causes maximum improvement in vortex breakdown location of 15% chord. Vortex breakdown slows down when blowing is done from a port downstream of natural burst location. Vortex breakdown occurs at blowing port for blowing upstream of natural burst.

A research was conducted to analyze the impact of fully modulated pulsing on the penetration, entrainment and mixing features of transverse jets in a crossflow. The study focuses on the distinct effects of the pulsing parameters, particularly the jet-on fraction for each cycle. To identify jet penetration for the various values of injection time and duty cycle, pulsed, nonreacting transverse jets were utilized. The results are discussed.

A study of the spreading rate and the penetration length of a nonharmonic unsteady jet of considerable duration, when compared to the pulsed jets, reveals that the visible spreading rate of an unsteady jet is less than half of the steady jet value. This is shown by flow-visualization experiments conducted on a simple apparatus. During the run, there is almost no change in the spreading rate, though there is a significant variation in the velocity. The unsteady effects on entertainment and mixing can be understood better as a result of these findings.