Free turbulent mixing in a coflowing stream

The major points are described of a turbulent transport model of the classical, gradient transport, eddy viscosity type. The relationship is discussed of the developed model to the Prandtl (jet mixing) model, the Schlichting (wake) model, and the Clauser (boundary layer) model. Limitations of the model and test cases are summarized

Real jet effects on dual jets in a crossflow

A 6-ft by 6-ft wind tunnel section was modification to accommodate the 7-ft wide NASA dual-jet flate model in an effort to determine the effects of nonuniform and/or noncircular jet exhaust profiles on the pressure field induced on a nearby surface. Tests completed yield surface pressure measurements for a 90 deg circular injector producing exit profiles representative of turbofan nozzles (such as the TF-34 nozzle). The measurements were obtained for both tandem and side-by-side jet configurations, jet spacing of S/D =2, and velocity ratios of R=2.2 and 4.0. Control tests at the same mass flow rate but with uniform exit velocity profiles were also conducted, for comparison purposes. Plots for 90 deg injection and R=2.2 show that the effects of exit velocity profile nonuniformity are quite significant

Unified analysis of turbulent jet mixing

Model analysis for viscosity in jet mixing flow

Experimental study of surface pressures induced on a flat plate and a body of revolution by various dual jet configurations

The effect of the angle of a jet to a crossflow, the performance of dual jet configurations, and a jet injected from a body of revolution as opposed to a flat plate were investigated during experiments conducted in the 7x10 tunnel at NASA Ames at Velocities from 14.5 m/sec to 35.8 m/sec (47.6 to 117.4 ft/sec.). Pressure distributions are presented for single and dual jets over a range of velocity ratios from 2 to 10, spacings from 2 to 6 diameters and injection angles of 90, 75, 60, and 105 degrees. For the body of revolution tests, the ratio of the jet to body diameters was set as large (1/2) in order to be more representative of V/STOL aircraft applications. Flat plate tests involved dual jets both aligned and in side by side configurations. The effects of the various parameters and the differences between the axisymmetric and planar body geometrics on the nature, size, shape, and strength of the interaction regions on the body surfaces are shown. Some flowfield measurements are also presented, and it is shown that a simple analysis is capable of predicting the trajectories of the jets

Turbulent boundary layer over solid and porous surfaces with small roughness

Skin friction and profiles of mean velocity, axial and normal turbulence intensity, and Reynolds stress in the untripped boundary layer were measured directly on a large diameter, axisymmetric body with: (1) a smooth, solid surface; (2) a sandpaper-roughened, solid surface; (3) a sintered metal, porous surface; (4) a smooth, perforated titanium surface; (5) a rough solid surface made of fine, diffusion bonded screening, and (6) a rough, porous surface of the same screening. Results obtained for each of these surfaces are discussed. It is shown that a rough, porous wall simply does not influence the boundary layer in the same way as a rough solid wall. Therefore, turbulent transport models for boundary layers over porous surfaces either with or without injection or suction, must include both surface roughness and porosity effects

Turbulent boundary layer over solid and porous surfaces with small roughness

The wind tunnel models and instrumentation used as well as data reduction and error analysis techniques employed are described for an experimental study conducted to measure directly skin friction and obtain profiles of mean velocity, axial and normal turbulence intensity, and Reynolds stress in the untripped boundary on a large diameter axisymmetric body. Results are given for such a body with a (1) smooth, solid surface; (2) a sandpaper roughened, solid surface; (3) a sintered metal, porous surface; (4) a ""smooth'' performated titanium surface; (5) a rough, solid surface made of fine diffusion bonded screening; and (6) a rough, porous surface made of the same screening. The roughness values were in low range (k+ 5 to 7) just above what is normally considered ""hydraulically smooth''. Measurements were taken at several axial locations and tow or normal stream freestream velocities, 45.1 m/sec and 53.5 m/sec

Interference Drag Associated with Engine Locations for Multidisciplinary Design Optimization

This research aims to quantify the interference drag for various engine locations on a traditional tube and wing, 150-passenger commercial aircraft flying at 35,000 ft and Mach 0.8. Engine locations are varied in the chord wise, span wise, and vertical directions near the wing, both under and above the wing, as well as along the fuselage. Euler simulations are performed with representative powered modern engines. The results are intended to supplement empirical drag estimates suitable for multidisciplinary design environments. Large interference drag increases, as compared to the isolated air frame and engine geometry, are found to occur when the engine is placed directly above or below the wing. Interference effects are significantly reduced, and in some instances result in benefits compared to the isolated bodies, when the engines are placed fore or aft of the wing. Interference drag increases are partially explained by flow channels leading to choked flow and shock interactions between bodies

Effects of velocity profile and inclination on dual-jet-induced pressures on a flat plate in a crosswind

An experimental study was conducted to determine surface pressure distributions on a flat plate with dual subsonic, circular jets exhausting from the surface into a crossflow. The jets were arranged in both side-by-side and tandem configurations and were injected at 90 deg and 60 deg angles to the plate, with jet-to-crossflow velocity ratio of 2.2 and 4. The major objective of the study was to determine the effect of a nonuniform (vs uniform) jet velocity profile, simulating the exhaust of a turbo-fan engine. Nonuniform jets with a high-velocity outer annulus and a low-velocity core induced stronger negative pressure fields than uniform jets with the same mass flow rate. However, nondimensional lift losses (lift loss/jet thrust lift) due to such nonuniform jets were lower than lift losses due to uniform jets. Changing the injection angle from 90 deg to 60 deg resulted in moderate (for tandem jets) to significant (for side-by-side jets) increases in the induced negative pressures, even though the surface area influenced by the jets tended to reduce as the angle decreased. Jets arranged in the side-by-side configuration led to significant jet-induced lift losses exceeding, in some cases, lift losses reported for single jets

Skin friction reduction in supersonic flow by injection through slots, porous sections and combinations of the two

An experimental study of skin friction reduction in a Mach 3.0 air steam with gaseous injection through a tangential slot, a porous wall section, and combinations of the two was conducted. The primary data obtained were wall shear values measured directly with a floating element balance and also inferred from Preston Tube measurements. Detailed profiles at several axial stations, wall pressure distributions and schlieren photographs are presented. The data indicate that a slot provides the greatest skin friction reduction in comparison with a reference flat plate experiment. The porous wall section arrangement suffers from an apparent roughness-induced rise in skin friction at low injection rates compared to the flat plate. The combination schemes demonstrated a potential for gain

Turbulent mixing of multiple, co-axial helium jets in a supersonic air stream

An experimental study of a strut-mounted, five-port, coaxial gaseous fuel injector assembly in a Mach 4 air stream with P sub o = 145 psia and T sub o = 546 R was conducted. Helium was used as the injectant, and the interjet spacing was the main parameter varied. The principal data are in the form of helium concentration profiles at six axial stations and pitot pressure profiles at two axial stations. Schlieren photographs are also presented. The slight sensitivity of the mixing rate to decreased interjet spacing was determined in the range 3.5 or = to S/D or = to 5.0