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Modeling Plume Impingements in Very Low Ambient Pressures with a Navier-Stokes and Hybrid Navier-Stokes/Boltzmann Solver
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Mixing and Recovery Performance of Triplet Impinging Injectors with Varying Flow Areas for Detonative Combustion
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Enhanced thin film evaporation via impinging electrospray liquid jets with entrained air streaming
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Study of lubricant jet flow phenomena in spur gears - Out of mesh condition
An analysis was conducted for oil jet lubrication on the disengaging side of a gear mesh. Results of the analysis were computerized and used to determine the oil jet impingement depth for several gear ratios and oil jet to pitch line velocity ratios. An experimental program was conducted on the NASA gear test rig using high-speed photography to experimentally determine the oil jet impingement depth on the disengaging side of mesh. Impingement depth reaches a maximum at gear ratio near 1.5 where chopping by the leading gear tooth limits the impingement depth. The pinion impingement depth is zero above a gear ratio of 1.172 for a jet velocity to pitch time velocity ratio of 1.0 and is similar for other velocity ratios. The impingement depth for gear and pinion are equal and approximately one-half the maximum at a gear ratio of 1.0. Impingement depth on either the gear or pinion many be improved by relocation of the jet from the pitch line or by changing the jet angle. Results of the analysis were verified by experimental results using a high-speed camera and a well lighted oil jet.
Study of Lubricant Jet Flow Phenomena in Spur Gears: Out of Mesh Condition
Oil jet lubrication on the disengaging side of a gear mesh was analyzed. Results of the analysis were computerized and used to determine the oil jet impingement depth for several gear ratios and oil jet to pitch line velocity ratios. A gear test rig using high speed photography was used to experimentally determine the oil jet impingement depth on the disengaging side of mesh. Impingement depth reached a maximum at gear ratio near 1.5 where chopping by the leading gear tooth limited impingement depth. The pinion impingement depth is zero above a gear ratio of 1.172 for a jet velocity to pitch time velocity ration of 1.0 and is similar for other velocity ratios. The impingement depth for gear and pinion are equal and approximately one half the maximum at a gear ration of 7.0.
Particle trajectory computation on a 3-dimensional engine inlet
A 3-dimensional particle trajectory computer code was developed to compute the distribution of water droplet impingement efficiency on a 3-dimensional engine inlet. The computed results provide the essential droplet impingement data required for the engine inlet anti-icing system design and analysis. The droplet trajectories are obtained by solving the trajectory equation using the fourth order Runge-Kutta and Adams predictor-corrector schemes. A compressible 3-D full potential flow code is employed to obtain a cylindrical grid definition of the flowfield on and about the engine inlet. The inlet surface is defined mathematically through a system of bi-cubic parametric patches in order to compute the droplet impingement points accurately. Analysis results of the 3-D trajectory code obtained for an axisymmetric droplet impingement problem are in good agreement with NACA experimental data. Experimental data are not yet available for the engine inlet impingement problem analyzed. Applicability of the method to solid particle impingement problems, such as engine sand ingestion, is also demonstrated.
Noise of the Harrier in vertical landing and takeoff
The noise of the Harrier AV8C aircraft in vertical takeoff and landing was measured 100 feet to the side of the aircraft where jet noise dominates. The noise levels were quite high - up to 125 dB overall sound level at 100 feet. The increased noise due to jet impingement on the ground is presented as a function of jet height to diameter ratio. The impingement noise with the aircraft close to the ground was 14 to 17 dB greater than noise from a free jet. Results are compared with small-scale jet impingement data acquired elsewhere. The agreement between small-scale and full-scale noise increase in ground effect is fairly good except with the jet close to the ground. It is proposed that differences in the jet Reynolds numbers and the resultant character of the jets may be partially responsible for the disparity in the full-scale and small-scale jet impingement noise. The difference between single-jet impingement and multiple-jet impingement may also have been responsible for the small-scale and full-scale disagreement.
Experimental studies of hypersonic shock-wave boundary-layer interactions
Two classes of shock-wave boundary-layer interactions were studied experimentally in a shock tunnel in which a low Reynolds number, turbulent flow at Mach 8 was developed on a cold, flat test surface. The two classes of interactions were: (1) a swept interaction generated by a wedge ('fin') mounted perpendicularly on the flat plate; and (2) a two-dimensional, unseparated interaction induced by a shock impinging near an expansion corner. The swept interaction, with wedge angles of 5-20 degrees, was separated and there was also indication that the strongest interactions prossessed secondary separation zones. The interaction spread out extensively from the inviscid shock location although no indication of quasi-conical symmetry was evident. The surface pressure from the upstream influence to the inviscid shock was relatively low compared to the inviscid downstream value but it rose rapidly past the inviscid shock location. However, the surface pressure did not reach the downstream inviscid value and reasons were proposed for this anomalous behavior compared to strongly separated, supersonic interactions. The second class of interactions involved weak shocks impinging near small expansion corners. As a prelude to studying this interaction, a hypersonic similarity parameter was identified for the pure, expansion corner flow. The expansion corner severely damped out surface pressure fluctuations. When a shock impinged upstream of the corner, no significant changes to the surface pressure were found as compared to the case when the shock impinged on a flat plate. But, when the shock impinged downstream of the corner, a close coupling existed between the two wave systems, unlike the supersonic case. This close coupling modified the upstream influence. Regardless of whether the shock impinged ahead or behind the corner, the downstream region was affected by the close coupling between the shock and the expansion. Not only was the mean pressure distribution modified but the unsteadiness in the surface pressure was reduced compared to the flat-plate case.
Igniters for Liquid Oxygen/Liquid Methane Technology Development
As part of NASA's technology development of liquid methane / liquid oxygen engines for future exploration missions, two different igniters were recently studied at NASA Marshall Space Flight Center. The first igniter tested was an impinging injection, spark-initiated torch igniter, and the second was a microwave-generated plasma igniter. The purpose of the ignition tests was to define the ignition limits under vacuum conditions and characterize the transient start-up performance as a function of propellant mixture ratio (MR), mass flow rates, inlet temperatures, and pre-ignition chamber pressure. In addition, for the impinging igniter two different spark plugs were tested, and for the microwave igniter the magnetron filament warm-up time and the magnetron input power were both varied. The results gathered from these tests indicated that the impinging igniter is capable of operating over an MR range of 2 - 27, with methane and oxygen inlet temperatures as low as -161 F and -233 F, respectively. The microwave igniter was tested over an MR range of 2 - 9, with methane and oxygen inlet temperatures as low as -90 F and -200 F, respectively. The microwave igniter achieved ignition over this range, although an upper ignition limit was determined for the oxidizer mass flow rate. In general, the torch exhaust temperatures for the microwave igniter were not as high as those attained with the impinging igniter. The microwave igniter, however, was hot-fired 17 times and was still operational, whereas the impinging igniter spark plugs experienced thermal shock and erosion over nine hot-fire tests. It was concluded that for the microwave igniter better mixing of the propellants might be required in order to both raise the torch exhaust temperature and decrease the required magnetron input power, and for the impinging igniter the spark plug position within the igniter chamber should be varied in future tests to identify a more optimal location. All of the igniter tests were supported by the Propulsion & Cryogenics Advanced Development project, which is part of NASA's Exploration Technology Development Program.
Correlation of spray dropsize distribution and injector variables
The atomization characteristics of impinging stream rocket engine injection elements are studied to determine the effects of hydraulic and geometric parameters on the mass median drop size. The major conclusions are: (1) the velocity profile of impinging jets affects mean drop size, this effect is greater when the jets are laminar than when they are turbulent; (2) the drop size/injection velocity dependence for turbulent jet impingement differs from that obtained with non-turbulent jets; (3) the level of turbulence intensity does not affect mean drop size; (4) the impingement of disintegrated or nearly disintegrated jets substantially decreases atomization; and (5) even though an emulsion is formed when immiscible jets impinge, the level of emulsification is small.
Experimental and Analytical Investigation of the Coolant Flow Characteristics in Cooled Turbine Airfoils
The flow characteristics of turbine airfoil cooling system components were experimentally investigated. Flow models representative of leading edge impingement, impingement with crossflow (midchord cooling), pin fins, feeder supply tube, and a composite model of a complete airfoil flow system were tested. Test conditions were set by varying pressure level to cover the Mach number and Reynolds number range of interest in advanced turbine applications. Selected geometrical variations were studied on each component model to determine these effects. Results of these tests were correlated and compared with data available in the literature. Orifice flow was correlated in terms of discharge coefficients. For the leading edge model this was found to be a weak function of hole Mach number and orifice-to-impinged wall spacing. In the impingement with crossflow tests, the discharge coefficient was found to be constant and thus independent of orifice Mach number, Reynolds number, crossflow rate, and impingement geometry. Crossflow channel pressure drop showed reasonable agreement with a simple one-dimensional momentum balance. Feeder tube orifice discharge coefficients correlated as a function of orifice Mach number and the ratio of the orifice-to-approach velocity heads. Pin fin data was correlated in terms of equivalent friction factor, which was found to be a function of Reynolds number and pin spacing but independent of pin height in the range tested.
Study of lubricant jet flow phenomena in spur gears
Lubricant jet flow impingement and penetration depth into a gear tooth space were measured at 4920 and 2560 rpm using a 8.89 cm (3.5 inch) pitch diameter 8 pitch spur gear at oil pressures from 70,000 to 410,000 n/sqm (10 psi to 60 psi). A high speed motion picture camera was used with xenon and high speed stroboscopic lights to slow down and stop the motion of the oil jet. An analytical model was developed for the vectorial impingement dept and for the impingement depth with tooth space windage effects included. The windage effects for oil drop size greater than .0076 cm (.003 inches). The analytical impingement dept compared favorably with experimental results above an oil jet pressure of 70,000 n/sqm (10psi). There was further penetration into the tooth space after impingement, but much of this oil was thrown out of the tooth space without further contacting the gear teeth.
Into Mesh Lubrication of Spur Gears with Arbitrary Offset Oil Jet. 2: for Jet Velocities Equal to or Greater than Great Velocity
An analysis was conducted for into mesh oil jet lubrication with an arbitrary offset and inclination angle from the pitch point for the case where the oil jet velocity is equal to or greater than gear pitch line velocity. Equations were developed for minimum and maximum oil jet impingement depth. The analysis also included the minimum oil jet velocity required to impinge on the gear or pinion and the optimum oil jet velocity required to obtain the best lubrication condition of maximum impingement depth and gear cooling. It was shown that the optimum oil jet velocity for best lubrication and cooling is when the oil jet velocity equals the gear pitch line velocity. When the oil jet velocity is slightly greater than the pitch line velocity the loaded side of the driven gear and the unloaded side of the pinion receive the best lubrication and cooling with slightly less impingement depth. As the jet velocity becomes much greater than the pitch line velocity the impingement depth is considerably reduced and may completely miss the pinion.
Effect of geometry on airfoil icing characteristics
A droplet trajectory computer code is used to predict the water droplet impingement characteristics of several low- and medium-speed airfoils. The maximum impingement efficiency, total collection efficiency, and limits of impingement are analyzed as functions of the airfoil geometry and freestream conditions. The airfoil geometry is represented by leading edge radius, maximum thickness, maximum camber, and angle of attack. The analysis shows that the primary effects are an increase in maximum impingement efficiency with a decrease in leading edge radius, a reduction in total collection efficiency for thicker airfoils, and a change in the limits of impingement for airfoils of different maximum camber.