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At least 307 records · Page 17

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NASA NTRS1973

Terminal shock position and restart control of a Mach 2.7, two-dimensional, twin duct mixed compression inlet

Experimental results of terminal shock and restart control system tests of a two-dimensional, twin-duct mixed compression inlet are presented. High-response (110-Hz bandwidth) overboard bypass doors were used, both as the variable to control shock position and as the means of disturbing the inlet airflow. An inherent instability in inlet shock position resulted in noisy feedback signals and thus restricted the terminal shock position control performance that was achieved. Proportional-plus-integral type controllers using either throat exit static pressure or shock position sensor feedback gave adequate low-frequency control. The inlet restart control system kept the terminal shock control loop closed throughout the unstart-restart transient. The capability to restart the inlet was non limited by the inlet instability.

Cole, G. L.↗

NASA NTRS1973

Sediment distribution and coastal processes in Cook Inlet, Alaska

Regional hydrologic and oceanographic relationships in Cook Inlet, Alaska have been recognized from sequential ERTS-1 MSS imagery. Current patterns are visible in the inlet because of differential concentrations of suspended sediment. The circulation patterns within Cook Inlet are controlled primarily by the interaction between the semi-diurnal tides and the counter clockwise Alaska current. In general, heavily sediment laden water is seen to be confined to portions of the inlet north of the Forelands and west of Kalgin Island. Tongues of clear oceanic water are observed to enter the inlet through Kennedy Channel along the east shoreline in the vicinity of Cape Elizabeth. A recurring counterclockwise circulation pattern observed around Kalgin Island seems to result from the interplay of the northerly moving water along the east shore and the southerly moving, sediment laden, water along the west side of the inlet. Prominent, fresh water plumes, heavily laden with sediment are visible at the mouths of all major rivers. Relect plumes from as many as three tidal stages have been recognized.

Anderson, D. M.↗

NASA NTRS1974

Terminal-shock and restart control of a Mach 2.5, axisymmetric, mixed compression inlet with 40 percent internal contraction

Results of experimental tests conducted on a supersonic, mixed-compression, axisymmetric inlet are presented. The inlet is designed for operation at Mach 2.5 with a turbofan engine (TF-30). The inlet was coupled to either a choked orifice plate or a long duct which had a variable-area choked exit plug. Closed-loop frequency responses of selected diffuser static pressures used in the terminal-shock control system are presented. Results are shown for Mach 2.5 conditions with the inlet coupled to either the choked orifice plate or the long duct. Inlet unstart-restart traces are also presented. High-response inlet bypass doors were used to generate an internal disturbance and also to achieve terminal-shock control.

Baumbick, R. J.↗

NASA NTRS1974

Low-speed test of translating lip axisymmetric inlets for subsonic transports

Translating lip, axisymmetric inlets have been tested at freestream Mach numbers between 0.0 and 0.30 and at angles of attack between 0 and 90 degrees. Three isolated inlet models were tested. One model represented the inlet geometry at cruise, that is, with no lip translation. The other two models had forward translating lips with different contours. The low forward speed inlet angle-of-attack capability with the translating lip was increased more than twenty degrees over the basic untranslated lip configuration at the higher inlet airflows. The static inlet performance with the translating lip was also greatly improved. The design translation distance, defined by potential flow analysis, was near optimum.

Henne, P. A.↗

NASA NTRS1974

On the inlet vortex system

The flow field of a jet engine with an inlet vortex, which can pick up heavy debris from the ground and damage the engine, was simulated in a small water tunnel by means of the hydrogen bubble technique. It was found that the known engine inlet vortex is accompained by a vortex system, consisting of two inlet vortices (the ground based and the trailing one), secondary vortices, and ground vortices. Simulation of the ground effect by an inlet image proved that the inlet vortex feeds on free stream vorticity and can exist without the presence of a ground boundary layer. The structural form of the inlet vortex system was explained by a simple potential flow model, which showed the number, location, and the importance of the stagnation points. A retractable horizontal screen or an up-tilt of the engine is suggested as countermeasure against debris ingestion.

Bissinger, N. C.↗

NASA NTRS1975

Effects of selected design variables on three ramp, external compression inlet performance

Two inlet performance tests and one inlet/airframe drag test were conducted in 1969 at the NASA-Ames Research Center. The basic inlet system was two-dimensional, three ramp (overhead), external compression, with variable capture area. The data from these tests were analyzed to show the effects of selected design variables on the performance of this type of inlet system. The inlet design variables investigated include inlet bleed, bypass, operating mass flow ratio, inlet geometry, and variable capture area.

Kamman, J. H.↗

NASA NTRS1975

Design of a very-low-bleed Mach 2.5 mixed-compression inlet with 45 percent internal contraction

A full-scale, mixed-compression inlet was designed for operation with the TF30-P-3 turbofan engine and tested at Mach numbers of 2.5 and 2.0. The two-cone axisymmetric inlet had minimum internal contraction consistent with high total pressure recovery and low cowl drag. At Mach 2.5, inlet recovery was 0.906 with only 0.021 centerbody bleed mass-flow ratio and no cowl bleed. Increased centerbody bleed gave a maximum inlet unstart angle of attack of 6.85 deg. At Mach 2.0, inlet recovery was 0.94 with only 0.014 centerbody bleed mass-flow ratio and no cowl bleed. Inlet performance and angle-of-attack tolerance is presented for operation at Mach numbers of 2.5 and 2.0.

Wasserbauer, J. F.↗

NASA NTRS1975

Effect of entry-lip design on aerodynamics and acoustics of high throat Mach number inlets for the quiet, clean, short-haul experimental engine

Results of scale model tests of high-throat-Mach-number inlets designed to suppress inlet-emitted engine machinery noise produced in a V/STOL wind tunnel are presented. A vacuum system was used to induce inlet airflow with a siren as a noise source. Inlet mass flow was 11.68 kilograms (25.75 lb. min) per second at a throat Mach number of 0.79. The effect of entry-lip design (contraction ratio and diameter ratio) on inlet total-pressure recovery, steady-state pressure distortion, performance at high incidence angles, and noise suppression was determined. With proper entry-lip design, total-pressure recovery in excess of 0.988 could be obtained statically at an average throat Mach number of 0.79. Total-pressure distortion was 5 percent. The reduction in the siren tone sound pressure level transmitted through the inlet was 10 to 14 db relative to that measured at throat Mach 0.6.

Miller, B. A.↗

NASA NTRS1975

Effects of inlet treatment location and treatment cavity depth on compressor noise

The ability of acoustic liners to reduce compressor noise inside and in front of an inlet was studied. An axial flow research compressor and a specially designed inlet were used inside an anechoic chamber. Acoustic and performance data were obtained for a range of inlet treatment locations and cavity depths to determine their effects on inlet noise over a range of blade passing frequencies. The greatest noise reductions in front of the inlet were obtained with acoustic treatment located close to the compressor and backed with the deepest cavities tested. Inside the inlet the maximum noise level reductions were obtained in the area of the treatment regardless of treatment location. No appreciable losses in compressor performance were measured.

Clark, L. R.↗

NASA NTRS1976

Analysis of experimental results of the inlet for the NASA hypersonic research engine aerothermodynamic integration model

An aerodynamic engine inlet analysis was performed on the experimental results obtained at nominal Mach numbers of 5, 6, and 7 from the NASA Hypersonic Research Engine (HRE) Aerothermodynamic Integration Model (AIM). Incorporation on the AIM of the mixed-compression inlet design represented the final phase of an inlet development program of the HRE Project. The purpose of this analysis was to compare the AIM inlet experimental results with theoretical results. Experimental performance was based on measured surface pressures used in a one-dimensional force-momentum theorem. Results of the analysis indicate that surface static-pressure measurements agree reasonably well with theoretical predictions except in the regions where the theory predicts large pressure discontinuities. Experimental and theoretical results both based on the one-dimensional force-momentum theorem yielded inlet performance parameters as functions of Mach number that exhibited reasonable agreement. Previous predictions of inlet unstart that resulted from pressure disturbances created by fuel injection and combustion appeared to be pessimistic.

Andrews, E. H., Jr.↗

NASA NTRS1976

Investigation of two bifurcated-duct inlet systems from Mach 0 to 2.0 over a wide range of angles of attack

A 15.354 percent/scale lightweight fighter type inlet/forebody was tested over a Mach number range of 0 to 2.0. Model configurations consisted of side mounted normal shock and fixed overhead ramp type inlets. Each configuration consisted of two inlets ducted (bifurcated) to supply a single engine face. The normal shock inlet variables included a boundary layer splitter bleed system, alternate boundary layer splitter plates, alternate upper and lower cowl lip shapes, and a blow-in-door (auxiliary inlet) in one lower lip. The only variable of the fixed overhead ramp inlet was the boundary layer bleed flow. Reynolds numbers ranged from 7.6 x 1 million to 19.5 x 1 million/m. Angle of attack ranged from -10 to 35 deg and angle of sideslip from -8 to 8 deg. Test measurements included engine face total pressure recovery, steady state distortion, dynamic distortion, and surface static pressures on the forebody and inlet surfaces.

Latham, E. A.↗

NASA NTRS1977

Fan inlet disturbances and their effect on static acoustic data

There is evidence that measurements of fan-rotor inlet noise taken during static test situations are at variance with aircraft engine flight data. In particular, static tests generally yield a significantly higher tone at blade passing frequency than that measured during flight. An experimental program was carried out to investigate this discrepancy. Inlet ground vortices and large-scale inlet turbulence were generated intentionally in an anechoic test chamber. Far-field acoustic measurements and inlet flow field hot film mappings of a fan rotor were then carried out to study the influence of such inlet disturbances at a static test facility. Experimental results indicate that the acoustic effect of such disturbances appears to be less severe for supersonic than for subsonic tip speeds. Further, a reverse flow that occurs on the exterior cowl in static test facilities appears to be an additional prime candidate for creating inlet disturbances and causing variance between flight and static acoustic data.

Bekofske, K. L.↗

NASA NTRS1977

Atmospheric effects on inlets for supersonic cruise aircraft

Mixed-compression inlet dynamic behavior in the vicinity of unstart, was simulated and analyzed to investigate time response of an inlet's normal shock to independent disturbances in ambient temperature and pressure and relative velocity (longitudinal gust), with and without inlet controls active. The results indicate that atmospheric disturbances may be more important than internal disturbances in setting inlet controls requirements because they are usually not anticipated and because normal shock response to rapid atmospheric disturbances is not attenuated by the inlet, as it is for engine induced disturbances. However, before inlet control requirements can be fully assessed, more statistics on extreme atmospheric disturbances are needed.

Cole, G. L.↗

NASA NTRS1977

Phugoid characteristics of a YF-12 airplane with variable-geometry inlets obtained in flight tests at a Mach number of 2.9

Flight tests were conducted with the YF-12 airplane to examine the airplane's longitudinal characteristics at a Mach number of approximately 2.9. Phugoid oscillations as well as short period pulses were analyzed with the variable geometry engine inlets in the fixed and the automatic configurations. Stability and control derivatives for the velocity and altitude degrees of freedom and the standard short period derivatives were obtained. Inlet bypass door position was successfully used to represent the total inlet system, and the effect of the inlets on the velocity and altitude derivatives was determined. The phugoid mode of the basic airplane (fixed inlet configuration) had neutral damping, and the height mode was stable. With the addition of the inlets in the automatic configuration, the phugoid mode was slightly divergent and the height mode was divergent with a time to double amplitude of about 114 seconds. The results of the derivative estimation indicated that the change in the height mode characteristics was primarily the result of the change in the longitudinal force derivative with respect to velocity.

Powers, B. G.↗

NASA NTRS1978

Low speed test of a high-bypass-ratio propulsion system with an asymmetric inlet designed for a tilt-nacelle V/STOL airplane

A large scale model of a lift/cruise fan inlet designed for a tilt nacelle V/STOL airplane was tested with a high bypass ratio turbofan. Testing was conducted at low freestream velocities with inlet angles of attack ranging from 0 deg to 120 deg. The operating limits for the nacelle were found to be related to inlet boundary layer separation. Small separations originating in the inlet diffuser cause little or no performance degradation. However, at sufficiently severe freestream conditions the separation changes abruptly to a lip separation. This change is associated with a significant reduction in nacelle net thrust as well as a sharp increase in fan blade vibratory stresses. Consequently, the onset of lip separation is regarded as the nacelle operating limit. The test verified that the asymmetric inlet design will provide high performance and stable operation at the design forward speed and angle of attack conditions. At some of these, however, operation near the lower end of the design inlet airflow range is not feasible due to the occurrence of lip separation.

Syberg, J.↗

NASA NTRS1978

Performance of a short annular dump diffuser using suction-stabilized vortices at inlet Mach numbers to 0.41

A short, annular dump diffuser was designed to use suction to establish stabilized vortices on both walls for improved flow expansion in the region of an abrupt area change. The diffuser was tested at near ambient inlet pressure and temperature. The overall diffuser area ratio was 4.0. The inlet height was 2.54 cm and the exit pitot-static rakes were located at a distance from the vortex fence equal to two or six times the inlet height. Performance data were taken at near ambient temperature and pressure for nominal inlet Mach numbers of 0.18 to 0.41 with suction rates of 0 to 18 percent of the total inlet airflow. The exit velocity profile could be shifted toward either wall by adjusting the inner- or outer-wall suction rate. Symmetrical exit velocity profiles were unstable, with a tendency to shift back to hub- or tip-weighted profile. Diffuser effectiveness was increased from about 47 percent without suction to over 85 percent at a total suction rate of about 14 percent. The diffuser total pressure losses at inlet Mach numbers of 0.18 and 0.41 decreased from 1.1 and 5.6 percent without suction to 0.48 and 5.2 percent at total suction rates of 14.4 and 5.6 percent, respectively.

Smith, J. M.↗

NASA NTRS1978

Wind tunnel evaluation of YF-12 inlet response to internal airflow disturbances with and without control

The response of terminal-shock position and static pressures in the subsonic duct of a YF-12 aircraft flight-hardware inlet to perturbations in simulated engine corrected airflow were obtained with and without inlet control. Frequency response data, obtained with inlet controls inactive, indicated the general nature of the inherent inlet dynamics, assisted in the design of controls, and provided a baseline reference for responses with active controls. All the control laws were implemented by means of a digital computer that could be programmed to behave like the flight inlet's existing analog control. The experimental controls were designed using an analytical optimization technique. The capabilities of the controls were limited primarily by the actuation hardware. The experimental controls provided somewhat better attenuation of terminal shock excursions than did the YF-13 inlet control. Controls using both the forward and aft bypass systems also provided somewhat better attenuation than those using just the forward bypass. The main advantage of using both bypasses is in the greater control flexibility that is achieved.

Cole, G. L.↗

NASA NTRS1979

Free jet phenomena in a 90 deg-sharp edge inlet geometry

The effects of free-jet phenomena, jetting, in a 90-deg-sharp-edge inlet tube are analyzed. Mass-limiting flow data and associated pressure profiles for tubes of 53, 64, 73 and 105 L/D with a 90 deg-sharp-edge or orifice-type inlet are compared to Borda-type inlet data to determine bounds of the free-jet phenomena. For smooth tubes the limits appear to be one-dimensional and dependent only on inlet stagnation conditions. The upper L/D boundary is related by stagnation characteristics and the lower bound appears to be saturation conditions at the inlet. It is noted that similar free-jet effects were found for fluid hydrogen indicating that fluid jetting might be common to all fluids flowing through 90 deg-sharp-edge inlet geometries.

Hendricks, R. C.↗