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Soderman, P. T.

Publications and source records attributed to Soderman, P. T..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Temperature and Forward Flight Effects on an Underexpanded Jet Noise

An experimental investigation was carried out in the NASA Ames 40'x80' wind tunnel to investigate the far field noise characteristics of a supersonic jet exiting from an axisymmetric convergent nozzle. The nozzle geometry conforms to the ASME specifications for the long radius nozzle. The nozzle pressure ratio NPR, (stagnation pressure/ambient pressure) was varied from 2.5 to 4.5. The temperature ratio, TR (stagnation temperature/ambient temperature) was varied from 2.5 to 3.5. The resulting Reynolds number range, based on the nozzle exit diameter of 12.55cm, is from 0.98 -1.27 x 10(exp 6). The far field directivity was obtained using 1/4 inch diameter condenser microphone with the Flow-Induced Tone Eliminator (FITE) aerodynamic microphone fore body. Appropriate microphone corrections, developed by Allen et al., were made for accurate in-flow acoustic measurements at high frequencies. The narrow band (band width = 64 Hz) frequency spectra covering a range from 0 to 70 KHz were obtained with an accuracy of plus or minus 0.6dB. Typical narrow-band spectra representing far field noise in the forward quadrant, normal to the jet axis and the aft quadrant are shown. The three dominant components of the noise, the screech tone, broad-band shock associated noise and the mixing noise, are clearly identifiable in the spectra. The variation of the screech tone with the exit Mach number (calculated from the isentropic equation relating NPR to Mach number), is shown. The solid line in the figure is calculated using Tam's formula. The model developed by Tam seems to work well even at high temperatures. The appearance of the screech tone is confined to the forward quadrant (theta less than or equal to 60 degrees; the angle theta is measured from the inlet axis). The amplitude of the tone is about 10 dB higher than the broad band noise, which is less than the normally observed amplitude for cold jets operating at similar conditions.

Krothapalli, A.↗
NASA NTRS1995

Internal Acoustics Measurements of a Full Scale Advanced Ducted Propulsor Demonstrator

Acoustics measurements of a Pratt & Whitney full-scale ADP (Advanced Ducted Propulsor), an ultrahigh by-pass ratio engine, were conducted in the NASA Ames 40- by 80-Foot Wind Tunnel. This paper presents data from measurements taken from sensors on a fan exit guide vane in the ADP. Data from two sensors, one at mid-span and the other at the tip of the fan exit guide vane, are presented. At the blade passage frequency (BPF), the levels observed at the various engine and wind speeds were higher at the mid-span sensor than the tip sensor. The coherence between these internal sensors and external microphones were calculated and plotted as a function of angle (angles ranged from 5 degrees to 160 degrees) relative to the ADP longitudinal axis. At the highest engine and wind speeds, the coherence between the tip sensor and the external microphones was observed to decrease at higher multiples of the BPF. These results suggest that the rotor-stator interaction tones are stronger in the mid-span region than at the tip.

Santa Maria, O. L.↗
NASA NTRS1994

Modification of the Ames 40- by 80-foot wind tunnel for component acoustic testing for the second generation supersonic transport

The development of a large-scale anechoic test facility where large models of engine/airframe/high-lift systems can be tested for both improved noise reduction and minimum performance degradation is described. The facility development is part of the effort to investigate economically viable methods of reducing second generation high speed civil transport noise during takeoff and climb-out that is now under way in the United States. This new capability will be achieved through acoustic modifications of NASA's second largest subsonic wind tunnel: the 40-by 80-Foot Wind Tunnel at the NASA Ames Research Center. Three major items are addressed in the design of this large anechoic and quiet wind tunnel: a new deep (42 inch (107 cm)) test section liner, expansion of the wind tunnel drive operating envelope at low rpm to reduce background noise, and other promising methods of improving signal-to-noise levels of inflow microphones. Current testing plans supporting the U.S. high speed civil transport program are also outlined.

Schmitz, F. H.↗
NASA NTRS1994

Measurements of Forward Flight Effects on the Advanced Ducted Propulsion Demonstrator Engine

The performance of the Pratt & Whitney Advanced Ducted Propulsion (ADP) UHB concept has been recently evaluated with studies of a 17 in. diameter fan simulator. Following the model scale tests, a 118 in. diameter demonstrator was tested at the NASA Ames 40- by 80-Foot Wind Tunnel. The 18 blade fan was driven by the low compressor shaft of a PW2037 core through a reduction gear system fabricated by Fiat with approximately 1:3.7 reduction ratio. ne variable pitch fan was hydraulically actuated with settings for take-off, cruise, feather, and reverse thrust. The low-pressure turbine was built by MTU to provide higher shaft power in comparison with the standard PW2037. The demonstrator was provided with 45 vanes located 2.6 fan chords downstream of the rotor, and 10 case struts approximately 1 fan chord downstream of the vanes. The inlet, mid-duct, and exhaust linings were acoustically treated. Acoustic surveys were taken in the for-ward thrust mode for fan speeds of 898, 1120, 1205, and 1302 R.P.M., and at tunnel speeds of 25, 50, 100, and 140 kts. The lowest speed was achieved with the wind tunnel fans at flat pitch, but with the engine pumping the test section Microphone signals were recorded for 30 seconds at 5 deg. increments. These measurements will be used to assess the effects of forward speed on UHB engines, to compare these effects with the corresponding characteristics of conventional bypass ratio engines, and to discuss the various aspects of testing large engines in the wind tunnel.

Horne, W. C.↗
NASA NTRS1993

Fiber-optic interferometric sensors for measurements of pressure fluctuations - Experimental evaluation

A fiber optic interferometric sensor that is being developed at NASA Ames Research Center for pressure fluctuation measurements in wind tunnels is considered. Preliminary evaluation indicates that the fiber optic interferometric sensor can be successfully used as an aeroacoustic sensor and is capable of providing a powerful instrument to solve complex acoustic measurement problems in wind tunnels.

Cho, Y. C.↗
NASA NTRS1990

Pressure fluctuations in the tip region of a blunt-tipped airfoil

The characteristics of turbulence generated in the tip region of a blunt-tipped airfoil were studied using surface pressure measurements. The model was a NACA 0012; tests were performed at flow speeds of 75, 55, and 35 m/s and angles of attack of 6, 12, and 16 deg. Reynolds numbers based on the wing chord were 1.9, 3.0, and 4.1 million. Pressure fluctuations measured near the primary tip-vortex on the upper, low pressure side of the wing tip were uncorrelated with those on the blunt tip. Fluctuations on the high pressure side of the wing were strongly correlated with those on the flat tip, but 10-20 dB less intense. Spectra measured on the flat tip displayed pronounced peaks at dimensionless frequencies of 0.8 to 1.3. Cross correlations between some of the flat-tip pressures displayed two echolike groupings. A model is proposed that explains these correlations.

Mcinerny, S. A.↗
NASA NTRS1986

An experimental investigation of wing tip turbulence with applications to aerosound

Wind tunnel tests were performed to measure the turbulence characteristics of flow in the wing tip region of a blunt tipped NACA 0012 airfoil at angles of attack of 16, 12 and 6 deg and flow speeds of 75, 55, and 35 m/s. Reynolds numbers based on the chord length ranged from 1.8 x 10(exp6) to 3.8 x 10(exp 6). Hot wire measurements were made at an angle of attack of 12 deg and U(infinity) = 55 ms. These indicate fluctuation velocities on the order of 0.13 U(infinity) in the tip region. Surface pressure spectra are presented for alpha = 12 deg and 16 deg; surface-pressure cross-correlations are presented for alpha = 16 deg. These suggest the presence of a well organized turbulence structure with a peak Strouhal number 0.8 to 1.1 based on the wing thickness. High frequency turbulence of lesser intensity was measured at positions near the primary tip vortex on the upper wing surface. A separation region with a spectral peak of St approximately equal to 0.4 was recorded at alpha = 16 deg for the transducer located on the low pressure side of the wing nearest the trailing edge. Surface-surface cross correlations display a double, echo like structure. Near-far field correlations indicate that the well ordered tip turbulence and the separation region on the upper surface both radiate significant levels of far field sound. The use of cross correlation techniques in the wind tunnel has permitted treatment of radiated sound levels which are 25 and more dB below tunnel background levels.

Mcinerny, S. A.↗
NASA NTRS1986

An experimental investigation of wing tip turbulence with applications to aerosound

Wind tunnel tests were carried out to measure the turbulence characteristics of flow in the wing tip region of a blunt tipped NACA 0012 airfoil at 16-, 12-, and 6-deg angles of attack and 75-, 55-, and 35-m/s flow speeds. Results suggest the presence of a well organized turbulence structure with a peak Strouhal number 0.8 to 1.1 based on the wing thickness. At positions near the primary tip vortex on the upper wing surface, high frequency turbulence of lesser intensity was measured. Near-far field correlations reveal that the well-ordered tip turbulence and the separation region surface on the upper surface both radiate significant levels of far field sound.

Mcinerny, S. A.↗
NASA NTRS1986

Noise radiation directivity from a wind-tunnel inlet with inlet vanes and duct wall linings

The acoustic radiation patterns from a 1/15th scale model of the Ames 80- by 120-Ft Wind Tunnel test section and inlet have been measured with a noise source installed in the test section. Data were acquired without airflow in the duct. Sound-absorbent inlet vanes oriented parallel to each other, or splayed with a variable incidence relative to the duct long axis, were evaluated along with duct wall linings. Results show that splayed vans tend to spread the sound to greater angles than those measured with the open inlet. Parallel vanes narrowed the high-frequency radiation pattern. Duct wall linings had a strong effect on acoustic directivity by attenuating wall reflections. Vane insertion loss was measured. Directivity results are compared with existing data from square ducts. Two prediction methods for duct radiation directivity are described: one is an empirical method based on the test data, and the other is a analytical method based on ray acoustics.

Soderman, P. T.↗
NASA NTRS1986

Optimum full-scale subsonic wind tunnel

The needs and reasons for performing full-scale subsonic research have been studied. Full-scale wind-tunnel requirements are described; recommended size, airspeed, acoustic capabilities, and flow quality are developed; and data-acquisition systems, productivity, automation, and some cost elements are discussed. It is proposed that the optimum full-scale, subsonic wind tunnel be large enough to accommodate aerodynamic and acoustic investigations on most advanced aircraft, which exhibit complex engine/lifting-surface flow-field interactions, including advanced rotorcraft.

Mort, K. W.↗
NASA NTRS1984

Effect of boattail geometry on the acoustics of parallel baffles in ducts

Sound attenuation and total pressure drop of parallel duct baffles incorporating certain boattail geometries were measured in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The baseline baffles were 1.56 m long and 20 cm thick, on 45-cm center-to-center spacings, and spanned the test section from floor to ceiling. Four different boattails were evaluated: a short, smooth (nonacoustic) boattail; a longer, smooth boattail; and two boattails with perforated surfaces and sound-absorbent filler. Acoustic measurements showed the acoustic boattails improved the sound attenuation of the baffles at approximately half the rate to be expected from constant-thickness sections of the same length; that is, 1.5 dB/n, where n is the ratio of acoustic treatment length to duct passage width between baffles. The aerodynamic total pressure loss was somewhat sensitive to tail geometry. Lengthening the tails to reduce the diffusion half-angle from 11 to 5 degrees reduced the total pressure loss approximately 9%. Perforating the boattails, which increased the surface roughness, did not have a large effect on the total pressure loss. Aerodynamic results are compared with a published empirical method for predicting baffle total pressure drop.

Soderman, P. T.↗
NASA NTRS1983

The acoustic response of a propeller subjected to gusts incident from various inflow angles

The acoustic effect of perturbing the inflow field of a propeller was studied. The perturbation was caused by a jet of air blowing into the propeller disc from various angles, creating spanwise and chordwise flow disturbances along the blades. The effects of the gust angle, speed and turbulence, and propeller rpm and thrust are shown with narrowband spectra and directivity plots of the acoustic field. A prediction method for the peaks of the harmonics of the blade passing frequency for various gust and propeller conditions is presented.

Jonkouski, G. C.↗
NASA NTRS1983

Aeroacoutic characteristics of a large, variable-pitch, variable-speed fan system

The acoustic and aerodynamic performance of the new drive fans for the NASA Ames 40- by 80-/80- by 120-foot wind tunnel was investigated. Results show that a fan system with variable-speed and variable-pitch rotor blades allows the operator to control noise and energy consumption, at a given mass flow rate, through the choice of blade speed and pitch. A low speed and high blade pitch will generally create the least noise at the least energy cost. An empirical method is described which predicts the sound power of this fan system reasonably well.

Soderman, P. T.↗
NASA NTRS1982

A comparison of wind tunnels suitable for rotorcraft noise studies

Many good small scale facilities are available for rotorcraft noise research. Ames 40 x 80/80 x 120 probably is a good large scale facility for acoustic research of large or small rotorcraft, but the acoustic quality of the modified facility was not yet measured. DNW is probably the best aeroacoustic facility, but may be expensive. Other parameters to consider besides background noise are turbulent level and scale, restructed measurement field, local reflections, and speed range. Advanced measurement techniques improve data quality from any facility.

Soderman, P. T.↗
NASA NTRS1982

A study of resonant-cavity and fiberglass-filled parallel baffles as duct silencers

Acoustical performance and pressure drop were measured for two types of splitters designed to attenuate sound propagating in ducts - resonant-cavity baffles and fiberglass-filled baffles. Arrays of four baffles were evaluated in the 7- by 10-foot wind tunnel number 1 at Ames Research Center at flow speeds from 0 to 41 m/sec. The baffles were 2.1 m high, 305 to 406 mm thick, and 3.1 to 4.4 m long. Emphasis was on measurements of silencer insertion loss as affected by variations of such parameters as baffle length, baffle thickness, perforated skin geometry, cavity size and shape, cavity damping, wind speed, and acoustic field directivity. An analytical method for predicting silencer performance is described and compared with measurements. With the addition of cavity damping in the form of 25-mm foam linings, the insertion loss above 250 Hz of the resonant-cavity baffles was improved 2 to 7 db compared with the undamped baffles; the loss became equal to or greater than the insertion loss of comparable size fiberglass baffles at frequencies above 250 Hz. Variations of cavity size and shape showed that a series of cavities with triangular cross-sections (i.e., variable depth) were superior to cavities with rectangular cross sections (i.e., constant depth). In wind, the undamped, resonant-cavity baffles generated loud cavity-resonance tones; the tones could be eliminated by cavity damping.

Soderman, P. T.↗
NASA NTRS1981

Design and performance of resonant-cavity parallel baffles for duct silencing

Resonant-cavity parallel baffles, either empty or with a thin absorbent lining, have been investigated as an alternative to fiberglass-filled baffles commonly used to control noise emission from large ducts. A method for predicting silencer attenuation is described, and it is shown that the new type of baffle is characterized by an acoustic performance similar to that of fibrous baffles, while being virtually immune to such problems as clogging, erosion, or settling. The emphasis of the study is on insertion loss measurements in a 7 by 10 ft wind tunnel.

Soderman, P. T.↗
NASA NTRS1980

Calibration of the Ames Anechoic Facility. Phase 1: Short range plan

A calibration was made of the acoustic and aerodynamic characteristics of a small, open-jet wind tunnel in an anechoic room. The jet nozzle was 102 mm diameter and was operated subsonically. The anechoic-room dimensions were 7.6 m by 5.5 m by 3.4 m high (wedge tip to wedge tip). Noise contours in the chamber were determined by various jet speeds and exhaust collector positions. The optimum nozzle/collector separation from an acoustic standpoint was 2.1 m. Jet velocity profiles and turbulence levels were measured using pressure probes and hot wires. The jet was found to be symmetric, with no unusual characteristics. The turbulence measurements were hampered by oil mist contamination of the airflow.

Hickey, D.↗