High-speed propeller performance and noise predictions at takeoff/landing conditions
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Nallasamy, M.↗
Engineering topics
Woodward, R. P.
Publications and source records attributed to Woodward, R. P..
High speed propeller performance and noise predictions at takeoff/landing conditions
The performance and noise of a high speed SR-7A model propeller under takeoff/landing conditions are considered. The blade loading distributions are obtained by solving the three-dimensional Euler equations and the sound pressure levels are computed using a time domain approach. At the nominal takeoff operating point, the blade sections near the hub are lightly or negatively loaded. The chordwise loading distributions are distinctly different from those of cruise conditions. The noise of the SR-7A model propeller at takeoff is dominated by the loading noise, similar to that at cruise conditions. The waveforms of the acoustic pressure signature are nearly sinusoidal in the plane of the propeller. The computed directivity of the blade passing frequency tone agrees fairly well with the data at nominal takeoff blade angle.
Nallasamy, M.↗
High speed propeller performance and noise predictions at takeoff/landing conditions
The performance and noise of a high speed SR-7A model propeller under takeoff/landing conditions are considered. The blade loading distributions are obtained by solving the three-dimensional Euler equations and the sound pressure levels are computed using a time domain approach. At the nominal takeoff operating point, the blade sections near the hub are lightly or negatively loaded. The chordwise loading distributions are distinctly different from those of cruise conditions. The noise of the SR-7A model propeller at takeoff is dominated by the loading noise, similar to that at cruise conditions. The waveforms of the acoustic pressure signature are nearly sinusoidal in the plane of the propeller. The computed directivity of the blade passing frequency tone agrees fairly well with the data at nominal takeoff blade angle.
Nallasamy, M.↗
Low flight speed fan noise from a supersonic inlet
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Woodward, R. P.↗
Tone generation by rotor-downstream strut interaction
Previously cited in issue 10, p. 1378, Accession no. A83-25957
Woodward, R. P.↗
Fan noise reduction achieved by removing tip flow irregularities behind the rotor - forward arc test configurations
The noise source caused by the interaction of the rotor tip flow irregularities (vortices and velocity defects) with the downstream stator vanes was studied. Fan flow was removed behind a 0.508 meter (20 in.) diameter model turbofan through an outer wall slot between the rotor and stator. Noise measurements were made with far-field microphones positioned in an arc about the fan inlet and with a pressure transducer in the duct behind the stator. Little tone noise reduction was observed in the forward arc during flow removal; possibly because the rotor-stator interaction noise did not propagate upstream through the rotor. Noise reductions were maded in the duct behind the stator and the largest decrease occurred with the first increment of flow removal. This result indicates that the rotor tip flow irregularity-stator interaction is as important a noise producing mechanism as the normally considered rotor wake-stator interaction.
Dittmar, J. H.↗
Low flight speed acoustic results for a supersonic inlet with auxiliary inlet doors
A model supersonic inlet with auxiliary inlet doors and boundary layer bleeds was acoustically tested in simulated low speed flight up to Mach 0.2 in the NASA Lewis 9 x 15 Anechoic Wind Tunnel and statically in the NASA Lewis Anechoic Chamber. A JT8D refan model was used as the noise source. Data were also taken for a CTOL inlet and for an annular inlet with simulated centerbody support struts. Inlet operation with open auxiliary doors increased the blade passage tone by about 10 dB relative to the closed door configuration although noise radiation was primarily through the main inlet rather than the doors. Numerous strong spikes in the noise spectra were associated with the bleed system, and were strongly affected by the centerbody location. The supersonic inlet appeared to suppress multiple pure tone (MPT) generation at the fan source. Inlet length and the presence of support struts were shown not to cause this MPT suppression. Previously announced in STAR as N83-27794
Woodward, R. P.↗
Tone generation by rotor-downstream strut interaction
A JT15D fan stage was acoustically tested in the NASA Lewis anechoic chamber as part of the joint Lewis-Langley Research Center investigation of flight simulation techniques and flight effects using the JT15D engine as a common test vehicle. Suspected rotor-downstream support strut interaction was confirmed through the use of simulated support struts which were tested at three axial rotor-strut spacings. Tests were also performed with the struts removed. Inlet boundary layer suction in conjunction with an inflow control device was also explored. The removal of the boundary layer reduced the fan fundamental tone levels suggesting that the mounting and mating of such a device to the nacelle requires careful attention. With the same inflow control device installed good acoustic agreement was shown between the engine on an outdoor test stand and the fan in the anechoic chamber.
Woodward, R. P.↗
Tone generation by rotor-downstream strut interaction
A JT15D fan stage was acoustically tested in the NASA Lewis anechoic chamber as part of the joint Lewis-Langley Research Center investigation of flight simulation techniques and flight effects using the JT15D engine as a common test vehicle. Suspected rotor-downstream support strut interaction was confirmed through the use of simulated support struts which were tested at three axial rotor-strut spacings. Tests were also performed with the struts removed. Inlet boundary layer suction in conjuction with an inflow control device was also explored. The removal of the boundary layer reduced the fan fundamental tone levels suggesting that the mounting and mating of such a device to the nacelle requires careful attention. With the same inflow control device installed good acoustic agreement was shown between the engine on an outdoor test stand and the fan in the anechoic chamber.
Woodward, R. P.↗
Wind tunnel measurements of blade/vane ratio and spacing effects on fan noise
(Previously cited in issue 24, p. 4128, Accession no. A81-48628)
Woodward, R. P.↗
Forward acoustic performance of a model turbofan designed for a high specific flow (QF-14)
Forward noise and overall aerodynamic performance are presented for a high-tip-speed fan having an exceptionally high average axial Mach number at the rotor inlet. This high Mach number is intended to attenuate forward noise at both the design-speed takeoff point, and at the unconventional low-pressure-ratio, design-speed approach point. As speed was increased near design, all forward noise components were reduced, and rear noise in the discharge duct was increased, indicating that the high Mach number flow at the rotor face is attenuating forward noise at takeoff. The fan at takeoff is some 5.5 to 11 dB quieter than several reference fans. Data at the point closest to approach indicated tentatively that the design-speed approach mode was 3 dB quieter than the conventional mode.
Lucas, J. G.↗
Low flight speed acoustic results for a supersonic inlet with auxiliary inlet doors
A model supersonic inlet with auxiliary inlet doors and bounday layer bleeds was acoustically tested in simulated low speed flight up to Mach 0.2 in the NASA Lewis 9x15 Anechoic Wind Tunnel and statically in the NASA Lewis Anechoic Chamber. A JT8D refan model was used as the noise source. Data were also taken for a CTOL inlet and for an annular inlet with simulated centerbody support struts. Inlet operation with open auxiliary doors increased the blade passage tone by about 10 dB relative to the closed door configuration although noise radiation was primarily through the main inlet rather than the doors. Numerous strong spikes in the noise spectra were associated with the bleed system, and were strongly affected by the centerbody location. The supersonic inlet appeared to suppress multiple pure tone (MPT) generation at the fan source. Inlet length and the presence of support struts were shown not to cause this MPT suppression.
Woodward, R. P.↗
Effects of blade-vane ratio and rotor-stator spacing on fan noise with forward velocity
A research fan stage is acoustically tested in an anechoic wind tunnel with a 41 m/sec tunnel flow. Two stator vane numbers giving cut-on and cut-off conditions are tested at three rotor stator spacings ranging from 0.5 to 2.0 rotor chords. Hot-film anemometer turbulence measurements are made at the leading edge of the stator for each spacing, and a crossed film anemometer is radially transversed to define streamwise and upwash characteristics of the rotor blade wakes. Trends in the acoustic results are observed in the front and aft quadrants at 80% design fan speed. Aft quadrant results demonstrate a fundamental tone 9 dB lower for the 25 vane stator than for the 11 vane stator, while overtone levels are 3 dB higher. The cut-off criterion strongly controls fundamental tone level at all spacings, and spacing trends of the wake-defect upwash component show good agreement with corresponding cut-on acoustic tone levels.
Woodward, R. P.↗
Effects of blade-vane ratio and rotor-stator spacing of fan noise with forward velocity
A research fan stage was acoustically tested in an anechoic wind tunnel with a 41 m/sec tunnel flow. Two stator vane numbers giving cut-on and cut-off conditions were tested at three rotor-stator spacings ranging from about 0.5 to 2.0 rotor chords. These two stators were designed for similar aerodynamic performance. Hot film anemometer turbulence measurements were made at the leading edge of the stator for each spacing. The cut-off criterion strongly controlled the fundamental tone level at all spacings. The trends with spacing of the wake defect upwash component at the stator tip showed good agreement with the corresponding cut-on acoustic tone levels.
Woodward, R. P.↗
Effect of inflow control on inlet noise of a cut-on fan
A cut-on, high tip speed fan stage was acoustically tested with three configurations of an inflow control device in the NASA Lewis anechoic chamber. Although this was a cut-on design, rotor-inflow interaction appeared to be a much stronger source of blade passing tone radiated from the inlet than rotor-stator interaction for the 1.6 mean rotor chord separation. Aft external suction applied to the area where the inflow control device joined the inlet produced a further reduction in blade passing tone suggesting that disturbances in the forward flow on the outside of the inlet were superimposed on the inlet boundary layer and were a significant source of tone noise.
Woodward, R. P.↗
Forward acoustic performance of a shock-swallowing high-tip-speed fan (QF-13)
Forward noise and overall aerodynamic performance data are presented for a high-tip-speed fan having rotor blade airfoils designed to alter the conventional leading-edge bow shocks to weak, oblique shocks which are swallowed within the interblade channels. It was anticipated that the swallowed shocks would minimize the generation of multiple-pure-tone noise. In the speed range where the shocks presumably were swallowed, the multiple-tone noise was lowered only about 3 decibels. Comparison with several high-speed fans on a thrust-corrected basis indicates that the present fan was the quietest in total forward noise at low speeds but offered no advantage at high speeds.
Lucas, J. G.↗
Effect of inflow control on inlet noise of a cut-on fan
The control of turbulence and other inflow disturbances in anechoic chambers for static turbofan noise studies was studied. A cut-on, high tip speed fan stage was acoustically tested with three configurations of an inflow control device in an anechoic chamber. Although this was a cut-on design, rotor inflow interaction appeared to be a much stronger source of blade passing tone radiated from the inlet than rotor stator interaction for the 1.6 mean rotor chord separation. Aft external suction applied to the area where the inflow control device joined the inlet produced a further reduction in blade passing tone, suggesting that disturbances in the forward flow on the outside of the inlet were superimposed on the inlet boundary layer and were a significant source of tone noise.
Woodward, R. P.↗
Aerodynamic and acoustic effects of eliminating core swirl from a full scale 1.6 stage pressure ratio fan (QF-5A)
Fan QF-5A was a modification of fan QF-5 which had an additional core stator and adjusted support struts to turn the core exit flow from a 30 deg swirl to the axial direction. This modification was necessary to eliminate the impingement of the swirling core flow on the axial support pylon of the NASA-Lewis Quiet Fan Facility that caused aerodynamic, acoustic and structural problems with the original fan stage at fan speeds greater than 85 percent of design. The redesigned fan QF-5A did obtain the design bypass ratio with an increased core airflow suggesting that the flow problem was resolved. Acoustically, the redesigned stage showed a low frequency broadband noise reduction compared to the results for fan QF-5 at similar operating conditions.
Woodward, R. P.↗