The first schedule protects against compressor stall, and the second protects
`against turbine overtemperature. Both functions are scheduled as functions of
`corrected core speed. The digital control memory incorporates logic to select
`the lower of the acceleration fuel limits which are computed from the two func-
`tions. Figure 87 depicts the OTW engine acceleration fuel schedule. The cor-
`rected core speed function is calculated from measured core speed, fan speed,
`and fan inlet temperature. The corrected acceleration fuel limit is a function
`of fuel flow, compressor discharge pressure, fan speed, and fan inlet tempera-
`ture. The digital control logic compares the scheduled acceleration fuel limit
`with the real-time calculated level of the acceleration fuel function and mul-
`tiplies the difference by compressor discharge pressure to establish the actual
`engine-fuel-flow limit. This calculation process is repeated approximately 80
`times per second.
`The OTW control also incorporates limits for engine protection.
`
`3.8.9 OTW Transient Thrust Response
`
`As noted earlier the QCSEE was required to have rapid thrust-response
`capability. The UTW and OTW requirements were the same. Figure 88 shows the
`results of a thrust-response study using a transient model of the OTW engine.
`The thrust-response requirement is noted on the
`The dashed line on the
`figure shows the predicted response of a conventional turbofan in which fan
`speed and core speed are both varied with changes in engine fuel flow. With a
`conventional system, the required response could not be achieved due to the
`acceleration fuel schedule - which is designed to prevent compressor stall and
`turbine overtemperature.
`Since the required response could not be achieved using conventional
`methods, a study was conducted to determine if the thrust-response time could
`be improved by more effective use of the core stators.
`It was determined
`that, by setting the stators closed from the nominal schedule, the thrust-re-
`sponse rate could be increased. When the core stators are closed, the core
`speed increases to maintain sufficient power to hold the fan speed and main-
`tain the thrust setting. Therefore, with closed core stators the core engine
`was not required to accelerate to achieve thrust response. The core stator
`closure was implemented by biasing the base stator schedule with the power-
`demand signal and by an operating-mode signal. With a step increase in the
`power-demand signal, the core stators would open rapidly to provide the power
`for fan acceleration to takeoff speed. The solid line on Figure 88 shows the
`predicted thrust response of the OTW engine with the core stator reset func-
`t ion.
`
`3.8.10 Failure Indication and Corrective Action
`One propulsion-control-technology objective in the QCSEE program was to
`reduce the impact of control-system sensor failures. This concept was imple-
`mented by using the inherent capability of a digital computer to rapidly com-
`pare and act on a large amount of data.
`138
`
`GE-1011.156
`
`

`
`Temperature
`Limits
`
`Steady-State
`Operating Line
`
`Idle
`
`Takeoff
`
`Corrected Core Speed
`
`Figure 87. OTW Acceleration Fuel Schedule.
`
`Corrected
`- Acceleration
`Fuel Limit
`
`f-' W
`W
`
`GE-1011.157
`
`

`
`I
`I
`I
`Conventional Turbofan
`(No Core Stator Reset)
`
`Time to 95%
`Net Thrust,
`Seconds
`
`2.5
`
`2.0
`
`, ,
`
`,..,
`" ....
`
`1.5
`
`1.0
`
`---
`
`Requirement
`
`J
`
`"
`
`" . "
`---- ---..
`"-
`-
`
`0.5
`
`With Core Stator Reset ..
`(Selected)
`•
`50
`
`I
`
`70
`60
`Initial % Net Thrust
`Figure 88. OTW Predicted Transient Response.
`
`'.-..
`"
`
`r--... -'---
`
`'" '"" " ..... -
`---"'- -
`
`80
`
`GE-1011.158
`
`

`
`The digital control memory incorporated a nonlinear model of the OTW en-
`gine cycle. This model was combined with a logic-update scheme to forman
`extended Kalman-Bucy filter which provided a calculated estimate of the engine
`sensor outputs. These calculated sensor values were compared with the mea-
`sured sensor values.
`If the difference was small, the engine model was up-
`dated to calculate new estimated sensor outputs.
`If an engine sensor fails
`excessive error is detected, the engine sensor is automatically disconnected,
`and the engine continues to operate using the calculated value of the sensed
`output. The calculated value of a given sensor is based on the fact that
`sensed variables are interrelated through the engine model. Figure 89 is a
`schematic of the sensor failure indication and corrective action (FICA) con-
`cept. Figure 90 shows the 'results of dynamic-simulator study on the OTW en-
`gine with the FICA concept incorporated. The data on the far left show nor-
`mal system operation with all sensors operating during a power chop and a power
`burst. The center set of data shows engine operation with a compressor-dis-
`charge sensor failure. The data on the right show operation with a fan-speed
`sensor failure. Even with the failed sensors, the dynamic simulation indicates
`that the engine should perform satisfactorily.
`
`3.9 LOW-EMISSIONS COMBUSTOR
`In July 1973, the U.S. Environmental Protection Agency (EPA) issued stan-
`dards to regulate and minimize the quantities of carbon monoxide
`hydro-
`carbons (HC), oxides of nitrogen (NOx ) , and smoke emissions that may be dis-
`charged by aircraft operating within or near airports, These standards were
`defined for several different categories and types of fixed-wing, commercial-
`aircraft engines and are presented in terms of a calculated parameter called
`the EPA Parameter (EPAP). This parameter is based on an EPA-defined, landing/
`takeoff cycle consisting of specific operating times at engine power settings
`for ground idle, takeoff, climbout, and approach. The CO and HC emissions are
`mostly generated at the low-power ground idle conditions while the NOx emis-
`sions are generated at the higher power settings including takeoff, climbout,
`and approach.
`
`3.9.1 Design Requirements
`The requirements for the QCSEE combustor were predicated on meeting the
`very stringent EPA standards for certified Class T2 subsonic engines. These
`standards, shown below, are presently scheduled to become effective in 1979:
`•
`4.3
`CO
`•
`HC
`0.8
`•
`3.0
`NOx
`•
`Smoke
`22
`
`Ibm/IOOO lbf/hr
`
`SAE-SN
`
`141
`
`GE-1011.159
`
`

`
`Actuator!
`
`Engine
`
`Sensors ,---
`
`Engine Sensor Outputs
`....
`......
`
`vIA
`.....
`It...
`
`..
`
`-.
`
`\;
`Sensor
`Control Logic K-r- r-- Disconnect
`!.'
`
`.A
`
`"
`
`Update
`Real-Time
`Engine Model
`
`I I
`
`k:=-
`... ">
`...
`
`-
`
`+
`
`7
`
`>-
`
`Excess Vt Error
`Error
`r-...
`-,
`....,
`Detect
`
`TI 0
`<)
`Failure
`Indication
`Signal
`To Aircraft
`
`Figure 89. OTW Failure Indication and Corrective Action.
`
`GE-1011.160
`
`

`
`I Normal Transient I
`
`I P3 Sensor Failed I I Fan Speed Sensor
`
`I-c
`
`»
`
`....
`
`....-
`
`<'
`
`'--'
`
`--
`
`"'---
`
`='
`
`lor&-
`
`1
`
`A
`
`I
`
`Net Thrust 100% ...
`
`50% V
`Fan Speed 100% -
`
`Stall Margin
`
`Turbine Inlet
`Temperature
`
`50%
`50%
`
`0%
`
`100%
`
`70%
`
`V'
`
`--I I-- 1 sec.
`
`A
`
`...
`
`Figure 90. FICA
`
`Simulation Results; Power Chop to 60% and Power Burst to 100%.
`
`f-'
`II>.
`W
`
`GE-1011.161
`
`

`
`Proposed amendments to these standards are currently being reviewed
`by the EPA. Revised standards could possibly result in relaxation of the
`requirements and the effectivity dates for Class T2 engines.
`In addition to the combustor-emissions requirements, the combustor must
`be sized to fit within the dimensional envelope of the existing core engine
`and meet performance requirements such as combustion efficiency, exhaust-
`temperature distribution, and altitude ignition typically required for any
`advanced, high-bypass engine.
`As shown in Table XX, meeting the CO and HC emissions requirements 1n
`the QCSEE applications is particularly challenging because of severe combus-
`tor-inlet operating conditions at ground idle compared to those of a current
`state-of-the-art engine such as the CF6-50. The CO and HC emissions of the
`QCSEE are strongly and adversely affected by these lower combustor-inlet tem-
`peratures and pressures.
`In addition, the requirements must be met with a
`combustor sized to fit within the confines of the very 'short, compact envelope
`of the F10l combustor casing., Figure 91 shows the most recent version of a
`combustor configuration sized to fit the QCSEE and designed
`specifically for low emissions.
`The QCSEE UTW and OTW configurations both use the FlOl core, resulting in
`low-pressure'-ratio cycle designs. With the low combustor-inlet temperatures
`and pressures associated with this low cycle pressure ratio, the NOX emis-
`sions would not be expected to be a problem. Since the technology being de-
`veloped was intended for higher-pressure-ratio engines, the development was
`carried out in a test rig using the
`cycle conditions
`listed in Table XXI. The use of this "emissions program" cycle did result In
`improved combustor inlet conditions at the QCSEE ground idle power setting of
`4.5% of sea level takeoff thrust.
`In addition, the higher combustor inlet
`temperatures and pressures associated with this higher-pressure-ratio cycle
`result in higher NOx emission levels than would be expected with the orig-
`inal QCSEE cycles, making the EPA NOx emissions standard more challenging.
`Table XXII shows the CO, HC, and NOx emission levels of the single-
`annular combustor in terms of the EPA parameter compared to the program goals.
`As is Shown in the table, the combustor did not meet the program goals for CO
`or NOx emissions with the high-pressure-ratio cycle. Therefore, to meet the
`emissions goals in the short, compact, combustor envelope, a more advanced
`combustor concept was required.
`
`3.9.2 ,Approach
`The primary approach was to design and develop a double-annular dome com-
`bustor, as shown in Figure 92, based on technology developed previously in the
`NASA/GE Experimental Clean Combustor Program (ECCP). Figure 93 shows the much
`smaller size of QCSEE double-annular combustor compared to the CF6-S0 size
`double-annular combustor developed in the ECCP. The QCSEE double-annular dome
`combustor uses many of the features of the CF6-50 double-annular combustor,
`
`144
`
`GE-1011.162
`
`

`
`Table XX. QCSEE Combustor Design Challenges •
`
`• Meet 1979 CO/HC Emissions Standards with Low Ground Idle
`Combustor Inlet Operating Conditions
`QCSEE
`
`CF6-S0
`
`Combustor Inlet
`Temperature
`Combustor Inlet
`Prellure
`Engine Thrust
`at Idle (% Takeoff)
`
`415K (287 F)
`I 2.4 Atm. (36 psla)
`I
`4.0
`
`429K (313 F)
`
`I
`
`2.9 Atm. (43 psla)
`
`3.4
`
`• Meet Very Stringent NOX Emissions Goals
`
`Figure 91. QCSEE Single-Annular, Low-Emissions Combustor.
`
`145
`
`GE-1011.163
`
`

`
`Table XXI. Emissions Program Cycle
`
`UTW
`Engine
`
`OTW
`Engine
`
`Emissions
`Program
`
`Pressure Ratio
`
`14
`
`17
`
`25
`
`Pressure, N/cm2 (psi)
`
`143 (208)
`
`172 (250)
`
`245 (356)
`
`Temperature, K(OR)
`
`684 (1231)
`
`726 (1307)
`
`789 (1416)
`
`Table XXII. QCSEE Single-Annular Combustor.
`
`I:
`
`I
`
`• With 4% Ground Idle Thrust
`• With Sectorized Burning at Idle
`• High PIP QCSEE Cycle
`• Jet A Fuel
`
`Emissions Status
`
`Goals
`
`7.2
`.6
`3.8
`
`4.3
`.8
`3.0
`
`Pounds Per
`1000 Pounds
`Thrust
`Per Hour
`Per Cycle
`Conclusion:
`Advanced Combustor Concept Required to
`. Meet Emissions Goals
`
`}
`
`CO
`HC
`NOX
`
`146
`
`GE-1011.164
`
`

`
`Outer Dome
`Reverse Flow
`Swirlers
`
`Pressure Atomizing
`Fuel .Nozzles
`
`Quick Quench
`Inner Liner
`Dilution Holes
`
`Inner Dome
`Reverse Flow
`S""irlers
`
`f-'
`>I:>.
`--l
`
`Figure 92. QCSEE Double-Annular Dome Combustor.
`
`GE-1011.165
`
`

`
`- - - , . / CF6-50
`
`.. Q C S E E
`
`NASA QCSEE D o u b l e - A n n u l a r C o m b u s t o r .
`
`F i g u r e 9 3 ,
`
`j I
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`j
`
`GE-1011.166
`
`

`
`such as independently staged domes, counterrotating air-blast swirl cups, and
`pressure-atomizing fuel nozzles. However, a substantial scale-down was needed,
`particularly in length and dome heights, compared to the ECCP design. The
`staged combustor concept permits operation of only the pilot-stage dome, which
`is designed specifically to obtain low CO and HC emissions levels, at the low-
`power operating conditions. At the high-power operating condition both domes
`are operated with fuel staging selected to obtain low NOx emission levels.
`
`3.9.3 Development Program
`The development program was conducted using a sector combustor, shown in
`Figure 94. A disassembled view of this five-swirl-cup, 90° sector combustor
`is shown in Figure 95. The tests were conducted in a rig designed to accept
`the sector combustor and duplicate exactly the flowpath of the FlOl; engine.
`Figure 96 shows a photograph of the test rig with the sector combustor instal-
`led. Although the major effort was focused on developing low CO and HC emis-
`sions at idle, the NOx emissions levels of the QCSEE double-annular combus-
`tor were also evaluated at simulated high-power conditions; however, it was
`necessary to derate the pressure at higher power conditions and to
`the
`measured NOx emissions for the pressure difference.
`
`3.9.4 Test Results
`The number and types of combustor development tests conducted in the sec-
`tor combustor program and the total number of test conditions at which data
`were acquired for each test category are shown below.
`
`Number of Test
`
`Data
`Points
`Emissions Development
`310
`32
`Ignition Development
`26
`2
`1
`Combustor Performance
`8
`Fuel Spray Development
`18
`6
`Figure 97 shows the four major categories of combustor configurations
`tested and the key design features of each. As shown in Figure 98, the base-
`line configuration exceeded the emissions goals by a large margin. Signifi-
`cant improvements were obtained with modified geometry by increasing the
`pilot-zone length in conjunction with cooling- and dilution-airflow modifica-
`tions. Even further improvements in CO emissions were obtained by reducing
`the cup spacing in the pilot dome. Reduced cup spacing was obtained by re-
`locating the pilot stage to the inner annulus. This configuration produced
`lower CO and HC emission levels than any of the previous configurations.
`The lower CO and HC emissions are believed to result from a reduction or eli-
`mination of the quenching regions between swirl €Ups. However, the very low
`CO and HC emission levels occurred at a fuel/air ratio below the QCSEE ground
`
`149
`
`GE-1011.167
`
`

`
`..... U1 o
`
`Main
`
`Pilot
`
`GE-1011.168
`
`Figure 94. Double-Annular Test Sector.
`
`

`
`
`
`.~3nE®mw<opaownmnouowm.H.mH.D.Q.G<.IwHD.DOQ.mmmhsmfim
`
`
`
`
`
`GE-1011.169
`
`

`
`Figure 96. Double-Annular Combustor Test Rig.
`
`GE-1011.170
`
`

`
`Combustor Configurations
`• Baseline
`• Modified Geometry
`(Increased Combustion
`Zone Length)
`
`• Inner Annular Pilot Dome
`• Selected Final Design-
`(Radial Axial Air Blast Swirlers)
`
`Figure 97. Key Development-Test Results.
`
`I-'
`(}1 w
`
`GE-1011.171
`
`

`
`EIHC,....gr/kg
`
`200
`
`100
`
`Final Design
`Goal
`.......
`
`200 I
`
`t I
`
`EICO-gr/kg
`
`100
`
`HC
`
`• Jet A Fuel
`• SLS Standard Day
`
`co
`
`Figure 98. Key Emissions-Test Results.
`
`154
`
`GE-1011.172
`
`

`
`idle design fuel/air ratio. Therefore, to further reduce the CO emission
`levels at the QCSEE ground idle fuel/air ratio, an improved pilot-stage swirl-
`cup design with higher airflow capacity and improved atomization was developed
`as the final design.
`Figure 99 shows the improved pilot swi:rl-cup design and a similar design
`developed for the main stage.
`These design-improvement features were incor-
`porated with the previously developed design, features to obtain the final con-
`figuration. Figure 100 shows the preferred sector combustor configuration and
`the key dimensions.
`Table XXIII shows the emissions levels for the final double-annular com-
`bustor configuration compared to those expected with the best single-annular
`combustor. Compliance with the program emissions goals, with a ground idle
`thrust of 4.5% takeoff thrust, is projected with this selected configuration.
`The final configuration was also tested to investigate other important
`combustor-performance, characteristics. Figure 101 shows the altitude i.;;ni-
`tion results obtained with the final double-annular combustor configuration.
`These tests were conducted with the sector combustor subjected to combustor-
`inlet conditions based on the altitude windmilling characteristics expected
`with QCSEE. The Jet A fuel temperatures were maintained at 244 K to simulate
`in-flight conditions. As shown, excellent altitude-relight results were ob-
`tained with successful ignition obtained in all regions tested within the
`fl ight envelope.
`Although sector combustors are not generally conducive to accurate mea-
`surement of exhaust gas temperature-pattern factors, due to their limited cir-
`cumferential size, data were acquired to examine trends. Because of the lim-
`ited combustor airflow available for profile control and the very short length
`of this combustor design, it is expected that additional tailoring of the com-
`bustor profile would be required before introduction into a production engine.
`In conclusion, it was demonstrated in a prototype sector combustor test
`that a double-annular dome combustor suitable fOr/the QCSEE application can be
`developed which will satisfy the emissions goals of the program at a ground
`idle thrust of 4.5%. Furthermore, the selected final configuration demonstrated
`excellent altitude-relight performance for a combustor at this early stage of
`development. Other performance characteristics of this double-annular design
`will require further dev'elopment before engine testing.
`
`3.10 ACOUSTIC DESIGN
`A schematic showing the QCSEE noise objectives is presented in Figure 102.
`These objectives are for a four-engine aircraft operating in the powered-lift
`mode from a 6l0-m (2000-ft) runway. The noise levels are those that would be
`heard by an observer on a l52-m (500-ft) sideline parallel to the runway cen-
`terline. At takeoff, the noise goal was 95 EPNdB with the engines at 100%
`thrust and on a 12.5° flight path. Under approacn conditions, with the engines
`
`155
`
`GE-1011.173
`
`

`
`-, I , • __ ,;"'.,
`
`Figure 99,
`
`'Swirl Cups.
`
`GE-1011.174
`
`

`
`TrBnJB.4T.0H
`
`T.UBT.DOHIa
`
`J.
`
`HJ9T.00
`
`3151
`
`(‘w zo'9) tun VSL
`
`GE-1011.175
`
`

`
`Table XXIII. Emission Results for QCSEE Double-Annular Combustor.
`
`Idle Thrust
`
`CO
`
`HC
`
`NOX
`
`158
`
`High PIP QCSEE Cycle
`Best Single Annular
`with Sector Burn at Idle
`4.0%
`
`Double Annular
`
`4.0%
`
`4.5%
`
`5.6
`
`.32
`
`4.3
`
`.13
`
`3.0*
`
`3.0*
`
`7.2
`
`.57
`
`3.8
`
`6.7
`
`.43
`
`3.8
`
`* Estimated Based on Sector Combustor Results at
`Simulated High Power Conditions
`
`4.5% -
`
`Goals
`
`4.3
`
`.8
`
`3.0
`
`\
`
`Ib/1000 Ib
`Thrust Per
`Hour-Cycle
`
`GE-1011.176
`
`

`
`10 I
`
`Flight
`
`• Cold Air
`• Jet A Fuel (Cold)
`
`v
`
`•
`
`/
`
`/
`
`•
`•
`
`I -i 30,00,0
`
`J J 20,000
`•
`/'
`
`It
`I 10,000
`I
`
`I
`
`Envelope - ---
`•
`•
`•
`/
`•
`"
`•
`
`I
`4 I
`I
`
`Altitude 6'-
`kM
`
`• Ignition
`
`2
`Q Unstable Ignition
`o 1
`0 No Ignition
`0.2
`
`I-'
`C]1
`U)
`
`0.3
`
`0.4
`
`!(
`0.6
`0.5
`Mach Number
`Figure 101. Altitude Ignition Results.
`
`0.7
`
`10
`
`0.8
`
`0.9
`
`GE-1011.177
`
`

`
`.....
`OJ o
`
`• 4 Engines
`• 400 KN (90,000 Ibs)
`Installed Thrust (Fn)
`• 610m (2000 ft) Runway
`
`100% Fn
`61 m (200 tt) Alt.
`
`."!
`
`.'
`EPNdB Takeoff
`
`100 PNdB Reverse
`
`.
`
`----
`""
`
`65% Fn
`61 m (200 tt) Alt.
`
`---- ---,,'"
`
`---,
`
`"
`\
`
`,
`
`,
`
`152.4m (500 tt) Sideline
`
`95 EPNdB Approach
`
`Figure 102. QCSEE Acoustic Objectives.
`
`GE-1011.178
`
`

`
`...".
`
`developing 65% of takeoff thrust and the aircraft on a 6° glide path, the goal
`was also 95 EPNdB. After touchdown on the 610-m (2000-ft) runway, with the
`engines developing reverse thrust at 35% of takeoff thrust, the noise goal was
`100 PNdB on the l52-m (500-ft) sideline. These noise objectives were very
`challenging; this can be seen more clearly by examination of Figure 103. The
`figure shows the relative decrease in EPNL over the years for the older narrow-
`body aircraft, current widebody, next-generation widebody, and finally an Ener-
`gy Efficient Engine (E3) powered aircraft. QCSEE powered aircraft that meet
`the 95 EPNdB goal are about 10 EPNdB below the next-generation aircraft.
`These stringent noise goals meant that any noise source on the engine
`which had the potential for contributing to the far field had to be evaluated.
`The sources which were considered are listed below:
`•
`Fan-inlet-radiated noise
`•
`Fan-exhaust-radiated nOlse
`•
`Turbine nOlse
`•
`Combustor noise
`•
`Jet/flap nOlse
`•
`Compressor noise
`•
`Gear noise
`•
`Treatment regenerated flow nOlse
`•
`Strut noise
`•
`Splitter trailing-edge noise
`The design procedure for each noise constituent was to estimate the level
`by scaling existing test data from similar fan and core engines or by using
`the latest analytical techniques available. These estimated levels were then
`extrapolated to a simulated-flight condition of 6l-m (200-ft) altitude, l52-m
`(500-ft) sideline. Precontract studies had indicated that maximum noise
`levels would occur with the aircraft at 6l-m (200-ft) altitude during either
`takeoff or approach. As an example the predicted, unsuppressed, fan-exhaust-
`radiated noise spectrum for the UTW engine at takeoff is shown in Figure 104.
`This spectrtml was then noy-weighted to determine the frequencies at which sup-
`pression or source-noise reduction techniques should be applied for maximum
`acoustic benefit.
`It can be seen that the second-harmonic tone required more
`reduction than the blade-passing frequency and that, after noy-weighting,
`treatment should be tuned to 2500 to 3150 Hz to provide the best broadband
`suppression.
`A similar procedure was followed for each potential noise source for each
`of the three operating conditions. After several iterations, the levels of
`suppression which were required to meet the noise goals were established.
`Test and component programs were then conducted t9 verify that the required
`levels of suppression could be achieved and that the basic source noise (un-
`suppressed) levels were correct. System noise levels were updated and re-
`vised continuously as new data became available.
`
`i
`
`161
`
`GE-1011.179
`
`

`
`Relative
`EPNL, EPNdB
`
`+10
`
`+5
`o
`
`-5
`
`-10
`
`-15
`
`Narrowbody-Turbofans
`
`Widebody-Turbofans
`
`New Generation Widebo y
`
`Q--aCSEE
`
`1960
`
`1970
`
`1980
`
`1990
`
`Figure 103. Aircraft Noise Trends.
`
`GE-1011.180
`
`

`
`(I
`
`1200 J
`
`•
`
`/
`
`J
`
`I
`jY
`
`,-...
`
`• 152m (500 ft) Sideline
`• 61 m (200 ft) Altitude
`
`1/3 Octave
`Band SPL,
`dB
`
`90
`
`80
`
`70
`
`60 '
`100
`
`Second Harmonic-I"'"
`
`BPF
`
`"
`1000
`500
`Frequency, Hz
`
`J
`5000
`
`,_J.-IuI
`
`t-'
`CSl
`W
`
`Figure. 104. Unsuppressed Fan Exhaust Spectra.
`
`GE-1011.181
`
`

`
`3.10.1 Engine Acoustic Features
`Before discussing the component tests which led to the treatment designs,
`the basic acoustic features on each engine will be reviewed. These acoustic
`features can be divided into two main categories:
`those dealing with reduc-
`tion of the source itself and those dealing with the reduction of noise after
`it has been generated.
`fan was se-
`UTW features are shown in Figure 105. A
`lected primarily to keep jet/flap interaction noise as low as possible by re-
`ducing the fan-bypass exit velocity. This low pressure ratio also aided in
`keeping exhaust-radiated fan noise low. The fan had a subsonic tip speed of
`290 m/sec (950 ft/sec) at takeoff which eliminated high noise levels from
`multiple pure tones associated with supersonic tip-speed fans. A wide rotor/
`stator spacing of 1.5 rotor tip chords was selected to lower rotor/stator
`interaction noise. Additional reduction could have been achieved with wider
`spacing; however, an acoustic splitter could achieve the reduction with less
`weight penalty than that associated with a fan frame weight increase due to
`wider spacing. The vane/blade ratio of 1.83 was selected based upon analysis
`to minimize propagation of the UTW fan second-harmonic tone - which makes a
`major contribution to the noy-weighted spectrum.
`A high throat Mach number (0.79) inlet was used to suppress inlet-radi-
`ated fan noise at takeoff; wall treatment having a length equal to 0.74 fan
`diameters was added to provide suppression at approach and in reverse thrust.
`Fan exhaust suppression utilized inner- and outer-wall suppression with
`variable-depth, variable-porosity treatment sections to provide wide suppres-
`sion bandwidth. Preliminary design studies indicated that wall treatment a-
`lone would not achieve sufficient suppression in the length allowable;
`there-
`fore, a 1.02-m (40-in.) acoustic splitter was added to provide the required
`exhaust suppression. Mach number in the fan exhaust duct was limited to 0.47
`to minimize strut noise, treatment regenerated noise, and splitter trailing-
`edge noise. Treatment was added to the core inlet to suppress high-frequency
`compressor tones. Fan frame treatment consisted of wall treatment to suppress
`fan
`tones and treatment on the pressure surface of the
`outlet guide vanes (OGV's) to attenuate high-frequency, broadband, fan noise.
`The single-degree-of-freedom (SDOF) treatment that was specified on the
`UTW was an integral part of the support and load-carrying structure of the
`composite nacelle.
`The engine utilized a "stacked" treatment core suppressor which was
`designed to attenuate both low-frequency combustor noise and high-frequency
`turbine noise.
`In order to maintain commonality, the OTW engine shown in Figure 106
`utilized essentially the same composite fan frame design as the UTW. With
`the 33 vanes and 28 fan blades, the OTW vane/blade ratio is a low 1.18.
`This low vane/blade ratio was a departure from the usual design practice of
`
`164
`
`GE-1011.182
`
`

`
`• pIp = 1.27
`• Tip Speed = 290m/sec (950 ft/sec)
`33 Treated Vanes
`Variable Thickness
`Treatment
`
`High Frequency
`Turbine Noise
`Treatment
`
`0.79 Throat Mn
`
`Low Frequency
`Combustor Noise
`Treatment
`
`Treated
`LID =.0.74
`
`1.5 Rotor/OGV Spacing
`1.83 Vane/Blade Ratio
`
`1 m (40") Long Splitter
`
`Figure 105. UTW Engine Acoustic Features •
`
`...... en 01
`
`GE-1011.183
`
`

`
`• pIp = 1.34
`• Tip Speed = 350m/sec (1150 ft/sec)
`Variable
`Thickness
`Treatment
`
`High Frequency Turbine
`Noise Treatment
`
`Bulk Absorber
`Treated L/D = 0.74
`
`33 Treated
`Vanes
`
`·79 Throat
`Mach No.
`
`1--- ---- - -+--
`
`28 Rotor
`1 m (40") Long Splitter
`Blades
`1.93 Rotor/OGV Spacing
`1.18 Vane/Blade" Ratio
`
`Low Frequency Combustor
`Noise Treatment
`
`Figure 106. OTW Engine Acoustic Features.
`
`GE-1011.184
`
`

`
`--=
`
`having a vane/blade ratio value near 2 to cut-off rotor/stator interaction
`noise.
`It was felt that the wide spacing of 1.93 rotor tip chords for the
`OGV/fan rotor WOUIO reduce rotor/stator interaction noise to the point where
`it would not be a major contributor; thus, there was no need for "overkill"
`by selecting a high vane/blade ratio.
`Other acoustic features of the OTW are very similar to the UTW including
`the treated vanes, "stacked" core treatment, variable-depth and variable-
`porosity fan exhaust wall treatment, 1.02-m (40-in.) acoustic splitter, and
`high throat Mach number inlet. At approach and reverse thrust, the OTW inlet
`provides suppression with bulk absorber wall treatment.
`
`3.10.2 Fan Inlet Design
`Preliminary system studies conducted on both engines indicated that
`achieving a balanced design would require the following levels of inlet PNL
`suppression:
`
`OTW
`UTW
`(PNdB)
`(PNdB)
`Takeoff
`13 .5
`12.8
`Approach
`10.4
`6.3
`Reverse Thrust
`11.5
`4.5
`These high levels of required suppression could be achieved with a conventional
`inlet; however, with wall treatment only the treated-length-to-diameter ratio
`would be much greater than 1.0 and/or inlet splitters would be required. Pre-
`vious experience has shown that large levels of inlet suppression can be
`achieved from high throat Mach number inlets. As shown in Figure 107, which
`compares inlet-noise-reduction concepts, takeoff suppression can be achieved
`with a treated high throat Mach number inlet. At approach and reverse thrust,
`suppression is achieved with the wall treatment only since the inlet Mach num-
`ber is much lower.
`In order to demonstrate that the high levels of inlet suppression can be
`achieved, a scale-model test program was conducted in the General Electric
`anechoic chamber shown in Figure 108. The anechoic chamber can handle models
`for inlet-radiated-noise studies or for exhaust-radiated noise as will be dis-
`cussed later. The models are powered by a 1.86-MW (2500-hp) drive system.
`Physical dimensions of the chamber are approximately 10.7 m (35 ft) long by
`7.6 m (25 ft) wide by 3 m (10 ft) high with microphones located at model-
`centerline height on a 5.2-m (l7-ft) arc.
`It was
`An exact scale model of the UTW fan was used for these studies.
`5.8 cm (20 in.) in diameter and could be manually adjusted for various blade
`angles including those required to demonstrate reverse thrust. Test objec-
`tives are summarized below:
`
`167
`
`GE-1011.185
`
`

`
`• Takeoff
`
`I
`
`Mach Number Suppression
`
`• Approach
`
`• Reverse Thrust T
`
`-------·-0
`
`Treatment Suppression
`
`Increasing Mach Number
`
`Reverse Thrust - UTW
`
`Increasing L TID
`
`Figure 107. QCSEE In1et-Noise-Reduction Concepts.
`
`GE-1011.186
`
`

`
`GE-1011.187
`
`GE-1011.187
`
`

`
`Forward Thrust
`•
`Define unsuppressed spectrum and level
`•
`Define suppression due to high throat Mach number
`Define suppression due to treated wall
`•
`Reverse Thrust
`•
`Define unsuppressed spectrum and level
`•
`Define suppression due to treated wall
`Figure 109 presents the variation in inlet noise with throat Mach number and
`the PNL suppression that was achieved. These results indicate that the UTW
`takeoff suppression requirement of 12.8 PNdB could be met at an average throat
`Mach number of 0.79. The suppression due to high Mach number alone was about
`10 PNdB with the wall treatment adding almost 3 PNdB.
`In reverse thrust, the model tests indicated (as shown in Figure 110)
`that the objective level of suppression could be achieved; however, the
`unsuppressed levels were higher than expected. As will be shown later, this
`fact resulted in the UTW system-noise estimate in reverse thrust being re-
`vised to be above the goal of 100 PNdB.
`Both inlets, as finally designed, are shown schematically in Figure Ill.
`Both are high throat Mach number inlets designed to achieve takeoff suppres-
`sion at a 0.79 throat Mach number. The treated-length-to-diameter ratio was
`0.74 for both inlets. Wall treatment utilized on the inlets is shown sche-
`matically in Figure 112. The UTW utilized single-degree-of-freedom resonator
`treatment with a faceplate porosity of 10% and cavity depths ranging from 1.2
`cm (0.5 in.) to 3.9 cm (1.5 in.). A bulk absorber type treatment was incor-
`porated into the OTW inlet to provide wider bandwidth suppression. The bulk
`absorber consisted of seven compressed layers of a Kevlar material.
`It was
`a constant depth of 2.54 cm (1 in.) with porosity of 14% over the first half
`and 22% over the latter half. Although a scale model of the OTW fan was not
`tested, the inlet design was based upon General Electric experience from pre-
`vious tests and consideration of the results of UTW model tests.
`
`3.10.3 Fan Exhaust Design
`As pointed out earlier in Figures 105 and 106, the engine designs incor-
`porated both source-noise-reduction techniques apd significant amounts of
`acoustic treatment to reduce exhaust-radiated noise. Source-noise-reduction
`techniques and treatment configurations were
`on the basis of past
`experience and the results of testing a low-pressu're-ratio, variable-pitch,
`model fan (NASA Rotor 55) in the General Electric anechoic chamber. A photo-
`graph of the model as installed in the exhaust mode is shown in Figure 113.
`Testing evaluated such source-noise-reduction concepts as optimizing vane/
`blade ratio to minimize second-harmonic-tone propagation, rotor/stator spac-
`ing, and rotor/OGV treatment.
`
`170
`
`GE-1011.188
`
`

`
`• Scaled to Full Size
`• 61 m(200 ft) Sideline
`
`60!\
`
`i
`
`,
`
`-
`
`,....
`
`--II"
`... -
`
`--..
`
`.&c
`
`-...... ..-. .-
`
`I
`........
`
`12.8 dB
`
`"
`
`-t:::J}l>-
`.-. ,"
`.. "2/ 1•
`
`' ..
`--..'
`
`ill
`
`•
`•
`
`Baseline Bellmouth
`Treated High Throat
`Mach No. Inlet
`• Hardwall High Throat
`Mach No. Inlet
`120
`
`Perceived
`Noise
`Level,
`PNdB
`
`110
`
`100
`
`90
`
`80
`
`0.45
`
`. 0.50
`
`"
`
`0.75
`0.70
`0.65
`0.60
`0.55
`Average Throat Mach Number, Mth
`
`0.79 Mth
`,_..I
`I
`0.80
`
`Figure 109. High Throat Mach No. Inlet Suppression, 50.8 em (20 in.) Simulator Test.
`
`i-'
`-...J
`i-'
`
`GE-1011.189
`
`

`
`110
`
`105
`
`100
`
`Perceived
`Noise
`Level, PNdB
`
`• High Throat Mach No. Inlets
`
`___
`
`Hardwall
`
`__ +-____ __
`
`I t--
`35% of Takeoff Thrust
`
`Suppressed
`90 __________________________________________________ _
`60
`70
`75
`80
`85
`·90
`6