1、SAE AIR*1289A 92 m 79113725 05062L8 7111 m REV. AIR1289 A mA =For The Advancing Engimhg Mobility Sociey AEROSPACE INFORMATION -Land Sea Air and Space INTERNATIONA L Issued 1976-09 Revised 1992-03-31 400 Commonwealth Drive, Warrendale, PA 15096-0001 RE PORT Submitted for recognition as an American Na
2、tional Standard I EVALUATION OF HELICOPTER TURBINE ENGINE LINEAR VIBRATION ENVIRONMENT 1. SCOPE: This SAE Aerospace Informat i on Report (AIR) out1 ines a recommended procedure for evaluation of the vibration environment to which the gas turbine engine powerplant is subjected in the helicopter insta
3、llation. This analysis of engine vibration is normally demonstrated on a one-time basis upon initial certification, or after a major modification, of an engine/hel icopter configuration. This AIR deals with linear vibration as measured on the basic case structure of the engine and not, for example,
4、torsional vibration in drive shafting or vibration of a component within the engine such as a compressor or turbine airfoil. In summary, this AIR discusses the engine manufacturers “Installation Test Code“ aspects of engine vi bration and proposes an appropriate measurement method. 2. REFERENCES: Th
5、ere are no referenced pub1 ications specified herein. 3. BACKGROUND: 3.1 The vibratory excitation which a gas turbine engine experiences is a function of the vibration produced by the engine and the vibration produced by the installation. level be within a range to which the engine is tolerant. 3.2
6、The vibrations measured on the engine casing may provide only an indication of the state of vibratory motions and stresses of individual components within the engine. The method of measurement, the chosen limits, and the location of the sensor should ensure a credible evaluation appropriate to the m
7、ajority of cases. A satisfactory system requires that this combined vibratory SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary. and its applicability and suitabi
8、lity tor any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.“ SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. C Copyr
9、ight 1992 Society of Automotive Engineers, Inc. All rights reserved. Printed in U.S.A. SAE AIR*kL287A 72 m 7743725 050b2l17 650 m SAE AIR1289 Revision A 3.3 3.4 3.5 The source of a vibratory input is normally detectable by the frequency of the excitation which is measured in cycles per second and ex
10、pressed as “Hertz“ (Hz). approximately 60 to 15 O00 Hz; however, frequencies above 2000 Hz are generally of no interest due to the low input energy level. Engine-generated vi brat ion may be produced at frequencies corresponding to the rotational speeds of the engine output shaft, the gas generator
11、and power turbine rotors, major accessories and at gear tooth meshing frequencies, bearings, and harmonics of this and possible subharmonic resonance of shaft i ng . The helicopter may expose the engine to vibratory inputs from 3 Hz to as high as approximately 1000 Hz if the engine is direct-mounted
12、 to the main transmission. The major sources of low frequency excitation from the he1 icopter are: The gas turbine engine may produce frequencies from a. b. c. Harmonics of the latter Main rotor forces and moments at one-per-rev Main rotor blade passing frequency (main rotor frequency times the numb
13、er of blades) Tail rotor and drive shafting produce other higher frequency vibrations. Airframe-aenerated vibrations may be amp1 ified or attenuated by the airframe structura7 dynamics. The stiffness and/or damping important factors of the eng inputs. The vibration spectrum to wh characteris ne/airf
14、rame ics of the engine mounts are dynamic response to vibratory ch the sens r is subjected is composed of a number of superimposed harmonic (sinusoidal) vibrations of different frequencies expressed by the general function: where: x, = Peak value of x,(t) oi = Angular frequency of the excitation -2-
15、 SAE AIRLL287A 92 7743725 050b220 372 SAE AIR1289 Revision A 3.5 (Continued): In a helicopter installation there are several main sources of excitation: he1 icopter main rotor frequency (U mr), he1 icopter rotor blade passing frequency (N O mr, N = number of blades), gas generator rotating frequency
16、 (U gg), engine drive shaft and reduction gearbox rotating frequency (U ds) and when applicable free power turbine rotating frequency. of the response to these excitations is: The summation S i=nl j=n2 1 =n3 - S(t) = E x, sin i o,t + E yj sin j o,t t E i=l j-1 1=1 m-4 z, sin 1 uqqt t C O m sin m odr
17、t m= 1 In practice the contributions from higher level harmonics corresponding to n 2 are generally quickly decreasing, have low energy, and therefore the significant vibratory signal can be limited to the second harmonic of each excitation (i .e., 2/rev of each excitation mentioned). In cases where
18、 the response to n 2 is significant, there usually is a resonance of an engine mode with that harmonic. 3.6 Vibration measurements may be accomplished by sensing various parameters which are characteristic of the excitation: a. b. c. Displacement magnitude Id“ in microns (.O01 nun) or mils (.O01 in)
19、 Velocity magnitude “v“ in centimeters per second or inches per second Acceleration magnitude “a“ in meters per second per second or in gs (vector quantity, 980 cm/s2 = 1 g or 386 in/s2 = 1 g) d. Frequency If“ in hertz (cycles per second) In practice accelerometers and velocimeters are used to measu
20、re the vi bration. The overall acceleration signals may be processed through different signal conditioning methods: a. Peak value method, correct only for a pure sinusoidal vibration signal b. Average value method, defined as -3- SAE AIR*1289A 92 7943725 050b221 209 SAE AIR1289 Revision A 3.6 (Conti
21、nued): which consists in averaging the signal. automatically compensating for frequency but has the disadvantage of masking peak values by flattening the sampling. sinusoidal function over which the average is calculated.) This method has the advantage of (T being the period of the c. The first two
22、methods are only mentioned for information, the rms value is the basis of the method used in this AIR, although any of the three can be used successfully as long as it is used consistently throughout engine deve1 opment. Root mean square value method (rms) which is more representative of the energy
23、content of the vibration. 3.6.1 RMS Value Method: For an instantaneous value of the general function xi (t) = x, sin o,t (where x, is the peak value) (Eq.4) the rms value is given by: where: T = Period of the sinusoidal function For a given harmonic, xi xi rms = - is the rms value of x,(t) 42 A typi
24、cal vibration spectrum is given in Figure 1. Acceleration, velocity, and displacement are used to characterize the oscillating motion with regard to the limits to be adopted for an engine. By measuring the acceleration through sensors fitted on the engine structure, the processing to transform it in
25、to displacement and velocity is directly provided from the equation of the harmonic function: -4- SAE AIR*ls289A 92 m 7943725 0506222 I145 m SAE AIR1289 Revision A microns mr) MI INST SPEC CH H rinc MRIN i 6OOinlJ GETUP w21 FLEX 14400 0000 X 241JHz 1 Oilu PMS LIN i1Hr + LIN RHS VELOCITY I I 1 freque
26、ncy Hz RIS ACCELERATION _ frequency Hr RMS DISPLACEIENT e frequency Hz W20 TlnE CH H RERL MAIN I 2 OZU Y 5 OU X 1 :Oins 6 Ons + 15 SETIJP w21 VIBRATION SIGNAL UPON SELECTED TIME SAUPLING (62.5 ms) time ms - FIGURE 1 - Typical Vibration Spectrum SAE AIR*L28A 92 m 7943725 0506223 08L m SAE AIR1289 Rev
27、ision A 3.6.1 (Continued): (Eq.7) a, for a given harmonic, a, rms = - is the rms value of a,(t) vi rms = - is the rms value of v,(t) J2 52 v, = rms oi di 52 a, rms 4 d, rms = - is the rms value of d,(t) - - Acceleration, velocity, and displacement magnitudes a, vi, and di (respectively i = 1,2,.n) a
28、re determined as functions of the angular frequency o, from analysis of recorded vibration signals by vibration sensors connected to a fast Fourier transform (FFT) analyzer. Figure 1 shows the same spectrum plotted in velocity, acceleration, and displacement together with a time sampling related rec
29、ord of the signal. 3.7 For each acceleration, ve established by the engine have to be compared. The significant parameter displacement, velocity, o which itself depends upon to excitation inputs. ocity, and displacement parameter, 1 imits should be manufacturer against which the actual measurements
30、with which the vibration is to be expressed, the engine/airframe structure combination response acceleration depends upon the frequency range The whole engine being considered as a beam that operates in the either so- called rigid body mode or the flexible body mode according to frequency, the bound
31、ary between both being of the order of 100 Hz. In the rigid body mode the vibration response to excitation is characterized by two limits which correspond to two ranges of frequency: a. From O to 10 Hz (approximately), corresponding to a pure rigid body, the limit is given by the relative motion bet
32、ween the relevant components. The displacement (d rms) is, therefore, the appropriate factor to represent the motion. b. From 10 to 100 Hz (approximately), still in the rigid body mode but corresponding to rigid resonant structure, 1 imited by stress (typically in the mountings), for which the accel
33、eration (a rms) is the appropriate factor. -6- SAE AIRtlsZA 92 7943725 050b224 TLB = SAE AIR1289 Revision A 3.7 (Continued) : c. Above 100 Hz, there is a range from 100 Hz (approximately) to 2000 Hz, corresponding to flexible system resonant mode, also 1 imited by stress (typically in the casings),
34、for which a limit has to be established. In this range, the velocity (v rms) is the appropriate factor to figure out the vibratory mode. A typical example is shown The line indicates the enve as exposed in 3.6. nF ope gure 2a. of limit values for the relevant frequencies For convenience of monitorin
35、g and data reduction presentation the use of the velocity parameter over the entire frequency range affords great flexibility in test facility and overhaul shop instrumentation. may be defined, for example, from approximately 3 to 50 Hz and 50 to 2000 Hz where a constant velocity val ue can be estab
36、l i shed. discrete fil tered frequencies may then be converted to the appropriate parameters for review. Two frequency bands only Velocity measurements at A typical example is shown in Figure 26. 3.8 The threshold level of vibratory damage to a gas turbine engine is determined by the engine manufact
37、urer during the engine development program. vibration level consistent with good service life should be established. Still lower engine-generated vibration limits must be met on production engines during the final acceptance test, to be assured that the installed engine vibrational environment is wi
38、thin the limits of good service life. The engine and airframe manufacturers conduct qualification tests to verify this. A For qualification, the airframe manufacturer will check on a prototype aircraft that every vibration parameter measured in flight is within the specification limits provided by t
39、he engine manufacturer in the installation instructions. An investigation of the airframe induced vibratory stresses in the engine mounts and structural elements by strain-gauge should also be carried out during flight testing. Subsequent sections of this AIR outline a recommended method of test, an
40、alysis, and evaluation of the gas turbine engine vibrational environment in the he1 icopter installation. 4. PRE-SURVEY REQUIREMENTS: The engine manufacturer should establish at the earliest practical time the following technical data for a given engine installation configuration. This should be bas
41、ed upon an exchange of data between airframe and engine manufacturers. -7- SAE AIR*:L289A 92 7943725 0506225 95q SAE AIR1289 Revision A O 1 10 100 IO00 HZ transient - steady erate FIGURE 2a - Frequency (Hz), Displacement d rms $III), Velocity v rms (m/s), Acceleration a rms (m/s) -8- SAE AIR*L283A 9
42、2 m 7343725 0506226 890 SAE AIR1289 Revision A O. 0.05 I I i I I a 3 I. n I I IO 50 io0 IO axis of measurement). ned to prevent whipping action which can 5.1.1 The dynamic response range and the frequency range for the vibration transducers should be specified and calibrated over desired frequency r
43、ange. 5.1.2 Continuous records should be made on magnetic tape, or by an equivalent method, of the following: a. Vi bration: (1) Al 1 vi bration transducer signals b. Airframe: (1) (2) Airspeed (3) Helicopter main rotor speed (4) Rate of climb Ai rcraft c. g accel erat i on c. Engine: Power turbine
44、rotor speed(s) - N, Gas producer rotor speed(s) - N, Torque owing data may be collected by log entry: ne: Turbine out1 et temperature b. Airframe: (1) Pressure altitude (2) Outside air temperature (3) Gross weight (4) Center of gravity c. Miscellaneous: (1) Date (2) lime (3) lest condition - 12 - SA
45、E AIRt1289A 92 7943725 050bZ30 2Ll SAE AIR1289 Revision A 5.2 Test Conditions : The following test conditions are considered typical of those desired for the vi brat ion survey: a. Ground: (1) Engine start to idle (2) (3) 20%, 40%, 60% 80% and 100% maximum obtainable power (4) Acceleration from idle
46、 to flight rotor speed Other conditions peculiar to installation; maximum range of Np variation should be considered when applicable b. Flight in Ground Effect: (1) Jump takeoff (2) Hover (3) Typical left and right turn Rearward and sideward flight Other conditions peculiar to installation; maximum
47、range of Np variation should be considered when applicable Normal 1 andi ng lized Flight Out of Ground Effect: Hover 20%, 40%, 60% 80%, and 100% V, in level flight 110% VNE (demonstration only or upon specific request) (5) Maximum range of Np variation should be considered when applicable VNE d. Man
48、euvers : Maximum continuous power climb Left and right turn: the helicopter operating range Cyclic pullup: he1 i copter operating range Normal decel from V, to nominal low airspeed Stabilized auto-rotation at 0.5 V, with application of power required for level flight Stabilized auto-rotation at 0.7
49、V, with application of power required for level flight Normal flare and landing Other test points peculiar to installation which may be unusually severe or occur frequently, maximum range of Np variation should be considered when applicable 0.6 V, and 0.9 V, at 1.5 gs and at limit of 0.6 V, and 0.9 V, at 1.5 gs and at limit of the VH VNE = Never exceed velocity = Maximum velocity in horizontal flight at maximum continuous power SAE AIR*L28A 92 7943725 050b23L L58 SAE AIR1289 Revision A 5.2 (Continued): Vibration data at each of the test points should be obtaine
