Experimental Investigation of Tandem Blade Cascades With Double-Circular ARC Profiles

Transcription

1 TrIE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47 St., New York, N.Y The Society shall not be responsible for statements or opinions advanced in papers or in dis cussion at meetings of the Society or of its Divisions or Sections, or printed in its publications. Discussion is printed only if the paper is published in an ASME Journal. Papers are available from ASME for fifteen months after the meeting. Printed in USA. Copyright 1985 by ASME It 85-IGT-94 tit* Experimental Investigation of Tandem Blade Cascades With Double-Circular ARC Profiles WU GUOCHUAN, ZHUANG BIAONAN, GUO BINGHENG Department of Aero-engine Nanjing Aeronautical Institute Nanjing, Jiangsu Province The People's Republic of China ABSTRACT 24 double circular are tandem blade cascades of three different chord-ratios were investigated under different displacements in peripheral and axial direction. The inlet Mach number was 0.3. The Reynolds number based on blade chord was 2.7x The characteristics of the tandem blade cascades, such as the dependence of turning angle and coefficient of total pressure loss on incidence angle were obtained. The ranges of main geometrical parameters under optimal conditions were recommended. rear blade segment total or overall conditions NOMENCLATURE a axial displacement, mm a/cf relative axial displacement c blade chord length, mm C T /t blade solidity, i.e., chord to spacing ratio F channel convergence, ratio of gap at inlet to gap at outlet of channel (Fig. 1) gap between blade segments, mm (Fig. 1) G/CT relative gap of the channel, gap to chord ratio h displacement in peripheral direction, mm h/t relative displacement in peripheral direction K angle between tangents to mean camber lines of b-b rear blade segment and front blade segment at the points of intersection with the line containing FxG (Fig.l),deg. L overlap between blade segments, mm (Fig. 1) L/C T relative overlap, overlap to chord ratio t blade pitch, mm /3y complementary angle of stagger angle, deg. fluid turning angle, deg. ;/8 blade camber, deg. ca, blade loss coefficient, i.e., total pressure loss to inlet dynamic pressure ratio Subscripts: Max maximum min minimum F front blade segment INTRODUCTION FIG. 1 TANDEM BLADE GEOMETRIC VARIABLES Tandem blades (Fig. 2) have been used on stators in some fans and compressors of areo-engines, in inducers and diffusers of high-pressure centrifugal compressors, etc. The use of tanden blades in rotors is still at the research stage. It seems to be one of the abvanced variants in the development of raising stage load and enlarging the range of stable operation (1). In the experimental aspect of tandem blade investigation, Sheets (1956)(2), Linnemann (1964) (3), Siverding (1966) (4), Lueders ( ) (5), Nosek and Kline (1969) (6), Bettner (1969) (7), Thibert (1975)(8), Simmon and Bohn (1974)(9), Bammert, et al., (10, 11, 12), etc. made great efforts. This paper introduces one of the achievements attained by the authors in the experimental investigation of tandem blade cascades, i.e., the experimental investigation of flow performance of tandem compressor blade Presented at the 1985 Beijing International Gas Turbine Symposium and Exposition Beijing, People's Republic of China September 1-7, 1985

2 cascades of double-circular arc blade shapes. The experimental results were analysed, compared and discussed. EXPERIMENTAL INSTALLATION, TEST MODEL AND INSTRUMENTA- TION Experimental Installation Air supply. For low-speed test air was supplied by a centrifugal ventilator of 30 kw driven by an a.c. electric motor. The pressure at the exit was abs. atm. The air flow was 80m3 /min (at inlet). The Mach number at inlet to cascade 1.4,= 0.3. For high-speed test air was supplied by axial flow compressors. The maximum Mach number at inlet to cascade was 0.8. The cascade wind tunnel. The size of the test section was 300mm x100mm. If the pitch of the cascade was 40mm, the number of blades would be eight. If the chord was 40mm, the aspect ratio would be 2.5. There were two slots on the endwall at the inlet section of cascade and an injector was used for boundary layer suction. The flow at the middle section of the channel may be considered as two-dimensional, and all measurements were taken around the blades tt middle of the row. The Reynolds number Re= 2.7 x10 based on blade chord. Test models Test cascades, both single and tandem blade, were designed using a FORTRAN program for computing coordinates of circular arc blade sections. The camber lines were parts of ellipses. The tandem blades studied Table I. Item Cascades ( COF ; 95R/4 f./ 078 ) ( CIlleF.0.73/. OR* 'l 302) N / /6 24/ , Pr 55' '1 ----go 77/3 77%3 77/ ' C _ CR C OF OR CPy T (OP/6,6=f018 ; ) 35'18 54'40 56'40 54'0 54' 'io 54'46 50% / dd , / / ,_ 317 3/ o ,- r ' / 351 t / i _ '2 2, _ , I-- d i-- 5; , Q AE d ,.a qg , el ' ;645,326 2(7'11 2( 9 2,3,5,, /9 0 t _ '3 2778,2998 / (41-0,3 X , ' I / (252 '1 792 / 06, , 2 -, ,, kic, CrIt , _ _ , 09 (312 I 17 ', _ ' 766 2, / , 57 2,00, ' / a,1 : , /5 r '_5 300' 760 I ,7'306, j,,! / '268 2' /49 -/ / , -23 -/4 ' , / Qbg cycp r o / / Operaton ror9e (..Z.a6) : , i (-7-4) 1-7-6' (-5-47) 4 13,..r (2,,,,e) _ F2 29 _ Z ,43) 1(415). / 4452 (564) (.1,13p843) 0 Oa ad L45,,,,, d A ( 1,-, (5.,, ) / T

3 were classified into three groups. They had same total chord, total camber, constructional inlet and exit angles, solidity as the three reference tandem blades of Turmo 111c, 369 and J85 gas turbine engines respectively. The tandem blades of each group were of different axial and peripheral displacements, and stagger angles. There were 24 tandem blade cascades of different geometry. The details of each cascade were shown in table I. For the convenience of analysis and comparison, the cascades were numbered as follows. The first group cascades of tandem blades having same parameters as the reference tandem blade of Turmo IIIc was designated 241. There were 8 cascades in this group. they were The second group of tandem blades having J69 parameters was designated 242. There were 9 cascades in this group. They were The third group of tandem blades having J85 parameters was designated 243. There were 7 cascades in this group. They were Instrumentation Total and static pressures were measured with SYD-1 pressure transducers using XJ-100 pressure acquisition device and a LS-5 printer. In addition, U-tube manometers were employed for check-up. The flow direction was measured by two pressure transducers, Traversing gear driven by steppermotor was controlled by a Z-80 single board computer. It could move along x axis (the direction perpendicular to cascade axis), the maximum displacement being 140 mm; along y axis (spanwise), the maximum displacement being also 140 mm; and could also rotate within the range of 147. Three programs were used in the Z-80 single board computer. 1) The probe moved along x axis in the middle of the height of the blade, and then around the periphery of the test section. The steps were 1 mm, 2 mm, 5 mm, and 10 mm. Anyone of them could be selected. 2) It could acquire data on the section located in the central part in the middle of the height of blade. The maximum displacement was 80 mm. The step was 1 mm. 3) Selected points. One could select any measuring points. The maximum speed with which the probe moved was 5mm/sec. Having reached the selected point, the probe was automatically aligned to the flow and the data were taken and printed. The traversing mechanism could also be operated manually ;1 :412 o v FIG. 3 EXPERIMENTAL RESULTS AND DISCUSSION 1) The tandem blade cascades of the first group No. 241 had eight variants. Their performance characteristics were shown in Fig. 3 and Fig. 4. These figures showed that the fluid turning angle in cascade 2416 was the largest and that in cascade 2417 was the smallest under the same incidence angles. The difference between the two values was approximately 4. The loss coefficient of the 2418 was the lowest, it was about For -65 smaller than 0.06, the maximum turning angle of the 2418, 48, was the largest. It was about 60. The operatiorfange of the 2418 was the widest, from -4.3 to 7.5. The overall performance of the 2418 was the best. The relative displacement in peripheral direction of the 2418,, was the largest, 0.833, i.e., it had a smaller gap between blade segments. The air accelerated in the gap, and the diffusion on suction surface of the front segment was small. The boundary layer was thin. Therefore the loss of the front segment was small. In the meantime the boundary layer on rear segment was energized, and the flow on the rear segment was improved. Therefore the loss on LU 0 MI o 2Z , D FIG. 4 3

4 the rear segment decreased. The combination of h/t and a/cf for the 2418 was well. 2) The tandem blade cascades of the second group No. 242 had nine variants. Their performance characteristics were shown in Fig. 5 and Fig. 6. These figures showed O 2_^21 zs 2422 O 2423 o that the fluid turning angle in cascade 2424 was the largest and that in cascade 2423 was the smallest under the same incidence angles. The difference between them was 6,-7. The loss coefficients of 2423 and 2427 were the smallest. 53 min were and respectively. For TAsmaller than 0.06, the maximum turning angle of the 2424, A lemax, was the largest, dpmax z The operation range of the 2424 was the widest, from -4 0 to According to the test results shown in Fig.5 and Fig. 6, the overall performance of the 2424 was the best. Its AB max was 53.3 and 7)5 min was slightly grew-. ter than the minimum,i,45 min= The operation range was from -4.5 to +a. The reason of having better performance was that it had larger value of h/t and fine combination of a/c and h/t. The flow conditions in both front and rear blades were improved. 3) The tandem blade cascades of the third group No. 243 had seven variants. Their performance characteristics were shown in Fig. 7. Figure 7 showed that the turning angle in cascade 2432 was the largest and that FIG f! X 24 32,),1 5 5 o24/ c, 2L;i * e 6' 8'i FIG. 7 FIG. 6 in 2433 was the smallest, under the same incidence angles. The difference between them was 8,.9. The 48 of the other five cascades were approximately equal. The c.-3 of the 2432 was the largest and that of the 2433 was the smallest. The difference between them was above All loss coefficients of cascades of the third group were larger than Therefore for i5 smaller. than 0.08, the dpmax of the 2437 was the largyst, 44.8, and the of the 2433 was the smallest. The operation range of the 2433 was the widest. It was from -7 to In conclusion, the performance of the 2434 and 4

5 243T was better than the others. 4/3max were larger, they were 44.5 and 44.8 respectively, 53 min were 0.07 and respectively. The performance characteristics of the above mentioned three groups of blade shapes showed that the loss coefficients of the profile No. 243 were larger, greater than One of the reasons was that its chord ratio C H /c? was large. On the one hand, as chord ratio increased the boundary layer on suction surface of the front blade showed an increasing tendency to separate. On the other hand, the decreased chord length partially cancelled out this effect, and the boundary layer on pressure sus ace of the front blade became thinner. The net effect was a relatively constant Z5 1,. So far as the rear blade was concerned, the increasing of the blade surface length allowed the boundary layer to grow to a greater thickness. Therefore the rear blade loss increased. In conclusion, as the chord ratio C R /C F increased, the total loss of the cascade increased too. Therefore the total loss of profile 243 was larger than the other two profiles. The performance of the 243 was worse. 4) The effect of geometric parameters (axial displacement, a, and displacement in peripheral direction, h) on the cascade performance can be seen from the test results plotted in three-dimensional coordinates in Fig. 8. Fig. 8 showed that for cascade No. 241, as h/t increased from 0.6 to 0.85 under a constant value of a/c F(z0.06), dp max increased initially and then decreased, (h/t) = (74.) increased Opt, 4/3 max Min initially, then decreased,and then increased again, (h/t)..._ =0.8. As a/cf increased from to o pt co, min 0.15 under a constant value of h/t (=0.7), 4 /3max decreased slightly and then increased, and W min varied the other way. It increased initially and then decreased. Figure 8 showed that for cascade No. 242, as h/t increased from 0.6 to 0.7 under a constant value of a/cf (^40.04), Apmax increased gradually. (h/t) optodpmax = , 63 min increased initially and then decreased. (h/t) opt,a5mirz The range of the variation of a/cf was too small to draw any conclusion. Figure 8 showed that for cascade No. 243, most tests were done under negative values of a/c F. As h/t increased from 0.06 to 0.85 under a constant value of a/c F (:=:-0.03), ZAmax decreased initially and then increased.(h/t) t opt, x() j rnin. decreased initially, then had a Apmax tendency towards remaining constant and at last increased slightly. As a/ci, increased from to , Eb rilin decreased initially and then increased. (a/c ) F opt, gmin =-0.05., The results of above analysis were shown in following table: mid FIG. 8 THE RELATION BETWEEN AtBmax, Z5 min AND a/cf, h/t 5

6 No. of Profiles a/cf (h/t) ax (h/t) opt,65min ,..., ,,a a, ", The test results in this table showed that the optimal axial displacement and displacement in peripheral direction for maximum fluid turning angle did not coincide with that for minimum loss coefficient. Selections should be different for different aims and requirements. In general, in selecting the values of displacement in peripheral direction and axial displacement one is concerned not only in fluid turning angle and loss coefficient, but also in the range of operation of the cascade. The following value for h/t and equation for determing value of h/t from a/cf were recommended: h/t 0.75 (h/t) x I a/cf The values calculated from this equation agreed with that of Bammert's (10) quite well. 1 Wu, G. C., Zhuang. B. N. and Guo, B. H.: The application of Tandem Blade Cascade in Aeronautical Gas Turbine Engine. The Third Conference of the Chinese Society of Engineering Thermophysics, April, Sheets, H. E., Groton, Conn: The slotted-blade axial-flow blower, Transactions of the ASME vol. 78, No. 8, Nov. 1956, P Linnemann, H.: Untersuchungen eines einstufigen Axial-geblases mit Tandemgittern. Konstruktion 1964, Heft 4, S Sieverding, C.: Experimental data for tandem cascades in the high subsonic region, VKI IN 15, September, Lueders, H. G.: Experimental investigation of advanced concepts to increase turbine blade loading, III. performance evaluation of tandem rotor blade, NASA CR (1968). 6 Nosek, S. M. and Kline, J. F.: Two-dimensional cascade investigation of a turbine tandem blade design, NASA-TMX-1836 (1969). 7 Bettner, J. L.: Experimental investigation in an annular cascade sector of highly loaded turbine stator blading, III. performance of tandem blade, NASA CR-1341 (1969). 8 Thibert, J. J.: Redresseurs auiaux a forte deviation, L'Aeronautigue et L'Astronautique No P Simon, H. and Bohn, D.;Experimental investigations of a recently developed supersonic compressor stage, ASME 74-GT Bammert, K. and Staude, R.: Optimization for rotor blades of tandem design for axial flow compressors, Journal of Engineering for Power, Transactions of the ASME, April, Bammert, K. and Beelte, H.: Investigations of an axial flow compressor with tandem cascades, Journal of engineering for Power, Tansactions of the ASME,Vol. 102, October, 1980, P Bammert, K. and Staude, R.: New features in the design of axial-flow compressors with tandem blades. ASME Pap. n 81-GT-113. CONCLUSION From the experimental results, the following conclusions can be drawn: 1) The advantages of tandem blade cascade were large fluid turning angle and small loss coefficient. For t74) smaller than 0.06, the maximum fluid turning angle,.:1,8, reached 60 and the minimum loss coefi_max ficient,w, was approximately min 2) The values h/t=0.75,., 0.85 were recommended. Larger or smaller values will not lead to satisfactory result. 3) There is an optimal value of relative displacement in peripheral direction for a definite relative axial displacement. The equation for calculation was recommended as follows: (h/t) opt= xl a/cf ) The solidity of the tandem blade cascade should be a little higher, for instance C T/tz2.0 5) The blade chord ratio, c R/C F, should be selected in the range of ) The camber ratio, 0011/op, should be greater than 1. REFERENCES 6