the application of counter-rotating turbine in rocket

Hindawi Publishing CorporationInternational Journal of Rotating MachineryVolume 2008, Article ID 426023, 7 pagesdoi:10.1155/2008/426023

Research ArticleThe Application of Counter-Rotating Turbine inRocket Turbopump

Tang Fei,1, 2 Zhao Xiaolu,1 and Xu Jianzhong1

1 Institute of Engineering Thermophysics, Chinese Academy of Sciences, P.O. Box 2706, Beijing 100080, China2 Graduate School of Chinese Academy of Sciences, P.O. BOX 2706, Beijing 100080, China

Correspondence should be addressed to Tang Fei, [email protected]

Received 1 May 2007; Revised 20 August 2007; Accepted 31 October 2007

Recommended by Chunill Hah

Counter rotating turbine offers advantages on weight, volume, efficiency, and maneuverability relative to the conventional turbinebecause of its special architecture. Nowadays, it has been a worldwide research emphasis and has been used widely in the aero-nautic field, while its application in the astronautic field is seldom investigated. Researches of counter rotating turbine for rocketturbopump are reviewed in this paper. A primary analysis of a vaneless counter rotating-turbine configuration with rotors of dif-ferent diameters and rotational speeds is presented. This unconventional configuration meets the requirements of turbopump andmay benefit the performance and reliability of rocket engines.

Copyright © 2008 Tang Fei et al. This is an open access article distributed under the Creative Commons Attribution License, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. INTRODUCTION

Turbopump is one of the main modules of liquid rocketengine and represents a large part of rocket engine overallcost. So improving the efficiency of turbopump and reduc-ing its weight are effective ways to improve the performanceof rocket engine [1]. Furthermore, to simplify the mechani-cal architecture of turbopump may improve the reliability ofrocket engine.

Because of difference in densities of propellants, oxidizerpump and fuel pump of rocket engine require different ro-tational speed to avoid the caviation erosion. Generally, ox-idizer’s rotational speed is higher because the density of theoxidizer is higher than that of the fuel. What’s more, for lowdensity fuel, improving rotational speed can reduce the fuel-pump diameter and volume remarkably.

At early age, some LH2/LOX engines with a single turbinedrive the LH2 pump, and by gearbox the LOX pump directly.But gearbox brings excess weight and reduces credibility ofengine in the cryogenic environment of LH2. Two turbinesin series driving pumps, separately, is another solution, how-ever, this configuration will bring excess losses and make theengine more complex and less credible.

The counter rotating turbine is an axial turbine with afirst stator followed by a first rotor, an optional second stator,

and a second rotor, which rotates in opposite direction of thefirst stage. In 1958, Wintucky [2] presented the basic analy-sis of counter rotating turbine with restricted hypothesis likethe same mean diameters for each rotor, the same rotationalspeed, and constant axial velocity. In 1980s, the scientific re-searchers made wide researches on counter-rotating turbineby stimulation of IHPTET (the integrated high-performanceturbine-engine technology program), and now several coun-tries have developed counter-rotating turbines for aircrafts.

Because of its unconventional architecture, counter-rotating turbine offers advantages on weight, volume, ef-ficiency, and maneuverability relative to traditional mul-tistage turbines. It must be emphasized that configura-tion of counter-rotating rotors can reduce the torque onthe aircraft remarkably, so the maneuverability of air-craft driven by counter-rotating turbine engine is muchhigher.

These advantages are also helpful for rocket engines. Thecounter-rotating turbine with two rotors, which have differ-ent rotational speeds and powers to drive the fuel pump andoxidizer pump, respectively, is proposed (see Figure 1). Thisconfiguration can avoid the disadvantages of gearbox andtwo turbines configuration is mentioned in the above para-graphs.

mailto:[email protected]

2 International Journal of Rotating Machinery

2. REVIEW OF COUNTER-ROTATINGTURBINE FOR TURBOPUMP

In 1984, Narou [3] of ISAS presented the idea of applicationof counter-rotating turbopump on upper-stage LOX/LH2rocket engine.

In a research of NASA ACE project (advanced chemicalengine), Huber and Veres [4–6] design a counter-rotatingturbine for the upper-stage rocket engine. They take full-scaled experiments upon the turbine, and the experimen-tal data accord well with the theoretical prediction. An un-conventional blade with a 160◦ turning angle is introducedinto this counter-rotating turbine. Earlier investigation onthis blade in the National Launch System project [7, 8] in-dicates that it can improve turbine efficiency and decreaseblade number remarkably.

In 1993, researchers of NAL [9–13] designed a counter-rotating turbine experiment facility and took a series of the-oretical analysis, numerical simulations, and experiments onthe counter-rotating turbine. Their research included a sec-ondary flow loss of ultra-high-load turbine, feasibility ofcounter-rotating turbine and rotor-rotor interaction. NALcounter-rotating turbine also adopts UHLTC [10] (ultra-highly loaded turbine cascade) with 160◦ turning angle. Ex-perimental data show the flow structures, and the loss mech-anisms in UHLTC were basically the same as those seen inthe conventional cascades, except for stronger-passage andleakage vortices. A large internal loss generates in cascadepassage, and a large downstream mixing loss is found. Ya-mamoto figures out that those losses come from the strongpassage vortices and the associated laminar flow separationdue to the extremely large turning angle. Preliminary com-parison between the experimental results and Hah’s numeri-cal predictions shows a good agreement [13].

Pratt and Whitney have developed a twin rotor turbop-ump (TRT) [14] for NASA ablative engine. The TRT is aliquid LOX/Kerosene turbopump that incorporates a back-to-back counter-rotating turbine. Although the counter-rotating turbine for a turbopump is theoretically good, thereis no flight-proven counter-rotating turbine for fluid rocketengine despite of the above scientific projects.

3. VANELESS CONFIGURATION OFCOUNTER ROTATING TURBINE

In order to obtain higher-engine performance, vaneless con-figuration of counter-rotating turbine is proposed. In the fol-lowing, paragraphs, this kind of turbine will be called 1 + 1/2counter-rotating turbine. The “1” means a full high-pressurestage (HP) with stator and rotor, while the “1/2” means thevaneless low-pressure stage (LP). This vaneless configurationoffers significant potential advantages.

(i) The weight and volume of the engine is reduced re-markably because of the abolition of LP stator row.

(ii) Losses associated with LP stator blade are avoided.

(iii) The reliability of the engine is improved because theturbine structure is simplified.

Although the vaneless configuration may benefit turbineefficiency and engine reliability, it will bring difficulties to or-ganize the flow in low-pressure rotor passage. So actually, it’snot easy to get theoretic high efficiency.

In 1993, Huber and Veres [4] conducted contrastive ex-periments on 1 + 1/2 and 1 + 1 counter-rotating turbines. Asthe experiments results show, the removal of the LP statoris predicted to cause a significant increase in gas-incidenceangle entering the LP rotor. This off-design incidence is pre-dicted to decrease overall turbine efficiency approximately3% at the design point. Performance estimates based on theirtest results indicate that an LP rotor designed for 1 + 1/2 tur-bine would achieve an increase in efficiency of 2% relative toa 1 + 1 counter-rotating turbine at the aero design point, andup to 7% higher efficiency at reduced-speed operation.

Yamamoto [12] also took experiments on vanelesscounter-rotating turbine to investigate the cascade internalflow and loss mechanisms under the rotating condition. Hefound that low-energy fluids tend to migrate to the tip end-wall in the rotating case while to the hub endwall in the sta-tionary case.

Pempie and Ruet [15] compared three solutions forLOX/LH2 turbopump: 1+1 counter-rotating turbine, 1+1/2counter-rotating turbine, and two turbines in series. As theresults show, the configuration of 1 + 1 counter-rotating tur-bine is considered the best choice because of its good integra-tion of arrangement and efficiency.

Pempie and Ruet also compared conventional turbineand counter-rotating turbine in another application toLOX/Methane main rocket engine. According to the com-parison results, the counter-rotating turbine they design issmaller than the conventional single turbine, and reducesmass-flow rate remarkably. As a result of optimization, therocket engine employing counter-rotating turbine obtainsthe specific impulse of 1.7 second increases.

Theoretical analysis presented by Ji Lucheng [16] indi-cates that the work ratio (the ratio of HP rotor work to LProtor work) is propitious to obtain high efficiency. Generally,high-work ratio is unsuitable for the aircraft engine. How-ever, it meets the requirements of the rocket turbopump bythe square because the pumps of rocket engines demand dif-ferent input powers (see Figure 2).

4. COUNTER-ROTATING TURBINE WITHROTORS OF DIFFERENT DIAMETERS

Previous analysis has indicated that the counter-rotating tur-bine with rotors, which have different rotational speeds, canavoid the disadvantages of the gearbox and two turbines con-figurations.

In 2003, Pempie and Ruet [15] presented their solutionof the counter-rotating turbine for the rocket turbopump.They introduced a counter-rotating turbine with rotors ofdifferent rotational speeds and mean diameters, which isquiet different to the existing one, and present a basic one-dimensional design theory for this turbine basing on the tra-ditional turbine design method.

Tang Fei et al. 3

LH2 pump LOX pump

Counter rotating turbine

Figure 1: Counter-rotating turbopump.

Two rotors are used to drive the pumps, respectively, sorotational speeds and works of the rotors are determined byrequirements of pumps:

NA = NO, NB = NF ,

ΔhA∗

ΔhB∗ =

PFPO

= UA(VU1 −VU2

)

UB(VU3 −VU4

) .(1)

The velocity triangle-calculation process of the counter-rotating turbine is similar to the traditional multistage tur-bine except for the difference of rotors mean diameters. Ac-cording to the conservation laws of mass and momentummoment, parameters on LP outlet section and HP inlet sec-tion must satisfy

ρ2DAHAV2M = ρ3DBHBV3M

DAV2U = DBV3U.(2)

The following equation expresses the efficiency of tur-bine:

η = UA(VU1 −VU2

)+UB

(VU3 −VU4

)

Δh. (3)

The degrees of freedom are the following:

(i) the mean diameters of rotors: DA, DB;(ii) the mean blade speed: UA, UB;

(iii) the degree of reaction Ω and the pressure distributionthrough the turbine blade.

5. PRIMARY EFFICIENCY ANALYSIS OFTHE COUNTER-ROTATING TURBINE

In 2001, Lucheng [16] presented a primary efficiency anal-ysis of 1 + 1/2 counter-rotating turbine basing on conven-tional multistage turbine-analysis theory. Although his anal-ysis does not take the difference of rotor diameters into ac-count, the existing analysis method can be also suitable forthis new-style counter-rotating turbine after giving somemodification on velocity-diagram calculation according toPempie’s one-dimensional design theory.

In order to simplify the architecture of the rocket engine,the simplest 1 + 1/2 configuration is adopted, which consists

0 0.2 0.4 0.6 0.8 1

λA

1

2

3

4

5

6

Δh∗ A/Δh∗ B

0.7

0.8

0.87

0.9

0.91

Figure 2: Influence of work ratio on HP efficiency.

UB

UB

V3W3

V4

W4

UA

W2

V2W1

V1

UA

Figure 3: Velocity triangle diagram.

of HP stator, HP rotor for fuel pump, and LP rotor for oxi-dizer pump. Turbine inlet and outlet flow directions are as-sumed to be axial. Velocity triangles of the turbine are illus-trated by Figure 3.

The work-speed coefficient λ is introduced to correlateturbine efficiency. It’s defined as the ratio of the square of theblade velocity to the specific work of the stage as follows:

λA = U2A/ΔhA

∗ = UA/ΔVA

λB = U2B/ΔhB

∗ = UB/ΔVB.(4)

Referring to the velocity triangle diagram, the changes ofcircumferential absolute velocities can be derived as follows:

V1U =W1U +UA

V2U =W2U +UA

V3U =W3U +UB

V4U =W4U +UB=0

=⇒ΔVA =W1U −W2U

ΔVB =W3U−W4U=V3U.(5)


In this analysis, it’s assumed that row loss is in direct pro-portion to average kinetic energy at row inlet, so the effi-ciency of the high-pressure stage can be written as

ηA =ΔhA

∗

ΔhA∗ + kSω(V0

2 +V12) + kRω(W1

2 +W22)

, (6)

where ω represents the ratio of a blade-surface area to anequivalent weight flow per unit-annular area, and as an as-sumption, the relation between rotor-loss coefficient kR andstator-loss coefficient kS is obtained as kR = 2kS. According tosome experiential relation expressions in [17], the expressionof ηA can be modified to

ηA = λAλA + 0.01172·tan

∣∣α1∣∣·Π (7)

Π = (1 +Ψ)2(6 ctg2α1 + 1)

+ 2(1 +Ψ−λA

)2+ 2(Ψ−λA

)2,

Ψ = UB/UA·λA/λB.Expression of ηB can be obtained by applying the method

used in deriving ηA as follows:

ηB =λB

λB + T tan∣∣α3

∣∣{

4 ctg2α3 + 2[(

1− λB)2

+ λ2B

]} .

(8)

The efficiency of turbine can be expressed as

η = 1/λA +(UB/UA

)2(1/λB

)

1/λAηA +(UB/UA

)2(1/λBηB

) . (9)

In order to obtain these analytical expressions, some ex-periential relation expressions are introduced, and reheat ef-fect and the secondary flow loss due to the change of rotorsdiameter are ignored. So the results of this primary analy-sis are instructional to the selection of design parameters butnot so exact.

6. EFFICIENCY OPTIMIZATION

According to the above-mentioned analysis, turbine effi-ciency is expressed as terms of blade-velocity ratio UB/UA,work-speed coefficient λA, λB, and flow angle α1 and α3. Sothe performance of turbine can be optimized by adjustingthese parameters, and the optimization processes are illus-trated with contour charts of efficiency in Figures 4–6. Thesecharts are plotted on the condition of α1 = 60◦, α3 = 60◦,UB/UA = −0.3, and more charts corresponding to variousconditions are not shown here for limitation on extent. Ac-cording to the comparison of Figures 4–6, turbine efficiencyη is mainly decided by the high-pressure stage.

The influence of α1 on HP efficiency is illustrated byFigure 7 plotted on the condition of λA = 0.6, UB/UA=−0.3.When α1 satisfies the following equation, ηA can achievemaximum:

α1 = arctg

√√√√ 6Ψ2

Ψ2 + 2(1 +Ψ− λB

)2+ 2(Ψ− λB

)2 . (10)

0.2 0.4 0.6 0.8 1

λA

0

0.2

0.4

0.6

0.8

1

λ B

0.70.8

0.85

0.88

0.9

Figure 4: Contour of HP stage efficiency.

−90 −60 −30 0

α2

0

0.2

0.4

0.6

0.8

1

λ B

0.7

0.8

0.85

0.9

0.93

Figure 5: Contour of LP stage efficiency.

When α3 satisfies the following equation, ηB can achievemaximum:

α3 = arctgλB

λB + 0.09376√λB

2 − λB + 0.5. (11)

7. INFLUENCE OF ROTORS DIAMETER CHANGE

For a certain design project, pump rotational speed ratioNO/NF and pump work ratio PF/PO are given by require-ments of pumps, so blade velocity ratio UB/UA can be ex-pressed as

UB

UA= NB

NA

DB

DA= NO

NF

DB

DA. (12)

Combine definition expressions of λA and λB to yield

λB =(ΔhA

∗

ΔhB∗

)(UB

UA

)2

λA =(PFPO

)(NO

NF

DB

DA

)2

λA. (13)

Tang Fei et al. 5

0.2 0.4 0.6 0.8 1

λA

0

0.2

0.4

0.6

0.8

1

λ B

0.7

0.8

0.85

0.88

0.9

Figure 6: Contour of turbine efficiency.

0 30 60 90

α1

0

0.2

0.4

0.6

0.8

1

λ B 0.93

0.91

0.9

0.87

0.8


Then the turbine efficiency can be expressed as terms ofrotors diameter ratio DB/DA, λA, α1, and α3. Referring to therequirements in Table 1 and condition of α1 = 50◦, α3 = 60◦,contour charts of efficiency are plotted as Figures 8 and 9.

As these figures show, high-rotor-diameter ratio DB/DA

may benefit the performance of turbine, but actually, exces-sive DB/DA may make the duct geometry between two rotorsunconventional and bring some excess losses.

The primary fluid mechanical problem of this type ofduct is caused by the tendency of the boundary layer to sep-arate from walls if the channel curvature is too high. The re-sult of too high curvature is always large losses. On the otherhand, if the curvature is too low, the fluid is exposed to anexcessive length of duct and friction losses.

Duct pressure loss, defined as the following expression, isintroduced to evaluate the losses in duct:

LossD =p2∗ − p3

∗

p2∗ . (14)

0 0.2 0.4 0.6 0.8 1

λA

1

1.5

2

2.5

3

3.5

4

DB/D

A

0.7

0.8

0.85

0.88

0.9


0 0.2 0.4 0.6 0.8 1

λA

1

1.5

2

2.5

3

3.5

4

DB/D

A

0.7

0.8

0.85

0.88

0.9

Figure 9: Contour of turbine efficiency.

Duct total pressure loss is a function of the duct geometryand the inlet dynamic pressure head [18] as follows:

LossD = L(p2∗ − p2

), (15)

where duct geometry is accounted by a loss coefficient L.Value of L for a given geometry must initially be determinedfrom experience and by using commercially available corre-lations. The variation of L with inlet swirl angle is illustratedby Figure 10. So once duct geometry has been set, then totalpressure loss only varies with inlet dynamic head and swirlangle.

Considering the complicated influence of duct geometryon turbine efficiency, to select a moderate diameter ratio isvery important for optimization of turbine performance. Inorder to reduce duct losses, the duct geometry between tworotors has to be designed carefully, and as shown in [18], to-tal pressure loss of well-treated swan-neck duct is no more


0 10 20 30 40 50

Duct inlet swirl angle (deg)

0.9

1

1.1

1.2

1.3

1.4

1.5

Loss

coeffi

cien

trel

ativ

eto

zero

swir

l

Conical diffuser, or swan neckduct with no struts

Conical diffuser with strutsfollowed by a pump and turn through

90 degrees up an exhaust stack

Figure 10: Effect of inlet swirl on loss coefficient (P. P. Walsh, P.Fletcher, Gas Turbine Performance).

Table 1: Requirements of LH2/LOX pumps.

LH2 Pump LOX Pump

Work 2500 kW 390 kW

Rotational speed 91000 rpm 18800 rpm

than 2.5%. However, if DB/DA is too high, boundary layerseparation may occur and secondary flow loss will be high.At this time, the 1 + 1 counter-rotating turbine will be moresuitable because the LP stage stator can benefit the flow fieldorganization.

Finally, it must be emphasized that this evaluation of ductlosses is just approximate and only for primary analysis.

8. CONCLUSION

Counter-rotating turbine can improve performance and reli-ability of rocket engine because of its special architecture andhigh performance. The counter-rotating turbine with two ro-tors of the different diameters and rotational speeds can op-timize performance and configuration of rocket engine. Re-view of research on counter-rotating turbine for rocket tur-bopump is presented in this paper.

Primary analysis basing on conventional turbine-designtheory for this unconventional 1 + 1/2 counter-rotating tur-bine has been proposed. The influence of optimization pa-rameters on turbine efficiency is illustrated by contour chartsand analytical expressions. For a certain project, free designparameters are DB/DA, λA, α1, and α3, and as the resultsshow, the overall turbine efficiency is determined mainly bythe high-pressure stage. Finally, influence of rotors diame-ter changes, and duct geometry between two rotors on theturbine efficiency is discussed. To reduce losses in the duct,moderate diameter ratio and well-treated duct geometry arenecessary. LP stator is also helpful to avoid the secondary flowin the duct, if necessary.

NOMENCLATURE

A: AreaD: Mean diameter of rotorsG: Mass flowh: EnthalpyH: Blade heightk: Loss coefficientN: Rotational speedU: Rotor blade velocityV: Absolute velocityW: Relative velocityP: Power (or work)p: PressureQ: Average dynamic pressureα: Angle with absolute velocityβ: Angle with relative velocityλ: Work-speed coefficientη: Efficiency

SUBSCRIPT AND SUPERSCRIPT

A: High-pressure stageB: How-pressure stageD: Duct (between two rotors)F: Fuel pumpO: Oxidizer pumpS: StatorR: RotorU: Circumferential (velocity triangle)M: Axial (velocity triangle)∗: Stagnation0: Inlet of high-pressure stator1/2: Inlet/outlet of high-pressure rotor3/4: Inlet/outlet of low-pressure rotor

REFERENCES

[1] Z. Yuanju, Design of Liquid Rocket Turbopump, BUAA Press,Beijing, China, 1995.

[2] T. Wintucky and W. L. Stewart, “Analysis of two stage counterrotating turbine: efficiencies in terms of work and speed re-quirements,” NACA RM E57L05, 1958.

[3] Y. Naruo, N. Tanatsugu, and K. Kuratani, “Development studyof LOX/LH2 propulsion system in ISAS,” ISTS, 1984.

[4] F. W. Huber and J. P. Veres, “Design and test of a small twocounter rotating turbine for rocket engine application,” AIAAPaper 93-2136, 1993.

[5] D. P. Davidson and A. K. Finke, “The design and fabricationof a small highly instrumented counter rotating turbine rig,”ASME 93-GT-396, 1993.

[6] J. P. Veres, “Two stage turbine for rockets,” NASA N94 24669,1994.

[7] L. W. Griffin and F. W. Huber, “Turbine technology team: anoverview of current and planned activities relevant to the na-tional launch system,” AIAA 92-3220, 1992.

[8] F. W. Huber and L. W. Griffin, “Design of advanced turbop-ump drive turbines for national launch system application,”AIAA 92-3221, 1992.

[9] A. Yamamoto, “Recent fundamental research on turbinesteady and unsteady aerodynamics at the national aerospace

Tang Fei et al. 7

laboratory in Japan proceedings of colloquium on turboma-chinery,” 1996.

[10] A. Yamamoto and E. Outa, “Low speed annular cascade testsof an ultra-highly loaded turbine with tip clearance, part I—near design incidence,” ASME 99-GT-212, 1999.

[11] T. Kawakami and A. Yamamoto, “Investigation of flow inpltra-highly loaded turbine cascade by PTV method,” in 8thInternational Symposium on Flow Visualization, January 1998.

[12] A. Yamamoto, T. Matsunuma, and E. Outa, “Three dimen-sional flows and losses in an ultra-highly loaded turbine,”ISROMAC-7, 1998.

[13] C. Hah, Turbomachinery Fluid Dynamics and Heater Transfer,Marcel Dekker, New York, NY, USA, 1995.

[14] Twin Rotor Turbopump Program Progress Report, ContractNAS8-97161, 1997.

[15] P. Pempie and L. Ruet, “Counter rotating turbine designed forturbopump rocket engine,” AIAA Paper 2003-4768, 2003.

[16] J. Lucheng, Z. Wentao, and X. jianzhong, “Primary analysisand design of a vaneless counter rotating turbine,” Journal ofEngineering Thermophysics, vol. 22, no. 2, 2001.

[17] W. L. Stewart, “Analytical investigation of multistage turbineefficiency characteristics in terms of work and speed require-ments,” NACA RM E57k22b, 1958.

[18] P. P. Walsh and P. Fletcher, Gas Turbine Performance, BlackwellScience, Oxford, UK, 2nd edition, 2004.

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