steam turbine

Renewable Energy 29 (2003) 529–547

www.elsevier.com/locate/renene

Computed effects of tip clearance onperformance of impulse turbine for wave

energy conversion

A. Thakker �, T.S. DhanasekaranWave Energy Research Team, Department of Mechanical and Aeronautical Engineering,

University of Limerick, Limerick, Ireland

Received 3 June 2003; accepted 10 September 2003

Abstract

This paper depicts numerical analysis on Impulse turbine with fixed guide vanes for waveenergy conversion. From the previous investigations, it is found that one of the reasons forthe mismatch between computed and experimental data is due to neglecting tip clearance ef-fect. Hence, a 3-D model with tip clearance has been generated to predict the internal flowand performance of the turbine. As a result, it is found that the comparison between com-puted and experimental data is good, quantitatively and qualitatively. Computation hasbeen carried out for various tip clearances to understand the physics of tip leakage flow andeffect of tip clearance on performance of such unconventional turbine. It is predicted thatthe turbine with 0.25% tip clearance performs almost similar to the case of without tip clear-ance for the entire flow coefficients. The designed value of 1% tip clearance has been vali-dated numerically and computed that the efficiency of the turbine has been reduced around4%, due to tip clearance flow at higher flow coefficients.# 2003 Elsevier Ltd. All rights reserved.

Keywords:Wave energy; Impulse turbine; CFD; Tip clearance flow

1. Introduction

For the last two decades, scientists have been investigating and defining different

methods for power extraction from wave motion. These devices utilize the principle

of an oscillating water column (OWC). OWC-based wave energy power plants

� Corresponding author. Tel.: +353-61-202223; fax: +353-61-202944.

E-mail address: [email protected] (A. Thakker).

0960-1481/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/j.renene.2003.09.007

convert wave energy into low-pressure pneumatic power in the form of bidirec-

tional airflow. Self-rectifying air turbines (which are capable of operating uni-

directionally in bidirectional airflow) are used to extract mechanical shaft power,

which is further converted into electrical power by a generator. Two different tur-

bines are currently in use around the world for wave energy power generation,

Wells turbine, introduced by Dr. A. A. Wells in 1976 and Impulse turbine with

self-pitch controlled guide vanes by Kim et al. [1]. Both these turbines are currently

in operation in different power plants in Europe, Canada, Australia and Asia on an

experimental, as well as a commercial basis. The present work deals with the Im-

pulse turbine. A 1.0-m diameter Impulse turbine with self-pitch controlled guide

vanes was designed, fabricated and is being operated by National Institute of Tech-

Nomenclature

ACL axial chord lengthb height of bladeCT torque coefficientCA input power coefficientHs significant wave heightH � non-dimensional wave heightlr chord length of rotor bladem area ratioQ flow raterR mid span radiusTs mean time periodUR circumferential velocity at rRT torque generatedva axial flow velocityz number of rotor blades

Greek symbols

dp total pressure drop across the rotorg efficiency of turbine�gg mean turbine efficiency under irregular flow conditiongmax maximum turbine efficiency under steady flow condition/ flow coefficientq density of airr solidityc hub-to-tip ratiox angular velocitye percentage of computational error

A. Thakker, T.S. Dhanasekaran / Renewable Energy 29 (2003) 529–547530

nology at Vizhinjam, a site near Thiruvanandapuram, which is a city on the westcoast of India [2]. The guide vanes pitch at the wave frequency. Such movingparts lead to maintenance and operating life problems and increased cost andhence the performance of the turbine with fixed turbine has been investigated byMaeda et al. [3].There are few reports presented on the numerical analysis on Impulse turbine

and Wells turbine. An optimal installation angle of the Impulse turbine has beeninvestigated by numerical and experimental analysis (Kim et al. [4]). The perform-ance of the Impulse turbine with unstructured grids and various turbulencemodels has been studied by Thakker et al. [5]. CFD analysis on CA9 Wells turbinehas been made to validate the performance of the turbine and to analysisaerodynamics characteristics [6]. In all the earlier studies, tip clearance has notbeen incorporated in the numerical model. The tip leakage flow is one of the mostprevalent and influential features of the flow through turbomachine rotors. In ad-dition, the tip leakage flow is a phenomenon that is difficult to measure in mostturbomachines. Computed effects of solidity on Wells turbine performance with tipclearance have been investigated by Watterson and Raghunathan [7]. The predictedeffect of solidity on the turbine pressure drop, torque and efficiency agreed qualitat-ively and quantitatively with the experimental data. Few authors [8–11] have beeninvestigated the effect of tip clearance on the performance of Wells turbineexperimentally and numerically with CFD codes and found that the turbine is verysensitive to tip clearance when compared to a conventional turbine. They haveconcluded that the decrease in tip clearance advances the stall but increases thecyclic efficiency as a result of reduced leakage losses. Also it has been proved thatthe turbine with a relatively large tip clearance could operate over a muchwider range of flow rate range of flow rate without stalling. To investigate the ef-fect of blade sweep on the performance of the Wells turbine, numerical investi-gation was carried out under steady flow condition with a fully 3-D Navier–Stokescode for two kinds of blades, NACA 0020 and CA9 by Kim et al. [12]. Extensivework has been performed in the realm of tip clearance studies on conventionalturbine [13–15].This paper describes the use of CFD method to investigate the effect of tip clear-

ance on performance of Impulse turbine, which is working under bidirectional air-flow for wave energy conversion. The method employs structured grids, whichallow inclusion of such features as the blade tip and casing treatments. The 3-DCFD model has been generated with tip clearance to validate the computed resultswith experimental data. The study has shown that the numerical method is able topredict with reasonable accuracy; the variations of pressure drop across the turbinerotor, torque and efficiency with flow coefficient, and the effect of tip clearance. Anoptimum tip clearance has been suggested where the effect of tip clearance isalmost negligible. Furthermore, the design tip clearance (1 mm) has been validatednumerically. In addition, the performance of Impulse turbine with various tipclearances has been computed under irregular wave condition by using numericalsimulation technique.

531A. Thakker, T.S. Dhanasekaran / Renewable Energy 29 (2003) 529–547

2. Review of experimental apparatus

A schematic layout of the experimental rig of Wave Energy Research Team at

University of Limerick is shown in Fig. 1. It consists of a bell mouth entry, 0.6 m

test section with a hub-tip ratio of 0.6, drive and transmission section, a plenum

chamber with honeycomb section, a calibrated nozzle and a centrifugal fan. Air is

drawn into the bell mouth shaped open end, it passes through the turbine and then

enters the plenum chamber. In the chamber, the flow is conditioned and all swirls/

vortices are removed prior to passing through a calibrated nozzle and is finally

exhausting at the fan outlet. Using a valve at fan exit controls the flow rate. Details

of the test rig calibration can be found from Thakker et al. [6]. The turbine was

mounted on a shaft in a cylindrical annular duct, with a blade tip clearance of 1

mm. The shaft is coupled to a motor/generator via a torque meter. The two guide

vanes were mounted on the up-stream and down-stream hubs of the rig. The tur-

bine was tested by keeping a constant axial velocity of 8.49 m/s. Data was col-

lected by varying the rotational speed from 1250 to 125 rpm, thus giving a flow

coefficient range of 0.27 to 2.7 under unidirectional steady flow conditions. The Rey-

nolds number based on the blade chord length was 0:74� 105 at peak efficiency.

The specification of the turbine is listed in Table 1.The overall performance of the turbine was evaluated by the turbine angular velo-

city x. Torque generated T, flow rate Q and total pressure drop dp across the rotor.The results are expressed in the form of torque coefficient CT, input power coefficient

CA and efficiency g in terms of flow coefficient /. The definitions are given below

CT ¼ T=fqðv2a þU2RÞblrzrR=2g ð1Þ

CA ¼ dpQ=fqðV2a þU2

RÞblrzva=2g ð2Þ

Fig. 1. Schematic diagram of the test rig.


/ ¼ va=UR ð3Þg ¼ Tx=ðdpQÞ ¼ CT=ðCA/Þ ð4Þ

3. Computational fluid dynamics analysis

3.1. Governing equations

Gambit 2.0 and FLUENT V6 were used for meshing and analyzing the pro-blems, respectively. FLUENT V6 solves the Navier–Stokes equations for conver-sion of mass and momentum (Eqs. (5)–(8)). Additional conservations of k and eequations are solved for turbulence closure. Governing Navier–Stokes transportequations are:MASS

@ quð Þ@x

þ @ qvð Þ@y

þ @ qwð Þ@z

¼ 0 ð5Þ

MOMENTUM

@ Pð Þ@x

þ @ sxxð Þ@x

þ @ syxð Þ@y

þ @ szxð Þ@z

¼ divðquuÞ ð6Þ

@ Pð Þ@y

þ @ sxyð Þ@x

þ @ syyð Þ@y

þ @ szyð Þ@z

¼ divðqvuÞ ð7Þ

@ Pð Þ@z

þ @ sxzð Þ@x

þ @ syzð Þ@y

þ @ szzð Þ@z

¼ divðqwuÞ ð8Þ

Table 1

Specification of the turbine

Parameter Symbol H=T ¼ 0:6

Blade profile

Number of blades z 30

Tip diameter D 598.0 mm

Chord length lr 100.0 mm

Pitch Sr 50.0 mm

Blade inlet angle c 60v

Guide vanes profile: Plate type

Pitch Sg 58.0 mm

Chord length lg 131.0 mm

Number of guide vanes g 26

Guide vanes inlet/outlet angle h 30v


3.2. Solver parameter

The solver treats each cell in the domain as a finite volume with a node at its

center and the flow properties for the entire model are solved at each of these

nodes. In order to predict the flow properties at the edge of control volume, the

flow properties must be interpolated between two nodal points. The discretisation

scheme governs the accuracy of its interpolation by controlling the number of

terms in Taylor series used for the interpolation. The discretisation scheme found

to be the most accurate for the second order scheme; this scheme was the highest

order available in the code being used.

3.3. The mesh and the solver

The computational grid is visualized in Fig. 2, where only the grid lines attached

to the surfaces are shown. Here, the resolution of all the boundary layers is visible.

An enlarged view at tip clearance is shown in Fig. 3. The complex 3-dimensional

computational domain has been meshed with hexahedral elements. This has been

achieved by partitioning the entire geometry into meshable pieces and meshed by

mapping and submapping algorithms. The grids clustered near the hub, casing, and

tip was close enough to give appropriate y+ values. The mesh was checked for low

level of skewness and reasonable aspect ratio and volume change. The grid inde-

pendence test has been carried out on the computational domain with 350,000,

400,000, and 450,000 cells (Fig. 4). The performance curves of turbine are seen to

be almost similar for the cases with cells 400,000 and 450,000. Hence the grid cells

400,000 have been utilized for all the numerical studies in the present investigation.

The computational domain extended to 8.5 chord length upstream and down-

steam, it is restricted to one blade to blade and guide vane to guide vane passage

with periodic boundaries. Computation has been carried out for various tip

clearances; 0, 0.25, 1, 2, 4 and 6% of axial chord and for each case with various

flow coefficients.

Fig. 2. Computational grid.


3.4. Boundary conditions

It was necessary to set up three fluid zones using mixing plane technique. Three

zones are the upstream guide vane, the rotor and the downstream guide vane. In-

flow is set as mass flow inlet, outflow is set as pressure outlet and periodic walls are

set as transitional to allow cascade effect on blade and guide vane to be simulated.

The fluid at rotor is defined as a moving reference frame with the angular speed

equivalent to that of the blade. The flow is set as fully turbulent.

Fig. 3. Grids at the tip region.

Fig. 4. Grid independence test.


3.5. Near-wall modeling

Near-wall modeling has a great impact on quality of numerical solution as thevariables mainly change near to the wall. The non-equilibrium wall functions wereused, as they are capable of dealing with complex flows involving separations, reat-tachment or any other non-equilibrium effects and also severe pressure gradients.The near-wall cells were assumed to consist of a viscous sublayer and an inertiadominated layer.

4. Results and discussion

4.1. Validation of numerical procedure

The present numerical model has been validated with the experimental data with1% tip clearance. Fig. 5a–c show the comparison between computed and measuredvalues for input coefficient, torque coefficient and efficiency against flow coefficient,respectively. From Fig. 5a, it can be observed that the computed values overpredictthe measured values at high flow coefficients. But good agreement has beenreached between computed and measured CT values, Fig. 5b. Computed efficiencyof turbine matches very well with experimental results, for the entire flow coef-ficient, except at very low coefficients (Fig. 5c). This implies that the turbulencemodel k–e produces good results in the lower rotational speed of the turbine. Accu-racy of the present computational model has been plotted as the percentage oferror, e on computed CT, CA and efficiency deviated from experimental values(Fig. 6). From the figure, it can be observed that the accuracy of computed resultsvaried with flow coefficient. In particular, the error of CT and CA fall approxi-mately 10 percentage points from the experimental value in the normal operatingcoefficients. At the two extreme flow coefficients, the percentage of error is seenconsiderably more due to the nature of flow which seems highly unsteady andthree-dimensional in the blade passages. As far as the computed efficiency of theturbine is concern, the error is almost zero. In particular, at peak efficiency, where

Fig. 5. Comparison between computed and measured values. (a) Coefficient of input; (b) Coefficient of

torque; (c) Efficiency.


the flow through the blade passage is more favorable in generating torque, the

computed error is close to zero (Fig. 6).

4.2. Effect of tip clearance on the performance of the turbine under steady flowconditions

Fig. 7a–c shows the variations of CA, CT and efficiency, respectively, for the

cases of 0, 0.25, 1, 2, 4 and 6% tip clearances. Fig. 7a shows that the input coef-

ficient is almost the same for the tip clearances 0 to 1%, up to the value of flow co-

efficient 1.0. The reason for this behavior is explained in the following section.

Beyond this flow coefficient, the input coefficient is increasing as tip clearance

increases. When the tip clearance increase from 1%, there is considerable effect due

to tip clearance throughout the operating range of turbine. It can be noted that the

value of CA keeps remains similar for the cases of 0% and 0.25% tip clearance. It is

evident that there is tremendous pressure drop across the turbine due to tip leakage

flow beyond 1% tip clearance. This effect has been reflected in terms of torque con-

verted by the blades (Fig. 7b). Hence the efficiency of the turbine is almost the

same for the cases of 0% and 0.25 tip clearance (Fig. 7c). The efficiency with 1% tip

clearance remains the same as in the above cases up to the value of flow coefficient

about 1.0 and keeps reducing gradually beyond this value. Also it can be noted

that the efficiency curve for the cases above 1% tip clearance is apparently sharp

Fig. 6. Computational error on coefficient of torque, coefficient of input, and efficiency of the turbine.


compare to the other cases. The peak efficiency of the turbine is shifted towards the

left hand side as the tip clearance increases.Fig. 8 shows the distribution of maximum efficiency with tip clearance ratio.

Here the effect of tip clearance of impulse turbine has been compared with the

Wells turbine [10], as both the turbines operate in bidirectional flow applications.

The maximum efficiency of the Impulse turbine is almost constant up to 1% tip

clearance, after this value there is sudden decrease in efficiency. The reason for this

behavior is explained by physics of flow in the following section. Beyond 4% tip

clearance there is no noticeable decrease in efficiency. Hence it is validated that the

design value of 1% tip clearance is an optimum value. Even though both turbines

are very sensitive to the tip clearance compared to conventional turbine, the Im-

pulse turbine is relatively less sensitive when compared to the Wells turbine (Fig. 8).

Fig. 7. Effect of tip clearance. (a) Coefficient of input; (b) Coefficient of torque; (c) Efficiency.

Fig. 8. Effect of tip clearance on max efficiency of various turbines.


For example, the Impulse turbine finds no effect due to tip clearance up to 1% tip

clearance. But in the case of the Wells turbine, there is a drop in efficiency which

starts from the 0.6% tip clearance itself. Generally, both the turbines seem sensitive

in the range of tip clearance from 1 to 4 percentage points.

4.3. Flow physics and the effect of tip clearance height

Fig. 9a–f show the velocity contours at 96 percentage points of blade height for

the cases of 0, 0.25, 1, 2, 4 and 6% tip clearances, respectively, for the flow coefficient

of 1.68. From the figures, while considering the lead edge region of the blade,

without tip clearance and 0.25% tip clearance show similar distribution and the

forward portion of the blade passage, which are typical of a stagnating or low-

velocity flow. This supports the contention that for the front part of the blade tip

Fig. 9. Velocity contours at various tip clearances. (a) 0% tip clearance; (b) 0.25% tip clearance; (c) 1%

tip clearance; (d) 2% tip clearance; (e) 4% tip clearance; (f) 6% tip clearance.


clearance gap could be blocked by the inlet boundary layer (‘aerodynamicallyclosed’) and therefore could be sustaining a horseshoe vortex system. In the casesof relatively open 1% and above tip clearances, size of the horseshoe vortex is togradually reduce (Fig. 8c–f).The size and location of vortex released from tip clearance can be clearly cap-

tured from the above figures. Even though there is no tip leakage vortex formed incase of without tip clearance, the flow separation from the suction surface can beseen from Fig. 9a. In the case of 0.25% tip clearance, the vortex takes place afterapproximately 50% of axial chord length (ACL) apart from suction surface of theblade, Fig. 9b. In the case of low tip clearance, the trailing edge of the blade alsoclosed aerodynamically. But the flow leaks through the clearance from 65 to 70%axial chord length. But in the cases of 1% and above tip clearances, (Fig. 9c–f)there is no aerodynamic lock seen in the trailing edge of the turbine, causing largemass flow of air leak through the tip clearance. Hence tip leakage vortex size islarge when compared to the case of the 0.25% tip clearance. From the figures, itcan be observed that the vortex grows in size from the location of 60% axial chordto downstream of the blade trailing edge. As the strength of leakage vortex increa-ses from 1% tip clearance, it enhances the flow separation at the downstream guidevanes (Fig. 9c–f). This may be the reason for the sudden decrease in efficiency ofthe turbine beyond 1% tip clearance (Fig. 8). The interpretation of this is that thepressure drop across the rotor plays an important role rather than torque in the ef-ficiency of the turbine.To picture the growth of the tip leakage flow vortex, and its interaction with

separated flow from the suction side of the blade, distribution of total pressure co-efficient has been plotted at 90% of axial chord length for various tip clearances.These contours have been plotted for two flow coefficients of 0.67 and 1.68. Theseflow coefficients have been chosen as the effect of tip clearance seems significantlydifferent in the above two flow coefficients (Fig. 7c). Fig. 10a–d shows the totalpressure contours for the cases of 0.25, 1, 4 and 6% tip clearance, respectively, forthe flow coefficient of 1.68. From Fig. 10a, it can be noted that the tip leakage vor-tex is almost diffused for the case of 0.25% tip clearance. In case of the 1% tipclearance, the vortex has been shed fully and the size of vortex keeps growing astip clearance increases (Fig. 10b–d). It can be seen very clearly that the vortex oc-cupied nearly 10% of blade passage width for the case of 1% tip clearance andnearly 40% in case of 6% tip clearance. So from the Fig. 9, it can be interpretedthat the tip leakage flow induces a significant area of low-momentum fluid.At the flow coefficient of 0.67, there is no considerable effect due to tip clearance

for the cases of 0.25 and 1% tip clearance (Fig. 11). Also, there is no visible vortexseen due to tip clearance leakage flow in the above tip clearances. This may be dueto the high-pressure drop across the turbine, which occurs before 55% of ACL. Asthe velocity of flow entering the tip clearance is low, it has less energy to create avortex. Hence the efficiency of the turbine is same for the both tip clearances of0.25 and 1%. But in case of higher tip clearances, as the mass flow through the tipgap increases, a vortex has been shed but on a small scale. Hence there is reductionin efficiency of the turbine after 1% tip clearance in low flow coefficient also. This


trend reveals that the lower tip clearances (below 1% tip clearance) affects the tur-

bine performance in the higher flow coefficients only (after peak efficiency). As the

tip clearance increases from 1%, it gradually advances the turbine performance in

the lower flow coefficients. Static pressure distribution on the suction and pressure

side of the blade is shown in Figs. 12 and 13, respectively, for the flow coefficient

1.68. There is considerable effect due to tip clearance in the static pressure distri-

bution as seen throughout the blade length. However, the effect is more predomi-

nant after 65% of ACL. The low-pressure region at the mid portion of the suction

side of the blade has been shifted towards the hub of the blade due to tip leakage

flow (Fig. 12b–d). On the other hand, static pressure distribution on the pressure

side is seen to be shifted upwards, as the blade passage flow is diverted through the

tip gap (Fig. 13a–d).Static pressure distribution on the tip surface of the blade for various tip clear-

ances at the flow coefficient 1.68 is shown in Fig. 14a–d. The effective leakage area

through the tip surface can be clearly captured from the above figures. At low tip

clearance, the blade passage flow released through the suction surface effectively,

about 65–70% due to aerodynamic lock in the blade leading and trailing edges.

Hence the vortex has been formed at negligible sizes and do not affect the main

flow significantly (Fig. 10a). But in the case of 1% tip clearance, leakage takes

place from 60% ACL to the trailing edge of the blade and beyond 1% tip

Fig. 10. Total pressure contours at 90% ACL at / ¼ 1:68. (a) 0.25% tip clearance; (b) 1% tip clearance;

(c) 4% tip clearance; (d) 6% tip clearance.


clearance, the leakage takes place through the entire tip surface of the blade. It cre-

ates the relatively large vortex and makes a considerable impact on the efficiency of

the turbine.

4.4. Performance of the Impulse turbine with various tip clearances under irregularflow conditions

The conditions faced by the turbine in an actual wave energy power plant are ir-

regular and unsteady due to the random nature of the sea waves. So, the perform-

ance of 0.6 m, 0.6 H/T ratio Impulse turbine with various tip clearances have been

evaluated using numerical simulation techniques under such conditions. Consider-

ing quasi-steady flow conditions, typical turbine characteristics shown in the uni-

directional CFD results for the said turbine were used for this simulation. The

numerical simulation techniques used by Inoue et al. [16] and Setoguchi et al. [17]

for the performance prediction of 0.3-m diameter Wells and Impulse turbines

under irregular flow conditions were adopted for these analyses. The numerical

technique has been further fine-turned by adding the compressibility effect in the

OWC device by Thakker et al. [18]. A simple OWC device geometry with width 10

m with a turbine duct area to air chamber area ratio, m ¼ 0:00181 was adopted for

the simulation as shown in Fig. 15.

Fig. 11. Total pressure contours at 90% ACL at / ¼ 0:67. (a) 0.25% tip clearance; (b) 1% tip clearance;

(c) 4% tip clearance; (d) 6% tip clearance.


The actual sea data based on the water surface elevation time history were usedto simulate irregular test wave provided by Irish Utility, Electricity Supply Boardof Ireland (ESBI). The test waves had a mean time period, Ts ¼ 6:5 s and a signifi-cant wave height, Hs ¼ 2:091 m. For this simulation, 30 waves were used with atotal time span of 1 month. A plot of non-dimensional wave height, H� vs. non-dimensional time, t� is shown in Fig. 16 for 164 s. The mean output Co and themean input coefficient Ci can be defined, respectively [18] as follows:

�CCo ¼1

t�

ðt�0

CT ð/ÞðK �xx�Þ2 þ va

�2

2

� �r

4ð1 mÞ1þ m

� ��xx�dt� ð9Þ

and

�CCi ¼1

t�

ðt�0

CAð/ÞðK �xx�Þ2 þ va

�2

2

� �r

4ð1 mÞ1þ m

� �va

�dt� ð10Þ

It can be noted from the above two equations that the performance of the tur-bine can be calculated as a function of Kx� and va

�, when torque coefficient CT

Fig. 12. Static pressure contours on suction side of turbine blade at / ¼ 1:68. (a) 0.25% tip clearance;

(b) 1% tip clearance; (c) 4% tip clearance; (d) 6% tip clearance.


Fig. 13. Static pressure contours on pressure side of turbine blade at / ¼ 1:68. (a) 0.25% tip clearance;

(b) 1% tip clearance; (c) 4% tip clearance; (d) 6% tip clearance.

Fig. 14. Static pressure contours on tip surface of turbine blade at / ¼ 1:68. (a) 0.25% tip clearance; (b)

1% tip clearance; (c) 4% tip clearance; (d) 6% tip clearance.


(/), input coefficient CA (/), solidity, r, hub-to-tip ratio, c and non-dimensional

angular speed are specified. Where / ¼ va�=ðK �xx�Þ, va� ¼ mTsva=Hs and �xx� ¼ xTs.

The mean efficiency of the turbine can be defined as

�gg ¼ �CCo

��CCi: ð11Þ

The mean efficiency of Impulse turbine with various tip clearance under such ir-

regular condition is shown in Fig. 17.

Fig. 16. Test irregular flow.

Fig. 15. Schematic layout of a simple OWC device.


5. Conclusion

The present computational model has been validated with experimental resultswith reasonable accuracy and found to be suitable for further design analysis. It isfound that k–e turbulence model can predict the performance of turbine in the lowrotational speed of turbine. The performance curves of the Impulse turbine withvarious tip clearances have been arrived at numerically. The flow physics of theblade passage flow interacting with tip leakage flow has been analyzed with thecomputed results. It is investigated that the turbine is very sensitive to tip clearancewhen compared to a conventional turbine. It is predicted that the turbine with0.25% tip clearance performs almost similar to the case with no tip clearance forthe entire flow coefficients. The designed value of 1% tip clearance has been vali-dated numerically.

Acknowledgements

The authors would like to acknowledge the financial support given by ESBI, Ire-land and also by the Wave Energy Research Team, Department of Mechanical andAeronautical Engineering, University of Limerick.

References

[1] Kim TW, Kaneko D, Setoguchi T, Inoue M. Aerodynamic performance of an impulse turbine with

self-pitch-controlled guide vanes for wave power generator. Proceedings of the first KSMY-JSME

Thermal and Fluids Engineering Conference, Korea. 1998.

Fig. 17. Simulated mean efficiency of turbine under irregular flow condition.


[2] Santhakumar S, Jayashankar V, Atmanand MA, Pathak AG, Ravindran M, Setoguchi T, Takao

M, Kaneko M. Performance of an impulse turbine based wave energy plant. Proceedings of the

Eighth International Offshore and Polar Engineering Conference (Montreal, Canada, May 24–29).

1998, p. 75–80.

[3] Maeda H, Santhakumar S, Setoguchi S, Takao M, Kinoue Y, Kaneko K. Performance of an

impulse turbine with fixed guide vanes for wave energy conversion. Renewable Energy 1999;17:

533–547.

[4] Kim TS, Lee HG, Kyoo III P, Lee YW, Kinoue Y, Setoguchi T. Numerical analysis of Impulse

turbine for wave energy conversion. Proceedings of the Tenth International Offshore and Polar En-

gineering Conference (Seattle, USA, May 28–June 2). 2000.

[5] Thakker A, Frawley P, Khaleeq HB, Abugihalia Y, Setoguchi T. Experimental and CFD analysis

of 0.6 m Impulse turbine with fixed guide vanes. Proceedings of the Eleventh International Offshore

and Polar Engineering Conference 2001, Stavanger, Norway, June 17–22. 2001.

[6] Thakker A, Frawley P, Sheik Bajeet E. Numerical analysis of Wells turbine performance using a

3D Navier–Strokes explicit solver. Proceedings of the Eleventh International Offshore and Polar

Engineering Conference 2001, Stavanger, Norway, June 17–22. 2001.

[7] Watterson JK, Raghunathan S. Computed effects of solidity on Wells turbine performance. JSME

International Journal, Series B 1998;41(1):199–205.

[8] Raghunathan S, Setoguchi T, Kaneko K. Aerodynamics of monoplane Wells turbine—a review.

Proceedings Offshore and Mechanics and Polar Engineering Conference, Edinburgh. 1991.

[9] Tagori R, Arakawa C, Suzuki M. Estimation of prototype performance and optimum design of

Wells turbine. Research in Natural Energy SPEY 1987;20:127–32.

[10] Raghunathan S. The Wells air turbine for wave energy conversion. Prog Aerospace Sci

1995;31:335–86.

[11] Watterson JK, Raghunathan S. Computed effects of tip clearance on Wells turbine performance.

35th Aerospace Sci Mtg and Exh AIAA paper 97-0994, Reno, Nevada 1997.

[12] Kim TH, Setoguchi T, Kaneko K, Raghunathan S. Numerical investigation on the effect of blade

sweep on the performance of Wells turbine. Renewable Energy 2002;25:235–48.

[13] Xiao X, McCarter A, Lakshminarayana B. Tip clearance effects in a turbine rotor. Part I: Pressure

fields and losses. ASME Journal of Turbomachinery 2000;123:296–304.

[14] Ho Y, Lakshminarayana B. Computational modeling of three dimensional endwall flow through a

turbine rotor with strong secondary flows. ASME Journal of Turbomachiney 1996;118:250–61.

[15] Stauter RC. Measurement of the three dimensional tip region flow field in an axial compressor.

ASME paper no.92-GT-211, 1992.

[16] Inoue M, Kaneko K, Setoguchi T, Saruwatari T. Studies on the Wells turbine for wave power gen-

eration (Turbine characteristics and design parameters for irregular wave). JSME International

Journal, series 2 1998;31(4):676–82.

[17] Setoguchi T, Takao M, Kinoue Y, Kaneko K, Inoue M. Comparative study of performance of tur-

bines for wave power conversion. Proceeding of the Tenth International Offshore and Polar Engin-

eering Conference, Seattle, USA. 2000.

[18] Thakker A, Dhanasekaran TS, Khaleeq H, Usmani Z, Ansari A, Takao M, Setoguchi T. Appli-

cation of numerical simulation method to predict the performance of wave energy device with

impulse turbine. Journal of Thermal Science 2003;12(1):38–43.


steam turbine

Documents

Transcript of steam turbine