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  Abstract: Computational Fluid Dynamics (CFD) analysis is very          requirement of the prevailing site conditions, a unique
useful tool for predicting hydraulic machinery performance at            performance prediction has to be made for a separate turbine.
various operating conditions. For designers, prediction of               This can be done either by theoretical methods, experimental
operating characteristics performance is most important task.            methods or by computational method (i.e. CFD). Among all
All theoretical methods for predicting the performance merely
                                                                         methods CFD stands its unique importance, since by this
gives a value, and one is unable to determine the root cause for
the poor performance. Due to the development of CFD code,                method study of the flow inside turbine space can be made.
one can get the performance value as well as observe actual              Flow pattern in intricate portions of the component can also
behaviour of flow in the domain. Analysis and variation of               be analysed and variation of the results can be known with
performance can be find out by using CFD analysis.                       the varying conditions. CFD method consumes less money,
                                                                         less gestation period in comparison to the experimental
  In the present work 3-Dimensional (3-D) real flow analysis is
done for experimentally tested turbine and the characteristics           method which requires model fabrication and test rig set up.
of prototype turbine were predicted in actual operating regimes.         CFD approach is a combination of numerical technique and
Aim of the work is validation of CFD results with the                    computational power. With the help of CFD technique even
experimental output .The operating conditions considered are             complex flow pattern inside hydraulic turbine parts can be
in accordance with that, where actual prototype turbine is to be         analysed in detail and modifications can be implemented.
installed. Flow structure inside the machine is analysed and it          It can be used for increasing the efficiency by making
showed the scope of improvement in the design (for example               necessary modification in the design of hydraulic turbine
casing tip portion). Results obtained by Computational tool were         and checking relevancy of alternate optimizatimised design
very close to experimental results. This provides confidence on
                                                                         before the turbine is finally manufactured. However in
Computational tools. Present paper elaborates model selection
for prototype turbine, details of methodology used, visualization        order to check the reliability of selected optimized design,
of results in CFX-post & then validation of Computational                validation of the results is to be done with experimental results.
results.                                                                 CFD technique has lead to significant enhancement in
                                                                         efficiency of hydraulic turbine. CFD can also be used to check
  Keywords: Computational fluid dynamics (CFD), francis turbine,
                                                                         efficiency of alternate design of hydraulic turbine for
Efficiency, Head, Unit discharge, unit speed, unit power, pressure,
unit discharge, specific speed, flow parameter.                          optimization before final testing is done. To improve reliability
                                                                         of CFD technique, validations of results are required with
                                                                         experimental results. In present work Francis turbine
I. INTRODUCTION                                                          considered with Horizontal axis. CFD analysis is done on
  Among all hydraulic turbine machines used for energy                   varying working conditions and tabulations of results are done
conversion, vast operating regime of Francis turbine enables             to get the clear picture of changes in the results.
it to be used for varying range of small to large hydro power              In the present paper emphasis is given on predicting the
plant. This makes Francis turbine most popular and hence it              turbine performance in actual condition for a prototype turbine
is used in maximum number of hydro power plants. In order                and then to validate the results. Hydraulic turbine which is
to develop a reliable machine for this highly demanding                  considered for validation of results is a actual turbine which
operation, the behaviour of the flow in the entire turbine               is to be manufactured and installed at the site. For this turbine
regime has to be predicted by a reliable computational method            head and discharge available are known. With the help of
like CFD which is very economical method. The prediction                 these known quantities other necessary parameters for study
of prototype turbine performance in actual prevailing                    like power available, specific speed, diameter of runner, unit
conditions is very important for engineers. In order to know             speed, unit power and scale ratio are calculated. These
the feasibility of the turbine, it is essential to project the results   quantities are useful for final modelling of prototype hydraulic
in advance. Since turbines are tailor made as per the                    turbine components. Feasibility of working turbine at actual
MIT International Journal of Mechanical Engineering Vol. 1 No. 2 Aug 2011, pp 93-100                                                                 94
ISSN No. 2230 – 7699 © MIT Publications
                Table 2: Turbine specification                      site condition where prototype turbine is to be installed. For
                                                                    the selection of prototype turbine, first of all model turbine is
         Turbine model                     Francis Turbine          selected (satisfying specification as per Table 2) which is
   Shaft alignment                         Horizontal Axis          homologous to the prototype turbine. Based on these data,
                                                                    efficiency of prototype turbine is calculated. Also all the
   Ns of turbine                           266.19 m-kW
                                                                    parameters are calculated for the prototype turbine based on
   Model selected                          F280                     the selected model. For present study conditions available at
   Desired P generator output              3000 kW                  the actual site conditions are given in Table 2.
   Rated head available                    48 m                       The integrated and cross sectional view of assembled hydro
   Desired P turbine output                3142 kW                  turbine is shown in Figure 2 and Figure 3.
   Rated flow                              7.25 m3/s
   Rated N of turbine                      600 rpm
   Prototype runner diameter               1.01 m
   Model runner diameter                   0.35 m
   Scale up ratio                          2.88
   Site elevation                          EL 143 m
   Turbine overload                        10 % Prated
V. EXPERIMENTAL INVESTIGATION
  Experimental tested results of turbine at reduced scale
(CRED-KBL) are projected w.r.t. model whose specific speed
resembles with the prototype turbine. The geometrical
specifications of experimentally tested Francis turbine model
are given in Table 2.
  There is a vast number of iterations available depending
upon the guide vane opening of the turbine. Initially for best
guide vane opening results are calculated which are tabulated
in the Table 2. These Data are obtained by scaling up the
models results of various parameters obtained after conducting
the experimental wind tunnel testing.
   Runner diameter of prototype turbine is calculated
satisfying the specifications mentioned in Table 1, depending
upon the diameter of prototype turbine, scale ratio is
calculated. Respective model drawings are scaled up as per
scale up ratio. Obtained results for prototype turbine are
tabulated in Table 3. An iterative method is used to find that              Figure 5: Variation of head & efficiency wrt
optimum efficiency can be obtained when diameter of runner                        discharge of prototype turbine
is 1010 mm which is duty point. For duty point and rated
turbine speed of 600 rpm, value of N11 is 87.50. Head and                              Table 4: Model details
efficiency variations wrt discharge for prototype turbine are
shown in Figure 5. For broader visualisation of results,                Axis of turbine                         vertical
experimental and CFD investigation is done at design and                Type of draft tube                      elbow tube
off-design points.
                                                                        Model head                              28 m
           Table 3: Experimental results of prototype                   Specific speed of turbine               266.19 m-kW
Sl. N11      P11   hexp.    H       Pr.        P    Q    Q11            Runner diameter                         0.35 m
No.                 %      (m)     (Pa)      (kW) (m3/s)                No. of runner blades                    13
 1    70    9.00 89.00 74.95 735221.46 5956.75 9.10 1.03                No. of guide vanes                      18
 2    80    9.30 92.80 57.38 562903.93 4123.57 7.89 1.02                PCD of guide vanes                      0.40 m
 3 87.5 9.28 93.10 47.97 470541.74 3144.74 7.18 1.01
                                                                        No. of stay vanes                       18
 4    90    9.22 93.00 45.34 444763.60 2864.98 6.93 1.01
                                                                        Best efficiency                         92.10 %
 5 100 8.70 89.50 36.72 360258.52 1975.06 6.13 0.99
                                                                        N11 at best efficiency point            83.8
                                                                        P11 at best efficiency point            8.85
  From Tables 5 and 6 it is seen that for maximum efficiency        can be used for investigating the actual performance of
total losses is minimum. Pressure contour and velocity contour      prototype turbine, to get possible sources of improvement in
shown in Figure 12 and 13 respectively describes the flow           the design geometry with cost effective technique in lesser
structure inside various components of francis turbine.             time. Validation of results done by this method will lead to
Velocity profile from Figure 12 inside the turbine assembly         become very good source of optimization technique for
indicates that casing and runner domain has smooth velocity         hydraulic turbine performance.
profile whereas as soon as water enters draft domain velocity         Results from experimental evaluation and Simulation
starts decreasing and profile becomes non uniform. Similarly        performed at different unit speed range for optimum guide
from Figure 13 it becomes clear maximum energy conversation         vane opening and at rated speed of runner 600 rpm. Results
takes place inside the casing domain where pressure is highest      show that optimum turbine performance at actual site will
and as water moves further its pressure decreases gradually.        occur when the unit speed of turbine is near 87.5 working
  The best operating regimes, losses and flow pattern can be        under a head of 48 m and accordingly other parameters are
investigated from the calculated flow parameters of numerical       available. On the basis of computational results design
simulation. Thus it can be concluded that CFD simulation            analysis of prototype turbine can be done accordingly.
    results is due to error in discretising the governing equations                  Reports on Turbine Testing Problem Oriented Research
    and flow domain. Losses not considered very precisely. There                     Laboratory (Fluid Mechanics and Hydraulic Mechanics Lab)
    can be human and instrumental error in experimental                              Bhopal, India.
    calculations. Prediction of turbine performance by CFD gives [3]                 P. Krishnamachar, Dr. V.V. Barlit (Russia), M.M. Deshmukh,
    the idea to know the flow behaviour inside the turbine                           Manual on Hydraulic Turbine (MANIT, Bhopal).
    model and get the information about the intricacy of flow [4]                    Guoyi Peng, Shuliang Cao, Masaru Ishizuka, Shinji Hayama
    pattern, since the flow inside the turbine in actual is very                     (2002); Design optimisation of axial flow hydraulic turbine
    complicated. CFD results gives the qualitative information.                      runner: Part II-Multiobjective Constrained Optimzation
    It provides the tool to simulate the flow conditions with                        Method, International Journal for Numerical Methods in
    different geometries in lowest possible time, thus providing                     Fluids, Vol. 39, Issue 6, pp. 533-548.
    reduction in design analysis and yet developing robust [5]                       Guoyi Peng (2005): A practical combined combined
    technology along with aiding in reducing gestation                               computation method of mean through-flow for 3D inverse
    period.                                                                          design of hydraulic turbine machinery blades, ASME Journal
                                                                                     of fluid engineering.
                                  NOMENCLATURE                                 [6]   V. Prasad, CFD approach for design optimization and
                                                                                     validation for axial flow hydraulic turbine, Indian J of Eng
        H = Net head (m)
                                                                                     and Materials Sciences, Vol. 16, August 1999, 229-236.
        Q = Discharge through turbine (m 3/s)
                                                                               [7]   Bernard M., Maryse P., Robert M. and Anne. M. G., Proc.
        N = Rotational speed of turbine (rpm)                                        ASCE Water Power Conference, Las Vegas, USA 1999.
        h = Mass density of water (kg/m3)                                      [8]   Peng G., Cao S., Ishizuka M. and Hayama S., Int. J. Numer
        g = Gravitational acceleration (m/s 2)                                       Methods Fluids, 39(6) (200) 533-548
        P = Turbine power (kW)                                                 [9]   Daniel B, Romeo R., and Sebastian M, Proc. Int. conf. on
                                                                                     CSHS03, Belgrade, (2003) 29-36.
        Prated = Power output of turbine at rated condition (kW)
                                                                               [10] Liplej A., Proc. Inst. Mech. Eng., Pt. A. J. Power and Energy,
        Pgeneratoroutput = Power output of generator (kW)                           218 (2004) 43-50.
        EL = Elevation level wrt mean sea level.                               [11] Guoyi P., J. Fluids Eng., 27 (2005) 1183-1190
        PCD = Pitch circle diameter (mm)                                       [12] C.A.J. Fletcher, Computational Techniques for Fluid
        N11 = Unit speed                                                            Dynamics Vol. 1, Springer Pub. 1991.
        Q11 = Unit discharge                                                   [13] Lewis RI, Turbo machinery performance analysis (Arnold,
        P11 = Unit power                                                            Londan), 1996.
Pr. = Pressure (Pa) [14] CFX 11, User Manual, Ansys Inc. 2004.
        Hexp. = Head by experimental testing (m)                               [15] Liplez A., Proc. Inst. Mech. Eng., Pt. A. J. Power and Energy,
                                                                                    218 (2004) 43-50.
        Hcfd = Head by CFD testing (m)
                                                                               [16] Guoyi P., J. Fluids Eng., 27 (2005) 1183-1190.
        hexp. = Efficiency obtained by experimental testing
                                                                               [17] Shukla M., CFD Analysis of 3-D flow and it's validation for
        hcfd = Efficiency obtained by CFD testing                                   francis turbine, 34th National Conference on FMFP, BIT
                                                                                    Mesra (2007) 732-737.
                               ACKNOWEDGEMENTS                                 [18] Wu J., Shimmel K., Tani K., Niikura K. and Sato J. J., Fluid
      Author would like to express sincere gratitude towards all Engg., 127(2007) 159-168.
    related to MANIT, Bhopal and KBL Pune, for continuous [19] Rao, V. Shrinivas, Tripathi, S.K. (2007): Role of CFD analysis
    encouragement and cooperation made available to do the       in hydraulic design optimization of hydro turbines, Proceeding
    associated paper work.                                       of National Seminar on CFD-The 3rd Dimension in Flow
                                                                                     Analysis & Thermal Design, Bhopal(India), pp.196-201.
                                    REFERENCES                                [20] Vishnu Prasad; V.K. Gahlot, P. Krishnamachar (2009) CFD
    [1]          Kirloskar Brothers Limited Data for Francis turbine model,      approach for design optimization and validation for axial flow
                 Corporate Research and Engineering Division (CRED-KBL),           hydraulic turbine, Indian Journal of Engineering and
                 Pune, India.                                                      Material Sciences, pp. 229- 236 .
    [2]          Maulana Azad National Institute of Technology, Project