INTRODUCTION:

Today a huge part of worlds population is using non-renewable energy and thereby vanishing our future resources too. Recently, hydropower is an attractive source of renewable energy not only because of its eco-friendly pollution free nature but also for its promising future development. Many developing nations are searching a way to use their available resources efficiently in such a manner that the capital needed for the same will not affect their economy adversely. The cross-flow turbine is probably a good option for such nations due to ease in fabrication and low head installation.

The cross flow turbine is a hydraulic turbine that may be categorised as an impulse turbine with partial admission. A crossflow turbine in its simplest form consists of a runner and a nozzle. The runner is built from two or more parallel disks connected near their rims by a series of curved blades. The function of the rectangular nozzle is to convert potential energy of water into kinetic energy and to directs the flow into the runner. The rectangular water jet issuing from the nozzle first enters the runner, where the first stage power is generated, then the water flows diametrically through the centre of runner , hits the blades again and leaves the runner, thus generates second stage power.

C.A. Mockmore and Fred Merry Field [1] gives description of appropriate design of the cross flow turbine. He also established that maximum efficiency at constant head can be achived at constant speed irrespective of gate opening. Akerkar [2] reported the effect of various factors such as angle of attack, nozzle entry arc and nozzle entry configuration on the turbine efficiency. He concluded that the flow pattern inside the cross flow turbine runner is concave when viewed from the shaft center. The jet angle at the first stage exit is greater for the vertical position of the nozzle than either the slant or the horizontal positions, indicating that there would be more cross flow.

An experimental test performed on the laboratory turbin by L.A. Hamierl [3] shows measurement of the turbine efficiency and power output and its dependency on design variable and operating parameter. P.Verhaart, [4] compares between Francis and cross flow turbine under equivalent initial condition i.e. the size and specific speed, are identical for both under the same running condition. Energy output obtained in cross flow turbine is reported to be greater than Francis turbine.

Shahram Khosrowpanah et al [5] investigated the effect of the number of blades, the runner diameter, and the nozzle entry arc under flow/head variations. The results show that the maximum efficiency of the CFT at any flow/head combination increases as the nozzle entry arc increases or the aspect ratio of the runner decreases. The maximum efficiency of the CFT at any flow/head combination increases by increasing the nozzle entry . The optimum number of blades in this experiment was approximately 15.

Based on the available site conditions, a cross flow turbine has been designed by Javed A. Chattha, et. al., [6],. The diameter and length of the turbine runner the number of blades and radius of curvature have been determined along with other design parameters. Design of high efficiency cross-flow turbine for hydro-power plant by Bilal Abdullah Nasir [7]. In this paper all design parameters of cross-flow turbine were calculated at maximum efficiency. The maximum efficiency was found to be 88% constant for different values of head and water flow rate

Experimental investigation of the key parameter influencing cross flow turbine efficiency was discussed by V.C. Desai and N.M Aziz [8]. The experiments included the measurements of torque, rotational speed, flow rate, and total head in physical model of turbines and nozzles. Analysis performed on the result identified the impact of the different parameter on the turbine efficiency. The result indicates that with the careful selection of the cross-flow turbine parameters, efficiency as high as 88% with an uncertainty of ±2.4% can be achieved.

In the parametric study on the performance of cross flow turbine by B. Joshi, et. al. [9]. the effect of blade number, nozzle entry arc, and head on the performance characteristics of a cross-flow turbine have been investigated. It has been observed that the efficiency of the turbine increases, with increase in blade number, nozzle entry arc, and head. Abbas A., et. al., [10] studied the power outputs of two stages of cross flow turbine.

In the present work, the effect of design parameters on velocity of flow across cross-flow turbine is computed experimentally. The key design parameters involved in the study are blade angles, the angle of attack, horizontal distance of nozzle tip from the runner shaft centre and different nozzle tip elevation.

DESIGN PARAMETERS AND CONSTRUCTION:

In the present work an assembly frame, runner and nozzle is used to construct the setup. The experimental setup including nozzle along with runner and frame is fabricated. The specifications and parameters have been taken from experimental research paper [1].

HP_out=

(1)

HP_in= (2)

η = (3)

The experimental setup is prepared for medium and low head. The inlet angle β₁of blade will be maintained around 26º to 28º and outlet ange β₁’as 90º i.e. radial outlet. The parameters such as nozzle inlet angle ( ), nozzle tip elevation (t_e) and its horizontal distance from centre of the runner shaft (d) is varied for different heads as per different sites. The runner consist of 12 blades symmetrically arranged between two circular plates at the plate periphery.

Rectangular nozzle is constructed to provide water flow throughout the blade length, with two pipes for inlet of water from source. Adjustable sockets are used to change direction and to open/close pipes according to requirements. Frame is constructed to support and fix nozzle and runner. It is provided with facility to change nozzle angle, distance, height and runner distance from nozzle and operate the turbine under different operating parameter combinations.

Figure-1. Installed crossflow turbine

RESULTS AND DISCUSSION:

In the present study, an experimental setup of crossflow turbine has been designed for the head of 3 m and volumetric flow rate upto 0.059 m³/s, and tested under the head of 0.38m and volumetric flow rate 0.005355 m³/s.

The runner of the turbine consists of 12 blades symmetrically arranged between two plates. The efficiency and rpm dependence of nozzle inlet angle ( ), nozzle tip distance (d) and nozzle tip elevation(t_e) are analyzed. In the present work the value of α varies from 0۫ to 20۫, the value of d varies from 4 to 40 m and the value of t_e varies from 13 m to 17 m.

The graph of efficiency versus nozzle tip distance and runner rpm versus nozzle tip distance for various values of angle of attack (α), and nozzle tip elevation is plotted. The various consolidated graph showing the effect of angle of attack and horizontal distance of nozzle tip on efficiency and runner RPM, for different nozzle tip elevation are shown in fig.2(a-c) and fig.3(a-c) respectively.

(a) Nozzle tip elevation t_e = 13 cm

(b) Nozzle tip elevation t_e = 15 cm

Figure-2. Efficiency versus horizontal distance of nozzle tip from axis of shaft (d) for different angle of attack (α) at various nozzle tip elevation

From the results, fig.2(a-c) it is clear that the efficiency is higher for low angle of attack and this trend is observed in all the graphs plotted for various distance of nozzle tip. It is also observed that as the distance from the nozzle tip increases, efficiency of runner first increases upto certain values and then decreases due to losses in K.E., so it is advised to keep the nozzle at efficient distance to runner.

In Fig.3(a-c) graph of runner RPM versus horizontal distance of nozzle tip from axis of shaft, is plotted for various values of angle of attack (α) for different nozzle tip elevations. It is evident from fig.3(a-c) that runner RPM for almost every angle of attack decreases with the increase in in horizontal distance of nozzle tip for nozzle tip elevation 13 cm and 15 cm from shaft axis. This is due to large flow volume entering the blades tangentially for low horizontal dictance of nozzle tip. In case of high tip elevation of range 17 cm nature is similar for angle of attack equal to and greater than 8˚ but for angle of attack less than 8˚ runner RPM first increase upto certain value than decrease. This is due to large volume flow above runner, for small angle of attack.

(a) Nozzle tip elevation t_e = 13 cm

(b) Nozzle tip elevation t_e = 15 cm

Figure-3. Runner RPM versus horizontal distance of nozzle tip from axis of shaft (d) for different angle of attack (α) at various nozzle tip elevation

In Fig 4(a-f) graph is plotted between runner RPM versus horizontal distance of nozzle tip from axis of shaft to observe, effect of variation of nozzle tip distance from shaft axis for different angle of attack. For angle of attack ) = 0˚ and 4˚ maximum runner RPM is at nozzle tip distance 12cm to 18 cm. For all other angle of attack maximum runner RPM obtained is at nozzle tip distance 4cm, for nozzle tip elevation 17 cm.

(a) angle of attack ( ) = 0˚

(b) angle of attack ( ) = 4˚

(d) angle of attack ( ) = 12˚

(e) angle of attack ( ) = 16˚

(f) angle of attack ( ) = 20˚

Figure-4. Runner RPM versus horizontal distance of nozzle tip from axis of shaft (d) for different elevation t_e at various angle of attack ( )

CONCLUSION:

This work is concentrated in the development of cross flow hydro turbine which can be locally produced at low cost. Maximum efficiency upto 93% is obtained at angle of attack of 8˚. Maximum efficiency is obtained at minimum nozzle tip distance from the centre of runner shaft 4 cm for all angle of attack greater than 4˚ and for all nozzle tip elevation from centre of runner shaft ,but for smaller angle of attack upto 4˚ maximum efficiency and maximum runner RPM is obtained at nozzle tip distance from runner shaft at around 10 cm to 15 cm. Maximum efficiency 93% and runner speed of 252 rpm is obtained for Nozzle tip elevation from centre of runner shaft at 17 cm. Similar trend is observed for almost all angle of attack and nozzle tip distances. Which ensure optimum elevation of nozzle tip from shaft at nozzle tip just above the top blade.

NOMENCLATURE:

Q Flow rate

C Coefficient for nozzle roughness

D₁ Outer diameter of the runner

D₂ Inner diameter of the runner

HP_outOutput horse power

HP_in Input horse power

U₁ Tangential velocity of runner outer periphery

V₁ Absolute velocity of the entering water jet

GREEK SYMBOLS:

α₁- angle of attack

β₁ - angle between runner inner periphery and relative velocity of entering water jet

β₂- angle between runner inner periphery and relative velocity of exiting water jet

η - Assumed system efficiency

γ - Specific weight of water

ψ- Coefficient for blade roughness

REFERENCES:

[1] C.A. Mockmore and Fred Merry Field 1949 “The Banki water turbine”, Engineering environmental station, Oregon state system of higher education, Oregon state college Corvalis, Bulletine series no.25

[2] Akerkar, B. P. 1989 “A Study of the Performance of the CrossflowTurbine”, M.S. thesis, Clemson University, Clemson, SC

[3] L.A. Hamierl, 1960 “The cross flow turbine”, Water power engineering magazine 12.5- 13.

[4] P.Verhaart 1983 “Blade calculation for water turbine of banki type”, Department of mechanical engg. Eindhoven University of Technology.

[5] Shahram Khosrowpanah, Albertson and Fiuzat 1988 “Experimental study of cross flow turbine”, Journal of. Hydraul. Eng. voi.114, pp. 299-314.

[6] Javed A. Chattha, Mohammad S. Khan, Syed T. Wasif, Osama A. Ghani, Mohammad O. Zia, Zohaib Hamid 2010 “Design of a cross flow turbine for a micro-Hydro-power application”. Asme Power Conference, Chicago, IL, USA.

[7] Bilal Abdullah Nasir 2013. “Design of High Efficiency Cross-Flow Turbine for Hydro- Power”, International Journal of Engineering and Advanced Technology. vol.2 pp. 308- 311.

[8] V.C. Desai and N.M Aziz 1994 “Parametric evaluation of cross flow turbine performance”, Journal of. Energy Eng. vol.120 pp. 17-34.

[9] C. B. Joshi, V. Seshadri and S. N. Singh 1995 “Parametric study on performance of the cross-flow turbine”, Journal Energy Eng. 121, 28-45.

[10] Abbas A. Fiuzat and Bhushan P. Akerkar 1991 “Power outputs of two stages of cross flow”, Journal Energy Eng. vol.117 pp. 57-70.

Received on 12.06.2016 Accepted on 24.06.2016

Int. J. Tech. 2016; 6(1): 49-56.

DOI: 10.5958/2231-3915.2016.00008.0