MDSRC Proceedings, November, 2015 Wah/Pakistan

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1 CFD ANALYSIS OF A LOW HEAD MICRO HYDRO KINETIC TURBINE FOR NORTHERN AREAS OF PAKISTAN Mumtaz Ahmad 1, M. Ihsan Ul Haq 1, Naveed Hussain 2, M. Tayyab Muneeb 3, Ahmad Hussain 1, Azeemuddin 1 1 Department of Mechanical Engineering Nazeer Hussain University, Karachi-75950, Pakistan m.ahmad@nhu.edu.pk 2 Karachi Institute of Power Engineering, Karachi-75950, Pakistan 3 NFC Institute of Engineering and Fertilizer Research, Faisalabad, Pakistan ABSTRACT Pakistan s economic growth is highly affected by severe energy shortage in the past few decades. One of the major reasons for this crisis is being dependent upon fossil fuels. Although hydro power is cheapest available renewable energy source, yet it requires a huge initial capital investment as well as long span of time. Low heads are commonly available in northern areas of Pakistan which can be utilized to meet the energy demands in those areas. In addition, low head turbines require less initial capital investment and time for fabrication and installation. Therefore, Micro-hydro turbine is a viable option to tackle the current energy crisis in remote areas of Pakistan. In this paper FEA analysis for directional deformation, equivalent elastic strain, shear stress and total deformation of the blades of turbine is carried out. The CFD analysis is carried out for single blade pressure distribution at jet angles from 5 to 20 at a fixed value of low head of 50 feet. Keywords: Micro-hydro turbine, CFD analysis, cross flow turbine, low head 1. INTRODUCTION Pakistan is facing severe energy crisis soaring to a height of more than 6000MW. Power theft, transmission losses, depletion of fossil fuels, short term planning and policies, underdeveloped and poorly managed infrastructure and rapid demand growth has led to severe electric crisis. Industries have shut down due to low electric supply and daily life of general public is affected too. Moreover, 38 % of Pakistan's population remains without access to electricity. Having ample hydropower potential 80% of which are still to be utilized, Pakistan also needs to pay attention on small scale projects to cope with the current crisis [1]. Cross-Flow Hydraulic Turbine is the most widely used turbine for small scale micro-hydro power plants in the world [2]. Pakistan is located between and latitude (North) and 61 and longitude (East) in Asia. Topography of Northern areas of Pakistan provides a fine location to exploit the natural flow of water for energy generation by installing micro hydro turbines. Moreover, its convenient manufacturing, portability and easy maintenance make it an encouraging approach for manufacturers as well as investors. 1.1 Current Energy Scenario of Pakistan Pakistan is divided into three major geographic areas northern highlands, Indus plain, and Baluchistan Plateau. Depending on the topography different powers resources are being employed to generate electricity. The main energy 1

2 resources of Pakistan include Fossil fuels, Hydro and Nuclear energy. Among the fossil fuels, coal is least used for electricity production. Coal found in Pakistan is of inferior quality and electricity generation through coal is an expensive process. It is mostly used to run industries, locomotives and steam ships. It is not feasible to use it for domestic electricity production due to limited resources and inferior quality. Oil and Gas are major components of Pakistan's energy mix meeting over 64% of energy needs. The large dependency upon fossil fuels for generation of electricity is one of the major causes of poor economic growth of the country. Apart from the economic effects, the environmental pollution is also increasing due to emissions from the fossil fuel based power plants. It costs Rs to produce a unit of electricity from fuel, while electricity from gas costs Rs. 5-6 per unit [4]. Gas reserves are declining sharply and diversion of gas to transport sector from power generation in recent years has worsen the crisis. Country cannot afford to keep on increasing the production from oil as availability of gas is declining. Therefore, other options should to be considered on urgent basis. Nuclear power makes a small contribution in power production in Pakistan. The Pakistan atomic energy commission is responsible for nuclear power generation in the country. KANUPP was the first nuclear power plant made by PAEC in Karachi, Sindh. It started its production in The second unit for nuclear power production is Chashma 1. It started up in 2000 and has designed life span of 40 years. Nuclear power production contributes only 4% to the total power generation in the country [3]. 1.2 Hydro Power in Pakistan Hydro-power is one of the cheapest ways to harness energy. Pakistan has potential of GW from hydro power. Unfortunately, Pakistan is only utilizing 20% of its total hydro-power generation capacity [3]. Traditionally the stress has only been laid upon 2 dams i.e., Tarbela and Mangla. Their production has decreased over the time due to poor maintenance and negligence of the authorities. The construction of large dams for power generation and water storage are highly affected by lack of investment, policies and political will. About 70% population of Pakistan lives in scattered rural areas, it s an arduous task to provide electricity through national grid to them. Pakistan should consider standalone projects to avoid long transmission lines stretching from national grid to these scattered rural areas. Small scale projects should be initiated as per climate conditions, topography and requirement of localities. Considering the mountainous topography of northern areas, it is hard to install and keep maintenance of transmission lines. This topography suits micro-hydro turbines to meet the needs to local people. Population of northern areas of Pakistan is 1.8 million.local production will lessen the burden on national grid and provide the locality with cheap, continuous and environmental friendly power production. A total of ( ) feasible sites are available for 50 MW or more electric production projects in northern areas while (814+71) feasible sites are available for small scale projects of less than 50 MW productions [4]. This paper presents FEA analysis for directional deformation, equivalent elastic strain, shear stress and total deformation of the blades of turbine. CFD analysis is also carried out for single blade pressure distribution at jet angles 2

3 from 5 to 20 at a fixed value of low head. 2. LITERATURE REVIEW The cross-flow turbine has been in use for about a hundred years ago, when it was invented. The cross flow-impulse turbine, also known as Banki-Michell turbine is named after its inventors and Osberge, the company that is producing these for over 5 decades. This is used for a variety of pressure heads overlying those of Pelton, and other turbines. It has the ability to operate with discharges between 20litres/sec and 10m 3 /sec. It can operate between 1m and 200m of head. The efficiency is practically constant for a wide range of flows and heads but it is lower than that of conventional turbines. Research and experiments in the field of turbines have resulted in huge improveements in the design of cross flow turbines. Khosrowpanah [5] led a study by varying the quantity of blades, by changing the diameter of the nozzle entry arc and runner under flow/ head variations on the efficiency of cross flow turbines. The outcomes of this experiment determined that the unit expulsion increases with nozzle entry arc and runner aspect ratio with a decline in the number of blades. As the nozzle entry arc increased from 58 to 90, the efficiency of the Banki Mitchel turbine proved to be the maximum. The optimum number of blades was found to be 15 provided that runner diameter is 12 Inches. Nakase et al. [6] changed the shape of the nozzle in his experiments. The blade inlet angle was set to be 30 degrees while the outlet angles was set to be 90 degrees and the outer diameter of the runner was 315mm with the runner having 26 blades. After classifying the flow through the both stages Nakase et al. [6] came to the conclusion that there are actually two kinds of flow in this turbine. One being crossed flow, which flows through two stages, while the other one is uncrossed flow that only flows through the stage one. The crossed flow compromises key share of the flow that actually rises to flow reduction triggering the flow to accelerate from first stage through the second. Nakase et al. [6] finally, concluded that the appropriate value of nozzle to throat width ratio (So/Rλ) is approximately 0.26 but it slightly varies with the nozzle entry arc. 3. DESIGN AND ANALYSIS The design of turbine casing along with jet cross model using Pro-E software is shown in Figure 1. Simulations are carried to find out flow distribution of water inside the casing, deformation in terms of stress distribution and strains on the blades of the runner using ANSYS Fluent CFD Software. Figure 1: Pro-E model of final turbine runner assembly The CFD analysis of the turbine for different angles of attack of nozzle at constant head of 50 feet is carried out on the whole turbine runner blades as well as on single blade. The whole turbine runner blades analysis focuses on calculating stresses and strains acting on the blades. Whereas a single blade analysis is 3

4 carried out for pressure distribution and jet splash leakages. The modeled turbine was analyzed for deformation with custom axis. It was analyzed that during the operation of the turbine maximum and minimum deformation are produced on the upper and lower tips of the blades respectively as shown in Figure 2. produced are along the top edges of the blades attached with side discs as shown in Figure 4. Figure 4: Maximum shear stress occurs at tips of blades Figure 2: Directional stress deformation on tips of blades. The elastic strain was analyzed using ANSYS software and it was found the very low strains are being produced in turbine. The maximum strains are produced on the mid-lower section of blade turbines, while minimum strains are produced on the runner and blade tips as shown in Figure 3. CFD analysis for total deformation on the turbine blades show that the maximum deformation occurs on the central top edge of the blades of turbine as shown in Figure 5. Figure 5: Total stress deformation Figure 3: Equivalent elastic strain distribution on turbine blades The analysis for shear stress developed in the turbine has also been carried out. The only significant shear stresses The complete velocity profile of the turbine model is shown in Figure 6. However, the detailed 3D analysis has been carried out on the single blade of the turbine. The design and model of the blade of turbine after meshing are shown in Figure 7 and Figure 8 respectively. The angle of attack of the jet was changed gradually and CFD analysis was done for 4

5 the range of 5 to 20 at a fixed head. It is evident from Figure 9 to Figure 12 that the magnitude of pressure vector is high at the tip of the blade as compared to the rest. In single blade analysis, pressure distribution tends to increase with increasing jet angle. AT an angle of more than 20, water jet tends to splash more as it hits the upper edge of the blade, and consequently pressure decreases and so the deformation. This is because the flow energy of the jet decreases due to splash leakage. Maximum jet splash can be seen at the blade tips in the Figure 13 and Figure 14. Figure 8: Single blade 3D geometry and meshing with fluid domain. Figure 6: Complete velocity profile inside the casing of turbine. Figure 9: Pressure (MPa) vectors distribution at jet angle of 5 Figure 7: Single blade design geometry modelled. Figure 10: Pressure (MPa) vectors distribution at jet angle of 10 5

6 Figure 11: Pressure (MPa) vectors distribution at jet angle of 15 Figure 12: Pressure (MPa) vectors distribution at jet angle of 20 Figure 13: Velocity (m/s) contour profile at jet angle of 20 Figure 14: Velocity (m/s) streamlines contour at jet angle of RESULTS AND CONCLUSION The CFD analysis of the blades of turbine is carried out to find out their ability to withstand the pressure of the jet during its realistic operation and before manufacturing. The directional deformation acting on the tip of the blade has maximum and minimum values of mm and mm respectively. Whereas, maximum and minimum values of equivalent elastic strain are mm and mm respectively, which is negligible and therefore, safe. The maximum value of shear stress acting on the blades is MPa. The maximum value of total stress deformation on the blades is MPa. The flow energy of the jet decreases due to the splash leakage. Effect of jet angle on the development of pressure on the blade is shown in graph as shown in Figure 15. The values of maximum pressure developed on turbine blade at jet angles of 5,10,15 and 20 are MPa, MPa, MPa and MPa respectively. 6

7 Pressure (MPa) MDSRC Proceedings, November, 2015 Wah/Pakistan Jet angle (degrees) Figure 15: Effect of jet angle on the development of pressure on the blade Therefore, this turbine design is applicable to run in Northern areas of Pakistan, where the head of approximately 50 feet is easily available. Moreover, the additional benefits of micro hydro kinetic turbine include reduction in the expenditure on transmission lines for providing electricity to far flung areas in Northern areas of Pakistan. [4] Hydro Potential in Pakistan. A Report of Pakistan Water and Power Development Authority, November 2011, pages1-5, ( wrpotialapril2011.pdf); (Accessed on June 4, 2015) [5] S.Khosrowpahan, Experimental Study of the Crossflow Turbine, Ph.D. Dissertation, Colorado State University, 1984, Fort Collins, CO. [6] Y.Nakase, J.Fukutomi, T.Wantanabe, T.Suessugu, and T.Kubota, A study of Crossflow Turbine, Small Hydro Power Fluid Machinery, pp , REFERENCES [1] Waqas Nawaz, Maryum Masood, Bilal Arif, Energy Crisis Mitigation through available resources in Pakistan in Proceedings of International Conference on Engineering & Emerging Technologies-December 2014, Islamabad. [2] A.H. Elbatran, O.B. Yaakob, Yasser M. Ahmed and H.M. Shabara Operation, performance and economic analysis of low head micro-hydropower turbines for rural and remote areas: A review, Renewable and Sustainable Energy Reviews, vol. 43, pp , [3] S.Z. Farooqui, Prospects of renewables penetration in the energy mix of Pakistan, Renewable and Sustainable Energy Reviews, vol. 29, pp ,