The ducted tidal turbine models have been developed to utilize the conversion of the kinetic energy on ocean currents. The research in refining the turbine characteristics has been carried out by modifying the turbine’s shape and size. This study investigated flow characteristics in the meridional section of five ducted turbines models for seawater flow with velocity U0 = 1.5 m/s. The ducted turbine design and construction have five different impeller house diameters and fixed inlet and outlet diameters. The potential energy flow theory and experimental data are used to analyze the flow characteristics of the model. The results show that flow velocity in the x-direction at the inlet and outlet cross-section is getting smaller, reducing the impeller house cross section. Each impeller house size reduction increases the flow speed in the impeller house cross-section and also pressure on all other cross-sections tested. In the inlet area, the increased pressure indicates a decrease in speed flow and discharge coefficient value. The discharge coefficient value decreases from CQ = 0.9 at the diameter ratio of dr = 1 to CQ = 0.56 at the diameter ratio of dr = 0.375. The maximum value of power coefficient was determined at dr = 0,61÷0.73 or dr = 0.69 which is equivalent to average internal flow velocity Vr =2.0÷2.6 m/s and the static pressure ps = 97.1÷ 94.4 kPa. At the ratio value of D0/D2 = 0.83, the optimal diameter ratio dropt=0,61÷0.73 is in line with the duct model of case 3 and case 4, but it may be determined solely as for case 4.
The ducted tidal turbine models have been developed to utilize the conversion of the kinetic energy on ocean currents. The research on refining the turbine characteristics has been carried out by modifying the turbine's shape and size. The study of the duct diameter ratio effect on the energy characteristics of the turbine was done in this work. This study was conducted by modifying the duct diameter ratio ̅ with the constant inlet and outlet diameters, D 0 and D 2. The flow conditions are analyzed for five cases of turbines with different shapes and diameters to determine the optimum conditions. The optimum value of the diameter ratio could be obtained at the maximum value of the power coefficient C velocity in the ducted turbine was measured at three turbine sections, namely; the inlet section, the impeller housing section, and the outlet section. The measurement of flow in turbines was carried out at the free stream velocity, U 0 , 1.5 m/s. The power coeffici C P and thrust coefficient C T were calculated based on flow velocity data on the turbine sections for each case. The power coefficient C P reaches the maximum value (Betz limit) at the resistance coefficient, value of the axial induction factor, a, 0.37. These values were founded at a diameter ratio, ̅ , 0.68. thrust coefficient C T reaches the maximum value at K of 3.9, a of 0.52 and ̅ of 0.53. The optimum value of the diameter ratio was founded at ̅ of 0.68.
Abstrak. Pengurangan emisi karbon dioxida secara signifikan sampai dengan 28% pada tahun 2030 menjadi isu penting sehingga diperlukan inovasi dan pemanfaatan energi angin sebagai salah sumber energi baru terbarukan hijau. Ada dua jenis tipe turbin angin dengan selubung (ducted) dan turbin angin aliran bebas (un-ducted). Aplikasi kedua turbin ini pada PLTB akan memberikan performance yang berbeda. Berapa perbedaan nilai parameter-parameter energi pada kedua turbin ini menjadi masih menjadi permasalahan dan fokus penelitian. Penelitian ini dilakukan untuk menentukan perbandingan performance energi dari kedua model turbin tersebut dengan diameter impeller DM= 1 meter dengan menggunakan profil blade NACA 63-412. Penelitian ini dilakukan melalui pengujian di laboratorium pada variasi kecepatan angin 2 – 8 m/s. Nilai momen diperoleh melalui pembebanan bertahap pada prony break sampai putaran mencapai nilai yang telah ditentukan atau dihitung sebelumnya. Hasil penelitian parameter-paremeter energi menujukan bahwa peformance pada turbin angin dengan selubung (ducted wind turbine) lebih tinggi dari turbin angin tanpa selubung (un-ducted wind turbine). Nilai kenaikan daya turbin dengan selubung (ducted wind turbine) untuk kecepatan 2 – 8 m/s berkisar pada nilai Pducted = (0 – 2.5)Pun-ducted, Sehingga dari aspek konversi energy direkomendakian penggunaan turbin angin ducted.
Cavitation is a complex phenomenon of dynamic processes in hydraulic machines that can cause a decrease in energy performance, vibration and damage the blade surfaces. Analysis of cavitation symptoms in hydraulic machines is carried out through cavitation performance studies, namely the relations between energy parameters. Each hydraulic machine has a critical value on a different cavitation performance curve. Therefore, a study of the effect of cavitation changes is needed to determine the working zone of hydraulic machines without cavitation. In this study, cavitation performance analysis was carried out on a waterjet propulsor model with 5 impeller blades and 7 stator blades using experimental methods. The cavitation coefficient was varied at σ = 2.25 to 0.25 by setting and controlling the inlet pressure on the cavitation test rig. The critical point value will be observed at the point where the thrust coefficient decreased to 3.28%. The results showed that cavitation begins at σ = 1, the critical point is obtained at σ = 0.75. From these studies, we find that waterjet must be operated at conditions where is σ > 0.75.
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