International Journal of Engineering Advanced Research eISSN: 2710-7167 | Vol. 4 No. 3 [September 2022]
Journal website: http://myjms.mohe.gov.my/index.php/ijear
NUMERICAL STUDY OF SHROUDED DIFFUSER WIND TURBINE
Ainaa Maya Munira Ismail1*, Fazila Mohd Zawawi2 and Azahari Mohamad Salleh3
1 2 School of Mechanical Engineering, Faculty of Engineering, University Technology Malaysia, Skudai, MALAYSIA
1 School of Mechanical Engineering, Faculty of Engineering, University of Technology MARA, Johor Branch, Pasir Gudang Campus, Bandar Seri Alam, MALAYSIA
3 Advantage Marine Services (Malaysia), Sdn Bhd, Gelang Patah, MALAYSIA
*Corresponding author: [email protected]
Article Information:
Article history:
Received date : 20 August 2022 Revised date : 14 September 2022 Accepted date : 14 September 2022 Published date : 15 September 2022
To cite this document:
Ismail, A. M. M., Mohd Zawawi, F., &
Mohamad Salleh, S. (2022). NUMERICAL STUDY OF SHROUDED DIFFUSER WIND TURBINE. International Journal of Engineering Advanced Research, 4(3), 82-89.
Abstract: Wind power is extensively assumed to be equal to wind speed as wind blows toward a wind turbine. This implies that even a small speed gain has a huge effect on the quantity of power it can generate. Shrouded diffuser was used by small wind turbines to increase wind speed when there is minimal wind. Hence, this article goal is to maximise the shrouded diffuser physical qualities by studying the flow characteristics. Computational Fluid Dynamic, CFD is utilized as numerical study to increase velocity where shrouded straight diffuser is considered in this investigation. Moreover, bare and shrouded straight diffuser wind turbines capability to produce power at various inlet velocity is evaluated and compared. Results obtained from CFD shows that wind turbine with shrouded straight diffuser increases the velocity and clearly enhanced the power of wind turbine. Thus, CFD analysis produces better outcomes than potentially prohibitively expensive experimental testing.
Keywords: wind turbine, CFD, shrouded straight diffuser wind turbine.
1. Introduction
Renewable energy sources include the sun, wind, rain, tides, waves, and geothermal heat. Since wind power is the most promising renewable alternative, a policy has been created to ensure that its role in energy resources is increased (Ismail, Mohd Ali, Md Isa, Abdullah, Muhammad, et al., 2021). Wind turbine has various sizes, by depending on its applications. Small wind turbines can be used as distributed generation for on-site applications while larger wind turbines are used in wind farms (Basrawi, Ismail, Ibrahim, Idris, & Anuar, 2017). Nowadays, small wind turbine offer a significant amount of alternative power for electrical devices (Harrouz, Colak, & Kayisli, Korhan, 2016). It is commonly installed on parks, suburban homes, or other locations where there is no electrical grid (off-grid) or where the grid has sustainability issues. Electricity output should be as sustainable as possible for off-grid applications (Yildiz & Ekinci, 2018), where the wind speed required to capture more power is lower (M. Keerthana et al., 2012) and more turbulent flow are the two main characteristics that stand out when considering the urban wind system (Paulides, Encica, Jansen, & Lomonova, 2013). A proper small turbine design is also important to consider because it can impact efficiency and energy capture (Ismail, Mohd Ali, Md Isa, Abdullah, & Mohd Zawawi, 2021). However, recent work has concentrated on creating effective and affordable wind turbines for urban settings, which can lessen reliance on fossil fuels and consequently lower greenhouse gas emissions (Dilimulati, Stathopoulos, & Paraschivoiu, 2018). Besides, to increase maximum power generation for small wind speeds, shrouded diffuser is suggested. Innovations to improve wind turbine performance have resulted in the use of ducts around the rotor to augment flow (Göltenbott, Ohya, Yoshida, & Jamieson, 2016). Wind turbines produce less than optimal power at low wind speeds. The mass flow rate that passes through the rotor is increased in the diffuser. This implies that the use of a diffuser is capable of improving wind turbine performance by increasing power efficiency (Riyanto et al., 2019) as it demonstrates the theoretical possibility of achieving a power coefficient approximately twice that of a conventional turbine (Silva et al., 2018). According to (Jafari & Kosasih, 2014), the purpose of adding a diffuser to a wind turbine is to boost the mass flow through the rotor, which will increase the power that can be extracted.
Diffuser creates a sub-atmospheric region at its outlet, which compared to a bare turbine seems to draw more wind through the rotor. Due to the strong vortex that forms behind the broad brim, a low-pressure area attracts more mass flow to the wind turbine inside the diffuser shroud (Ohya &
Karasudani, 2010). Findings by (Watanabe, Ohya, & Uchida, 2019) shows that wind turbine equipped with diffuser significantly increase their power output because its generates power proportionally to the cubed speed of an incoming wind; a small wind acceleration allows a turbine to achieve a significant increase in electricity generation. Hence, wind turbine with brimmed diffuser shrouds appeared to be very encouraging for wind energy generation, particularly in residential and urban areas (Hashem & Hafiz, 2016). Therefore, this article aims to investigate the flow characteristics to maximise the physical properties of the shrouded diffuser. Hence, shrouded straight diffuser is taken into consideration in this investigation, which uses Computational Fluid Dynamics, CFD as a numerical analysis to increase velocity. The ability of bare and shrouded straight diffuser wind turbines to produce power at constant speed is assessed and compared. CFD approach is employed to analyse the wind turbine in order to reduce the time and expense associated with the experimental tests. Numerous models can be used to conduct this CFD method such as inviscid, laminar, k-w model, and spalart allmaras (Khalil, Tenghiri, Abdi, & Bentamy, 2018).
Figure 1: Flow around a wind turbine with brimmed diffuser (Ohya & Karasudani, 2010)
2. Computational Fluid Dynamic, CFD 2.1 Geometry Modelling
Based on the literature, CFD can be used as a potential tool to study the detailed flow field around a wind turbine rotor (M. Keerthana et al., 2012). Therefore, ANSYS Fluent in CFD package is employed to obtain the outcome of flow characteristic of bare and shrouded straight diffuser wind turbines.
2.1.1 Mesh Model
Modelling was designed by using Solid work Software and converted into step file. Then, the geometry is imported into design module as illustrated in Figure 2.
(a) (b)
Figure 2: (a) Bare wind turbine; (b) Shrouded straight diffuser wind turbine
The method by which the spatial discretization of the CFD model is carried out is known as mesh generation where Tetrahedral element discretization forms is the basis of meshing. Surface and volume mesh were generated to obtain the type of meshing element and mesh element size. Both models are mesh with curvature size function and fine sizing as shown in Figure 3.
(a) (b)
Figure 3: Mesh model (a) Bare wind turbine; (b) Shrouded straight diffuser wind turbine
3. Results and Discussion 3.1 Velocity Distribution
The findings demonstrate that the velocity relatively increases at the turbine rotor of a wind turbine with a straight diffuser. Due to the inlet shrouded convergent profile, there is an augment in rotor velocity. Additionally, a notable increase in wake formation behind the diffuser has been noticed, creating a low-pressure area behind the turbine. The torque of the turbine is increased because of the low-pressure area bringing more air to strike the rotor as illustrated in Figure 4.
(a) (b)
Figure 4: Velocity distribution (a) Bare wind turbine; (b) Shrouded straight diffuser wind turbine
3.2 Velocity Vector
The recirculating flow at the shrouded of the straight diffuser wind turbine is observed, causing a turbulent flow field, which is not present in the base line model. By reviewed in Figure 5, the velocity vector captured around the outlet shrouded surface also clearly shown, which is larger in magnitude.
.
(a) (b)
Figure 5: Velocity vector (a) Bare wind turbine; (b) Shrouded straight diffuser wind turbine
3.3 Turbulence Kinetic Energy
The variation in turbulence kinetic energy along the wind turbine is depicted in Figure 6. The term turbulence kinetic energy is basically referring to turbulence intensity. Wake formation has been observed as a result of increased turbulence at the shrouded straight diffuser compared to bare wind turbine. A wake region is visibly seen at the shrouded region of the straight diffuser; the area with the highest intensity of turbulence is found downstream from the diffuser and has an asymmetric flow pattern. The maximum turbulence kinetic energy of a bare and shrouded straight diffuser is 13.362 m2/s2 and 22.426m2/s2, respectively.
(a) (b)
Figure 6: Velocity vector (a) Bare wind turbine; (b) Shrouded straight diffuser wind turbine
3.4 Power Output
The following Table 1 provides the average velocity measured at the wind turbine rotor for various inlet velocities.
Table 1: Power output in various velocity inlet
System Velocity
Inlet 1m/s
Velocity Inlet 3m/s
Velocity Inlet 5m/s
Velocity Inlet 7m/s
Velocity Inlet 9m/s
Velocity Inlet 11m/s
Velocity Inlet 13m/s
Velocity Inlet 15m/s
Bare Wind Turbine 1.34 3.93 5.72 7.57 9.11 11.56 13.63 16.12
Shrouded Straight Diffuser 2.65 7.88 11.45 15.03 18.22 23.12 27.26 32.24
Thus, the power output of wind turbine can be calculated by using the following equation;
𝑃 = 1
2𝜌𝐴𝑉2𝐶𝑝
where Power, P, Air Density, ρ (kg/m3), Rotor Area, A, Overall Rotor Diameter, D, and Wind Velocity, V (m/s).
The power output for both wind turbine is shows in Figure 7. The wind turbine equipped with shrouded straight diffuser is significantly high roughly double the power coefficient compared to bare wind turbine.
Figure 7: Power output for augmented wind turbine
5. Conclusion
The shrouded straight diffuser wind turbine boosts the velocity of air at the turbine rotor. As a result, the velocity increase yield of intensification wind turbine power. Hence, when compared to the bare wind turbine, the shrouded straight diffuser model typically can produce 23.17% more power.
6. Acknowledgement
The authors would like to express thankfulness and gratefully acknowledge to Universiti Teknologi Malaysia, UTM and Universiti Teknologi MARA, UiTM.
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