Effect of passive flow control on the aerodynamic performance, entropy generation and aeroacoustic noise of axial turbines for wave energy extractor

TLDR: In this paper, the authors investigated the effect of the angle of the slot angle on the entropy generation features around the turbine blade and the aerodynamics noise emission from the turbine airfoil during the normal operation.

About: This article is published in Ocean Engineering.The article was published on 2018-06-01 and is currently open access. It has received 19 citations till now. The article focuses on the topics: Wells turbine & Turbine blade.

Figures

Figure 19 The NACA0015 without and with suction slot at optimum angle under sinusoidal wave with time period 4 second (0.25 Hz) “---without suction slot — 𝜶𝑺𝑺 =0 degree”,“ — 𝜶𝑺𝑺 =10 degrees clockwise A) The hysteretic behavior B) The instantaneous torque coefficient C) The average torque coefficient

Table 7 the value of global entropy generation rate for NACA0015 with suction slot at different position angles under sinusoidal inlet velocity

Figure 10 Comparison between the average torque coefficients for the optimum angles of suction slot with sinusoidal inlet velocity and 𝒇 = 0.167 Hz A) based on Force analysis B) based on velocity analysis.

Figure 4 The validation results A) Measured torque coefficient from reference (Torresi 2007) and calculated torque coefficient from present CFD. B) Measured unsteady in-line force DF from reference (Nomura, Suzuki et al. 2003), (angle of attack= 0 degree) and DF calculated from the present CFD.

Figure 13 The pressure distribution around NACA0015 without slot and with the optimum angles of suction slot under sinusoidal velocity and 𝒇 = 0.167 Hz A) Contours of pressure coefficient B) pressure coefficient at the upper and lower surface

Figure 15 The Sound pressure level in dB for NACA0015 under non-oscillating velocity at a far field receiver located at 35 chord with different slot angle and different angles of attack A) 11.3 degrees B) 12.3 degrees C) 14.4 degrees

Frequently asked questions

Q1. What are the contributions in this paper?

In the following study, the impact of varying the angle for the slot on the 20 performance of Wells turbine in the stall regime was investigated. Furthermore, the first law of 21 thermodynamics and the entropy analysis has been used to examine the effect of the slot angle on 22 the entropy generation features around the turbine blade. Moreover, Investigation of slot angle 23 effect on the aerodynamics noise emission from Wells turbine airfoil during the normal operation 24 and the stall regime is covered in this study. Furthermore, using airfoil of blade turbine with a slot resulted in a reduction of 30 aeroacoustic noise by -21. 

Q2. What are the future works in this paper?

To conclude, future study and research should concentrate on progress the efficiency of 24 first law with a minimize entropy generation, by using numerical algorism [ 137 ] and experimental 25 laboratory studies, to enhance the overall Wells turbine performance under flow control method. 26 In addition, the passive flow control using slot with angle given very promising result for Wells 27 turbine, therefore, it be worth to investigate its effect on other turbine such as water turbine [ 138 ]. 28 Moreover, there are many parameters that can be used future study to reduction the aerodynamics 29 noise such as the number of suction slots, the distance between suction slots, the location of suction 30 25 slots and the angle of suction slots. Therefore, it is very important that to consider to the potential of wave energy in Egypt as the path 3 to minimize fossil fuel usage. 

Q3. What is the purpose of the DBD actuator?

The dielectric barrier discharge (DBD) plasma actuator is applied in the 8trailing edge of the turbine blade in order to improve performance and reduce aerodynamic load. 

Q4. What is the effect of the suction slot on the flow structures?

The suction slot effects directly on 2920the flow structures that located on the end of blade, and then leads to an improvement in the 1separation regime. 

Q5. How much entropy generation rate increased when Reynolds number was increased?

It was observed that, when Reynolds number was 24 increased from 6×104 till 1×105 the total entropy generation rate increased accordingly more than 25 double for tested airfoils. 

Q6. How does the aerodynamic efficiency of a Wells turbine change with the increase of the angle?

the aerodynamic efficiency increases with the 13 increase of the angle of attack or the flow coefficient up to an appointed value, after that it 14 decreases. 

Q7. What is the important reason behind the improvement in the cases for the ss equal?

5The most important reason behind the improvement in the cases for the 𝛼𝑠𝑠 not equal to 0 6 more than the cases for the 𝛼𝑠𝑠 equal to 0 due to the flow layers and pressure distribution around 7 the aerofoil. 

Q8. What are the parameters that can be used to reduce the aerodynamics noise?

there are many parameters that can be used future study to reduction the aerodynamics 29noise such as the number of suction slots, the distance between suction slots, the location of suction 3025slots and the angle of suction slots. 

Q9. What is the effect of the passive flow control method on the aerodynamics of the Wells?

23To conclude, future study and research should concentrate on progress the efficiency of 24first law with a minimize entropy generation, by using numerical algorism[137] and experimental 25laboratory studies, to enhance the overall Wells turbine performance under flow control method. 

Q10. What is the main challenge facing the wave energy extraction devices with oscillating water?

The main challenge facing the wave energy extraction devices with oscillating water 2column system is to find an economical and efficient means of converting bidirectional flow from 3the waves motion to unidirectional rotary motion for driving electrical generators [1-3], as seen in 4Figure 1 A. A self-rectifying air turbine such as Wells turbine, see Figure 1 B, [4-9] can be used 5 to extract the energy from the oscillating air column [10-15]. 

Q11. What is the reason behind the improvement in the cases with ss not equal to 0.?

2As it was mentioned above, the flow layers and pressure distribution around the aerofoil 3 are the most important reason behind the improvement in the cases with 𝛼𝑠𝑠 not equal to 0. 

Q12. What are the methods of flow control to achieve separation postponement?

Methods of flow control to achieve separation postponement, lift enhancement 1and drag reduction have been considered in these studies. 

Q13. What is the effect of the variable thickness blade on the lift and drag coefficients?

Such studies have demonstrated that 2adding suction slot could modify the pressure distribution over an airfoil surface and have an 3essential impact on both the lift and drag coefficients [58-63]. 

Q14. What is the agreement between the experimental data and the calculated torque coefficient?

A shows a very good agreement 24between the experimental data for the torque coefficient from reference [112, 135, 136] and the 25 calculated torque coefficients at Reynolds number equals 2x105 from CFD results.