Papers by Dr. Usman Latif
Computational analysis of inverted flag-based energy harvester in the wake of cylindrical bluff body
Ocean Engineering
In the current study, the penalty immersed boundary method (PIBM) is used to numerically analyze ... more In the current study, the penalty immersed boundary method (PIBM) is used to numerically analyze the flapping motion of an inverted flag, placed behind a bluff body using two-dimensional viscous flow. Direct numerical simulations (DNS) are carried out by changing the Reynolds number, bending stiffness, and streamwise gap (which represents the distance from the bluff body to the fixed end of the flag) behind the inverted D-shape cylinder to find their impact on the peak-to-peak amplitude, flapping frequency of the flag. The optimal values of the stated parameters are determined and explained in how the change in geometric and flow parameters affects the flapping behavior which has an ultimate impact on energy output. The addition of a bluff body caused the high strain due to higher bending modes and curvature in the flag. It is also shown that the alternating vortical flow structures have a strong influence on the dynamical behavior of the inverted flag placed inside the wake region of an inverted D-shape cylinder. Relationships between flow velocity, streamwise gap, and the flag's bending rigidity highlight consistent trends for the enhancement of energy production. Additionally, the lateral position of an inverted flag and its effect on vorticity and energy harvesting is discussed in detail with their power spectra to find the maximum amplitude and corresponding drag force. This research would help in concluding the optimal parameters of the inverted flag for the highest energy generation behind the bluff body.
Impact of solid and hollow bluff bodies on the performance and dynamics of flag-based energy harvester
Sustainable Energy Technologies and Assessments
This study investigates the energy harvesting potential of the wake of different bluff bodies usi... more This study investigates the energy harvesting potential of the wake of different bluff bodies using a piezoelectric membrane. Both hollow and solid C-shaped cylinders with similar dimensions in normal and inverted orientations are placed upstream of the membrane as a kinetic source of energy. A series of water channel tests are performed by varying stream-wise gap (x*) 0.5 ≤ x* ≤ 4.0 between the cylinder and membrane and flow velocity (V) 0.12 ≤ V ≤ 0.26 m/s. The instability region is expanded remarkably by using different cross-sections. Different flapping modes are observed, including biased, intermittent, and continuous. It is shown that the time-mean wake fluctuates with changes in the cross-section of the bluff body and has a substantial influence on the energy harvesting efficiency and dynamical behaviors of the membrane in terms of peak-to-peak oscillation amplitude and flapping frequency. A threshold flow velocity of 0.2 m/s for continuous energy harvesting is defined for all bluff bodies. The highest electrical energy is obtained at a flow velocity of 0.26 m/s and 2.5 diameters downstream from the hollow C-shaped bluff body when placed in an inverted orientation. A comparison of all the configurations of the bluff bodies indicates that the hollow C-shaped bluff body in inverted orientation produces the strongest wake, which results in a 36 % increase in flapping amplitude and a 35 % improvement in harvested power for the piezo-membrane based energy harvester compared to the baseline case (a solid C-shape).
Wake flow effects on the energy harvesting characteristics of piezoelectric tandem flags
INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2020, 2022
In this study, we experimentally investigate the effects of the interaction of piezoelectric flag... more In this study, we experimentally investigate the effects of the interaction of piezoelectric flags in the tandem configuration on energy harvesting efficiency. The flags are placed in wake flow behind the bluff body and their flapping behaviors are examined. The experiments are performed in a low-speed water tunnel by varying the flow velocity and streamwise gap behind an inverted C-shape cylinder to analyze the effect of wake flow on amplitude, flapping frequency, and harvested power by the piezoelectric flags. Threshold values for energy harvesting of the streamwise gap and freestream velocity are found to be the same for both flags i.e. 1.5 and 0.18m/s, respectively. While analyzing the dynamical behaviors of the flags, inverted drafting phenomenon is observed in flags: the flapping amplitude of the rear flag is increased by excitation from the vortices and wake of the front flag. This kind of interaction helps out in boosting the energy harvesting efficiency based on the random excitations with high amplitude of rear flag. Results show, as the streamwise gap in-between the flags changes, the influence of the front flag on downstream flag alters and dynamical behavior of front flag show variation when the distance between bluff body and front flag changes. The highest power is also obtained for the rear flag at streamwise gap equals to 1.75 and freestream velocity of 0.26m/s. The tandem configuration produces 216% more power and remarkably improved the energy harvesting efficiency as compared to the single flag energy harvester.
Parametric aerodynamic and aeroelastic study of a deformable flag-based energy harvester for powering low energy devices
Energy Conversion and Management
Numerical analysis on energy harvesting effectiveness of staggered piezoelectric flags
INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2020
The numerical study of staggered arrangement of the flags is studied in this work. In this comput... more The numerical study of staggered arrangement of the flags is studied in this work. In this computational model, a piezoelectric flag is placed behind the bluff body as it mimics a fish behind an obstacle. The effect of bluff body on the dynamics of the staggered arrangement of the flag has not been studied yet. In the computational model, the fluid flow equations are solved by using Direct Numerical Simulation (DNS) and the dynamics of the flags is explored using penalty-immersed boundary method. The span- and stream-wise distances are varied and the behavior of the vortex shedding from the downstream flag is investigated at these span- and stream-wise distances. The results show that the in-phase and out-of-phase motion of the flag and constructive-destructive behaviors of the vortices leaving the upstream flag has affected the drag on the downstream flag, which in turns effects the energy harvesting performance of the downstream flag. The voltage generation capability of flag depends on the drag and the induced deformation due to vortex-flag interaction. Numerical Simulations indicate that high energy harvesting efficiency is achieved over a range of stream- and span-wise distances and there is higher value of voltage generation when there is lock in between vortex sheet fluctuations and flag vibration. Large amplitude of oscillations and higher bending of the flag correspond to promising energy harvesting efficiency of the flag. The results show that the voltage generation of the piezoelectric material is increased irrespective of the span-wise distance for specific arrangements.
Ocean Engineering, 2023
In the current study, the penalty immersed boundary method (PIBM) is used to numerically analyze ... more In the current study, the penalty immersed boundary method (PIBM) is used to numerically analyze the flapping motion of an inverted flag, placed behind a bluff body using two-dimensional viscous flow. Direct numerical simulations (DNS) are carried out by changing the Reynolds number, bending stiffness, and streamwise gap (which represents the distance from the bluff body to the fixed end of the flag) behind the inverted D-shape cylinder to find their impact on the peak-to-peak amplitude, flapping frequency of the flag. The optimal values of the stated parameters are determined and explained in how the change in geometric and flow parameters affects the flapping behavior which has an ultimate impact on energy output. The addition of a bluff body caused the high strain due to higher bending modes and curvature in the flag. It is also shown that the alternating vortical flow structures have a strong influence on the dynamical behavior of the inverted flag placed inside the wake region of an inverted D-shape cylinder. Relationships between flow velocity, streamwise gap, and the flag's bending rigidity highlight consistent trends for the enhancement of energy production. Additionally, the lateral position of an inverted flag and its effect on vorticity and energy harvesting is discussed in detail with their power spectra to find the maximum amplitude and corresponding drag force. This research would help in concluding the optimal parameters of the inverted flag for the highest energy generation behind the bluff body.
Synergistic analysis of wake effect of two cylinders on energy harvesting characteristics of piezoelectric flag
Renewable and Sustainable Energy Reviews
In this study, the effect of asymmetric wake flow regime of two side-by-side cylindrical bluff bo... more In this study, the effect of asymmetric wake flow regime of two side-by-side cylindrical bluff bodies on power output is experimentally examined by using a piezoelectric flag. Different synchronization modes of the flag with wake flow are observed. It is demonstrated that the streamwise gap between the flag and cylinders (G x), and the center-to-center gap between cylinders have a significant impact on the flag's dynamical behavior that results in a fluctuation in the power output of the piezoelectric flag. The levels of output power are analyzed by varying the G x and the cross-stream or lateral gap (N/d) between the two cylinders. N/d values from 1.0 to 2.0 for different values of G x (2.0 ≤ G x ≤ 4.0) are experimentally tested. The comparison of the flapping response at each point is made to ascertain the impact of the harvester's dynamic behavior on the output energy. The power generated at each point is recorded for all cases and a comparative analysis is made to find the optimal configuration. Limited research is conducted in the past to enhance the energy output by using the bluff body with the improved wake dynamics. Hence, two cylinders are employed in a uniform flow and crosswise gap between cylinders is varied to change the characteristics of the wake region. The cylinder arrangement with N/d = 1.0, shows continuous oscillations and higher output power persisting for 2.0 ≤ G x ≤ 4.0. The monotonic rise in power output is observed till G x = 4.0. The stated configurations with N/d = 1.0 gives a significant advantage over a singlecylinder-based energy harvester as a kinetic source of fluid energy harvester from the flowing fluid. The output power became almost doubled with an increase of 95% approximately using side-by-side arrangement.
Dr. Usman Latif, 2023
Extensive wind tunnel experiments were performed to find the optimal and most influential paramet... more Extensive wind tunnel experiments were performed to find the optimal and most influential parameters for energy harvesting from piezoelectric membranes (thin elastic cantilevered plates), herein called flags. Four different piezoelectric flags were tested in conjunction with the seven different bluff bodies at various wind speeds and streamwise gaps between the bluff body and flag. Stiffness of the flags was also varied along with its length to assess the impact on harvested power. Various flapping modes are observed for different flags which correspond to the amount of harnessed power. The results revealed that altering the stiffness of flag can produce an increase of 29 and 31 times in power generation for long and short flags, respectively. It was found that the 120-degree bluff body produced the largest power with the capability to generate a strong wake region. Further analysis of the best performing flag (short and stiff) for various bluff bodies shows a remarkable increase of 661.2 % in generated power. This membrane shows rhythmic periodic flapping with higher modes of deformation in comparison to its other flag counterparts. These alternate flags show out-of-plane and twisting motion which wastes strain energy and causes a cancelation effect, reducing total energy output. The results show that in designing an efficient and reliable energy harvester, the flag's stiffness and length as well as the shape of the bluff body play an important role. Furthermore, in comparison with the flutter phenomenon (i.e. a dynamic instability of the flag in the absence of a bluff body), the results with a bluff body demonstrate that higher energy generation can be achieved at a lower wind speed, thus paving the way for small and practical energy harvesting devices specifically in remote areas.
Dr. Usman Latif, 2023
In this study, the effect of asymmetric wake flow regime of two side-by-side cylindrical bluff bo... more In this study, the effect of asymmetric wake flow regime of two side-by-side cylindrical bluff bodies on power output is experimentally examined by using a piezoelectric flag. Different synchronization modes of the flag with wake flow are observed. It is demonstrated that the streamwise gap between the flag and cylinders (G x), and the center-to-center gap between cylinders have a significant impact on the flag's dynamical behavior that results in a fluctuation in the power output of the piezoelectric flag. The levels of output power are analyzed by varying the G x and the cross-stream or lateral gap (N/d) between the two cylinders. N/d values from 1.0 to 2.0 for different values of G x (2.0 ≤ G x ≤ 4.0) are experimentally tested. The comparison of the flapping response at each point is made to ascertain the impact of the harvester's dynamic behavior on the output energy. The power generated at each point is recorded for all cases and a comparative analysis is made to find the optimal configuration. Limited research is conducted in the past to enhance the energy output by using the bluff body with the improved wake dynamics. Hence, two cylinders are employed in a uniform flow and crosswise gap between cylinders is varied to change the characteristics of the wake region. The cylinder arrangement with N/d = 1.0, shows continuous oscillations and higher output power persisting for 2.0 ≤ G x ≤ 4.0. The monotonic rise in power output is observed till G x = 4.0. The stated configurations with N/d = 1.0 gives a significant advantage over a singlecylinder-based energy harvester as a kinetic source of fluid energy harvester from the flowing fluid. The output power became almost doubled with an increase of 95% approximately using side-by-side arrangement.
AIP, 2022
Immersed boundary method, fluid-structure interaction, wake analysis, dynamic analysis, energy ha... more Immersed boundary method, fluid-structure interaction, wake analysis, dynamic analysis, energy harvesting.
Elsevier Ltd, 2023
This study investigates the energy harvesting potential of the wake of different bluff bodies usi... more This study investigates the energy harvesting potential of the wake of different bluff bodies using a piezoelectric membrane. Both hollow and solid C-shaped cylinders with similar dimensions in normal and inverted orientations are placed upstream of the membrane as a kinetic source of energy. A series of water channel tests are performed by varying stream-wise gap (x*) 0.5 ≤ x* ≤ 4.0 between the cylinder and membrane and flow velocity (V) 0.12 ≤ V ≤ 0.26 m/s. The instability region is expanded remarkably by using different cross-sections. Different flapping modes are observed, including biased, intermittent, and continuous. It is shown that the time-mean wake fluctuates with changes in the cross-section of the bluff body and has a substantial influence on the energy harvesting efficiency and dynamical behaviors of the membrane in terms of peak-to-peak oscillation amplitude and flapping frequency. A threshold flow velocity of 0.2 m/s for continuous energy harvesting is defined for all bluff bodies. The highest electrical energy is obtained at a flow velocity of 0.26 m/s and 2.5 diameters downstream from the hollow C-shaped bluff body when placed in an inverted orientation. A comparison of all the configurations of the bluff bodies indicates that the hollow C-shaped bluff body in inverted orientation produces the strongest wake, which results in a 36 % increase in flapping amplitude and a 35 % improvement in harvested power for the piezo-membrane based energy harvester compared to the baseline case (a solid C-shape).
Experimental hydrodynamic investigations on the effectiveness of inverted flag-based piezoelectric energy harvester in the wake of bluff body
Ocean Engineering, 2022
The flapping motion and energy harvesting performance of an inverted flag in the wake of a bluff ... more The flapping motion and energy harvesting performance of an inverted flag in the wake of a bluff body are experimentally studied. The experimental measurements are carried out by changing the bending rigidity, streamwise gap (which represents the distance from the bluff body to the tip of the flag), and Reynolds number to explore their impact on the flapping dynamics and power generated by the piezoelectric flag. The optimal values of the Reynolds number, bending rigidity, and streamwise gap are determined based on the power generated. Variation in the flapping modes ranging from continuous to deflected mode is observed. The results show that the inverted flag having a high peak-to-peak amplitude is preferred for piezoelectric energy harvesting as it produces high strain energy. It is also demonstrated that the vortices shed by the upstream bluff body have a strong effect on the flapping amplitude of the downstream inverted flag. This research would help in determining the most effective streamwise position of the inverted flag behind the bluff body and bending rigidity for generating voltage at low Reynolds numbers.
Experimental investigation of energy harvesting eel in the wake of bluff body under ocean waves
Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, 2020
Investigation of the energy harvesting from deep water waves by using flexible piezoelectric eel ... more Investigation of the energy harvesting from deep water waves by using flexible piezoelectric eel in a controlled environment is studied. Energy harvesting potential is examined as a function of streamwise distance from the fixed cylinder and spanwise gap along with the cylinder at different wave conditions. Output voltage and eel flapping behavior are dependent on cylinder vortices caused by local wavelength and wave amplitude. Maximum energy is harvested when the eel is placed near to the surface caused by high flapping amplitude and frequency. Similarly, at greater depth low flapping amplitude is observed resulting in small output voltage. Maximum output voltages are found at the shorter wavelength and at a streamwise distance of gx = 1.25 (where gx is the ratio of spacing “S” between cylinder and eel to the diameter of cylinder “D”) for all spanwise gaps along with the cylinder and minimum voltages are calculated at a longer wavelength and streamwise distance gx = 0.75. An increa...
Hydrodynamic energy harvesting analysis of two piezoelectric tandem flags under influence of upstream body’s wakes
Applied Energy, 2021
Abstract In this study, the effects of the interaction of piezoelectric flags in the tandem confi... more Abstract In this study, the effects of the interaction of piezoelectric flags in the tandem configuration on energy harvesting in a wake flow are experimentally investigated. The flags are placed behind the bluff body and their flapping behavior is examined in terms of the flapping frequency and amplitude (peak to peak motion). The experiments are performed in a low-speed water tunnel by varying the flow velocity and streamwise gap behind an inverted C-shape cylinder to determine the influence of wake flow on the oscillating amplitude, flapping frequency, and harvested power by the piezoelectric flags. Threshold values for energy harvesting of streamwise gap and water speed are found to be the same for both flags, 1.5 and 0.18 m/s, respectively. The results show that inverted drafting is observed in flags in which the flapping amplitude of the rear flag is increased by excitation from the vortices and wake of the front flag. This interaction boosts the energy harvester efficiency based on the flapping frequency and the random excitations with high amplitudes. It is observed that as the streamwise gap in-between the flags changes, the influence of the front flag on downstream flag alters, and dynamical behavior of front flag show variation when the distance between bluff body and front flag varies. The highest power is also obtained for the rear flag at a gap of 1.75 and water speed of 0.26 m/s. The tandem configuration produces 116% more power and significantly improves the energy harvesting efficiency as compared to the single flag energy harvester.
Experimental electro-hydrodynamic investigation of flag-based energy harvesting in the wake of inverted C-shape cylinder
Energy, 2021
Abstract Series of water tunnel experiments are performed to study the improvement in energy harv... more Abstract Series of water tunnel experiments are performed to study the improvement in energy harvesting by vortex-induced vibrations. Inverted C-shape cylinders with different cut angles are placed in the uniform fluid flow and electrical energy is harvested using the undulating behavior of the piezo-flag in the downstream vortices. Experimental results demonstrate different flapping modes like poorly and optimal coupling with the wake flow. It is also showed that the streamwise gap and flow speed have a significant impact on the amplitude and flapping frequency, which results in the variation of the energy output of piezo-flag. The results indicate that the highest gain in output power is 66% for an inverted C-shape cylinder with a 120° cut angle compared to a circular cylinder performance. For each cylinder and flow velocity, it is also observed that there exists a critical streamwise gap for which vortex shedding does not produce any energy using piezo-flag due to poor coupling with wake flow. The results show that there is no significant difference in the performance of circular and 60° inverted C-shape cylinders regarding energy harvesting. However, changing the shape and cut angle leads to a remarkable increase in the flapping amplitude and its growth rate along with the dominant frequency. Particle Image Velocimetry (PIV) experimentation also endorses the results as wake dynamics is in good agreement with the energy efficiency improvement. Therefore, a 120° cut angle configuration holds a vivid preeminence over a circular cylinder as the kinetic source of a fluid energy harvester. The present study contributes effectively to harvesting energy from impinging vortices by tuning the streamwise gap, flow velocity, and cut angle of the inverted C-shape cylinder.
Journal of Applied Mechanical Engineering, 2016
Offshore structures such as boats, ships, oil rigs etc. are under continuous wave loading. These ... more Offshore structures such as boats, ships, oil rigs etc. are under continuous wave loading. These waves exert pressure on the structure which in turn produces stresses in them. These waves can strike structure from any direction and it is very difficult to calculate the pressure exerted by the waves analytically as the shape of the offshore structures is rather complex. The pressures and associated stresses and buckling caused by the striking waves are harmful to the structure, and may lead to their failure. Keeping in view the above scenarios, the column of an offshore oil platform was designed on the basis of hurricane's history of Arabian Sea. The normal and worst sea environment conditions were kept in mind while designing the column and its subsequent analysis was made on the basis of stress and buckling in this study. After analyzing the structure, it is known that the offshore column design is safe for particular sea state. The factor of safety (fos) was 1.90 and 1.77 for the normal and worst conditions, respectively. The pressure was decreased with the increase in wave frequency, while increased with the increase in wave amplitude. Further, buckling modes of extraction were in the range of 1.23 to 1.59.
AIP, 2022
In this study, we experimentally investigate the effects of the interaction of piezoelectric flag... more In this study, we experimentally investigate the effects of the interaction of piezoelectric flags in the tandem configuration on energy harvesting efficiency. The flags are placed in wake flow behind the bluff body and their flapping behaviors are examined. The experiments are performed in a low-speed water tunnel by varying the flow velocity and streamwise gap behind an inverted C-shape cylinder to analyze the effect of wake flow on amplitude, flapping frequency, and harvested power by the piezoelectric flags. Threshold values for energy harvesting of the streamwise gap and freestream velocity are found to be the same for both flags i.e. 1.5 and 0.18m/s, respectively. While analyzing the dynamical behaviors of the flags, inverted drafting phenomenon is observed in flags: the flapping amplitude of the rear flag is increased by excitation from the vortices and wake of the front flag. This kind of interaction helps out in boosting the energy harvesting efficiency based on the random excitations with high amplitude of rear flag. Results show, as the streamwise gap in-between the flags changes, the influence of the front flag on downstream flag alters and dynamical behavior of front flag show variation when the distance between bluff body and front flag changes. The highest power is also obtained for the rear flag at streamwise gap equals to 1.75 and freestream velocity of 0.26m/s. The tandem configuration produces 216% more power and remarkably improved the energy harvesting efficiency as compared to the single flag energy harvester.
AIP, 2022
The numerical study of staggered arrangement of the flags is studied in this work. In this comput... more The numerical study of staggered arrangement of the flags is studied in this work. In this computational model, a piezoelectric flag is placed behind the bluff body as it mimics a fish behind an obstacle. The effect of bluff body on the dynamics of the staggered arrangement of the flag has not been studied yet. In the computational model, the fluid flow equations are solved by using Direct Numerical Simulation (DNS) and the dynamics of the flags is explored using penalty-immersed boundary method. The span- and stream-wise distances are varied and the behavior of the vortex shedding from the downstream flag is investigated at these span- and stream-wise distances. The results show that the in-phase and out-of-phase motion of the flag and constructive-destructive behaviors of the vortices leaving the upstream flag has affected the drag on the downstream flag, which in turns effects the energy harvesting performance of the downstream flag. The voltage generation capability of flag depends on the drag and the induced deformation due to vortex-flag interaction. Numerical Simulations indicate that high energy harvesting efficiency is achieved over a range of stream- and span-wise distances and there is higher value of voltage generation when there is lock in between vortex sheet fluctuations and flag vibration. Large amplitude of oscillations and higher bending of the flag correspond to promising energy harvesting efficiency of the flag. The results show that the voltage generation of the piezoelectric material is increased irrespective of the span-wise distance for specific arrangements.
Inspired by the energy harvesting eel, a flexible flag behind a D-shape cylinder in a uniform vis... more Inspired by the energy harvesting eel, a flexible flag behind a D-shape cylinder in a uniform viscous flow was simulated by using the immersed boundary method (IBM) along with low-speed wind tunnel experimentation. The flag in the wake of the cylinder was strongly influenced by the vortices shed from the upstream cylinder under the vortex-vortex and vortex-body interactions. Geometric and flow parameters were optimized for the flexible flag subjected to passive flapping. The influence of length and bending coefficient of the flexible flag, the diameters (D) of the cylinder and the streamwise spacing between the cylinder and the flag, on the energy generation was examined. Constructive and destructive vortex interaction modes, unidirectional and bidirectional bending and the different flapping frequency were found which explained the variations in the energy of the downstream flag. Voltage output and flapping behavior of the flag were also observed experimentally to find a more direc...
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Papers by Dr. Usman Latif