Browsing by Author "Sharma, Gaurav"

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Dynamic response of a cantilevered flexible vertical plate in a uniform inflow at Re = 100
(Springer, 2024-02) Sharma, Gaurav
We numerically study the dynamic flow-induced vibration (FIV) response of a flexible vertical plate cantilevered at its bottom in a two-dimensional flow at Reynolds number, Re = 100. The incompressible Navier–Stokes and continuity equations are solved for fluid flow, and the Saint Venant–Kirchhoff material model is used for the structure. Plate dynamics is studied concerning reduced velocity, which represents the ratio of solid to fluid dynamic time scales. A parametric study is performed by sweeping through its bending stiffness (or the non-dimensional elasticity) at a constant mass ratio of 10. The dynamic characteristics are studied in terms of amplitude and frequency variation of plate oscillations against the reduced velocity. The oscillation frequencies of the plate are compared with its first and second-mode natural frequencies to understand the lock-in behavior. The modal frequencies are calculated by approximating the plate as an Euler–Bernoulli beam. The observed response is broadly categorized into four regimes: (i) lock-in with the first mode, (ii) de-synchronization, (iii) lock-in with the second mode, and (iv) de-synchronization. Overall, the plate locks in and de-synchronizes with its natural modes as the reduced velocity changes. This behavior is similar to Vortex-Induced Vibrations (VIV) of an elastically mounted rigid cylinder.
Effect of shape of frontbody and afterbody on flow past a stationary cylinder at Re = 100
(AIP, 2022-06) Sharma, Gaurav
We numerically study the effect of the shape of frontbody and afterbody on the flow past a cylinder at a Reynolds number of 100. Two-dimensional simulations have been carried out using an in-house sharp-interface immersed boundary method-based flow solver. The cylinder cross section is considered as a semi ellipse on both windward and leeward sides. The semi-minor axis on the windward side (frontbody parameter, LF) and the leeward side (afterbody parameter, LA) varies from 0 to 0.5 to render cylinders of different cross sections. The effect of LF and LA is quantified on the following variables: drag coefficient, lift coefficient, the Strouhal number, vortex formation length, vortex fluctuation energy, the flow separation point, and cylinder bluffness. While the drag linearly decreases with both LF and LA, the gradient with respect to LF is nearly twice larger than LA. The computed vortex formation length scales directly with drag in the LF-LA plane, while the vortex fluctuation energy scales inversely. The lift and the Strouhal number vary non-monotonically in the LF-LA plane, explained in terms of vortex formation length and the flow separation point, respectively. We briefly quantify wake signatures in the LF-LA plane. The downstream vortex paths are traced, and in general, two vortex shedding patterns, 2S and C(2S), are correlated with values of LF and LA. A dynamic mode decomposition analysis of the flow modes helps to explain the computed fluid-flow characteristics.
Flow-induced reconfiguration and cross-flow vibrations of an elastic plate and implications to energy harvesting
(Elsevier, 2023-10) Sharma, Gaurav
We numerically study flow-induced vibrations (FIV) of an elastic cantilevered plate in a cross-flow configuration. The plate is kept upright in an open domain with a fixed bottom end. Such a configuration eliminates energy losses in the wall boundary. Due to allowed vortex shedding from its bottom end, the resulting novel dynamics of the fluid-structure interaction (FSI) system is explored. An in-house sharp-interface immersed boundary method-based flow solver, coupled with a Saint-Venant Kirchhoff material model-based open-source finite element solver, is employed. Two sets of simulations were carried out in two-dimensional Cartesian coordinates at Reynolds number of 100 for a wide range of reduced velocity (), by performing a parametric sweep of dimensionless Young’s modulus () and mass ratio (). In general, FIV characteristics of the plate are similar to the transverse vortex-induced vibration of an elastically-mounted cylinder. The plate deforms to a curved mean position depending on and and exhibits angular oscillations. In particular, the following FIV regimes are obtained with increasing : initial excitation, lock-in with the first mode, desynchronization after the first lock-in, lock-in with the second mode, and desynchronization after the second lock-in. During lock-in, the plate oscillation and vortex shedding frequency are closer to the first or second mode natural frequency of plate. A larger angular amplitude and increased energy exchange between the structure and fluid characterize the lock-in. We quantify the modal contributions of Euler-Bernoulli modes in the plate’s vibration response with a curved mean position. The spatiotemporal variation of energy exchange between the fluid and plate is analyzed to understand the observed plate dynamics. The flow physics of the wake is discussed using wake patterns, vortex formation length, and vortex strength. Drag over the plate reduces due to flow-induced reconfiguration and strongly correlates with these parameters. Lastly, based on the spatial distribution of strain energy density over the plate, we present a potential design for an ambient fluid energy harvester to harness the plate’s vibration energy with optimized piezoelectric patching. The optimum location and height of a piezoelectric patch on the plate for different cases are reported.
Flow-induced vibrations of elastically coupled tandem cylinders
(CUP, 2023-12) Sharma, Gaurav
We numerically study the transverse flow-induced vibration (FIV) of elastically coupled tandem cylinders at Reynolds number 100, using an in-house immersed boundary method-based solver in two-dimensional coordinates. While several previous studies considered tandem cylinders coupled through flow between them, a hitherto unexplored elastic coupling with fluid flow between them significantly influences FIV. We consider a wide range of gap ratio, reduced velocity, an equal mass ratio of both cylinders and zero damping. A systematic comparison between the classic elastically mounted tandem cylinders and elastically coupled cylinders is presented. The latter configuration exhibits two vibration modes, in-phase and out-of-phase, with corresponding natural frequencies approaching the Strouhal frequency of the system. We quantify variation of the following output variables with reduced velocity and gap ratios: cylinders’ displacement; fluid forces; amplitude spectral density of displacement and force signals; phase characteristics; energy harvesting potential; and discuss the wake characteristics using flow separation, pressure distribution, gap flow quantification, and dynamic mode decomposition characterization. The FIV response is classified into several regimes: initial desynchronization with and without gap vortices; final desynchronization; mixed mode; initial branch; lock-in; upper and lower branch; wake-induced vibration; galloping. We draw upon similarities of computed FIV characteristics with those of an isolated cylinder, in which the lower branch exhibits larger a amplitude than the upper branch. The elastically coupled cylinders show a galloping response similar to an isolated D-section cylinder. By invoking the elastic coupling, we demonstrate FIV suppression and augmentation for in-phase and out-of-phase systems. Our calculations show larger energy harvesting potential at reduced cost for elastically coupled cylinders.
Flow-induced vibrations of elastically-mounted C- and D-section cylinders
(Elsevier, 2022-02) Sharma, Gaurav
We numerically study the flow-induced vibration (FIV) response of an elastically-mounted cylinder in two-dimensional coordinates at Reynolds number of 100. In particular, the effects of shape of frontbody and afterbody are systematically investigated by varying the cylinder’s cross-section, keeping the mass ratio of 5 as constant. The following cross-sections are considered — circular, C-section, inverted D-section, D-section, and inverted C-section. We employ an in-house flow solver based on the sharp-interface immersed boundary method and the solver is one-way coupled with a forced harmonic oscillator equation with a single degree of freedom. We explain the FIV characteristics using displacement amplitude, spectral characteristics of displacement and force signals, and wake modes. Considering a circular cylinder as a baseline case, a modification in the shape of the frontbody from convex to flat to concave causes large amplitude vibrations. A D-section cylinder, which corresponds to the flat frontbody, shows a significant increase in the amplitude for a wide range of reduced velocity compared to the circular cylinder, explained by combined Vortex-induced vibration (VIV) galloping response. By contrast, a variation in the shape of the afterbody from convex to flat to concave results in reducing amplitude, implying VIV suppression. The suppression is explained by the reduction of unsteady pressure forcing during vortex shedding on the cylinder. We discuss wake structures and vortex shedding patterns as a function of reduced velocity for the cylinders and explain these signatures in terms of the respective FIV response. The fundamental insights reported here are potentially helpful for structural health monitoring and energy harvesting applications.
Harnessing flow-induced vibration of a D-section cylinder for convective heat transfer augmentation in laminar channel flow
(AIP, 2020-08) Sharma, Gaurav
Flow-induced vibration (FIV) of a D-section cylinder is computationally studied and utilized to augment convective heat transfer in a heated laminar channel flow. An in-house fluid–structure interaction (FSI) solver, based on a sharp-interface immersed boundary method, is employed to solve the flow and thermal fields. In conjunction, a spring–mass system is utilized to solve for the rigid structural dynamics. Using numerical simulations, we highlight that the oscillations of a D-section cylinder are driven by vortex-induced vibration and galloping. It is observed that as the cylinder vibrates, vortices are shed from the apex of the cylinder due to the separating shear layers. These vortices, categorized using shedding patterns, interact with the heated channel walls. This interaction results in disruption of the thermal boundary layer (TBL), thus leading to heat transfer augmentation. The enhancement in thermal performance has been quantified using time and space-averaged Nusselt numbers at the channel walls. It is observed that the oscillation amplitude of the D-section cylinder and the extent of vortex–TBL interaction are crucial for determining heat transfer augmentation. Both symmetric and asymmetric thermal augmentation at the top and bottom channel walls have been reported. Finally, to assess the effectiveness of heat transfer augmentation, the D-section cylinder FIV is compared to other FSI systems operating under similar conditions.
An immersed boundary method based fluid-structure interaction solver with applications in energy harvesting
(2020) Sharma, Gaurav
We present the development of an in-house fluid-structure interaction (FSI) solver and employ the solver for state-of-the-art applications in energy harvesting. An implicit partitioned approach is utilized to couple a sharp-interface immersed boundary method based flow solver and a finite-element method based structural solver. The code validations are presented for large-scale flow-induced deformation and vortex-induced vibration of an elastically mounted circular cylinder. We employ the FSI solver for analysis of vortex-induced vibration (VIV) of a cylinders, with different cross-sections. The suppression and agitation of VIV for different cylinders are discussed along with lock-in characteristics. An energy harvesting model is utilized to estimate the power generated per unit mass and it was found that the galloping of the D-cylinder is useful for broadband energy harvesting for a wide range of reduced velocities.
Random excitation technique for measurement of acoustic properties
(Springer Nature, 2017-08) Sharma, Gaurav
This chapter presents a case study approach for Modelling and Simulation of Random Excitation Technique for Measurement of Acoustic Properties like acoustic impedance and reflection coefficient. The basic theory, experimental formulation and set-up required are discussed in detail. Adequate options are suggested, if there is a variation of requirements from the given scenario.
Reverberation time improvement of lecture auditorium: A case study
(Sage, 2018-01) Sharma, Gaurav
In this study, reverberation time of a lecture auditorium has been analyzed experimentally and analytically. It is well-known fact that reverberation time affects the speech intelligibility and hence should be within the range of possible optimum values. Experiments were performed to calculate the reverberation time of a lecture auditorium constructed at Indian Institute of Technology Mandi (IIT Mandi), for different internal conditions such as furniture and curtains. Experimental results were compared with the theoretically calculated values of reverberation time. It is found that acoustic performance of the lecture auditorium has significantly improved using curtains on the windows and furniture. For further improvement, it has also been suggested to use the carpet on the floor of the auditorium. The theoretical value of reverberation time is also calculated to show the improvement which can be achieved using carpet. The effect of audience on reverberation time has also been studied theoretically.