Wind tunnel experiments on flow-induced vibration and energy harvesting: Vibrating and stationary cylinder interactions

Flow-induced vibrations of two circular cylinders in tandem arrangement. Part 1: Characteristics of vibration

Numerical investigation on flow-induced vibrations of two tandem cylinders localized selective roughness with different natural frequencies

An investigation on flow-induced response characteristics of two identical circular cylinders in staggered arrangement is conducted in the fluid mechanics laboratory of Kitami Institute of Technology, Japan. Each cylinder was two-dimensional, spring mounted, and allowed to vibrate independently in the cross-flow direction. Measurements were conducted at stagger angle α = 5°, 10°, 15°, 25°, 45° and 60°, L/D ranging from 0.1 to 3.2, with ΔL/D = 0.1, where L is the gap width between the cylinders, and D is the diameter of a cylinder. At each position (α, L/D) of the cylinders, dependence of vibration-amplitude-to-diameter ratio a/D on reduced velocity Ur (= U∞/(fnD)) is examined, where U∞ is the free-stream velocity and fn is the natural frequency of the cylinder. There are seven cylinder-response patterns, depending on whether vortex-excited and/or galloping vibrations of the cylinders are generated, in the range α = 5°–60°, L/D = 0.1–3.2 and Ur = 1.5–26. Pattern I corresponds to no generation of vortex-excited or galloping vibration of either cylinder. In Pattern II the upstream cylinder does not experience vortex-excited or galloping vibration, but the downstream one experiences a galloping vibration. Pattern III involves both vortex-excited and galloping vibrations of the downstream cylinder and only galloping vibration of the upstream cylinder. Pattern IV is associated with generation of vortex-excited vibration of both cylinders at the same Ur range. Pattern V refers to the case where the downstream cylinder experiences vortex-excited vibration, but the upstream cylinder does not. Pattern VI is characterized by vortex-excited vibration of the downstream cylinder in two regimes of Ur, whereas that of the upstream cylinder occurs in one regime only. In Pattern VII the upstream and downstream cylinders experience vortex-excited vibration at two different Ur regimes, respectively. The L/D regime of the vibration patterns generated at each α is identified.

Numerical investigation of noise suppression and amplification in forced oscillations of single and tandem cylinders in high Reynolds number turbulent flows

Flow-induced vibration of two tandemly arranged circular cylinders with attached splitter plates

Effect of porous media on wake-induced vibration (WIV) in tandem circular cylinder

Renewable energy converters, such as bio-inspired fluttering foils, are gaining popularity due to their eco-friendly properties. However, the system with multiple objects has received scant attention. Here, we analyze how spacing influences the transverse (one-degree-of-freedom) vortex-induced vibration of two tandem identical elliptic cylinders at a constant Reynolds number by employing a wide range of reduced velocities (Ur∈[2,14]) and space ratios (L∗∈[2,6]). The incompressible Navier–Stokes equations are solved using the overset mesh method in the OpenFOAM® library. The findings indicate that the wake structure goes through eight distinct wake modes, as well as two gap flow patterns (reattachment and co-shedding). Vibrational responses, force parameters, and flow patterns determine three spacing configurations. At a small spacing (L∗=2), the upstream cylinder (UC) has the traditional lock-in (the frequency ratio fy/fn≃0.95–1.05) at the reduced velocity (Ur≃7), and the downstream cylinder (DC) has a narrow lock-in region around Ur≃9. However, the UC has a wide soft-lock-in (the synchronization region of fy/fn≃1.15) at high reduced velocities (Ur≃8–10). Here, the transverse vibrations of both cylinders, but especially the DC, reach relatively high amplitudes. At a moderate spacing (L∗=3), the UC bears a lock-in zone analogous to a single cylinder with the same mass ratio, while the DC shows a vast soft-lock-in zone (Ur≃8–14). At a large spacing (L∗=4, 5, and 6), the amplitude of the DC is often larger than that of a single cylinder when it is in the lock-in region. The DC exhibits a peak in amplitude at Ur = 7 and a wake-galloping region for Ur > 12.

Aerodynamic noise generated by two circular cylinders arranged in tandem

Flow-induced in-line oscillation of two tandem circular cylinders has been experimentally studied by free-oscillation tests in a wind tunnel. Only one cylinder composed of two tandem cylinders was elastically supported easily to move in the in-line direction for reduced mass-damping parameter Cn≈1 and the other of the tandem cylinders was fixed to the tunnel sidewalls. The gap distance ratio between upstream and downstream cylinders was changed from 0.3 to 3. We measured the response amplitudes of the oscillatory cylinder in the in-line direction and the vortex-shedding frequency in the wake. The flow around the tandem cylinders was visualized by the smoke-wire method. The results of in-line oscillation of an upstream cylinder are as follows, there was a wide excitation region of reduced velocity, Vγ=1.5 to 2.5 in all ranges of gap ratio of 0.3 to 3. This excited oscillation was mainly induced by symmetric vortex shedding;the other excitation of Vγ= 2.8 to 3.5 at wide gap distance ratios of 1.75 to 3, was induced by alternate Karman vortex shedding, as in the case of the in-line oscillation of a single cylinder. The downstream cylinder had an excitation region in a wide range of Vγ=2 to 4 for the narrow gap distance ratios of 0.3 to 0.75. which seems to be induced by alternate Karman vortex shedding. The other excitation regions due to symmetrical vortices were limited to the region of gap distance ratio of 0.75 to 2. Furthermore, the downstream cylinder oscillated as a buffeting phenomenon influenced by wake-fluctuation of the upstream cylinder, when gap distance ratio was greater than 2.5.

Experimental investigation of downstream cylinder vibrations caused by FIV in the presence of upstream stationary cylinder

The heat transfer and wake-induced vibrations of a cylinder of circular cross section in the wake of another identical cylinder are numerically studied in this work at a Reynolds number (Re) = 100. The reduced velocities (Ur) are varied in the range of 2–14. The downstream cylinder is allowed to oscillate in two degrees of freedom, i.e., in the transverse as well as in the streamwise direction. The mass ratio (m*) is taken as 10, while the structural damping is ignored to get the maximum amplitude of vibration. The spacing ratio (L/D) between the cylinders is varied from 1.5 to 6, covering the major regimes, i.e., single body, reattachment, and co-shedding. The coefficients of lift (CL) and drag (CD), vibrational amplitudes of the cylinder, the Nusselt number (Nu), the Strouhal number (St), and vortex shedding patterns are studied. The results are discussed with the help of lift-displacement phase plots, cylinder trajectory plots, and vorticity and temperature contours. The lock-in condition at Ur = 8 is observed for all values of L/D, whereas the lock-in zone is the widest for the co-shedding regime at L/D = 6. By increasing L/D from 1.5 to 2.5 at Ur = 8, the CL of the downstream cylinder increases by 43%, whereas the CL of the upstream cylinder decreases by 61%. The downstream cylinder experiences lower drag as compared to the upstream cylinder and stationary isolated cylinder. A maximum decrease in the average drag coefficient of 107%, as compared to the stationary isolated cylinder, was observed for the downstream cylinder at L/D = 1.5 and Ur = 2, leading to the negative drag. Mostly, the 2S and C(2S) vortex shedding pattern is observed, whereas a steady flow and chaotic pattern emerged in a few cases. The results reveal that with increasing L/D, the average Nu for both the upstream and downstream cylinders increases as the effect of each cylinder on the other diminishes.

Flow-induced vibration (FIV) on two tandem cylinders with forced convection is numerically investigated at a constant Re = 150. Elastically mounted cylinder with four different values of corner radii (r* = r/R: r = radius of fillet; R = radius of circle) = 0 (square cylinder), 0.25, 0.75, and 1 (circular cylinder) with two spacing ratio (L/D) = 4 and 2 is studied. Transverse oscillations are generated from the cylinder having non-dimensional mass (m*) = 10. The structural damping coefficient is assigned a zero value with varying reduced velocity Ur=2−10. The two-dimensional incompressible Navier–Stokes and energy equations are solved together with Newton's second law governing the motion of the cylinders. Both cylinders' surfaces are maintained at a higher constant temperature of T*=1, and incoming flow is set to be at T*=0 with Prandtl number (Pr) = 0.7. The effect of r* and L/D is observed on the flow structure and FIV parameters. Flow characteristics at L/D=4 such as steady flow, reattachment, and unsteady flow are examined. A “shift” in vibrational amplitude is noted from r* = 1 and 0.75 to r* = 0 and 0.5, respectively. The downstream cylinder (DC) experiences a hike in vibration amplitude due to the impingement of vortex shedding from the upstream cylinder (UC). r* = 1 has 18.1% higher vibrational amplitude than r* = 0 at their respective lock-in regimes for DC. For L/D=2, vortices from upstream and downstream cylinders interact to form C(2S) and 2S types of vortex shedding. Different regimes, such as single body, reattachment, and co-shedding, have been observed while changing L/D. r* = 0.75 results in 13.3% higher oscillation amplitude as compared to r* = 0.5 for DC. The average Nusselt number (Nuavg) strongly depends on flow topology, corner radius, and vibrational amplitude A/D. At low L/D, heat transfer from the downstream cylinder is plummeted due to rolling of shear layers over the cylinder. There is a significant change in Nuavg due to higher vibration; for example, increase in 10.71% change is observed from Ur=2 to Ur=6 for r*=1 and L/D=4. Corner radii also alter the Nuavg as a decrease in 27.39% from r* = 1 to r* = 0 at Ur=10 and L/D=4 (UC).

Energy Harvesting from Wake-Induced Vibrations of a Downstream Cylinder in Tandem Arrangement

Interaction dynamics of upstream vortex with vibrating tandem circular cylinder at subcritical Reynolds number

Performance of helical strakes in suppressing the FIV fatigue damage of two long flexible cylinders in a tandem configuration