Non-dimensional Rotation Rate Research Articles

Numerical investigation of flow across three co-rotating cylinders in side-by-side arrangement

Flow across three side-by-side co-rotating cylinders is investigated at a Reynolds number of 100 and non-dimensional rotation rates varied from 0 to 8, for spacing ratios of L/D=1.5, 2, and 4 through two-dimensional numerical simulations, where D and L are cylinder diameter and the center-to-center spacing between the cylinders, respectively. For L/D=1.5 and 2, the wakes are classified into regime FF (flip-flopping) at smaller rotation rates and regime SB (single-body) at higher rotation rates. Each regime can be further divided into sub-regimes based on the wake patterns. Regime FF is a regime where the flow switches between two patterns intermittently. The three sub-regimes of SB at L/D=1.5: vortex shedding (SB-VS), steady state (SB-SS), and secondary instability (SB-SI) are the same as those of a single rotating cylinder as the flow through the gap is too weak to have effect on global wake. A new sub-regime single-body quasi-steady (SB-QS) is found for L/D=2, where the two shear layers in the wake of the three cylinders interact weakly with each other but do not form strong vortices. For L/D=4, two new regimes are found: regime 3V-to-3S (transition from three vortex shedding wake to three steady wake), where the vortex shedding from the three cylinders are suppressed consecutively one by one with the increase in the rotation rate, and regime TB (two-body) where two of the three cylinders behave as a single body. Regime TB for L/D=4 has two sub-regimes: steady state (TB-SS) and secondary instability (TB-SI). The effects of the flow regimes on the force coefficients are quantified. For all the spacing ratios L/D=1.5, 2, and 4, the standard derivation drag and lift coefficients are significantly greater than that of a single cylinder when vortex shedding occurs.

Effect Of Confinement On Flow Around A Rotating Elliptic Cylinder In Laminar Flow Regime

Abstract The flow phenomena around a rotating elliptic cylinder placed in a narrow channel is studied numerically. The walls of the channel act as a confinement that limits the flow in the transverse direction. The confinement ratio (β), non-dimensional rotation rate (α), and the Reynolds number (Re) span across multiple values. A parametric study is done to identify the variations in drag-coefficient (CD), lift-coefficient (CL), and moment coefficient (CM) with changes in β,α and Re. Near-field and far-field vorticity contours are discussed in detail. Fast Fourier transform (FFT) of the time-periodic lift signals are presented to understand the shedding-frequency characteristics. Furthermore, CM values are analysed for possible cases of autorotation. It is observed that confinement acts to delay the shedding of vortices. However, a complete suppression is not obtained even for the maximum value of β. This is likely because of the sharp flow separation at the edges of the cylinder, which tends to promote the formation of a vortex. Hovering vortices are observed for α>1, and a special case is identified for which the hovering vortex never dissipates.

Wake transitions behind a streamwise rotating disk

Direct numerical simulations are performed to investigate the wake transitions of the flow normal to a circular rotating disk. The diameter-thickness aspect ratio of the disk is $\chi =50$ . The Reynolds number of the free stream is defined as $Re_s=U_\infty D/\nu$ , with incoming flow velocity $U_\infty$ , disk diameter $D$ , and kinematic viscosity of the fluid $\nu$ . The rotational motion of the disk is described by the Reynolds number of rotation $Re_r=\varOmega Re_s$ , with non-dimensional rotation rate $\varOmega =\frac {1}{2}\omega D/U_\infty$ , where $\omega$ is the angular rotation speed of the disk. Extensive numerical simulations are performed in the parameter space $50 \leqslant Re_s \leqslant 250$ and $0 \leqslant Re_r \leqslant 250$ , in which six flow regimes are identified as follows: the axisymmetric state, the low-speed steady rotation (LSR) state, the high-speed steady rotation (HSR) state, the low-speed unsteady rotation (LUR) state, the rotational vortex shedding state, and the chaotic state. Although plane symmetry exists in the wake when the disk is stationary, a small rotation will immediately destroy its symmetry. However, the vortex shedding frequencies and wake patterns of the stationary disk are inherited by the unsteady rotating cases at low $Re_r$ . A flow rotation rate jump is observed at $Re_s\approx 125$ . The LUR state is intermediate between the LSR and HSR states. Due to the rotational motion, the wake of the disk enters the steady rotation state earlier at large $Re_r$ , and is delayed into the vortex shedding state in the whole range of $Re_r$ . In the steady rotation states (LSR and HSR), the steady flow rotation rate is linearly correlated with the disk rotation rate. It is found that the rotation of the disk can restrain the vortex shedding. The chaotic state can be regularized by the medium rotation speed of the disk.

The Wake Structure of a Stationary and a Rotary Wall-Mounted Low-Aspect-Ratio Cylinder

This paper investigates the wake structure of a low-aspect-ratio rotating cylinder mounted wall-normal to a flat plate at a diameter-based Reynolds number of . The cylinder is driven at a constant rotational rate about its respective axial coordinate. Four nondimensional rotation rates were selected: 0.5, 1, 2, and 3, representing rates based on the static cylinder’s natural shedding frequency and corresponding harmonics. Two aspect ratios were investigated: i) and ii) . The case of represents a cylinder height equal to the local boundary-layer thickness. Both streamwise and cross-stream (transverse) particle image velocimetry (PIV) planes are presented, and the resulting time-averaged flowfield is examined. Results for the rotating cylinder reveal the development of a dominant streamwise vortex that persists for several length scales downstream of the cylinder. Accompanying the streamwise vortex formation is an enhancement in the wall-normal velocity component (downwash) behind the rotating cylinder. Additionally, the maximum downwash occurs immediately behind the rotating cylinder near 0.27 diameters downstream in contradistinction to a stationary cylinder with peak downwash near 2–3 diameters. The maximum downwash, being in line with the formation of the dominant streamwise vortex, shortens the recirculation region in the cylinder’s wake, thus shifting the plate reattachment point further upstream. In the case of , where the cylinder is submerged within the boundary layer, although the length of the recirculation region reflected by the mean flow is lengthened by the rotary motion, the maximum downwash for the rotating cylinder is enhanced by a factor of 10 from that of the maximum downwash experienced by a static counterpart.

On reducing lift and drag forces of a stationary circular cylinder using side-by-side pair of inward rotating cylinders

Effect of side-by-side pair of inwardly rotating circular cylinders on the nature of drag and lift forces of the stationary circular cylinder is numerically investigated for Reynolds number Re = 100. Non-dimensional rotation rates of cylinders in consideration are α = 0, 1, 3, and 5. Center to center gap spacing between rotating cylinders is taken as 6D (D is cylinder diameter), and the stationary cylinder is centrally placed in the gap. For the case of two side-by-side inward rotating cylinders, above a certain critical rotation rate, Chan et al. [1] reported the formation of a virtually elliptical body accompanied by vortex suppression. Drag on both the cylinders became almost zero after the formation of a virtually elliptical body. The present study aims to use the same concept of a virtually elliptical body to reduce the drag and lift forces on a stationary circular cylinder. At α = 3, complete suppression of vorticity is observed, followed by the formation of a virtual elliptical body at α = 5. With an increase in α from 0 onwards, the drag coefficient for the stationary cylinder reduces and becomes zero at α = 5.

Gravo‐aeroelastic scaling of a 13‐MW downwind rotor for 20% scale blades

AbstractA 105‐m, 13‐MW two‐bladed downwind Segmented Ultralight Morphing Rotor (SUMR‐13) blade was gravo‐aeroelastically scaled by 20% to a 20.87‐m‐long demonstrator blade and confirmed through structural ground testing. The subscale model was achieved through geometric scaling and by aeroelastic scaling principles based on operational flapwise deflections combined with rotational and structural frequencies while retaining the turbine tip‐speed ratio. In particular, the subscale demonstrator was designed to replicate, as closely as possible, the nondimensional geometry, the ratio of centrifugal to gravitational moments, the tip‐speed ratio, and the nondimensional rotation rate. The intent for this demonstrator was to achieve the same nondimensional flapwise blade deflections and dynamics of the full‐scale 13‐MW rotor. The manufactured SUMR‐D blade resulted in less than half of the mass of the conventional two‐bladed Controls Advanced Research Turbine (CART2) rotor blade based on scaling and a lower power rating, though with some differences in mass and stiffness from the ideal scaled‐down design to meet safety requirements at the test site. To achieve proper scaling, operational pitch control set points were altered to account for the differences by evaluating simulated operation of both the SUMR‐13 and SUMR‐D rotors. Structural testing of the SUMR‐D blade investigated the response to well‐defined flapwise loads and indicated that the subscale blade had the appropriate elastic properties needed for both scaling and for safe operational field testing.

Discrete-vortex analysis of high Reynolds number flow past a rotating cylinder

Flow past a rotating cylinder is investigated using a two-dimensional discrete vortex simulation method in this study. The simplified Navier–Stokes equation is solved based on the relationship between the surface pressure gradient and the generated surface vortex strength. The Reynolds number based on the cylinder diameter and flow velocity is 105. The non-dimensional rotation rate, α (the ratio of the cylinder surface velocity and flow velocity), is varied between 0 and 19, and four different wake formations (vortex shedding, weak vortex shedding, wake, and rotating wake formations) have been derived by the imposed rotation. The relationship between the hydrodynamics and wake formation is illustrated. Under vortex shedding and weak vortex shedding formations, periodical hydrodynamics is induced. Under wake formation, no gap between the positive-vorticity and negative-vorticity layers results in the steady hydrodynamics. The separation of the rotating wake induces the huge fluctuation of hydrodynamics under rotating wake formation. These are significant for a flow control technique and for the design of ocean and civil engineering structures. With the increasing rotation rate, the variation of mean hydrodynamics has been discussed and the maximum mean hydrodynamics is considered to be decided by the rotation rate. According to these wake formations, the vortex shedding, weak vortex shedding, wake, and rotating wake areas are identified. Combining the initial, increasing, and equivalent areas for mean hydrodynamics, two different area-divisions have been conducted for mean hydrodynamics and the relationship between the two area-divisions has been illustrated. Finally, the disappearance of vortex shedding and variation of the Strouhal number have been discussed in detail. The critical value for the disappearance of vortex shedding is α ≈ 3.5, and the Strouhal number remains steady initially and then decreases.

Investigation of the motion characteristics for a spring-mounted rotating cylinder in flow

A spring mounted rotating cylinder placed in flow is investigated using a two-dimensional newly improved discrete vortex method at Reynolds number of 105. In this study, the non-dimensional rotation rate, $$\alpha$$ (rate of the cylinder surface velocity and flow velocity), varies from 0 to 16, and the reduced velocity $${\text{Ur}}$$, increases from 1 to 14. The relationship between the wake formation, hydrodynamics, and motion of the cylinder has been illustrated. Three different motions (VIV, reverse direction whirl, and same direction whirl) have been identified and illustrated. The VIV mainly occurs in the cross-flow direction, and it is generated at $$\alpha 3$$. The path of the same direction whirl looks like a slight round circle, and the moving direction is the same as the rotating direction. The frequency of the whirl is higher than that of the VIV at the same rotation rate. The same direction whirl starts from $$\alpha = 8$$ with $${\text{Ur}} = 13$$, and the frequency of this whirl increases with increasing rotation rate. Unlike that of the same direction whirl, the moving direction of the reverse direction whirl is opposite to the rotating direction, and the path of the whirl similarly seems to be a round circle. The reverse direction whirl is generated at $$2 \le \alpha \le 7.5$$. The frequency of the reverse direction whirl decreases with increasing the rotation rate due to the increased effective added mass. The relationship between the effective added mass coefficient and the rotation rate has been interpreted; the effective added mass coefficient remains steady at $$0 \le \alpha \le 1$$ then gradually increases at $$1 < \alpha < 2$$, and finally dramatically increases with increasing rotation rate at $$\alpha \ge 2$$.

Linear Shear Flow Past a Rotating Elliptic Cylinder

Simulations are carried out for linear shear flow past a rotating elliptic cylinder to investigate the effect of shear flow on hovering vortex. An in-house fluid solver that is based on immersed boundary method (IBM) is used to study the flow features and variation in aerodynamic forces. The simulations are carried out for various nondimensional rotation rates, axis ratio (AR) of the cylinder, and shear parameter. In shear flow past rotating elliptic cylinder, the negative vortices are sustained for longer distances in the downstream of the cylinder, and due to the velocity gradient, the sequence of the vortex street changes. It also has significant effect on the formation and composition of hovering vortex. To capture these features, each vortex is tracked as they form, detach, and move in the wake of the cylinder. Hovering vortex, formed due to coalescing of multiple vortices near the cylinder, is subdued for smaller rotation rates at moderate shear. It is also observed that lift forces increase linearly with shear, while the frequency of shedding shows no dependency on shear parameter.

Flow past a rotating circular cylinder with superhydrophobic surfaces

Superhydrophobic surfaces (SHSs) are widely reported and applied to modify flow features. In this work, the two-dimensional flows past a rotating circular cylinder with SHSs are studied to explore its effect. The present numerical simulations take SHSs into account by alternating shear-free and no-slip boundary conditions with different gas fraction (GF) for non-dimensional rotation rates of $$0\le \alpha \le 6$$ at $${ Re}=100$$ . Numerical results indicate that SHSs can obviously modify the critical rotation rates of vortex shedding, frequency of vortex shedding, force acting on the cylinder as well as the instantaneous and mean velocities near the cylinder. Moreover, such variation exhibits diverse behaviors in different flow regimes. For instance, both drag enhancement and drag reduction are found in the presence of SHSs. For the rotation rate corresponding to a vortex shedding regime, the drag of cylinder is reduced by SHSs. On the contrary, SHSs enhance the drag of cylinder in the steady regime. SHSs play different roles in different flow regimes so that the first critical rotation rate decreases monotonically with the increase of GF, while the second and the third critical rotation rates increase monotonically with increasing GF. The effect of SHSs in such flow could have some potential application.

Transient fluid flow and heat transfer over a rotating circular cylinder near a wall subject to a single gust impulse

Numerical results are presented investigating the effect of a gust impulse on the transient fluid flow and forced convection heat transfer from a rotating circular cylinder near a plane boundary in the two-dimensional, in-compressible flow regime. Reynolds numbers of 200, 600 and 1000 have been studied for a fluid of Prandtl number 7. Starting from static, the steady non-dimensional rotation rate is varied up to a maximum value of 5.5, in the counter clockwise direction, such that (α∈{0,0.5,1,2,2.5,4.7,4.9,5,5.5}). Gap to diameter ratio for this work is fixed at 3. Typical governing equations namely continuity, momentum and energy have been solved using the Constant Wall Temperature (CWT) boundary condition. This work notes that higher rotation rate of the circular cylinder, in the second vortex shedding regime and slight perturbations in the flow may cause a resultant effect which leads to short term disruption in the plane wall boundary layer dynamics even at larger values of gap to diameter ratio. Moreover, the gust impulse superimposed to the mean flow at the domain inlet causes creation of temporary convection zones in the cylinder wake which have significant impact on the heat transfer from the cylinder surface. Variations in Strouhal number, vorticity contours, peak vorticity trajectory plots, temperature contours and Nusselt number distribution are presented and discussed in comparison with the existing literature.

Vortex-induced vibration of a transversely rotating sphere

The effects of transverse rotation on the vortex-induced vibration (VIV) of a sphere in a uniform flow are investigated numerically. The one degree-of-freedom sphere motion is constrained to the cross-stream direction, with the rotation axis orthogonal to flow and vibration directions. For the current simulations, the Reynolds number of the flow, $Re=UD/\unicode[STIX]{x1D708}$, and the mass ratio of the sphere, $m^{\ast }=\unicode[STIX]{x1D70C}_{s}/\unicode[STIX]{x1D70C}_{f}$, were fixed at 300 and 2.865, respectively, while the reduced velocity of the flow was varied over the range $3.5\leqslant U^{\ast }~(\equiv U/(f_{n}D))\leqslant 11$, where, $U$ is the upstream velocity of the flow, $D$ is the sphere diameter, $\unicode[STIX]{x1D708}$ is the fluid viscosity, $f_{n}$ is the system natural frequency and $\unicode[STIX]{x1D70C}_{s}$ and $\unicode[STIX]{x1D70C}_{f}$ are solid and fluid densities, respectively. The effect of sphere rotation on VIV was studied over a wide range of non-dimensional rotation rates: $0\leqslant \unicode[STIX]{x1D6FC}~(\equiv \unicode[STIX]{x1D714}D/(2U))\leqslant 2.5$, with $\unicode[STIX]{x1D714}$ the angular velocity. The flow satisfied the incompressible Navier–Stokes equations while the coupled sphere motion was modelled by a spring–mass–damper system, under zero damping. For zero rotation, the sphere oscillated symmetrically through its initial position with a maximum amplitude of approximately 0.4 diameters. Under forced rotation, it oscillated about a new time-mean position. Rotation also resulted in a decreased oscillation amplitude and a narrowed synchronisation range. VIV was suppressed completely for $\unicode[STIX]{x1D6FC}&gt;1.3$. Within the $U^{\ast }$ synchronisation range for each rotation rate, the drag force coefficient increased while the lift force coefficient decreased from their respective pre-oscillatory values. The increment of the drag force coefficient and the decrement of the lift force coefficient reduced with increasing reduced velocity as well as with increasing rotation rate. In terms of wake dynamics, in the synchronisation range at zero rotation, two equal-strength trails of interlaced hairpin-type vortex loops were formed behind the sphere. Under rotation, the streamwise vorticity trail on the advancing side of the sphere became stronger than the trail in the retreating side, consistent with wake deflection due to the Magnus effect. This symmetry breaking appears to be associated with the reduction in the observed amplitude response and the narrowing of the synchronisation range. In terms of variation with Reynolds number, the sphere oscillation amplitude was found to increase over the range $Re\in [300,1200]$ at $U^{\ast }=6$ for each of $\unicode[STIX]{x1D6FC}=0.15$, 0.75 and 1.5. The VIV response depends strongly on Reynolds number, with predictions indicating that VIV will persist for higher rotation rates at higher Reynolds numbers.

Separation Performance of a Novel Liquid–Liquid Dynamic Hydrocyclone

To investigate the separation performance of a novel liquid–liquid dynamic hydrocyclone (LLDH), a series of experiments and numerical simulations were conducted. Algebraic slip mixture model was used to simulate the multiphase flow in the LLDH, in which the turbulence was modeled using Reynolds stress model and the rotation of the walls was modeled by multiple reference frame model. The numerical results showed a good agreement with the observations and measurements in experiments. The results showed that the increase of rotation speed would strengthen the swirling intensity in LLDH and thereby separation efficiency was raised. However, increase of flow rate would decrease the residence time of oil droplets, causing reduction in efficiency. By comparison, flow split ratio had slight influence on the flow field, and the efficiency rose a little as flow split ratio increased. The efficiency of the LLDH could remain high when the nondimensional rotation rate was large enough.

Experimental investigation of rotating cylinders in flow

Rotating cylinders with different diameters placed in uniform flow were investigated experimentally. The aspect ratios, $${\text{AS}}$$ (ratio of the length and the diameter) of cylinders, with the same length $$L=0.59\;{\text{m}}$$ were 1.85, 2.21, 2.73 and 5.78 with respective diameters of 0.319, 0.267, 0.216 and 0.102 m. The non-dimensional rotation rate, $$\alpha$$ , was the ratio of the rotating surface speed and the flow speed, which varied from 0 to 8 for the 0.319 m diameter cylinder. Hydrodynamics of the cylinders were analyzed based on two different conditions: cylinders in flow condition and rotating cylinders in flow condition. For the cylinders in flow, the influence of the aspect ratio and Reynolds number on the hydrodynamics coefficient and Strouhal number was discussed, the critical transition area was found at $$1.0 \times {10^5} \leqslant Re \leqslant 1.59 \times {10^5}$$ . For the cylinders rotating in flow, initial area, increasing area and equivalent area were defined to describe the variation of mean of hydrodynamics as the increase of rotation rates. The range of these areas was decided by the rotation rate and aspect ratio of the cylinders. Different from the mean hydrodynamics, for the Strouhal number (vortex shedding) and Root mean square of lift for the rotating cylinders, vortex shedding area, weak vortex shedding area and wake fluctuation area were defined to explain them and the range of these areas was only determined by rotation rate.

Second law of thermodynamic analysis for nanofluid turbulent flow around a rotating cylinder

This paper performs an entropy generation analysis for nanofluid turbulent flow around a rotating cylinder. A finite volume method based on SST k–ω turbulence model is employed to solve the governing equations and calculate the viscous and thermal entropy generations. The effects of different parameters containing the non-dimensional rotation rate, nanoparticle concentration, and Reynolds number on the viscous and thermal entropy generations and Bejan number are investigated. The obtained results indicate that there is an optimal non-dimensional rotation ratio at α = 1.5 as it has the minimal viscous entropy generation among other values of α. The viscous entropy generation seems to be enveloped around the cylinder. Finally, the viscous entropy generation is dominant in most of the domain except at the regions with an upward drift and a thin layer around the cylinder wall.

Experimental investigation of flow-induced vibration of a rotating circular cylinder

While flow-induced vibration of bluff bodies has been extensively studied over the last half-century, only limited attention has been given to flow-induced vibration of elastically mounted rotating cylinders. Since recent low-Reynolds-number numerical work suggests that rotation can enhance or suppress the natural oscillatory response, the former could find applications in energy harvesting and the latter in vibration control. The present experimental investigation characterises the dynamic response and wake structure of a rotating circular cylinder undergoing vortex-induced vibration at a low mass ratio ($m^{\ast }=5.78$) over the reduced velocity range leading to strong oscillations. The experiments were conducted in a free-surface water channel with the cylinder vertically mounted and attached to a motor that provided constant rotation. Springs and an air-bearing system allow the cylinder to undertake low-damped transverse oscillations. Under cylinder rotation, the normalised frequency response was found to be comparable to that of a freely vibrating non-rotating cylinder. At reduced velocities consistent with the upper branch of a non-rotating transversely oscillating cylinder, the maximum oscillation amplitude increased with non-dimensional rotation rate up to $\unicode[STIX]{x1D6FC}\approx 2$. Beyond this, there was a sharp decrease in amplitude. Notably, this critical value corresponds approximately to the rotation rate at which vortex shedding ceases for a non-oscillating rotating cylinder. Remarkably, at $\unicode[STIX]{x1D6FC}=2$ there was approximately an 80 % increase in the peak amplitude response compared to that of a non-rotating cylinder. The observed amplitude response measured over the Reynolds-number range of ($1100\lesssim Re\lesssim 6300$) is significantly different from numerical predictions and other experimental results recorded at significantly lower Reynolds numbers.

Gust response of a rotating circular cylinder in the vortex suppression regime

Numerical investigation is carried out to observe the effect of a single gust impulse on free stream flow and forced convection heat transfer across a two-dimensional steadily rotating circular cylinder. The non-dimensional rotation rate α is varied within the vortex suppression regime i.e. 2≤α≤5 at a Reynolds number of 140 and Prandtl number of 7. Seven different gust profiles in the order of increasing differential kinetic energy imparted to the mean flow; are implemented and their effects are compared. Constant wall temperature (CWT) boundary condition is used to solve the governing equations i.e. continuity, momentum and energy equations. This study notes vortex detachment and asymmetric convection of vortical structures even in the otherwise typical vortex suppression regime of the dimensionless rotation rate due to the inclusion of the gust impulse. Moreover, vortical structure detachment takes place at varying frequencies and only for a very short duration of time. Further evidence pertaining to the average Nusselt number and shear layer stretching and distortion is presented and discussed.

Unconfined laminar nanofluid flow and heat transfer around a rotating circular cylinder in the steady regime

AbstractIn this work, steady flow-field and heat transfer through a copper- water nanofluid around a rotating circular cylinder with a constant nondimensional rotation rate α varying from 0 to 5 was investigated for Reynolds numbers of 5–40. Furthermore, the range of nanoparticle volume fractions considered is 0–5%. The effect of volume fraction of nanoparticles on the fluid flow and heat transfer characteristics are carried out by using a finite-volume method based commercial computational fluid dynamics solver. The variation of the local and the average Nusselt numbers with Reynolds number, volume fractions, and rotation rate are presented for the range of conditions. The average Nusselt number is found to decrease with increasing value of the rotation rate for the fixed value of the Reynolds number and volume fraction of nanoparticles. In addition, rotation can be used as a drag reduction technique.

Recovery of drop in heat transfer rate for a rotating system by nanofluids

This paper simulates Al2O3–water nanofluid flow and forced convection around a rotating circular cylinder. The governing parameters are Reynolds number (1≤Re≤100), solid volume fraction of nanoparticles (0≤φ≤0.05) and non-dimensional rotation rate (0≤α≤3). The simulations are performed to study the effects of mentioned parameters on the heat transfer rate and fluid flow characteristics. The governing equations including the continuity, momentum, and energy equations are solved with a finite volume method. It is observed that the reduction of heat transfer with increase in rotation rate is in the vicinity of 6.9% and 32% for Re=5 and 100, respectively at φ=0.05. Furthermore, the augmentation of the heat transfer rate by adding the nanoparticles to the base fluid, water, is in the vicinity of 10.3% at Re=100, φ=0.05 and α=3.

Free stream flow and forced convection heat transfer around a rotating circular cylinder subjected to a single gust impulse

The effect of a single gust impulse on free stream flow and forced convection heat transfer across a two dimensional steadily rotating circular cylinder is numerically investigated. Reynolds number is varied between 80 and 160 while the non-dimensional steady rotation rate is restricted to a maximum value of 5 for a fluid with constant Prandtl number of 7. The governing equations namely continuity, momentum and energy equations have been solved using the Constant Wall Temperature boundary condition. Interesting results are presented depicting the behavior of the stretched boundary layer and the temperature field around the rotating cylinder. The convective heat transfer is observed to evolve differently for different combinations of the aforementioned parameters under the influence of the upstream gust.