Fin Size Research Articles

Theoretical modeling and optimization of fin-based enhancement of heat transfer into a phase change material

Phase change heat transfer is used commonly for enhanced thermal management and energy storage in several engineering applications. The rate of heat transfer from a heat source into a phase change material (PCM) is limited by thermal properties and geometry, due to which, the use of metal fins protruding into the PCM has been investigated. This paper derives and solves the governing energy conservation equations to determine the transient temperature distribution in the PCM due to the presence of a Cartesian fin. A perturbation method based solution for the Stefan problem with time-dependent temperature boundary condition is used to derive an equation for the fin temperature distribution. Results show that for a given total time available for heat transfer into the fin, the presence of a fin results in two competing effects – enhanced heat transfer into the PCM through the fin and reduced heat transfer into the PCM due to lower area of direct contact between PCM and heat source. This results in a non-monotonic dependence of total heat flow into the PCM on the fin size, and shows that a fin larger than a certain optimal size may actually impede overall heat flow into the PCM. For a given total time, the optimal fin size is shown to be a function of the fin thermal conductivity. The impact of thermal properties of PCM and fin on the rate of heat transfer is also examined. The theoretical work in this paper extends the well-known governing equation for a fin in a single-phase medium to a fin in a phase change material, which is a much more complicated, transient problem. In addition to extending the theoretical understanding of extended surfaces and phase change, this work also provides practical guidelines for the optimized design of phase change based energy storage and thermal management systems.

A critical appraisal of appendage disparity and homology in fishes

AbstractFishes are both extremely diverse and morphologically disparate. Part of this disparity can be observed in the numerous possible fin configurations that may differ in terms of the number of fins as well as fin shapes, sizes and relative positions on the body. Here, we thoroughly review the major patterns of disparity in fin configurations for each major group of fishes and discuss how median and paired fin homologies have been interpreted over time. When taking into account the entire span of fish diversity, including both extant and fossil taxa, the disparity in fin morphologies greatly complicates inferring homologies for individual fins. Given the phylogenetic scope of this review, structural and topological criteria appear to be the most useful indicators of fin identity. We further suggest that it may be advantageous to consider some of these fin homologies as nested within the larger framework of homologous fin‐forming morphogenetic fields. We also discuss scenarios of appendage evolution and suggest that modularity may have played a key role in appendage disparification. Fin modules re‐expressed within the boundaries of fin‐forming fields could explain how some fins may have evolved numerous times independently in separate lineages (e.g., adipose fin), or how new fins may have evolved over time (e.g., anterior and posterior dorsal fins, pectoral and pelvic fins). We favour an evolutionary scenario whereby median appendages appeared from a unique field of competence first positioned throughout the dorsal and ventral midlines, which was then redeployed laterally leading to paired appendages.

Investigations on various characteristics of novel cyclone separator with helical square fins

ABSTRACT Cyclone separators are very energy intensive devices primarily used in power and process industries to separate the particles from hot gases. Hence in the present study, the barrel wall of the cyclone separator was modified by fixing the helical square fins of sizes 5, 7.5, and 10 mm, with 30 and 50 mm pitch variations to improve its separation efficiency. Hence in the present study, various fluid dynamic characteristics which affect the separation efficiency such as axial and tangential velocities, axial pressure drops were investigated. Computational results were validated using the published experimental data for the non-finned cyclone separator and further CFD simulations were performed for novel finned cyclone separators. It was observed that for the particles’ sizes below 3 µm, finned cyclone separator with fin size 10 mm and pitch 50 mm was giving separation efficiency more than other 5 finned cyclone separators. Also 5 to 10% improvement in the separation efficiency was observed over the separation efficiency of the non-finned cyclone separator. Since main function of separating the particles from gas was unaffected rather it was improved using finned cyclone separator(s) which is important in a view of reducing serious fine particulate matter (PM2.5) emissions causing serious health issues. Abbreviation CFD: Computational fluid dynamics; DPM: Discrete phase modeling;RSM: Reynolds stress turbulence model

Experimental study on the solidification process of fluid saturated in fin-foam composites for cold storage

Cold storage can effectively turn electricity to cold energy during off peak hours and reduce electricity peak load by supplying cold energy for air conditioning. Solid-liquid phase change rate is seriously encumbered by the relatively-low thermal conductivity of phase change materials (PCMs). A novel fin-foam structure was established to enhance solidification heat transfer and the solidification characteristics were experimentally explored. An experimental system visualizing solid-liquid interface and temperature monitoring was built. The parameters of fin-foam structure, including fin sizes, fin pitch and number were investigated experimentally. Particular attention was paid to justifying the local thermal equilibrium state via measuring temperature on metallic ligament surface and the saturating fluid in pore space. Results showed that inserting fins into metal foam can make a promotional improvement on solidification rate of water by 28.35%. The solid-liquid interface became locally curved after inserting fins. Thermal adhesive and insulation adhesive did not affect the accuracy at pore-scale temperature measurement. Solidification process can be further enhanced through increasing fin width and number rather than fin pitch.

Multi-objective optimization of plate fin heat exchanger using constructal theory

In this paper a plate fin heat exchanger (PFHE) with constructal configuration is modeled and optimized and the results are compared with a conventional configuration. Effectiveness as well as the total annual cost (TAC) are considered as two objective functions and 12 design parameters related to the fin and size of PFHE are selected in constructal case (it is 6 in conventional case). Multi objective optimization is performed in each case using Particle Swarm Optimization algorithm. Constructal PFHE is a thermo-economically optimum for the effectiveness higher than 0.747 while conventional PFHE is thermo-economically optimum for the effectiveness lower than 0.747. In addition, the higher values of fin parameters and lower values of PFHE size are required in the constructal compared with conventional PFHE for a specific effectiveness. Moreover, the higher values of the fin sizing parameters are selected in the second part compared with first part of constructal PFHE. Furthermore, the higher values of PFHE sizing parameters are selected in the second part compared with first part of constructal PFHE. Finally, optimum results show that the higher heat exchanger volume is required in the second part than the first part of the constructal PFHE.

Constructal design of multi-scale diamond-shaped pin fins cooled by mixed convection

In the present paper, the heat transfer density rate from a multi-scale diamond-shaped pin fins cooled by mixed convection is maximized under fixed pressure drop based on constructal design. Instead of Richardson number, the ratio of Rayleigh number to Bejan number (Ra/Be) arises due to the imposed pressure drop. Two sizes of diamond-shaped pin fins are placed in a fixed volume in vertical cross flow. The smaller fins are placed in the entrance region of the unused fluid between the larger fins with the same leading-edge of the larger fins. All the larger and the smaller fins are kept at constant temperature. The equations of the buoyancy-pressure driven flow are solved by finite volume method (FVM) for steady, two-dimensional, laminar, and incompressible flow. The leading-edge angles of the larger and the smaller fins are varied from (30°) to (60°). Rayleigh number is kept constant at (Ra = 105), the range of Bejan number is (104 ≤ Be ≤ 106), the range of the ratio of Rayleigh number to Bejan number is (0.1 ≤ Ra/Be ≤ 10), and the air is used as a working fluid with (Pr = 0.71). The heat transfer density is maximized twice, the first maximization is done for the larger fins in the absence of the smaller fins, and the second maximization is done with the presence of the smaller fins at constant leading-edge angle of the larger fins (λ = 30°). The optimal spacing between the larger fins is found in the first maximization, and the optimal height of the smaller fins is found in the second maximization. In the first maximization, the design indicated that the optimal spacing between the larger fins is constant for all fin angles (λ) at constant (Ra/Be). And based on this indication, the number of fins installed in fixed area must be reduced as (λ) increases. As well as, the results show that the heat transfer density can be maximized twice for all the studied angles of the smaller fins (30°, 45°, and 60°), and for all ratios (Ra/Be = 0.1, 1, and 10). Also, the highest value of the second maximized heat transfer density is found at the angle of the smaller fins (λ1 = 30°) for all ratios (Ra/Be).

Constructal enhancement of thermal transport in latent heat storage systems assisted with fins

The aim of this study is to augment thermal transport in phase change materials (PCM) by an optimum installation of the fins. The study emphasizes to obtain best size and location of the fins to minimize the total melting time for the given fins to PCM volume ratio. Thus, the fins are resized and re-positioned according to the constructal theory. The fundamental principle of the theory is to configure limited numbers of fins at optimal position, where thermal transport potential is maximum. A numerical code based on conjugate heat transfer coupled enthalpy porosity approached is developed. The numerical results show that the reduction in size of fins at low temperature gradient and re-positioning them at high temperature gradient are found to be advantageous. In the present study, the fin to PCM volume is reduced by half based on the constructal theory. The proposed constructal fin design augments thermal performance by 4.38% than conventional configuration. The reduction in fins volume by half has not only increased thermal energy storage, but also decreased fins solid mass that can help to reduce the overall weight of thermal energy storage systems. It is also concluded that the fins should not be placed much near to the bottom surface to gain uniform thermal penetration throughout the enclosure.

Orientation effects on laminar natural convection heat transfer from branching-fins

The effect of orientation on the laminar natural convection heat transfer from branching fins attached to a rectangular plate has been numerically investigated. The orientations are termed ‘vBvF’ (vertical Base vertical Fin) and ‘hBvF’ (horizontal Base vertical Fin) when the base plate is vertical and horizontal respectively and the branching fins are attached orthogonally on the base plate. The third orientation is ‘vBhF’ (vertical Base horizontal Fin) when the fins are arranged horizontally on a vertical base plate. Besides orientation effect, the investigation also involves the effect of fin dimensions on the heat dissipation performance. Optimum branching angle of a ‘single’ branching fin is determined in each orientation. Fin size influences the optimum angle only in hBvF orientation. By studying the characteristics of buoyant fluid flow over the heat sinks, we have observed ‘vortex motion’, ‘geometry induced acceleration’ for certain sizes and orientations of the fins. These flow features are specific to the branching fins in natural convection. The dependency of the average heat transfer coefficient on the fin dimensions is explained and correlations to predict the Nusselt number in terms of non-dimensional parameters are developed. Highest thermal performance is obtained in vBvF orientation followed by hBvF and vBhF orientations. A comparison test has indicated that the branching fins have more effectiveness and efficiency than rectangular fins of equal mass and equal base area in all orientations.

Fish fin physique factor in food preferences

Some fish are built for power, scything sleekly through the water, powered by their tails, while others simply potter around rippling their fins. But, the members of one superfamily, comprising triggerfish and filefish (known collectively as the Balistoidea), are able to switch effortlessly between the distinctive styles: rippling the dorsal and anal fins – located above and below the base of their tails – at low speeds, and switching to beating the tail powerfully to and fro when they shift up the gears for a high-speed swim. Yet, each species performs the switch from low to high speed in subtly different ways. Intrigued by the fishes’ elaborate family tree and distinctive appearance, Andrew George and Mark Westneat from the University of Chicago, USA, wondered which aspects of their fin physique determine when they transition from one swimming mode to the other.Selecting members of the superfamily spanning the entire dynasty, from the orange-spotted filefish (Oxymonacanthus longirostris) to the orange-lined triggerfish (Balistapus undulatus), George filmed and observed the fish as they swam, gradually increasing the flow speed from 5 to 60 cm s−1, until the fish could no longer keep swimming against the water. During that time, he recorded the speed at which the animals stepped up a gear and began to beat their tail fin back and forth. ‘The most difficult part was controlling for variation in the fish's behaviour’, says George, adding how every single filefish initially tried to avoid swimming, by gripping the grill at the front of the tank with their jaws. In addition, George carefully photographed and measured the area and shape of the animals’ body and fins before painstakingly analysing the relationships between each fish's build and swimming performance.Impressively, the fastest fish for its size was the tiny (9 cm long) red-toothed triggerfish (Odonus niger) – which clocked up a speedy 55 cm s−1 – while the more sluggish bristle-tail filefish (Acreichthys tomentosus) and larger whitespotted filefish (Cantherhines macrocerus) trailed in at the more sedate speeds of 30 and 40 cm s−1, respectively. Comparing the swimming styles of the fishes, it was clear that the filefish rarely used their tailfins, preferring to use their dorsal and anal fins up to 94% of the time, while some triggerfish beat their tails almost 60% of the time. And when George compared the shape of the fishes’ fins with their swim speeds, it was clear that those with the triangular fins were able to power swimming at higher speeds than those with rectangular fins.However, the duo was surprised when they realised that the fish with rectangular anal and dorsal fins hit similar top swimming speeds (35–42 cm s−1) to the more powerful-looking fish with triangular anal and dorsal fins before they added in their tail fins. In contrast, the fish with short rounded anal and dorsal fins turned on their tail beat over a wide range of speeds, from the slowest at 21 cm s−1 up to 34 cm s−1. And when they analysed the fishes’ swimming styles relative to their fin sizes, it was clear that those with long chunky anal and dorsal fins rarely use their tail fins, while those with small stubby anal and dorsal fins use their tail fins a significant proportion of the time.But what does this all mean for the fishes’ lifestyles? ‘The ecological pattern that popped out most clearly was that species with similar fin and body shapes tend to eat similar food’, says George, pointing out that fishes with the highest swim speeds tend to consume plankton in fast-flowing water, while slower anal and dorsal fin-propelled fishes recruit their tail fin for a sudden burst of speed when dining on fast-moving fish and octopus snacks.

On the role of enclosure side walls thickness and heater geometry in heat transfer enhancement of water–Al2O3 nanofluid in presence of a magnetic field

The natural heat convection within a square enclosure filled with water–Al2O3 nanofluid has been studied numerically in the presence of a magnetic field. The effect of heat source geometry attached to the bottom wall on the Nusselt number was investigated by changing its nondimensional width and height, and side walls thickness of the enclosure ranging from 0.1 to 0.5, 0.1 to 0.8 and 0.05 to 0.2, respectively. A regression model has been obtained along with conducting a sensitivity analysis seeking an optimal heat transfer. Results, reveal that Nusselt number increases by enlarging the fin, and reaching a peak point before it declines. Thus, interestingly, the ever-increasing heat transfer by means of fin size does not retain and there is an optimal point wherein the maximum heat transfer occurs. Moreover, the thermal performance of the system largely depends on the fin size rather than the relative side walls thickness. However, its effect intensifies as the fin width increases. Results of optimization show that the maximum heat transfer occurs at $$W = 0.4615$$ , $$H = 0.6467$$ and $$L_{\text{b}} = 0.2$$ .

Size-dependent change in body shape and its possible ecological role in the Patagonian squid (Doryteuthis gahi) in the Southwest Atlantic

Cephalopods are a versatile group with several mechanisms in place to ensure the success of future generations. The Patagonian long-finned squid (Doryteuthis gahi) populations on the southern Patagonian shelf are believed to be genetically homogenous, but the mechanisms connecting them geographically and temporally are unresolved. Individual growth is highly variable within cephalopod populations and is likely to affect individual patterns of migration and, thus, population connectivity as a whole. Therefore, this study aimed to make inferences about population structure by analysing the size at which individuals were mature and aimed to describe the intrapopulation growth (allometric) trajectories of body shape, using landmark-based geometric morphometric techniques to describe phenotypes. Samples were collected from June 1999 to November 2017 around 52°S and 58°W. Smoothing curves from binomial generalised additive models (GAMs) suggested two size modes of maturity in females and one or multiple modes in males dependent on year and season. There was a gradual elongation of the mantle and an increase in the relative fin size throughout ontogeny. Shape scores from geometric morphometric shape coordinates revealed a continuous non-linear allometric trajectory with a significantly different slope angle for males exceeding 20.1 cm dorsal mantle length (DML). At the extreme of this continuum, the largest ‘super-bull’ form had a substantially more elongated body shape, a heavier fin and a larger fin area compared to the rest of the population, a body shape associated with enhanced swimming performance which may help to maintain population connectivity. The prevalence of these rare super-bulls in the fishery varied widely between years, suggestive of phenotypic plasticity. This study provides evidence that the D. gahi population on the southern Patagonian shelf has a complex population structure with high intraspecific variation.

Effective utilization of natural convection via novel fin design & influence of enhanced viscosity due to carbon nano-particles in a solar cooling thermal storage system

The present work proposes a novel fin design for high temperature solar cooling thermal storage system (TES) which utilizes natural convection more effectively. Different fin structures are investigated for quick heat absorption, and their thermal performance is compared with carbon nanoparticles based TES. It has been observed that the dispersion of carbon nanoparticles increase the effective viscosity of the nano-composite which severely deteriorates the natural convection heat transfer. Moreover, the effective viscosity correlations available in the literature are limited to spherical nanoparticles (without surfactant). Huge discrepancies would result using the same correlations for non-spherical particles like Graphene nanoplates (GNP) dispersed in the Phase change material (PCM). So, the empirical viscosity equations (at different concentration of GNP) are developed in the present work through a series of experimental trials carried on rotational Rheometer. Dynamic Differential scanning calorimetry (DSC) tests are performed to obtain the melting curve and specific heat correlations. The best eutectic PCM for double effect solar cooling system is suggested through systematic and comprehensive methodology using Multi attributes decision making (MADM) tools. The thermal performance of TES with a combination of both fins and GNP is further studied to propose a highly efficient storage system. The case study of a 23 kW solar absorption chiller is also presented to analyze the cost reduction using the proposed fin design. It is concluded that decreasing fin size configuration gives the highest rate of heat transfer. A maximum reduction of 43% in the melting time is observed for TES with the novel finned configuration (at 5% GNP).

Short Communication: Species confirmation of juvenile cloudy grouper, Epinephelus erythrurus (Valenciennes, 1828), based on a morphologic analysis and partial CO1 gene sequencing

Abstract. Ariyanti Y, Farajallah A. 2019. Species confirmation of juvenile cloudy grouper, Epinephelus erythrurus (Valenciennes, 1828), based on a morphologic analysis and partial CO1 gene sequencing. Biodiversitas 20: 914-921. The genus Epinephelus is the most species among the genera within the subfamily Epinephelinae. Species identification techniques for groupers, especially in the Epinephelus, are commonly based on color patterns and a suite of morphological characters, including body shape and the size and number of fins, scales and gill rakers. In some species, juveniles are morphologically distinct from adults of the same species, making morphological identification highly problematic. This present work will provide some morphological description or variations of juveniles that have been identified as Epinephelus erythrurus based on CO1 sequences. Further, the present study demonstrates that a molecular genetic technique, based on partial sequencing of the mitochondrial CO1 gene, may be used for the rapid species confirmation of every developmental stage and phase of an organism (juvenile E. erythrurus). Two DNA sequences of E. erythrurus from the Pangandaran District (7o43’8.31”S 108o30’11.59”E) have been submitted to GenBank under accession numbers KP998441 and KP998442.

Effect of Knurled Fin Surface on Thermal Performance of Perforated Fin Heat Sink

Fabricating perforations in fins causes improvement in heat dissipation rate with lower pressure drag up to a specific perforation number and size of perforation. Again knurled surfaces augment heat transfer rate due to turbulence promotion as well as substantial increase in surface area. The present work investigates thermal performance of heat sink using perforated pin fins with different knurled surfaces. Three-dimensional computational fluid dynamics simulations have been performed to explore the effects of various different knurling geometries on fin surface, perforation number, and size on system performance. A multicriteria decision-making optimization method such as Multi-Objective Optimization under Ratio Analysis (MOORA) has been applied to select the best heat sink configuration. It has been observed that the rate of heat transfer for perforated fins up to a particular perforated area is always greater than the solid fins, and with the variation in knurling geometry on fin surface, heat dissipation rate enhances significantly. Conversely, pressure drop around heat sink decreases with the increment of number and size of perforations. However, due to knurling on fin surface, pressure drop increases. Finally, exergy analysis has also been carried out to calculate second law efficiencies of circular perforated fins using different knurling patterns with increasing number of knurling teeth.

Effect of position of heat mode to heat transfer of a closed loop oscillating heat pipe with check valves on fins

This research aimed to determine the effect of position of heat mode to closed loop oscillating heat pipe with check valves (CLOHP/CV) on fins. To check on heat transfer rate needed to focus on evaporator temperature, air velocity, and position of heat mode. All heat exchangers used ethanol as working fluid with the filling ratio of 50% by total volume of tube, evaporator temperature at 60, 70, and 80 degrees Celsius, and air velocity at 0.5, 1.0, and 1.5 meter per second, size of fin was 0.5 centimetre. All heat exchangers used different positions at evaporator section and condenser section of heat pipe. The CLOHP/CV was made from copper capillary tube of (inner diameter: 5 mm), 24 turns 2 check valves. The length of evaporator and condenser and adiabatic section is 20, 20, and 10 centimetre respectively. From the experiment it’s was found that the heat exchanger of bottom heat mode had a temperature of 80 degrees Celsius and air velocity of 1.5 m/s with heat flux and thermal effectiveness the highest.

Description of a new deep-water dogfish shark from Hawaii, with comments on the Squalusmitsukurii species complex in the West Pacific.

Dogfish sharks of the genus Squalus are small, deep-water sharks with a slow rate of molecular evolution that has led to their designation as a series of species complexes, with low between-species diversity relative to other taxa. The largest of these complexes is named for the Shortspine spurdog (Squalusmitsukurii Jordan & Snyder), a medium-sized dogfish shark common to warm upper slope and seamount habitats, with a putative circumglobal distribution that has come under investigation recently due to geographic variation in morphology and genetic diversity. The Hawaiian population of Squalusmitsukurii was examined using both morphological and molecular analyses, putting this group in an evolutionary context with animals from the type population in Japan and closely-related congeners. External morphology differs significantly between the Hawaiian and Japanese S.mitsukurii, especially in dorsal fin size and relative interdorsal length, and molecular analysis of 1,311 base pairs of the mitochondrial genes ND2 and COI show significant, species-level divergence on par with other taxonomic studies of this genus. The dogfish shark in Hawaii represents a new species in the genus, and the name Squalushawaiiensis, the Hawaiian spurdog, is designated after the type location.

Heat transfer behavior of nanoparticle enhanced PCM solidification through an enclosure with V shaped fins

Thermal storage unit can be utilized to satisfy the balance of energy supply and demand. Copper oxide nanoparticles and V shaped fins are involved in storage unit in current research to expedite the solidification. To show the variation of energy storage efficiency, Finite element method has been employed. Important selected parameters are nanofluid concentration, angle of V shaped fin, copper oxide particle size and length of fins. Contours and profiles in various time steps are depicted. Outputs display that discharging rate augments with rise of angle of V shaped fin. Using copper oxide helps solidification. Length of fin has inverse relationship with discharging rate.

Effect of fin thickness, grooves depth, and fin attachment angle to the hot wall on maximum heat transfer reduction in a square enclosure

This study investigates the effect of optimal thickness, position, and length of a thick fin, optimal groove depth, position, and length of a horizontally grooved thin fin, and optimal position and length of an obliquely fin (at ±45° to the horizontal) attached to the hot wall of a square enclosure in reduction of free convection heat transfer through this enclosure. The results are analyzed for Rayleigh numbers of 104 and 106 and thermal conductivity ratios of 1, 10, and 1000. The continuity, momentum and energy equations of the enclosure are discretized by the finite volume method and then solved with SIMPLER algorithm. The particle swarm optimization (PSO) algorithm is used to optimize the fin size and position and groove depth so that heat transfer through the enclosure is minimized. The results are compared to determine the effects of aforementioned fin characteristics on heat transfer reduction performance. The results obtained with Rayleigh numbers of 104 and 106 show that, as can be expected, for the fins with thermal conductivity ratios of 1 and 1000, the optimal thickness values are, respectively, the upper and lower bounds set by problem definition (defined geometry). But for the fin with thermal conductivity ratio of 10, the optimal thickness varies with Rayleigh number. The results also show that after widening the range of allowed thickness values, the optimal values no longer stick to the upper and lower bounds of that interval. It is also shown that at low thermal conductivity ratios, the fin with horizontal grooves has the same heat transfer reduction performance as a solid thick fin, but allows some degree of conservation in materials. Moreover, the results show that at all thermal conductivity ratios in Ra = 106, the heat transfer reduction performance of the obliquely fin is better than both of the straight thick fin and horizontally grooved fin. However, at all thermal conductivity ratios, the straight thick and obliquely fin slightly underperform rather than horizontally grooved fin in Ra = 104. Overall, the obliquely fin and horizontally grooved fin can be confidently recommended for heat transfer reduction at all thermal conductivity ratios in high Rayleigh number Ra = 106 and low Rayleigh number Ra = 104, respectively.

Influence of adding nanoparticles on solidification in a heat storage system considering radiation effect

In this attempt, nanoparticle enhanced PCM is employed to enhance solidification rate. To augment low thermal conductivity of H2O, CuO nanoparticles were dispersed in it. Also Brownian motion impact was involved in properties of NEPCM. Graphs are obtained via FEM and displayed the impacts of radiation, length of fin and nanoparticles' size. Outputs display that selecting dp = 40nm leads to the fastest discharging. Discharging time reduces with increase of thermal radiation.

Using spanwise flexibility of caudal fin to improve swimming performance for small fishlike robots

This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical experiments by varying the spanwise flexible trajectories and the spanwise flexible size of the caudal fin while keeping the body kinematics fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the robot. Elliptical, parabolic and hyperbola trajectories are chosen to describe the spanwise flexible profile of the caudal fin. According to the sign (positive or negative) of the phase difference of the swinging motion, the spanwise flexibility can be divided into the fin surface of “bow” and the fin surface of “scoop”. It is observed that for both the fin surface of “bow” and the fin surface of “scoop”, the spanwise elliptical trajectory has the optimal swimming velocity, thrust, lateral force, and efficiency. With comparisons, using the flexible caudal fin with the fin surface of “bow”, the lateral force and the power consumption can be reduced effectively and the swimming stability can be increased while reducing little the swimming velocity and thrust. Meanwhile, using the flexible caudal fin with the fin surface of “scoop” can greatly improve the swimming velocity, thrust, and efficiency while increasing part of the lateral force and the power consumption. Three-dimensional flow structures clearly indicate the evolution process around the swimming robot. It is suggested that the fish, the dolphin, and other aquatic animals may benefit their hydrodynamic performance by the spanwise flexibility of the caudal fin.