Edge Of Fin Research Articles

Median fin function in bluegill sunfishLepomis macrochirus:streamwise vortex structure during steady swimming

Fishes have an enormous diversity of body shapes and fin morphologies. From a hydrodynamic standpoint, the functional significance of this diversity is poorly understood, largely because the three-dimensional flow around swimming fish is almost completely unknown. Fully three-dimensional volumetric flow measurements are not currently feasible, but measurements in multiple transverse planes along the body can illuminate many of the important flow features. In this study, I analyze flow in the transverse plane at a range of positions around bluegill sunfish Lepomis macrochirus, from the trailing edges of the dorsal and anal fins to the near wake. Simultaneous particle image velocimetry and kinematic measurements were performed during swimming at 1.2 body lengths s(-1) to describe the streamwise vortex structure, to quantify the contributions of each fin to the vortex wake, and to assess the importance of three-dimensional flow effects in swimming. Sunfish produce streamwise vortices from at least eight distinct places, including both the dorsal and ventral margins of the soft dorsal and anal fins, and the tips and central notched region of the caudal fin. I propose a three-dimensional structure of the vortex wake in which these vortices from the caudal notch are elongated by the dorso-ventral cupping motion of the tail, producing a structure like a hairpin vortex in the caudal fin vortex ring. Vortices from the dorsal and anal fin persist into the wake, probably linking up with the caudal fin vortices. These dorsal and anal fin vortices do not differ significantly in circulation from the two caudal fin tip vortices. Because the circulations are equal and the length of the trailing edge of the caudal fin is approximately equal to the combined trailing edge length of the dorsal and anal fins, I argue that the two anterior median fins produce a total force that is comparable to that of the caudal fin. To provide additional detail on how different positions contribute to total force along the posterior body, the change in vortex circulation as flow passes down the body is also analyzed. The posterior half of the caudal fin and the dorsal and anal fins add vortex circulation to the flow, but circulation appears to decrease around the peduncle and anterior caudal fin. Kinematic measurements indicate that the tail is angled correctly to enhance thrust through this interaction. Finally, the degree to which the caudal fin acts like a idealized two-dimensional plate is examined: approximately 25% of the flow near the tail is accelerated up and down, rather than laterally, producing wasted momentum, a loss not present in ideal two-dimensional theories.

Stratification and intra- and inter-specific differences in fatty acid composition of common dolphin ( Delphinus sp.) blubber: Implications for dietary analysis

Sixty-five fatty acids were quantified in the blubber of common dolphins ( Delphinus delphis, D. capensis) incidentally caught off the coast of southern California. Dolphins were grouped by sex, reproductive status and species, and a blubber sample was collected at a mid-lateral site located caudal to the trailing edge of the dorsal fin. Samples were divided horizontally into inner, middle and outer layers and gradients in fatty acid content (mass percent) were observed across the depth of the blubber. Levels of monounsaturated fatty acids were greatest in the outer layer, whereas levels of saturated and polyunsaturated fatty acids were greatest in the inner layer. Degree of stratification was greatest in sexually mature dolphins. Blubber of sexually immature, but physically mature, male dolphins was also highly stratified, suggesting that this difference may be attributed to differences in diet. Classification and regression tree analysis resulted in the fewest misclassifications when dolphins were grouped by species, possibly indicating that these closely related animals forage on different prey species. Dietary-derived fatty acids were typically selected as splitting criteria in classification and regression tree analyses, suggesting that the observed differences in fatty acid composition between the various groups of dolphins may be attributed to differences in diet.

Thermal performance of a spirally coiled finned tube heat exchanger under wet-Surface conditions

This paper is a continuation of the authors’ previous work on spiral coil heat exchangers. In the present study, the heat transfer characteristics and the performance of a spirally coiled finned tube heat exchanger under wet-surface conditions are theoretically and experimentally investigated. The test section is a spiral-coil heat exchanger which consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled finned tubes. Each tube is fabricated by bending a 9.6 mm diameter straight copper tube into a spiral-coil of four turns. The innermost and outermost diameters of each spiral-coil are 145.0 and 350.4 mm, respectively. Aluminium crimped spiral fins with thickness of 0.6 mm and outer diameter of 28.4 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Air and water are used as working fluids in shell side and tube side, respectively. The experiments are done under dehumidifying conditions. A mathematical model based on the conservation of mass and energy is developed to simulate the flow and heat transfer characteristics of working fluids flowing through the heat exchanger. The results obtained from the present model show reasonable agreement with the experimental data.

A New Eastern North Pacific Smoothhound Shark (GenusMustelus, Family Triakidae) from the Gulf of California

A new Smoothhound shark, Mustelus hacat, is described from the eastern North Pacific. Four species of the genus Mustelus had been previously recognized in this area: M. californicus, M. henlei, M. lunulatus, and M. dorsalis. Mustelus hacat is described on the basis of 36 specimens caught in the Gulf of California. Among the Smoothhound sharks in the eastern North Pacific, M. hacat is distinguished mainly by having color uniform dark gray-brown above, white below, with conspicuously white tips and trailing edges of dorsal, pectoral, anal, and caudal fins; upper jaw teeth cuspidate and distinctly asymmetric, with low rounded cusp and prominent cusplet present in teeth of juveniles; upper jaw labial folds notably longer than lower jaw labial folds; and inter-nostril and inter-orbital space wide. Because these species have long been misidentified, we present a key to species using morphological and morphometric features found to be useful taxonomic characters to distinguish them.En este trabajo describimos una nueva especie de tiburón Musola, Mustelus hacat, del Pacifico Noreste. Previamente, en esta área habian sido reconocidas cuatro especies del género Mustelus: M. californicus, M. henlei, M. lunulatus, y M. dorsalis. Mustelus hacat es descrita con base en 36 especimenes que fueron capturados en el Golfo de California. Entre los tiburones del género presentes en el Pacifico Noreste, M. hacat es distinguido principalmente por su patrón de coloración, el cual es café-gris oscuro uniforme arriba, blanco abajo, con puntas y bordes posteriores blancos en aletas dorsales, pectorales, anal y caudal; la forma de sus dientes, los cuales son notablemente asimétricos, con una cúspide redonda, y una cúspide accesoria prominente en los dientes de juveniles; por tener pliegues labiales superiores notablemente más largos que los pliegues labiales inferiores; y espacios inter-narial e inter-orbital amplios. Debido a que estas especies han sido mal identificadas desde hace mucho tiempo, presentamos una clave dicotómica usando caracteristicas morfológicas y morfométricas que han mostrado ser caracteres taxonómicos útiles para distinguirlas.

Threatened Fishes of the World: Noturus placidus Taylor, 1969 (Ictaluridae)

Common names: Neosho madtom (T). Conservation status: Listed federally as threatened 22 May 1990 (USFWS 1991). Identification: One of 25 madtom species, distinguished from four madtoms in its range by two distinct crescent-shaped bands of pigment on caudal fin and lack of dark pigment extending to edge of adipose fin (Taylor 1969). Pectoral spines have poorly developed saw-like teeth on front margin. Fin ray counts: anal rays 13–16 (14.72); pelvic rays 8–12 (9.06), soft pelvic rays 7–9 (7.99); caudal rays 49–59 (54.32); vertebrae: 32–36 (33.62). Adults typically greater than 50 mm TL (Bulger & Edds 2001). Males in spawning condition exhibit swollen cephalic epaxial muscles and elongated genital papillae; both sexes exhibit reddened tooth patches during spawning season. Photograph by Janice L. Bryan. Distribution: Endemic to Neosho River basin in Kansas, Missouri, and Oklahoma (Taylor 1969). Species’ range historically extended south to Illinois River in Oklahoma; currently restricted by reservoirs to approximately two-thirds of original range (Moss 1981). Abundance: Large population fluctuations occur seasonally and annually (Moss 1981). In 1 year, Wilkinson et al. (1996) reported a mean summer density of occurrence in the Spring River of 11.3 fish versus 30.0 per 100 m in the autumn when generational overlap ocurrs. Higher mean autumn densities found in the Neosho River compared to the Spring River (Wildhaber et al. 2000a). Habitat and ecology: Occur over gravel bars and riffles in fourth to sixth order streams having moderate current, permanent flow, and unconsolidated gravel (Fuselier & Edds 1994; Bulger & Edds 2001). Nocturnal benthic insectivores gathering prey from gravel interstices (Moss 1981). In nature, young-of-the-year (YOY) 15–49 mm TL; mature individuals reach 33–82 mm TL by end of first year (Fuselier & Edds 1994; Bulger & Edds 2001). Suspected life span 1–2 years. Reproduction: Sexual maturity reached during first year (Bulger & Edds 2001). Spawning occurs mid-summer; YOY found July–August. Nests excavated beneath large rocks in unconsolidated gravel. Male parental care lasts 18–19 days (Bulger et al. 2002). Clutch size 60; mean chorion diameter 3.1 mm. Threats: Impoundments restrict migration, alter natural hydrograph, and with gravel mining, eliminate preferred habitat (USFWS 1991). Water quality and quantity impacted by municipalities, agriculture, zinc–lead mining, urbanization, and industrialization (Wildhaber et al. 2000a). Conservation actions: Federally listed as threatened in 1990; threatened status in Kansas and endangered in Missouri and Oklahoma. Recovery plan published in 1991 (USFWS 1991). Five-year moratorium on gravel mining in Neosho River instituted spring 1991. Annual population monitoring conducted since 1991 (Wildhaber et al. 2000b). Recent and ongoing research efforts focused on Neosho madtom ecology. Conservation recommendations: Continue to limit gravel mining, prohibit dam construction, and encourage removal of unused dams. Further research needed on life history. Remarks: Cooperation of government agencies and private landowners crucial to recovery.

Micronuclei, nuclear lesions and interphase silver-stained nucleolar organizer regions (AgNORs) as cyto-genotoxicity indicators in Oreochromis niloticus exposed to textile mill effluent

In this study, cyto-genotoxic effects of a textile mill effluent on fish Oreochromis niloticus were investigated using the micronucleus (MN) test and methods to analyze interphase silver-stained nucleolar organizer regions (AgNORs). Fishes were exposed to three different concentrations of textile mill effluent (5, 10 and 20% (v/v)) for 3, 6 and 9 days. Cyclophosphamide (2 mg/l) was used as a positive control. Micronucleus frequencies were examined in peripheral blood erythrocytes and gill cells. Nuclear abnormalities (NA) other than micronuclei such as binuclei, lobed nuclei, blebbed nuclei and notched nuclei were also evaluated in peripheral erythrocytes. Interphase AgNOR parameters were examined in epithelial cells obtained from the edge of caudal fins after 90 and 180 min of exposure. As a result, dose-dependent increases in the frequencies of micronuclei and other NA in erythrocytes were observed. MN frequencies in gill cells also significantly increased, while the interphase AgNOR parameters in fin cells decreased, as a result of textile effluent and cylophosphamide treatments.

Allometric constraints on stability and maximum size in flying fishes: implications for their evolution

Flying fish wing area and wing‐loading both rise in strongly negative allometric fashion with increasing body length and mass. Evidence is presented to show that this occurs because: (1) the leading edge of the pectoral fin ‘wing’ is fixed at 24% of standard length ( LS) from the snout, (2) the wing length cannot exceed 76% of LS or the tips will interfere with propulsive tail beat and (3) increased mass demands faster flying and wings with better lift : drag ratios; this selects for tapered, higher aspect ratio wing shapes. A consequence of this situation is that larger flying fishes have centres of mass increasingly further behind the centre of wing pressure. Resultant longitudinal instability restricts the maximum size of the two‐winged design and the pelvic fins of four‐wingers act as a stabilizing tailplane. These data indicate that the accepted model of evolution of flight in flying fishes (by extension of ballistic leaps) is flawed; it is proposed that evolution of lift‐supported surface taxiing in half‐beaks with enlarged pectoral fins (enhanced by ground effect) was an essential preliminary; subsequent forward migration of the centre of mass to within the wing chord permitted effective gliding.

Evaluation of the genotoxic potential of lambda-cyhalothrin using nuclear and nucleolar biomarkers on fish cells

Micronucleus formation in fish erythrocytes, as an indicator of chromosomal damage, has been increasingly used to detect the genotoxic potential of environmental contaminants. Nucleolar organizer regions (NORs) stained with colloidal silver techniques indicate sites of active RNA transcription. The number and size of NORs in interphase nuclei reflect cellular activities such as proliferation and differentiation of cells. In this study, nuclear (micronucleus frequency) and nucelolar (changes in quantitative characteristics of nucleoli) biomarkers were used to evaluate the functional and structural genotoxic effects of the pyrethroid insecticide lambda-cyhalothrin on Garra rufa (Pisces: Cyprinidae). The frequency of micronuclei was examined in blood smears obtained from fishes exposed to three different concentrations (0.005, 0.01, 0.05 μg/l) for a period of 36 h. Nucleolar parameters (the average number of nucleoli per cell; the volume of a single nucleolus; and the percentage of cells with heteromorphic paired nucleoli) were examined in epithelial cells obtained from the edge of caudal fins at the 90th and 180th minutes of exposure. Results of both tests demonstrated the genotoxic potential of pyrethroid lambda-cyhalothrin on G. rufa. The frequency of micronucleated erythrocytes was significantly increased while the nucleolar parameters were repressed by lambda-cyhalothrin treatment. Our results confirmed that the use of nucleolar biomarkers on fish fin cells, in addition to micronucleus test, could provide valuable information in aquatic genotoxicity studies.

Three-dimensional kinematics and wake structure of the pectoral fins during locomotion in leopard sharks Triakis semifasciata.

The classical theory of locomotion in sharks proposes that shark pectoral fins are oriented to generate lift forces that balance the moment produced by the oscillating heterocercal tail. Accordingly, previous studies of shark locomotion have used fixed-wing aircraft as a model assuming that sharks have similar stability and control mechanisms. However, unlike airplanes, sharks are propelled by undulations of the body and tail and have considerable control of pectoral fin motion. In this paper, we use a new approach to examine the function of the pectoral fins of leopard sharks, Triakis semifasciata, during steady horizontal swimming at speeds of 0.5-2.0ls(-1), where l is total body length, and during vertical maneuvering (rising and sinking) in the water column. The planar orientation of the pectoral fin was measured using three-dimensional kinematics, while fluid flow in the wake of the pectoral fin and forces exerted on the water by the fin were quantified using digital particle image velocimetry (DPIV). Steady horizontal swimming in leopard sharks is characterized by continuous undulations of the body with a positive body tilt to the flow that decreases from a mean of 11 degrees to 0.6 degrees with increasing flow speeds from 0. 5 to 2.0ls(-1). Three-dimensional analysis showed that, during steady horizontal locomotion, the pectoral fins are cambered, concave downwards, at a negative angle of attack that we predict to generate no significant lift. Leopard shark pectoral fins are also oriented at a substantial negative dihedral angle that amplifies roll moments and hence promotes rapid changes in body position. Vortices shed from the trailing edge of the pectoral fin were detected only during vertical maneuvering. Starting vortices are produced when the posterior plane of the pectoral fin is actively flipped upwards or downwards to initiate rising or sinking, respectively, in the water column. The starting vortex produced by the pectoral fin induces a pitching moment that reorients the body relative to the flow. Body and pectoral fin surface angle are altered significantly when leopard sharks change vertical position in the water column. Thus, locomotion in leopard sharks is not analogous to flight in fixed-wing aircraft. Instead, a new force balance for swimming leopard sharks is proposed for steady swimming and maneuvering. Total force balance on the body is adjusted by altering the body angle during steady swimming as well as during vertical maneuvering, while the pectoral fins appear to be critical for initiating maneuvering behaviors, but not for lift production during steady horizontal locomotion.

Assisting manual dolphin identification by computer extraction of dorsal ratio.

Marine biologists use a measurement called the "Dorsal Ratio" in the process of manual identification of bottlenose dolphins. The dorsal ratio denotes the relative distances of the two largest notches from the tip on the dorsal fin. The manual computation of this ratio is time consuming, labor intensive, and user dependent. This paper presents a computer-assisted system to extract the dorsal ratio for use in identification of individual animals. The first component of the system consists of active contour modeling where the trailing edge of the dorsal fin is detected. This is followed by a curvature module to find the characteristic fin points: tip and two most prominent notches. Curvature smoothing is performed at various smoothing scales, and wavelet coefficients are utilized to select an appropriate smoothing scale. The dorsal ratio is then computed from the curvature function at the appropriate smoothing scale. The system was tested using 296 digitized images of dolphins, representing 94 individual dolphins. The results obtained indicate that the computer extracted dorsal ratio can be used in place of the manually extracted dorsal ratio as part of the manual identification process.

Comparison of the transmission-line matrix and finite-difference time-domain methods for a problem containing a sharp metallic edge

We compare Yee's finite-difference time-domain (FDTD) and symmetric condensed node transmission-line matrix (SCN-TLM) solutions for a cavity containing a metallic fin. Differential equation-based numerical methods are known to produce inaccurate results for this type of problem due to the rapid spatial variation of the field distribution in the vicinity of the singularity at the edge of the metal fin. This problem is relevant to the analysis of structures of practical interest such as microstrip and coplanar waveguides. Based on simulations, it is determined that for identical discretizations, SCN-TLM is more accurate than FDTD for this problem. We interpret this result as an indication that the symmetric condensed representation of fields (used within the SCN-TLM) lends itself to a more accurate algorithm than the distributed representation used by Yee. We estimate that the FDTD method requires 3.33 times more cells for a given three-dimensional problem than the transmission-line matrix (TLM) method (1.49 times more cells per linear dimension of the problem) in order to achieve the same accuracy. If we consider the requirements to update and store a single TLM or FDTD cell, we find the SCN-TLM algorithm is more efficient than the Yee FDTD algorithm in terms of both computational effort and memory requirements. Our conclusions regarding computational effort and memory requirements are limited to problems with homogeneous material properties.

The Three-Dimensional Hydrodynamics of Tadpole Locomotion

Tadpoles are unusual among vertebrates in having a globose body with a laterally compressed tail abruptly appended to it. Compared with most teleost fishes, tadpoles swim awkwardly, with waves of relatively high amplitude at both the snout and tail tip. In the present study, we analyze tadpole propulsion using a three-dimensional (3D) computational fluid dynamic (CFD) model of undulatory locomotion that simulates viscous and unsteady flow around an oscillating body of arbitrary 3D geometry. We first confirm results from a previous two-dimensional (2D) study, which suggested that the characteristic shape of tadpoles was closely matched to their unusual kinematics. Specifically, our 3D results reveal that the shape and kinematics of tadpoles collectively produce a small 'dead water' zone between the head-body and tail during swimming precisely where tadpoles can and do grow hind limbs--without those limbs obstructing flow. We next use our CFD model to show that 3D hydrodynamic effects (cross flows) are largely constrained to a small region along the edge of the tail fin. Although this 3D study confirms most of the results of the 2D study, it shows that propulsive (Froude) efficiency for tadpoles is overall lower than predicted from a 2D analysis. This low efficiency is not, however, a result of the high-amplitude undulations of the tadpole. This was demonstrated by forcing our 'virtual' tadpole to swim with fish-like kinematics, i.e. with lower-amplitude propulsive waves. That particular simulation yielded a much lower Froude efficiency, confirming that the large-amplitude lateral oscillations of the tadpole do, indeed, provide positive thrust. This, we believe, is the first time that the unsteady flow generated by an undulating vertebrate has been realistically modelled in three dimensions. Our study demonstrates the feasibility of using 3D CFD methods to model the locomotion of other undulatory organisms.

Sensory contributions to nocturnal prey capture in the dwarf scorpion fish (Scorpaena papillosus)

Dwarf scorpion fish live in broken rocky reef areas at depths of 5–25 m. By day they are found in crevices and beneath rock overhangs, whereas at night they are observed sitting in the open. Gut samples show that feeding occurs predominantly at night with the most common prey items being crabs and brittlestars. In the laboratory experiments, under an artificial day/night light regime (LD 12:12) the prey species show a strong daily rhythm of activity, with activity confined to the period of darkness. Activity is controlled by light level. An artificial “sunset”; in the middle of the day has both crabs and brittlestars emerging from cover at ambient light levels of about 4 × 10‐2μE.m‐2.s‐1 but not becoming fully active until dark. Under similar conditions, the dwarf scorpion fish's visual threshold for response to a moving visual target occurs at light levels of about 7 × 10‐3μE.m‐2.s‐1. Field measurements show light levels between these two values occur only for a limited period after sunset, and that light levels at night will probably be too low for visual feeding. The anterior lateral line system is described and its contribution to feeding shown in experiments where fish in the dark, or blinded fish, precisely locate stationary or moving crabs out to a range of about 10 cm. Particle streak photography shows that the respiratory currents generated by the crabs extend out to at least this range. Brittlestars are most commonly taken when they come into direct contact with the fish, particularly with the modified ventral edge of the pectoral fin. It is concluded that in the dwarf scorpion fish non‐visual senses make an important contribution to prey detection and capture.

Interaction of missile nose-tip vortices with a control surface

The interaction between vortices forming at the nose tip of a missile model and a single fin located down the axis of the model was investigated experimentally for a range of axial fin positions [2.6 < —180 deg), and Reynolds number (6 x 103 < Red < 3.4 x 10 4) for two angles of attack, 30 and 45 deg. Symmetric, attached vortices formed over the model at the lower angle of attack, whereas the vortices were asymmetric when the angle of attack was increased to 45 deg. The interaction was documented using flow visualization and mean pressure measurements on the fin surfaces. The pressure data were used to compute the normal force coefficients on the fin. The effects of the interaction on the fin are described; in particular, the similarities and differences in the flowfield at the two angles of attack are discussed for one axial fin location [(x/d)f = 7.1]. Nomenclature Cfp = normal force coefficient, port surface of fin C/.v = normal force coefficient, starboard surface of fin Cft = total normal force coefficient Cp = pressure coefficient d = model diameter Red = Reynolds number based on model diameter x = axial distance along model from nose tip x' = axial distance from leading edge of fin (x/d)f = dimensionless distance from nose to leading edge of fin y' = transverse (spanwise) distance from root chord of fin a = pitch angle (p azimuthal angle of fin, measured from leeward ray

Folded hydrophone array for narrow marine vehicles

An extendible linear sonar array for an Autonomous Underwater Vehicle (AUV) comprises a linear hydrophone array fixed in the nose of the AUV and two hydrophone array segments mounted at the leading edge of stabilization fins extendible from and retractable into the AUV. The stabilization fins are pivoted to move between extended and retracted positions where, in the extended position, the movable arrays together with the fixed nose array form a linear sonar array with extended width. In the retracted position, the stabilization fins with the hydrophone arrays pivot and fold back into stow channels in the AUV body. The stabilization fins may include movable control surfaces to control the attitude of the AUV, or the stabilization fins can be rotated when in the extended position to provide attitude control.

Mechanical control of swimming speed: stiffness and axial wave form in undulating fish models

The purpose of this study was to investigate the mechanical control of speed in steady undulatory swimming. The roles of body flexural stiffness, driving frequency and driving amplitude were examined; these variables were chosen because of their importance in vibration theory and their hypothesized functions in undulatory swimming. Using a mold of a pumpkinseed sunfish Lepomis gibbosus, we cast three-dimensional vinyl models of four different flexural stiffnesses. We swam the models in a flow tank and powered them via the input of an oscillating sinusoidal bending couple in the horizontal plane at the posterior margin of the neurocranium. To simulate the hydrodynamic conditions of steady swimming, drag and thrust acting on the model were balanced by adjusting flow speed. Under these conditions, the actuated models generated traveling waves of bending. At steady speeds, the motions of the ventral and lateral surfaces of the model were video-taped and analyzed to yield the following response variables: tail-beat amplitude, propulsive wavelength, wave speed and depth of the trailing edge of the caudal fin. Experimental results showed that changes in body flexural stiffness can control propulsive wavelength, wave speed, Froude efficiency and, in consequence, swimming speed. Driving frequency can control tail-beat amplitude, propulsive wavelength, Froude efficiency, relative rate of working and, in consequence, swimming speed. Although there is no significant correlation between rostral amplitude and swimming speed, rostral amplitude can control swimming speed indirectly by controlling tail-beat amplitude and relative power. Compared with live sunfish using undulatory waves at the same speed, models have a lower Froude efficiency. On the basis of the mechanical control of swimming speed in model sunfish, we predict that, in order to swim at fast speeds, live sunfish increase the flexural stiffness of their bodies by a factor of two relative to their passive body stiffness.

Speed effects on midline kinematics during steady undulatory swimming of largemouth bass, Micropterus salmoides

We used frame-by-frame analysis of high-speed videotapes to quantify midline kinematics during steady swimming in largemouth bass at five standardized speeds (0.7, 1.2, 1.6, 2.0 and 2.4 L s-1, where L is total length). By combining morphological data from X-ray photographs with mathematical reconstructions of the midline of each fish, we determined the amplitude and timing of lateral displacement (zmax), lateral flexion (ssmax) and the angle between the midline and the axis of forward travel (thetamax) for each vertebral joint, the hypural bones and four equally spaced segments of the caudal fin rays. Analysis of variance revealed pervasive significant effects of both swimming speed and longitudinal location on variables describing amplitude, phase and wavelength. The amplitudes of zmax, ssmax and thetamax generally increased in a non-linear fashion from approximately 25 %L to the tip of the caudal fin, and the greatest speed-related increases occurred between 0.7 and 1.6 L s-1. For the snout, the first caudal vertebra and the trailing edge of the caudal fin, mean values of zmax increased with speed from 0.004 to 0.012 L, from 0.005 to 0.012 L and from 0.053 to 0.066 L, respectively. For joints between the skull and the first vertebra, between the trunk and the tail vertebrae, and among the most posterior caudal vertebrae, mean values of ssmax increased with speed from 1.2 to 1.7 degrees, from 0.6 to 0.9 degrees and from 1.4 to 2.2 degrees, respectively. Within each swimming speed, values of ssmax of the distal caudal fin commonly exceeded twice those of the proximal caudal fin. Surprisingly, at a given longitudinal location, the times of maximum lateral displacement and bending did not occur simultaneously. Instead, the phase of zmax relative to ssmax was commonly shifted by more than one-sixth of a cycle. Furthermore, the phase shift between zmax and ssmax changed significantly with increased swimming speed. Angles of attack of the tail structures changed periodically from negative to positive values. Maximum angles of attack of the distal caudal fin ranged from 5 to 17 degrees, changed significantly with swimming speed and were less than those of the hypural bones of the tail. Mean tail-beat frequency increased significantly from 2.0 to 4.2 Hz with increased swimming speed. Estimated speeds of wave propagation showed considerable longitudinal variation, and the ratio of swimming speed to posterior wave speed increased from 0.59 to 0.83 with increased swimming speed.

Mechanism of heat transfer enhancement due to self-sustained oscillation for an in-line fin array

Numerical analysis of the instantaneous flow and thermal fields was carried out for an in-line type of fin array for the second laminar flow regime characterized by self-sustained flow oscillation. Flow instability occurring in the wake of a fin leads to the production of the series of counter-rotating vortices. They accelerate recovery of the wake and are thus effective in enhancing the heat transfer of the downstream fin. Such vortices hit the leading edge of the downstream fin one after another and induce two particular types of elementary fluid motions near the fin surface, which are effective again in the enhancement of the fin heat transfer. Such fluid motions are also found to produce the dissimilarity between the momentum transfer and heat transfer.

An Experimental Study of Flow Characteristics of Offset Fin and In-Line Fin Arrays. Effects of Fin Thickness and Fin Pitches on Flow Instability.

The flow visualization and the measurement of velocity fluctuations in the streamwise and the spanwise directions were carried out for in-line fin arrays. It was observed that the streakline becomes unstable and bends in the wake of a fin in the middle range of the Reynolds number and that the streakline bend exhibits a hook-shaped pattern in the neighbourhood of the leading edge of the downstream fin. The destabilized flow suggested by the presence of these unstable streaklines was estimated to cause the velocity fluctuation of fluid near the fins. The same flow visualization was performed for 5-row offset fin arrays. However, it was found that wake flow instability is promoted as the fin pitch becomes narrower and that the flow near a fin interacts and is synchronized with those of neighbouring fins. The frequency of appearance of the bend of a streakline is found to depend mainly on the fin pitch .

Enhancement of convective heat transfer in rectangular ducts of interrupted surfaces

Results are presented from systematic experimental investigations into the enhancement of heat transfer of 11 interrupted surfaces of one type and of different size formed by a multitude of short rectangular ducts with a constant cross-sectional aspect ratio of 7:1 in the absence of burrs and bends on the sharp edges of fins. Investigations were carried out with air in the range of Reynolds numbers from 500 to 10000 for geometric parameters l'/ d = 0.65−3.24 and δ = 0.058−0.114. Based on these investigations, standard experimental thermohydraulic characteristics of these surfaces are obtained as well as their correlations as functions of Re and geometric parameters l'/ d and δ/ d. New results are obtained on the effect of the geometric parameters l'/ d and δ/ d of interrupted surfaces on the enhancement of heat transfer in them and also on the experimental determination of the coefficients of overall pressure drop at the entrance and exit from the interrupted surface in a heat exchanger.