• Wind and Structures
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• v.30 no.5
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• pp.525-532
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• 2020

This work numerically investigates the effects of Reynolds number Re_D (= 100 - 150), cross-sectional aspect ratio AR = ( 0.25 -1.0), and attack angle α (= 0° - 90°) on the forces, Strouhal number, and wake of an elliptical cylinder, where Re_D is based on the freestream velocity and cylinder cross-section height normal to the freestream flow, AR is the ratio of the minor axis to the major axis of the elliptical cylinder, and α is the angle between the cylinder major axis and the incoming flow. At Re_D = 100, two distinct wake structures are identified, namely 'Steady wake' (pattern I) and 'Karman wake followed by a steady wake (pattern II)' when AR and α are varied in the ranges specified. When Re_D is increased to 150, an additional wake pattern, 'Karman wake followed by secondary wake (pattern III)' materializes. Pattern I is characterized by two steady bubbles forming behind the cylinder. Pattern II features Karman vortex street immediately behind the cylinder, with the vortex street transmuting to two steady shear layers downstream. Inflection angle α_i = 32°, 37.5° and 45° are identified for AR = 0.25, 0.5 and 0.75, respectively, where the wake asymmetry is the greatest. The α_i effectively distinguishes the dependence on α and AR of force and vortex shedding frequency at either Re_D. In Pattern III, the Karman street forming behind the cylinder is modified to a secondary vortex street. At a given AR and α, Re_D = 150 renders higher fluctuating lift and Strouhal number than Re_D = 100.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.325-333
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside the cooling passage of the gas-turbine blades. It is important to increase not only the heat transfer rates but also the uniformity of heat transfer in the cooling passage. The square duct has compound-angled ribs with $60^{\circ},\;70^{\circ}$ and $90^{\circ}$ attack angles, which are installed on the test plate surfaces. a naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wall and the vertices near the side-wall. The local heat transfer and the secondary flow in the duct are changed largely according to the rib orientation. Therefore, geometry and arrangement of the ribs are important fur the advantageous cooling performance. The angled ribs increase the heat transfer discrepancy between the wall and center regions because of the interaction of the secondary flows. The average heat/mass transfer coefficient and pressure drop of the ribs with the $60^{\circ}$ $-90^{\circ}$ compound-angle are higher than those with the $60^{\circ}$ attack angle. Also, the thermal efficiency of the compound-angled rib is higher than that with the $60^{\circ}$ attack angle. The uniformity of heat/mass transfer coefficient on the cross ribs may is higher than that on the parallel ribs array.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1137-1146
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• 2002

An experiment has been conducted on the flow and heat transfer characteristics of film coolant injected from a row of five holes with compound angle orientations of 35$^{\circ}$ inclination angle and 45$^{\circ}$ orientation angle. The Reynolds number based on the mainstream velocity and injection hole diameter 3.58${\times}$10$^4$. Three-dimensional velocity, film cooling effectiveness and heat transfer coefficient data are presented at three different mass flux ratios of 0.5, 1.0 and 2.0. Flow entrainment has been found between the vortices generated by adjacent injectants. The injectant with compound angle orientation entrains not only the mainstream boundary layer flow but also the adjacent injectant. Because of the flow entrainment, the injectant. With compound angle orientation is characterized by a single vortex while two bound vortices are usually observed in the case of simple angle injection. The strength of the secondary flow depends strongly on the mass flux ratio, which shows significant influence on the film cooling effectiveness and heat transfer coefficient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1355-1364
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• 2001

Characteristics of secondary vortices is topologically investigated in the near-wake region of a circular cylinder, where the Taylor's hypothesis does nut hold. The three-dimensional flow fields in the wake-transition regime were measured by a time-resolved PIV for various planes of view. The convection velocities of the Karman and secondary vortices are evaluated from the trajectory of the vortex center. Then, saddle points are determined by applying the critical point theory. It is shown that the inclination angle of the secondary vortices agrees well with the previous experimental data. The flow fields in a moving frame of reference have several critical points and the mushroom-like structure appears in the streamline patterns of the secondary vortices. Since the distributions of fluctuating Reynolds stresses defined by triple decomposition are closely related with the existence of secondary vortices, the physical meaning of them is explained in conjunction with the vortex center and saddle point trajectories.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.1-8
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• 1999

In the present paper an attempt has been made to simulate the secondary injection-primary flow interaction in the conical rocket nozzle and to derive the performance of secondary injection thrust vector control(SITVC) system. Complex three-dimensional flowfield induced by the secondary injection is numerically analyzed by solving unsteady three-dimensional Euler equation with Beam and Warming's implicit approximate factorization method. Emphasized in the present study is the effect of secondary injection such as secondary mass flow rates and the momentum of secondary/primary nozzle flow mass rates upon the gross system performance parameters such as thrust ratio, specific impulse ratio and deflection angle. The results obtained in terms of system performance parameters show that lower secondary mass flow rate is advantageous for to reduce secondary specific impulse loss. It is further found that the nozzle with secondary jet injected downstream and interacting with fast primary flow is preferable for efficient and stable SITVC over the wide range of use with the penalty of side specific impulse loss.

• Physical Therapy Rehabilitation Science
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• v.9 no.4
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• pp.281-286
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• 2020

Objective: This study examined the effects of dynamic tape applied to the patellofemoral joint on the knee valgus angle, muscle activity, and ground reaction force during a single leg squat (SLS) and single leg landing (SLL). Design: Cross-sectional study. Methods: Twenty-four subjects (11 male, 13 female) who met the inclusion criteria were screened by the knee palpation and patella compression tests. First, the knee valgus angle and muscle activity during SLS were measured. Second, the knee valgus angle and ground reaction force during SLL were measured. For the intervention, a patella joint loop using dynamic tape was used. The knee valgus angle, muscle activities in SLS and SLL after the intervention, and the ground reaction force were measured in the same way. A paired t-test was used to examine the difference between before and after the intervention. Results: The knee valgus angle showed a statistically significant improvement after dynamic taping application in SLS and SLL (p<0.05). The differences in muscle activity of the VL/VMO and ground reaction forces were not statistically significant after dynamic taping application in SLS and SLL. Conclusions: This study showed that dynamic taping applied around the patellofemoral joint was effective in improving the knee valgus angle in SLS and SLL and had a reduced risk of secondary injury during sports activity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.10
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• pp.825-831
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• 2017

Radar clutter in real environment is in general heterogeneous and especially nonstationary if radar geometry is of non-sidelooking monostatic structure or bistatic structure. These clutter properties lead to the insufficient number of secondary data of IID(Independent identically distributed) property, conclusively deteriorate clutter suppression performance. In this paper, we propose a clutter suppression algorithm that estimates the clutter signal belonging to cull under test via calculation using only prior information, rather than using the secondary data. Through analyzing the angle-Doppler spectrum of the clutter signal, we show the estimation of the clutter signal using prior information only is possible and present the derivation of a clutter suppression algorithm through eigen-value analysis. Finally, we show the performance of the proposed algorithm by simulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1640-1649
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• 2001

The present study investigates the effects of various rib arrangements on heat/mass transfer in the cooling passage of gas turbine blades. A complex flow structure occurs in the cooling passage with rib turbulators which promote heat transfer on the wall. It is important to increase not only the heat transfer rates but also the uniformity of heat transfer in the cooling passage. A numerical computation is performed using a commercial code to calculate the flow structures and experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. A square channel (50 mm $\times$ 50 mm) with rectangular ribs (4 mm $\times$ 5 mm) is used fur the stationary duct test. The experiments focus on the effects of rib arrangements and gap positions in the discrete ribs on the heat/mass transfer on the duct wall. The rib angle of attack is 60°and the rib-to-rib pitch is 32 mm, that is 8 times of the rib height. With the inclined rib angle of attack (60°), the parallel rib arrangements make a pair of counter rotating secondary flows in the cross section, but the cross rib arrangements make a single large secondary flow including a small secondary vortex. These secondary flow patterns affect significantly the heat/mass transfer on the ribbed wall. The heat/mass transfer in the parallel arrangements is 1.5 ∼2 times higher than that in the cross arrangements. However, the shifted rib arrangements change little the heat/mass transfer from the inline rib arrangements. The gap position in the discrete rib affects significantly the heat/mass transfer because a strong flow acceleration occurs locally through the gap.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.50-53
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• 2012

This paper describes experimental study on GM-type pulse tube refrigerator (PTR). In a PTR, the pulse tube is only filled with working gas and there exists secondary flow due to a large temperature difference between cold-end and warm-end. The stability of secondary flow is affected by orientation of cold-head and thus, the cooling performance is deteriorated by gas mixing due to secondary flow. In this study, a single stage GM-type pulse tube refrigerator is fabricated and tested. The cooing performance of the fabricated PTR is measured as varying cold-head orientation angle and the results are used as reference data. Then, we divided interior space of pulse tube into three segments, and fixed the various size of screen mesh at interface of each segment to suppress the performance degradation due to secondary flow. For various configuration of pulse tube, no-load test and heat load test are carried out with the fixed experimental condition of charging pressure, operating frequency and orifice valve turns. From experimental results, the fine screen mesh shows the effective suppression of performance degradation for the large orientation angle, but the use of screen mesh cause the loss of cooling capacity rather than the case of no insertion into pulse tube. It should be compromised whether the use of screen mesh in consideration of the installation limitation of a GM-type pulse tube refrigerator.

• Archives of Plastic Surgery
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• v.49 no.4
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• pp.510-516
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• 2022

Background Surgical correction of bilateral cleft lip deformities remains one of the most challenging areas in facial plastic surgery. Many surgical techniques and conservative devices have been offered for the early management of bilateral cleft lip in infants. The purpose of this study was to evaluate the effect of lip adhesion on the lip and nose of patients with bilateral cleft lip. Methods A retrospective review of 13 patients with bilateral cleft lip was performed and compared with age-matched noncleft children. Patients underwent lip adhesion at a mean age of 2.8 months, and cheiloplasty at 6.6 months of age using a modification the Mulliken method. Secondary rhinoplasty was performed at the age of 6 in 13 patients. The surgical results were analyzed using photographic records obtained at the age of 1 and 7 years. Twelve length measurements and one angle measurement were obtained. Results All measurements were not statistically different from those of the noncleft age-matched control group at the age of 1. At 7 years of age, upper lip height and vermilion mucosal height were shorter (p < 0.05) than in the control group. Nasal tip protrusion and the nasolabial angle were greater (p < 0.05) than in the control group. Conclusion Lip adhesion followed by secondary rhinoplasty resulted in an acceptable lip and nasal appearance. Although nasoalveolar molding is now widely used, lip adhesion can be an appropriate alternative if an orthodontist is not available due to geographical or economic constraints.