Investigation of Flow Phenomena and Aerodynamic Forces for Flow Past a Square Cylinder at Different Chamfer Ratios

무함마드아산나와즈 경북대학교 대학원 2020 국내석사

Flow past bluff bodies had been a topic of immense interest for engineers and scientists since more than a century. Fluid structure interaction has its potential application in many engineering applications in construction and different aeronautical applications. The purpose of this study is to investigate flow phenomena and variation in aerodynamic forces as a result of flow over the bluff bodies. The structures taken for investigation in the present study are square and its different chamfer dimensions. The chamfer ratio was defined as the ratio of chamfer length to the characteristic length of the body. The base cases for both extremes are square and diamond shaped cylinders in which square can be regarded as the body with zero chamfer ratio and diamond shaped as a body with 0.5 chamfer ratio. Six cases between these two baseline cases are considered for this study. Commercial finite volume code ANSYS Fluent is deployed for the present study. Three Reynolds number 100, 500, 2100 and 10,000 were taken for thorough explanation of effect of chamfer ratio on the flow phenomena and aerodynamic forces in current study. Validation and detailed explanation of all the bodies is conducted for Re=100 (laminar regime) and Re=2100(turbulent regime). It is observed that diamond cylinder gives the highest value of the drag coefficient and chamfer ratio=0.1 gives the least value among all the cases. Thus, it can be taken as a design parameter in all the engineering potential applications and it may be regarded as best case which outperforms even in turbulent regime as if its laminar one. 블러프 바디를 지나는 흐름은1 세기 이상 엔지니어와 과학자들에게 큰 관심의 주제였습니다. 유체 구조 상호 작용은 건설 및 다양한 항공 응용 분야의 많은 엔지니어링 응용 분야에서 잠재적으로 적용됩니다. 이 연구의 목적은 (절벽체)블러 프 바디를 통한 유동의 결과로서 유동 현상 및 공기 역학적 힘의 변화를 조사하는 것입니다. 본 연구에서 조사를 위해 취한 구조는 정사각형이며 모따기 치수가 다릅니다. 모따기 비율은 모따기 길이 대 바디의 특성 길이의 비율로 정의되었습니다. 두 극단의 기본 사례는 정사각형 및 다이아몬드 형태의 실린더로 정사각형은 모따기 비율이 0 인 바디로, 다이아몬드는 0.5 모따기 비율의 바디로 간주됩니다. 이 두 가지 기준 사례 사이의 6 가지 사례가이 연구에서 고려됩니다. 상업적인 유한 체적 코드 ANSYS Fluent가 본 연구를 위해 배치되었습니다. 현재 연구에서 유동 현상과 공기 역학적 힘에 대한 모따기 비율의 영향에 대한 철저한 설명을 위해 3 개의 레이놀즈 수 100, 500, 2100 및 10,000이 사용되었습니다. 모든 신체에 대한 검증 및 상세한 설명은 Re = 100 (라미 나 정권) 및 Re = 2100 (난류 정권)에 대해 수행됩니다. 다이아몬드 실린더는 항력 계수의 최고 값을 제공하고 모따기 비율 = 0.1은 모든 경우 중에서 가장 작은 값을 제공하는 것으로 관찰됩니다. 따라서 모든 공학적 응용 분야에서 설계 매개 변수로 간주 할 수 있으며 난류 영역에서도 마치 층류처럼 성능을 능가하는 최상의 경우로 간주 될 수 있습니다.

자동차 오일 공급용 제로터 펌프의 압력맥동 최소화 연구

김기용 경북대학교 대학원 2018 국내석사

다수의 부품들로 구성 된 자동차엔진은 오랜 시간동안 극한의 조건으로 운영된다. 이는 엔진 부품들의 발열, 부품 간 마모 등을 야기하게 되며, 이와 같은 문제점들을 미연에 방지하기 위해 엔진오일펌프를 사용한다. 오일은 적정량을 일정하게 공급되어야 하며, 에너지 손실이 적어야 유리하다. 이를 위해 일반적으로 제로터 타입의 펌프가 오일펌프로 사용된다. 제로터 펌프는 송출량이 높으며, 부품 수가 적으므로, 부품간의 간섭이 적어 유지보수에 용이하며, 오랜 시간 사용하더라도 효율변화가 적다는 장점을 가지고 있다. 하지만, 제로터 펌프는 체적에 유체를 담아 압축하여 유체를 이송하는 용적식 펌프(Positive displacement pump)로 유체흡입과 토출에 있어 급격한 압력변화를 가지게 된다. 급격한 압력변화는 펌프 내 유동에너지를 손실시킬 수 있을뿐더러, 불필요한 기체의 진동이나 소음을 발생시키는 주 된 원인이 된다. 이와 같은 문제점을 해소하기 위해서 제로터펌프의 측판 및 포트형상을 개선하고(1,2), 치형설계 최적화(3,4), 제로터 펌프 해석을 위한 CFD 설계 및 최적화(5,6,7,8,9) 등으로 압력맥동을 저감시키는 연구가 진행되었다. 하지만, 펌프 유로(Flow path)형상에 따른 압력맥동특성을 확인하는 연구는 아직 미비한 실정이다. 따라서, 본 연구에서는 로터회전에 의해 발생되는 압력맥동을 도출할 수 있는 해석모델을 설계하고, 해석모델을 통해 유로형상 변경에 따른 압력맥동특성을 연구하였다. Generally automotive engines operate in extreme conditions for long periods of time. This causes heat generation of the engine parts and wear between the parts, and an engine oil pump is used to prevent such problems in advance. The advantage of gerotor pump has a high discharge rate and low number of parts, which makes it easy to maintain maintenance and efficiency, but, the gerotor pump has a sudden pressure change in suction and discharge. A sudden pressure change can cause the flow energy loss and also cause the vibration and noise on automobile. To solve these problems, research has been conducted to improve the shape of the side plate (1, 2) and to reduce the pressure pulsation by optimizing the tooth profile (3, 4). CFD design and optimization for study (5,6,7,8,9). However, there is no research to confirm pressure pulsation characteristics according to the shape of the pump flow path. In this study, an analytical model is designed to confirm the fluid pressure generated by rotor rotation. The pressure pulsation characteristics were verified by changing the channel shape condition.

볼텍스 컵의 최적화를 위한 전산유동해석

김중희 경북대학교 대학원 2014 국내석사

The vortex cup is an effective method of non contact handling by creating suction pressure using tangential velocity. Air supplied from tangential nozzle inlet is rotated inside vortex cup and drained through the gap between the object and the vortex cup. This swirling air flow create suction pressure and at the same time have the lifting force to raise the object. In this paper, three dimensional numerical simulation of the air flow field in vortex cup are performed. The characteristics of the vortex cup and according to the conditions the suction pressure generated by the flow rate, the length of the vortex cup, the gap between the cup and the bottom surface and the throat diameter of the vortex cup are analyzed. Finally, through numerical results optimal conditions of generating suction pressure are presented to pickup the objects.

내부 표면거칠기 변화에 따른 양흡입 원심펌프의 성능변화 연구

임성은 경북대학교 대학원 2016 국내석사

In this study, the effects of surface roughness on hydro efficiency of double suction centrifugal pumps (Q= 70.7㎥/min, H=87m) were tested. The original surface of the Impeller and inner casing were coated and the surface roughness was reduced from 100~110㎛ to 0~0.08㎛ as a result. Experimental studies were conducted to measure the efficiency of the pumps and operating pump electro energy variations with different surface roughnesses. The experimental results showed that efficiency of pumps increased by about 1.7~2.9% and operating pump electro energy was reduced by around 4.38 ~ 6.04%. These results indicate that the performance of the pumps substantially depend on the surface roughness of the Impeller and inner casing and the reduction of surface roughness can improve the efficiency of the pump an reduce costs through the reduction of electro energy consumption. A performance change in similar size pump (Q= 60㎥/min, H=97m) was analyzed using CFD(Computational Fluid Dynamics) according to the change of surface roughness. After the surface roughness was reduced, the CFD results showed that efficiency of pumps increased by about 3.0%. The CFD results give good agreement with experimental results that the performance improved by reducing inner friction loss. The CFD results show the most significant roughness effects on the component of pump is impeller and least effect appeared on the inlet casing. And also, the CFD results show that the performance of pump strongly depend on the roughness of outward shroud surface of impeller.

원통 용기의 물 배수 시 공기기둥 생성에 미치는 물성치 연구 : 원통 용기의 배수구 형상 변화 및 점성이 공기기둥 발생에 미치는 영향

이예리 경북대학교 대학원 2014 국내석사

An air core is generated during liquid draining after rotating cylindrical tanks. In the present study, experiments were performed to investigate the liquid draining characteristics for different drain port shape (Flat bottom type, 30-degree funnel type and stepped bottom type). It was found that the air core generation and decay are influenced by the shape of bottom plate and stepped bottom is more effective to drain without air core. In addition, experiment was also conducted for suppressing air core by using air core suppressor on center of bottom plate with different configuration by changing the diameter and height. The experimental results with air core suppressor show that the drain time is significantly reduced as compared to without air core suppressor. Furthermore, the effects of temperature on liquid draining characteristics were investigated by experimentally and numerically. The experimental results showed that air core generation is very much depended on temperature of water, and when temperature of water increase then the drain time increases. To found the main properties of water to effect on the air core generation, numerical simulations were performed with the change of viscosity, surface tension and density along with temperature. The calculated results show that viscosity is the main property of water to generate an air core.

도시철도차량 디스크 제동 시스템의 패드 형상 및 제동 온도를 고려한 스퀼 소음 저감 연구

안서연 경북대학교 대학원 2023 국내박사

In this paper, a study was conducted to reduce the squeal noise caused by contact between the disc and the pad in the brake system of an urban railway vehicle. In that way, parameter optimization of the influencing factor of the brake pad, proposal of a brake pad shape for contact stress relief, and analysis of the field test results and a study on the effect of braking temperature on the analysis of squeal noise were conducted. The modulus of elasticity, coefficient of friction, and contact stiffness were selected as the effect factors of the brake pad, and a study on parameter optimization was conducted. Squeal noise was analyzed through complex eigenvalue analysis using ABAQUS and a commercial PIDO (Process Integration and Design Optimization) tool; PIAnO was used to optimize the parameters. Using the design of the experiment method, the selected effect factors were used to ascertain the effect on squeal noise generation and the relative importance was identified by ANOM (Analysis of means). Through the parameter study, the effects of the elastic modulus, friction coefficient, and contact stiffness on the magnitude and quantity of the real part were analyzed to confirm the effect of the squeal noise generated in the target system. In order to propose a brake pad shape for contact stress relief, a finite element model of the disc brake system was used, including the peripheral brake parts to increase accuracy. As for the verification of the analysis model, the reliability of the analysis model was secured through the analysis of the field test results on domestic urban railway lines, and then the shape of the pad that relieves the contact stress was proposed. And the braking temperature of the brake system was applied to the analytical model to proposes a brake pad shape to reduce the impact of squeal noise caused by nonuniform contact between the brake disc and the brake pad due to braking temperature. Through this study, it is predicted that the probability of squeal noise generation can be reduced by up to about 65% compared to the present by evenly distributing the concentration of contact stress relatively generated by instability through the application of chamfer to the brake pad and the change in slot shape. The results from the present study can be used to reduce squeal noise further.

POE 및 PVE 오일과 R-1234ze(E) 냉매의 상용성 연구

권정원 경북대학교 대학원 2017 국내석사

An experimental study on the miscibility of polyolester (POE) and polyvinylether (PVE) oils with low-GWP refrigerant R-1234ze(E) has been conducted. The ISO viscosity grades are 68 cSt for both oils (POE68 and PVE68). The miscibility of R-1234ze(E) with POE68 and PVE68 oils is measured in the temperature range of –35 °C to 80 °C and the mass fraction of the oil range of 0 wt% to 70 wt%. Saturation vapor pressures are also measured for refrigerant R-1234ze(E) and POE/PVE oil mixtures and are found to decrease with the increase in the mass fraction of the oil in both cases. The miscibility-test results indicate that the POE68 and PVE68 oils are completely miscible with the refrigerant R-1234ze(E) at the mass fraction of the oil below 20% and 10%, respectively, for all the temperature ranges considered. Refrigerant-oil phase separations are observed for certain mass fraction of the oil and temperature ranges, indicating that the refrigerant-oils are not miscible. It is concluded that POE68 is a more suitable oil for the refrigerant R-1234ze(E) than PVE68.

Energy harvester enhancement by oscillating trailing edge flap

펠린다얀 경북대학교 대학원 2023 국내석사

이 연구는 후방 가장자리 플랩의 디자인과 운동이 진동형 날개 에너지 수집기의 출력 성능에 미치는 영향을 탐구한다. 수치 해석을 통해 수직 L 자형 플랩, 평판, 수평 플랩을 갖는 이동체 날개와 같은 다양한 플랩 디자인을 분석하였다. 날개와 플랩 모두에 사인파, 비사인파 및 복합 운동과 같은 다양한 운동 패턴을 적용하여 그 효과를 평가하였다. 연구 결과, 날개와 플랩이 최대 피치 각도 50°에 도달할 때 최대 양력 출력이 달성된다는 것을 확인하였다. 그러나 플랩에 비사인파 운동을 적용하면 플랩 없는 진동형 날개에 비해 총 출력이 감소한다. 후방 가장자리 플랩에 복합 운동을 적용할 때 가장 높은 총 출력이 달성되며, 날개에는 사인파 운동을 적용한다. 이로 인해 평판에 비해 17.8% 증가하며, 날개와 플랩이 사인파 운동으로 이동할 때보다 6% 증가한다. 이러한 연구 결과는 실용적인 응용을 위한 효율적이고 신뢰할 수 있는 진동형 날개 에너지 수집기의 운동에 대한 추가적인 연구가 필요하다는 의문을 제기한다. This study explores the impact of design and motion of a trailing-edge flap on the power output of an oscillating wing energy harvester. Various flap designs, including vertical L-shaped, flat plate, and two-body wing with a horizontal flap, are analyzed numerically. Different motion patterns, such as sinusoidal, non-sinusoidal, and combined motions, are applied to both the wing and flap to assess their effects. The study finds that the maximum lift power output occurs when the wing and flap reach a maximum pitch angle of 50°. However, applying non-sinusoidal motion to the flap reduces the total power compared to an oscillating wing without a flap. The highest total power is achieved when a combined motion is applied to the trailing-edge flap, with sinusoidal motion applied to the wing, resulting in a 17.8% increase compared to a flat plate and a 6% increase compared to both wing and flap moving with sinusoidal motion. These findings raise further questions about the movement of efficient and reliable oscillating wing energy harvesters for practical applications, which warrant further research.

수중익형 형상 종류별 에너지 수확 성능에 대한 수치 해석

민경진 경북대학교 대학원 2019 국내석사

There is a system with dual oscillating foils in parallel configuration for energy harvesting in the water. In the duct type casing, the up and down flapping motion generated by the dual hydrofoil, which has a parallel configuration in the area where the flow passes, is converted into rotary motion through the device and energy is harvested by rotating the rotor of the generator. To investigate how the energy harvesting efficiency varies with the shape and vibration frequency of hydrofoil, we used the shape of the symmetry NACA 0012 standard and the plate shape with corrugate on the inspired surface of the wing of the dragonfly. The dimensionless frequency was used between 0.15 and 0.35 based on actual experimental data. Finally, the optimal hydrofoil shape for energy harvesting was presented to select objects through numerical results.

2자유도의 비접촉식 방법을 이용한 다중 실린더의 유동에 의한 진동 특성 연구

신준 경북대학교 대학원 2014 국내석사

Flow or vortex induced vibration (FIV or VIV) on a structure is caused by drag force and lift force which comes from Karman vortex. Most of previous studies concerning FIV have focused on flow-cross vibration by using directly contacted or restricted measuring methods. In this study, non-touch, two degrees of freedom measurement was conducted by using high speed camera, wind tunnel. From this method, characteristics of FIV could be analyzed without any restrictions. For two different diameter circular cylinders, the characteristics of different arrangement were studied with comparing the characteristics of two same-diameter cylinders. First, when large cylinder is in upstream, the flow-cross direction amplitude of upstream cylinder is similar with the upstream cylinder amplitude of same-diameter cylinders. But, the peak-amplitude of the downstream cylinder occurs in different region with these of same diameter cylinders. Next, when small cylinder is prior to large cylinder, the maximum amplitude of upstream cylinder occurs in different region with same diameter cylinders. For large downstream cylinder, the amplitude gradually increases without any peak value as the flow velocity increases. For three same diameter cylinders experiment, the amplitudes of first and second cylinders are similar with those of the two same diameter cylinders. But, the amplitude of last cylinder of three same diameter cylinders gradually increased as without any peak value, and this is different result of last cylinder of two same diameter cylinders. From this results, the presence of third cylinder have no affection to the vibration of upstream cylinders, and the resonance of third cylinder is suppressed by the upstream cylinders.