A study of the flow characteristics of developing turbulent pulsating flows in a curved duct

Hyun-Chull Sohn,Haeng-Nam Lee,Gil-Moon Park 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.12

Flow characteristics of turbulent pulsating flows in a square-sectional curved duct were experimentally investigated. Experimental studies for air flow were conducted to measure axial velocity profiles, secondary flow and pressure distributions in a square-sectional 180° curved duct by using an LDV system with a data acquisition and processing system which includes a Rotating Machinery Resolve (RMR) and PHASE software. Measurements were made at the seven cross-sections from the inlet (ø=0°) to the outlet (ø=180°) of the duct with 30° intervals. Pressure was measured by using a magnetic differential pressure gage. The experiment was conducted in nineteen sections from the inlet to the outlet of the duct at 10° intervals. Velocity profiles for turbulent pulsating flows were large at the outer wall for a bend angle of ø=30° because of the centrifugal force. The velocity profiles were similar to those of turbulent steady flows. The secondary flow of the turbulent pulsating flow had a positive value at a bend angle of 150° without regarding the phase. The dimensionless value of the secondary flow became gradually weak and approached to zero in the region of a bend angle of 180° regardless of the ratio of velocity amplitude. The pressure difference of turbulent pulsating flows was the largest near the region of a bend of angle of 90° in the case of the middle region and became small beyond 90.

트윈스크롤 터보과급기에서 맥동유동의 질량유량 측정

정진은,전세훈 한국산학기술학회 2019 한국산학기술학회논문지 Vol.20 No.12

Turbochargers are an effective device to reduce the fuel consumption. In this study, the mass flow rate of pulsating flow in the twin-scroll turbocharger for the gasoline engine of passenger vehicles was measured. Pulsating flow was achieved using a pulse generator and the mass flow rate of the unsteady pulsating flow was analyzed by comparing it with those of the steady flow. The pulse generator consisted of a rotating upper plate and a fixed lower plate. To measure the mass flow rate of unsteady flow, the orifice flow meter equipped with the difference pressure transducer was used. To analyze the low speed performance of the turbocharger, the measurement was carried out in the speed of turbocharger from 60,000rpm to 100,000rpm. The mass flow parameters of the unsteady pulsating flow showed a large difference compared to those of the steady flow. Those of the unsteady flow showed the hysteresis loop surrounding the mass flow parameters of the steady flow and the maximum variation of the mass flow parameters were 5.0 times those of the steady flow. This phenomenon is the result of the filling and emptying the turbine volute space due to pulsating flow. 터보과급기는 엔진에 장착하여 연비를 개선하는 효과적인 장치로 디젤엔진과 가솔린엔진 모두에서 광범위하게 사용되고 있다. 본 연구에서는 승용차용 가솔린엔진에 사용되는 트윈스크롤 터보과급기에서 발생하는 맥동유동의 질량유량을 측정하였다. 자체 설계 제작한 맥동유동장치를 사용하여 맥동이 있는 비정상상태에서 유동의 질량유량을 측정하였고, 맥동이 없는 정상상태의 질량유량과 비교 분석하였다. 맥동유동장치는 회전하는 상판과 고정된 하판을 사용하여 변하는 엔진의 배기밸브 유효면적을 반영하였다. 맥동이 있는 비정상상태 질량유량을 측정하기 위하여 차압식 압력계를 이용한 오리피스 유량계를 사용하였다. 이때 기체의 온도와 절대압력을 측정하여 기체 밀도 변화를 고려하였다. 터보과급기의 저속 성능을 분석하기 위하여 압축공기를 사용하여 터보과급기 회전속도 60,000rpm에서 100,000rpm의 범위에서 측정을 수행하였다. 비정상상태의 질량유량은 정상상태와 비교하여 크게 다른 결과를 보였다. 정상상태 질량유량 계수는 터빈 팽창비가 증가함에서 따라 증가하지만, 비정상상태 질량유량 계수는 정상상태 값 주변의 히스테리시스 루프를 형성하며 변화량은 정상유동 기준 최대 5.0배이다. 이것은 맥동유동에 의하여 터빈 볼류트 공간에서 충진과 방출이 일어나기 때문이다.

Numerical investigation on cooling performance of pulsating flow in a ribbed channel

Wei Wang,Yang Gao,Genwei Wang,Haiping Tian 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.4

The gas turbine vanes have to withstand the impact of the high temperature gas and keep working in this high temperature which is much higher than the metal melting point. For this reason, these vanes need effective cooling. The traditional coolant is the steady state air flow, whose cooling performance is not satisfied to some extent. The pulsating flow may have better cooling performance due to its more complicated flow characteristics. This paper performs a numerical study to investigate the cooling performance of pulsating flow for the internal convection cooling of the vane. The geometric model is a heated rectangular duct with rib turbulators cast on its internal surfaces. This rectangular duct has different geometric parameters such as different rib spacing (P/e) and channel width to height ratio (W/H). Also, the coolant pulsating flow has three different flow patterns (triangular wave, square wave and sinusoidal wave). Studies show that the pulsating frequence (fv), pulsating amplitude (A) and Reynolds number (Re) are the most immediate parameters characterizing the flow and heat transfer of the pulsating flow. The numerical results of the pulsating flow have been analyzed and compared with the steady flow.

Output power measurement of a blood pump considering pulsating flows

Chun, Se-Jong,Jin, Jong-Han 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.3

A blood flow simulator is one of the most useful tools for investigating the dynamic properties of a cardiovascular system. The blood pump in a blood flow simulator generates pulsating flows by oscillating a membrane mechanically at different pulse rates. To evaluate the performance of the blood pump properly, the flow characteristics of the pulsating flows should be considered. In this paper, two basic indicators for evaluating the blood pump characteristics, the output power and the overall efficiency, were determined with consideration of the pulsating flows, based on a phase-averaged analysis. These indicators were obtained by integrating closed contours in a $P-Q$ diagram. The measured output power was expected to be meaningful for understanding the dynamic effects caused by pulsating flows.

Natural Flow Characteristics of Liquid Rocket Engine Turbopump during Startup

Runze Zhou,Hui Chen,Liang Dong,Houlin Liu,Linglin Jiang,Zeyu Chen 한국유체기계학회 2022 International journal of fluid machinery and syste Vol.15 No.3

When the liquid rocket engine turbopump starts, the tank valve opens first before the pump is driven. Due to the tank and hydrostatic pressure, there is a passive flow phenomenon inside the pump called natural flow. The impeller is passively rotated by hydraulic impact, which impacts the stability of the turbopump during the initial startup period. In order to study the unsteady natural flow characteristics of the turbopump, the coupled CFD/6DOF solver is used for simulation and obtaining the variation of rotational speed, flow loss, and torque with time. The characteristics of the turbopump impeller's radial and axial force are analyzed. The internal flow field and pressure pulsation features were investigated. The results show that the rotational speed caused by natural flow increases exponentially with time. Furthermore, the natural flow loss and torque gradually decrease with the increased rotational speed and has distinct pulsation characteristics and periodicity. The backflow phenomenon in the flow channel becomes more complex. The suction chamber and the inducer have a buffering effect on the impact of the incoming flow, making the pressure distribution more uniform. Due to the matching angle and the rotor-stator interference, the pressure pulsation in the guide vanes has distinct sub-harmonic interference during the natural flow process.

Turbulent heat transfer characteristics in compound channels with gap

Hong, Seong-Ho,Seo, Jeong-Sik,Byun, Jae-Ki,Choi, Young-Don,Shin, Jong-Keun 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.9

To examine the characteristics of turbulent flow and heat transfer about the compound channel with gap, the present study has performed a numerical analysis by using large eddy simulation (LES). Our first aim was to analyze the cause of pulsating flow by investigating the turbulent flow through the unsteady analysis of compound channel. Next, to understand the correlations between gap width and heat transfer enhancement, we tried to verify the enhancement effect of heat transfer when a gap exists within the compound channel. From this numerical analysis, we could see that the lateral velocity occurs periodically around the gap and this is developed in the pulsating flow. The pulsating flow has generated a strong turbulent flow mixing within the compound channel. And the turbulent flow mixing in the pulsating flow plays an effective role of enhancing heat transfer effect by making the fluid temperature uniformly within the compound channel.

Computer Simulation of Anisotropic Turbulent Flows in Nuclear Subchannels

김휴찬,김신 濟州大學校 産業技術硏究所 1998 산업기술연구소논문집 Vol.9 No.2

The prediction of thermal hydraulic field in nuclear subchannels is important to the design and the safety analysis of nuclear reactor. The accurate prediction requires the detailed knowledge of the flow structure. which is complicate due to anisotropic turbulent phenomenon. The flow pulsation phenomenon in rod bundle flow fields has been proposed as one of main causes of anisotropic eddy diffusion. In this study. the anisotropy factor for the fluid flows through rod bundles is estimated with the scale analysis on the flow pulsation phenomenon. Based upon the assumption that the transport process is composed of isotropic turbulent motion (turbulent motion without the flow pulsation) and flow pulsation. the scale relation for the anisotropy factor is derived. The derived scale relation is compared with published experimental results and show good agreements. Also, an anisotropy factor model for the numerical calculation of the turbulent flow field in rod bundles is suggested based on the derived anisotropy factor scale relation.

디젤기관의 흡ㆍ배기관 맥동류가 체적효율에 미치는 영향

이상득(S. D. Lee),강희영(H. Y. Kang),고대권(D. K. Koh),안수길(S. K. Ahn) 한국동력기계공학회 2005 한국동력기계공학회 학술대회 논문집 Vol.- No.-

The pressure fluctuation in the intake and exhaust pipe of 4 stroke-cycle diesel engine is caused by reciprocating motion of piston for suction of fresh air and exhaust of burned gas. this gas dynamic effect can be utilized for increase the volumetric efficiency. Many empirical studies have been carried out to investigate the effects of intake pulsating flow on the volumetric efficiency. However, when the gas dynamic effects are utilized for the variable speed engine to increase its performance, The speed range in which the volumetric efficiency is maximum is limited and there occurs some difficulties in lay-out of intake system because it become too long. During induction process, as waves travel both directions, they are reflected and interacted each other and pressure waves are transmitted through it. Hence, the flow becomes more complex and unsteady flow. These pressure waves act upon intake pulsating flow and affects on the volumetric efficiency. In this paper the effects of pulsating flow of intake and exhaust pipes on volumetric efficiency were examined and evaluated. It was found that volumetric efficiency was affected by pulsating flow of intake and exhaust pipes.

다양한 작동유체로 충전된 폐쇄 루프 맥동 히트파이프 내부 유동패턴 비교

강석구(Seok Gu Kang),김성근(Seong Keun Kim),히발 아흐메드(Hibal Ahmad),정성용(Sung Yong Jung) 한국가시화정보학회 2019 한국가시화정보학회지 Vol.17 No.3

Thermal performance and flow patterns inside the closed loop pulsating heat pipe (CLPHP) were experimentally investigated. For investigating the effect of working fluids, CLPHP was filled with various working fluids including methanol, acetone and ethanol. The thermal resistance was calculated by temperatures in evaporator and condenser and flow patterns were visualized by a digital camera. The thermal resistances for all fluids were decreased as the heat increases. Flow patterns change from static slug to elongated slug flows, bulk circulation and annular flows as the heat increases. Dry-out occurs after annular flows. For reasonable comparison of thermal performances, normalized CHF, Kutateladze number (Ku), was compared. Even though ethanol has smallest CHF, Ku of ethanol is similar with that of methanol. In addition, acetone has the highest Ku that means CLPHP with acetone provides the higher thermal performance compared with CLPHP with other fluids.

연료유량 제어밸브의 작동특성에 따른 로컬 당량비 변화와 연소 및 질소산화물 발생의 관계

이후경,김종현,박정수,곽영태 한국연소학회 2022 한국연소학회지 Vol.27 No.3

The present work investigated the NOx reduction effect that can be obtained by periodically changing the local equivalence ratio by repeatedly controlling the fuel flow. When there was no pressure pulsation of the fuel, the NOx emission was 30.3 ppm (O2 vol.11%), and the NOx emission was reduced from 4% to 30% according to the pulsation variables. Since it is difficult to directly measure the instantaneous mass and volumetric flow rate during a periodic change on a 103-millisecond scale in an industrial-scale experiment, the measured pressure was used to calculate the mass and volumetric flow rate. The fuel and air supply pressure was fixed at 700 mmH2O, and when flow pulsation occurred in the fuel pipe, the pressure was changed within the range of 150 to 694 mmH2O. As a result of calculation through the one-dimensional model, it had a local equivalence ratio range of 0.108 to 0.776. In the chemical equilibrium domain of methane, the relationship between the local equivalence ratio change and combustion products according to the operating characteristics of the fuel-flow pulsation valve was discussed