Characteristics Of Swirling Flow Research Articles

206 まっすぐな円管内の乱流旋回流の特性 : 旋回強度の増加にともなう流れの変化(流体工学(乱流・混合・拡散))

206 まっすぐな円管内の乱流旋回流の特性 : 旋回強度の増加にともなう流れの変化(流体工学(乱流・混合・拡散))

Numerical Study on Optimum Designing of the Air Distribution Structure of a New Cyclone Combustor

A new type of cyclone combustor is designed based on the traditional pulverized coal liquid slag combustor in this paper. According to the characteristics of swirl combustion and flow, numerical simulation of pulverized coal combustion in a new cyclone combustor has carried out using Realizable k-ε equation model with swirl modified to gas phase and stochastic trajectory model under Lagrange coordinate system to particle phase. Flows and combustion characteristics under different working conditions are mainly studied by changing the angles of primary and secondary air inlets, and then structural characteristics of the combustor are analyzed. Results show that structural characteristics of the primary and secondary air have great influence on internal flow and combustion characteristics of the combustor. When the pitch angle, the rotation angle of the secondary air and the expansion angle of the primary air respectively are 20°, 51° and 60°, the combustion efficiency of the combustor can reach up to 98.1% and it is conducive to high-temperature liquid slagging. It is also helpful to prevented pulverized coal depositing and accumulating near the wall and then plugging the combusting channel during the starting stage in low temperature region.

Large-eddy simulation and acoustic analysis of a turbulent flow field in a swirl-stabilized combustor

To conduct a comprehensive study on the flow characteristics and acoustic oscillation in a gas turbine combustor, a 3D large-eddy simulation (LES) was implemented. The formulation consists of the Favre-filtered conservation equations of mass, momentum, and energy. The subgrid-scale dynamics are modeled using a compressible flow version of the Smagorinsky model. To investigate the dominant coherent structure, the proper orthogonal decomposition (POD) method was used for post-processing. The combustor of concern is the LM6000, lean-premixed dry low-NOx annular combustor, developed by General Electric Aircraft Engines (GEAE). Four important characteristics of swirl flow are visualized: vortex breakdown, procession and dissipation of vortical structures, recirculation zones, and helical waves immediately downstream of the swirl injector. It is shown that the turbulent motion of swirl flow directly affects acoustic oscillation through the cycle and spectral analysis. The four most dominant acoustic modes are extracted from the flow field by the POD analysis. The transverse modes in the y and z directions are dominant in all four modes, since the pressure fields are significantly affected by swirl flow.

Highly swirling transient flows in spray dryers and consequent effect on modeling of particle deposition

Cotton turf and hotwire measurements were used to experimentally assess the highly swirling flow characteristics in a spray dryer fitted with a rotary disc atomizer. The numerical simulation captured key features of the flow field. Analysis revealed that rapid rotation of an atomizing disc tends to centrifugally split the central inlet jet. The flow field exhibited significant long time-scale transient behaviour. However, this centrifugally split jet resulted in a balanced upward recirculation region in the chamber as expected by the jet-feedback mechanism. Detailed analysis using a ‘transient air-steady particle’ approach revealed that this approach is applicable for such highly swirling transient flows as well. However, caution should be exercised when interpreting the deposition results, particularly in regions of low particle velocities. This is anticipated be an important consideration in future attempts to simulate the predominantly transient flows in spray dryers.

1103 まっすぐな円管内の乱流旋回流の特性 : 旋回の減衰にともなう軸速度の変化(流体力学I)

1103 まっすぐな円管内の乱流旋回流の特性 : 旋回の減衰にともなう軸速度の変化(流体力学I)

Friction and heat transfer characteristics of laminar swirl flow through the round tubes inserted with alternate clockwise and counter-clockwise twisted-tapes

The thermohydraulic characteristics of the circular tubes equipped with alternate clockwise and counter-clockwise twisted-tapes (TA) for the Reynolds number ranging from 830 to 1990, are reported. In the experiments, the twisted tapes with three different twist ratios (y/W = 3, 4 and 5) were inserted individually into the uniform wall heat flux tubes where water was utilized as the working fluid. The plain tube and the tube inserted with twisted tape (TT) were also tested, for comparison. The obtained results reveal that, Nusselt number, friction factor and thermal performance factor associated by TA are higher than those associated by TT. Among the tapes examined, the one with the smallest twist ratio of y/W = 3 is found to be the most efficient for heat transfer enhancement. For the range studied, the applications of both TT and TA for heat transfer enhancement are found to be promising since the thermal performance factors determined under the same pumping power are all above unity. In addition, the empirical correlations for Nusselt number, friction factor and thermal performance factor have also been developed. The consequential results obtained from the correlations are found to be in good agreement with the experimental results within ± 8% variation for Nusselt number (Nu), ± 8% for thermal performance factor (η) and ± 5% for friction factor (f).

Investigation on the Effects of Various Swirl Generators on Heat Transfer and Fluid Flow in Decaying Swirling Flows

Influences of three typical vortex generators on flow pattern and ensuing heat transfer augmentation were investigated and compared at similar Re and swirl numbers inlet conditions. Studied swirlers such as propeller swirlers, jet-type swirlers, and rotating honeycombs were installed at the pipe inlet. Reynolds number ranges from 10000 to 30000. Swirlers were set on the swirl numbers 1.4, 0.89, and 0.52, which were obtained by propellers. This study has been carried out under uniform heat flux condition and air was employed as the working fluid. The obtained results provide the individual effects of each swirler configuration on mean flow and turbulence distribution as well as on enhancement of heat transfer. Considering S=1.4, jet-type swirlers pointed 133 per cent Nu enhancement compared to axial flow, whereas propellers and rotating honeycombs approached 105 per cent and 79 per cent, respectively. For S=0.89, relative treatment has been changed and propellers with 70 per cent Nu augmentation demonstrated tip-top performance behind of which other swirlers lined. By decreasing the swirl number, approximately closer heat performances were represented from all swirler configurations. Comparison of the results of various swirlers exhibited that Re and swirl numbers are not generally sufficient to determine the swirling flow characteristics and each swirler confirms an individual flow quality.

Investigation of the turbulent swirl flows in a conical diffuser

Results of the theoretical and experimental investigations of the turbulent mean swirl flows characteristics change along straight conical diffuser of incompressible fluid (air) are presented in this paper. The main swirl flow characteristics review is given. In addition: the specific swirl flow energy, the energy loss, the mean circulation, the swirl flow parameter, the ratio between the swirl and axial flow loss coefficients change along the diffuser are presented. Among other values: the Boussinesq number, outlet Coriolis coefficient and swirl flow loss coefficient dependences on inlet swirl flow parameter are also given. The swirl flow specific energy and outlet Coriolis coefficient calculation procedure are presented in this paper, as well as experimental test bed and measuring procedures. The swirl flow fields were induced by the axial fan impeller. Various swirl parameters were achieved by the impeller openings and rotational speeds.

410 まっすぐな円管内の乱流旋回流の特性 : 旋回の減衰にともなう流れの変化(流体工学/機素潤滑設計)

410 まっすぐな円管内の乱流旋回流の特性 : 旋回の減衰にともなう流れの変化(流体工学/機素潤滑設計)

まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における旋回の減衰(流体工学,流体機械)

まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における旋回の減衰(流体工学,流体機械)

Study on the effect of various parameters on flow development behind vane swirlers

Swirl flow has applications in many of the engineering equipments. Good amount of calculations exist which have been developed for design of propellers. However, swirler design for combustion applications is different from that for propeller applications. In the former swirl flow is generated by the application of tangential component to the axial flow whereas in the latter swirl is generated by the rotating propellers. Therefore it comes under the category of rotating flows. Quite a few studies have been carried out on vane generated swirl flows over the past four decades. Majority of the studies were based on experiments. Over the last one decade, attention has been focused on the numerical predictions. Due to the advent of fast digital computers, nowadays the CFD studies are becoming the part of the design methodologies. This study mainly focuses attention on arriving at best vane angle from aerodynamic aspects for the combustion applications. As there are large number of flow and geometric parameters involved arriving at the best design by experimental methods is rather difficult compared to CFD analyses. The important geometric parameters are vane angle, vane numbers and hub to tip ratio. The flow parameter involves the selection of appropriate turbulence model for the prediction. The uniqueness of this study is in arriving at the best vane angle using appropriate turbulence models for both weak and strong swirl. To this end experimental and numerical studies have been carried out. It is found that no single turbulence model is able to handle both weak and strong swirl. From this study it is concluded that for weak swirl standard k – ε model is sufficient whereas for strong swirl one has to resort to Reynolds stress model. The characteristics of swirl flow are evaluated by means of size of the recirculation zone, mass trapped in the recirculation zone and also the pressure drop. Over the range of vane angle investigated the best vane angle is found to be 45°.

405 まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における旋回の減衰機構(流体工学I)

405 まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における旋回の減衰機構(流体工学I)

Numerical and experimental examination of swirl flow in a cylindrical container with rotating lids

Swirl flow is the primary mechanism for separation of particles in a hydrocyclone and hence influences the performance. The study of examining the basic swirl flow mechanism is accomplished by using a cylindrical apparatus with rotating lids. The upper and lower lids of the cylinder are able to rotate in the counter and clockwise direction at different angular velocities. In this study, the basic mechanisms of swirling in the laminar regime are investigated using an optically clear cylinder with rotating lids. The cylinder is filled with a liquid and the upper and lower lids of the cylinder are allowed to rotate in the clockwise and counter-clockwise directions. The induced flow is measured with a laser doppler anemometer and is compared to the velocity predictions from an in house developed software which solves the equations of motion. The results presented here constitute the first step in a series of experiments with the ultimate goal to improve the separation mechanism of hydrocyclones by means of controlling swirling flow characteristics.

제3세대 LPLI 엔진 연소실내 스월유동 및 희박연소 특성 해석

The intake swirl motion, as one of dominant effects for an engine combustion, is very effective for turbulence enhancement during the compression process in the cylinder of 2-valve engine. Because the combustion flame speed is determined by the turbulence that is mainly generated from the mean flow of the charge air motion in intake port system. This paper describes the experimental results of swirl flow and combustion characteristics by using the oil spot method and back-scattering Laser Doppler velocimeter (LDV) in 2-valve single cylinder transparent LPG engine using the liquid phase LPG injection. For this, various intake port configurations were developed by using the flow box system and swirl ratios for different intake port configurations were determined by impulse swirl meter in a steady flow rig test. And the effects of intake swirl ratio on combustion characteristics in an LPG engine were analyzed with some analysis parameters that is swirl ratio, mean flow coefficient, swirl mean velocity, fuel conversion efficiency, combustion duration and cyclic variations of indicated mean effective pressure(IMEP). As these research results, we found that the intake port configuration with swirl ratio of 2.0 that has a reasonable lean combustion stability is very suitable to an 11ℓ heavy-duty LPG engine with liquid phase fuel injection system. It also has a better mean flow coefficient of 0.34 to develope a stable flame kernel and to produce high performance. This research expects to clarify major factor that effects on the design of intake port efficiently with the optimized swirl ratio for the heavy duty LPG engine.

719 まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における境界層発達(GS 流体工学(その2))

719 まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における境界層発達(GS 流体工学(その2))

522 まっすぐな円管内の乱流旋回流の特性 : 弱い旋回流入時の旋回減衰機構(流体工学VI)

522 まっすぐな円管内の乱流旋回流の特性 : 弱い旋回流入時の旋回減衰機構(流体工学VI)

304 まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における流れの変化(流体工学(1))

304 まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における流れの変化(流体工学(1))

2323 旋回流における界面活性剤水溶液の流動特性とレオロジー特性の関連性に関する研究(S42-5 複雑流体の流動現象(5),S42 複雑流体の流動現象)

2323 旋回流における界面活性剤水溶液の流動特性とレオロジー特性の関連性に関する研究(S42-5 複雑流体の流動現象(5),S42 複雑流体の流動現象)

209 まっすぐな円管内の乱流旋回流の特性 : 弱い旋回流入時の角運動量の変化(流体工学(2))

209 まっすぐな円管内の乱流旋回流の特性 : 弱い旋回流入時の角運動量の変化(流体工学(2))

まっすぐな円管内の乱流旋回流の特性 : 旋回の減衰に伴う壁近傍旋回角の変化(G.S. 内部流の実験と計算,OS2:乱流中の渦構造および流れの制御)

まっすぐな円管内の乱流旋回流の特性 : 旋回の減衰に伴う壁近傍旋回角の変化(G.S. 内部流の実験と計算,OS2:乱流中の渦構造および流れの制御)