Swirl Characteristics Research Articles

Large eddy simulation investigation of S-shaped intake distortion and swirl characteristics

Curvature change of an S-duct wall naturally causes total pressure and swirl distortions in a compressor inlet. In this study, the large eddy simulation (LES) method is used to investigate the internal flow of a continuous variable curvature S-duct without a downstream compressor. A comparison between the numerical results and the experimental data verifies the effectiveness of the LES method in analyzing the internal flow mechanism of an S-duct. Based on the SAE standard, the transient distortion descriptors of the research cross-section are quantitatively analyzed, and the distortion characteristics of the total pressure and swirl in the aerodynamic interface plane (AIP), downstream outlet plane, and their spatial–temporal variation processes are revealed. Furthermore, the proper orthogonal decomposition and sparsity-promoting dynamic mode decomposition methods are used to decompose the flow structures of the AIP velocity fields, and the main coherent structures affecting the flow and their corresponding frequency/attenuation characteristics are obtained. The results indicate that the twin two swirl pattern near the wall annulus of the S-duct is dominant at high Reynolds numbers, and turbulent mixing downstream inhibits the development of distortion and swirl. In addition, some stable low-frequency mode structures exist near the Starboard, exhibiting multi-spiking frequency properties. Thus, this study reveals the generation, development, and evolution mechanisms of distortion and swirl at the upstream of a compressor inlet, and the analysis results of distortion and swirl characteristics can provide important input conditions for subsequent compressor distortion research and influence analysis of mass injection pre-compressor cooling technology.

Analysis of internal flow characteristics and determination of the core structural parameters of a stellate labyrinth channel irrigation emitter

The hydraulic and anti-clogging performance of irrigation emitters are mainly governed by the internal flow characteristics in the flow channel. Computational fluid dynamics (CFD) and experiments were used to analyse internal flow characteristics and determine the key structural parameters of a stellate labyrinth channel irrigation emitter. Through experimental verification, the realisable k-ε model provided the best results for simulating the flow field. Five structural parameters of stellate labyrinth channel emitter were selected to study the influence on the flow characteristics inside the flow channel comprehensively. The velocity fields and profiles are presented along the stellate labyrinth channel. Turbulence properties and turbulent kinetic energy of flow inside the stellate labyrinth channel are analysed and discussed. The vortex zones consume energy and promote the deposition of particles. The swirling motion zone in stellate labyrinth channel emitter flow channel must be described to analyse flow characteristics. The advanced Q-criterion method was applied to identify and characterise the vortex zones in the stellate labyrinth flow channel. Through analysis results of the influence of different structural parameters on velocity fields, turbulence properties, and swirl characteristics, it was shown that a, r, h, and θ are main structural parameters that affect the flow characteristics in stellate labyrinth channel irrigation emitter. The results of this study provide references for the design theory of the new types of flow channel emitter.

The influence of the adverse pressure gradient on the flow characteristics of a serpentine nozzle with film cooling

With the increase of the turbine inlet temperature, the thermal load of serpentine nozzles increases greatly, leading to the stiffness degradation and structure deformation. Therefore, efficient cooling technologies are required. There are adverse pressure gradients (APGs) and strong swirl characteristics in the serpentine nozzle. Therefore, the film cooling design of serpentine nozzles faces greater difficulty than that of other exhaust systems. This paper aims to obtain the flow characteristics of serpentine nozzles with film cooling and to provide theoretical support for the film cooling design of serpentine nozzles. We obtained the influence of the APG and the favorable pressure gradient (FPG) on the flow characteristics of a serpentine nozzle with film cooling via the employment of numerical methods. The results show that the APG obstructs the flow of the cooling airflow, and causes a part of the cooling airflow to decelerate, to stagnate, and eventually to flow in the reverse direction, thus forming a recirculation zone. The counter rotating vortex pair (CRVP) induces the anti-counter rotating vortex pair (ACRVP) near the boundary layer of the wall, and the ACRVP develops rapidly in the recirculation zone. With the development of the ACRVP, the CRVP leaves the wall and gradually dissipates. As the blowing ratio increases, the recirculation zone moves downstream, and the recirculation zone first expands and then shrinks, such that the location where the ACRVP develops also moves downstream. There is no recirculation zone under the influence of the FPG, and the CRVP occupies the core of the cooling airflow along the flow direction.

Experimental investigations on flow and heat transfer characteristics in a high-speed rotor–stator disk cavity with axial throughflow

The rotor–stator disk cavity system is of great importance for turbine blade cooling and preventing gas invasion in the aircraft engine. This study presents an experimental investigation on a high-speed rotor–stator disk cavity with axial throughflow. The aims are to experimentally measure and reveal the pressure characteristics, windage heating, swirl characteristics, and relative temperatures at a high rotational speed of 0–9000 rpm with mass flow rates of 0.05–0.15 kg/s. Especially, a new measurement idea was proposed and tested that relative temperature in the rotor system can be obtained by measuring absolute parameters in the stator system. Experiment results reveal that rotational speed and inlet mass flow are the main parameters to determine flow characteristics in the rotor–stator cavity. The increase of rotational speed will enhance the effect of centrifugal boosting, windage heating, and swirl characteristics. But increasing inlet mass flow rate will lead to the opposite effect. When the airflow is in the heat balance state, relative total temperature and adiabatic temperature can be acquired by measuring absolute temperature and swirl ratio at the same radius. The maximum deviation is below 2 K. The results can be beneficial to the optimization design of rotor–stator disk cavity in the gas turbine engines.

Numerical investigation of injection parameters and piston bowl geometries on emission and thermal performance of DI diesel engine

Tightening noose on engine emission norms compelled manufacturers globally to design engines with low emission specially NOx and soot without compromising their performance. Amongst various parameters, shape of piston bowls, injection pressure and nozzle diameter are known to have significant influence over the thermal performance and emission emanating from the engine. This paper investigates the combined effect of fuel injection parameters such as pressure at which fuel is injected and the injection nozzle size along with shape of piston bowl on engine emission and performance. Numerical simulation is carried out using one cylinder naturally aspirated diesel engine using AVL FIRE commercial code. Three geometries of piston bowls with different tumble and swirl characteristics are considered while maintaining the volume of piston bowl, compression ratio, engine speed and fuel injected mass constant along with equal number of variations for injection nozzle size and pressures for this analysis. The investigation corroborates that high swirl and large turbulence kinetic energy (TKE) are crucial for better combustion. TKE and equivalence ratio also increased as the injection pressure increases during the injection period, hence, enhances combustion and reduces soot formation. Increase in nozzle diameter produces higher TKE and equivalence ratio, while CO and soot emission are found to be decreasing and NOx formation to be increasing. Further, optimization is carried out for twenty-seven cases created by combining fuel injection parameters and piston bowl geometries. The case D2H1P1 (H1 = 0.2 mm, P1 = 200 bar) found to be an optimum case because of its lowest emission level with slightly better performance.

Research on performance matching of intake and exhaust ports of marine medium speed dual fuel engine

The performance influence on the dual fuel engine by the intake/exhaust port flow coefficient and swirl are major factors to the dual fuel engine. Therefor the optimization of the intake and the exhaust ports was carried out to ensure the adaptability of the airway structure to the ACD320 dual fuel engine in this paper. According to the limitation conditions of the structural parameters, the multiple airways crossing the diameter of the intake/exhaust port were designed. The research on variation rules of flow and swirl characteristics in different intake/exhaust port circulation cross-sectional area by aerodynamics modeling and simulating approach to optimizing the matching degree between the cylinder and the intake/exhaust port of a marine dual fuel engine was presented. And the optimizing match results were verified and analyzed by the experimental results of the practical intake and exhaust port models. The influence on the performance by the intake/exhaust air flow area and the valve lift is analyzed comprehensively by the AVL test results of the intake and the exhaust ports. The suction and combustion processes at different size of intake and exhaust port are simulated by AVL Fire to validate the optimum matching. Results show that the intake flow coefficient tends to be stable when the diameter of the intake port greater than 83 mm, the swirl number tends to be stable when the diameter of the intake port greater than 88 mm and the exhaust flow coefficient tends to be stable when the diameter of the exhaust port greater than 80 mm. Analysis show that the mean flow coefficient present optimum consequence when the diameter of the intake port is 88.6 mm. By analyzing and comparing intake airflow, efficiency, emissions and indicate power, the fifth group (intake port 88.60 mm, exhaust port 80.00 mm) matching is the optimum matching for ACD320 type marine dual fuel engine. The results provide reference for the design and optimization of dual fuel engine.

Key Structural Parameters Analysis of Effective HydroClean Drill Pipe

In directional well, horizontal well and extended reach well, there is a common problem that cuttings bed is easy to form in the process of drilling in highly deviated section. To solve this problem, an Effective Hydro Clean Drill Pipe (EHCDP) is designed, and the flow characteristics of the annular flow field under the action of EHCDP are analyzed by using computational fluid dynamics (CFD) simulation technology. On this basis, the key structural parameters affecting the swirl characteristics of EHCDP are studied. The results show that when the number of spiral grooves is 3, the axial and tangential velocities of annular fluid in spiral groove section will be greater, which is conducive to carrying and removing cuttings. Compared with the inclination angle of spiral groove with 1000 mm lead, that of spiral groove with 500 mm lead is larger, which has more obvious stirring effect on flow field, and the effect of cuttings removal is better. In addition, the spiral groove with 90 degree groove angle is more conducive to cuttings removal than the spiral groove with 30 degree groove angle. The results can provide a basis for the selection and optimization of structural parameters of spiral groove.

A novel centrifugal gas liquid pipe separator for high velocity wet gas separation

Cyclones are the most widely used separators at present, but it's still difficult to reduce their size to serve as pipe separators. A new type of gas liquid pipe separator for high velocity wet gas is proposed in this paper. The separator is actually a short section of pipe, with a centrifugal device in the center portion and 3 narrow tangential conduits (NTC) in the pipe wall. As gas liquid mixture flows through the centrifugal device downwardly, a strong rotation flow is created. Liquid in the mixture is pushed to the pipe wall by centrifugal force and forms a uniform liquid film with high tangential velocity. Then nearly all the liquid film can directly enter the NTC and be discharged from the pipe relying on its own kinetic energy and inertial, because of the little resistance characteristic of NTC to the liquid film, therefore the whole separation process can be completed within the pipe. The swirl characteristics in the pipe were studied by numerical method, and the simulation results indicated that the swirling liquid film is fairly uniform and the suitable installation position for NTC is about 2.5 pipe diameters downstream of the centrifugal device. A separation model for the pipe separator was established and experiments were carried out to verify the proposed model. The superficial velocity ranges of gas and liquid were 22–72 m/s and 0.07–0.54 m/s, respectively. The experimental results showed that the separation efficiency always increases with the increase of both gas and liquid superficial velocity, generally it is over 0.81, and the maximum attainable is 0.97. However, the separation efficiency will begin to drop if liquid superficial velocity exceeds the critical value UCSL, due to the onset of unstable liquid film waves. Experimental results also showed that UCSL increases with the increase of gas velocity.

Grey-box modelling of the swirl characteristics in gas turbine combustion system

This paper has proposed a data-driven approach to study the airflow swirl characteristics in industrial gas turbine combustion system. A grey-box model is developed to represent the combustion system characteristics, based on real gas turbine measurements. The model inputs are the burner tip temperatures, and the outputs are the downstream gas temperatures. Then, the model parameters are determined using a hybrid genetic algorithm–quasi-Newton optimization scheme. The efficacy of the proposed approach is demonstrated through a case study. It is shown that the proposed model can be a useful tool that adds to the existing array of gas turbine combustion monitoring applications.

Optimizing swirl in compact uniflow cyclones

This paper presents an experimental examination of the velocity field distribution in the separation chamber of a uniflow cyclone with closed particle outlet to evaluate the swirl characteristics in the vortex finder region based on stereoscopic particle image velocimetry. A cold flow model with a closed particle outlet was used to assess different angles of attack and core size ratios at typical Reynolds numbers for the separation of low loaded gas‐solid flows. The focus of the study was on the relationship between swirl strength as well as performance data. At higher angles, the parabolic swirl strength distribution changed to a region with constant high acceleration of the particles in the separation zone. Integral and differential swirl numbers were correlated with the ratio of tangential to radial velocity and to the calculated cut size diameter. At low angles of attack, implying a strong redirection of flow perpendicular toward the main flow direction and small core size ratios, defined by the radial distance between hub and tip, the local differential swirl number can be more than twice as large as in the base configuration. Yet, the integral swirl number hardly changed. The velocity fields showed mean tangential to radial velocity ratios ranging from 0.73 to 6.85 at swirl vane angles of 15 °–60 °; core size ratios between 0.125 and 0.625 at vortex finder diameter were measured and calculated cut size diameters between 10 and 90 μm were derived. This data provides the foundation for further validation studies and the development of new design criteria. © 2018 American Institute of Chemical Engineers AIChE J, 65: 766–776, 2019

Experimental investigation of flows in a high-head pump-turbine draft tube at turbine mode

The accurate prediction of flow patterns is essential during the optimization design of a pump-turbine. To determine the flow patterns and validate the flow simulation inside a pump-turbine, Laser Doppler Velocimetry (LDV) measurements and 3D flow simulation in the draft tube cone of a high-head pump-turbine model have been performed at normal operating conditions in turbine and pump modes. Velocity distributions were measured for operating conditions covering the speed factor nED=0.21 and 0.19 at turbine mode for loads ranging from 40% to 100% the rated power as well as best efficiency point. Measurements of unsteady flows inside the draft tube cone were conducted at a high precision hydraulic model test rig with LDV system from TSI Co. The 3D flows through the pump-turbine model were numerically simulated with ANSYS/CFX® software at all the measured operating points. Both measured and simulated velocity profiles are presented and analyzed to show the influence of operating parameters on the velocity and swirl characteristics in draft tube inlet. Comparison of the measurement and simulation shows rather good agreement at the best efficiency point and full load but clear discrepancies at part load. The experiment data such as the velocity profiles, pressure signals, and amplitude and frequency characteristics of the instantaneous tangential velocity at various loads offers the possibility to assess the precision in performance prediction in the pump-turbine using the numerical simulation methods. The measured instantaneous tangential velocity at part loads reveals a periodic peak, which is asynchronous to that of runner’s rotating speed and can be used to determine the characteristic frequency of rotating vortex rope at part loads. Axial and tangential velocity fields obtained from LDV measurements at normal operating points can be used to validate the numerical simulation in optimization design.

Investigation of Cycle-to-Cycle Variation of In-Cylinder Engine Swirl Flow Fields Using Quadruple Proper Orthogonal Decomposition

It has been observed that the swirl characteristics of in-cylinder air flow in a spark ignition direct injection (SIDI) engine affect the fuel spray dispersion and flame propagation speed, impacting the fuel mixture formation and combustion process under high swirl conditions. In addition, the cycle-to-cycle variations (CCVs) of swirl flow often degrade the air–fuel mixing and combustion quality in the cylinder. In this study, the 2D flow structure along a swirl plane at 30 mm below the injector tip was recorded using high-speed particle image velocimetry (PIV) in a four-valve optical SIDI engine under high swirl condition. Quadruple proper orthogonal decomposition (POD) was used to investigate the cycle-to-cycle variations of 200 consecutive cycles. The flow fields were analyzed by dividing the swirl plane into four zones along the measured swirl plane according to the positions of intake and exhaust valves in the cylinder head. Experimental results revealed that the coefficient of variation (COV) of the quadruple POD mode coefficients could be used to estimate the cycle-to-cycle variations at a specific crank angle. The dominant structure was represented by the first POD mode in which its kinetic energy could be correlated with the motions of the intake valves. Moreover, higher order flow variations were closely related to the flow stability at different zones. In summary, quadruple POD provides another meaningful way to understand the intake swirl impact on the cycle-to-cycle variations of the in-cylinder flow characteristics in SIDI engine.

Evaluation of the swirl characteristics of a tidal stream turbine wake

Tidal stream turbines (TSTs) produce a rotating downstream wake. This paper describes the characteristics of the swirl flow in the wake of a TST with a view of comparing these against classical swirl theory and investigating whether swirl is an important factor in wake recovery prediction.Using computational fluid dynamics the paper describes the characteristics of velocities, pressure drop, viscosity and swirl number of 2, 3 and 4 bladed TSTs. To provide confidence in the results the characteristics are compared to the findings in the literature for a set of generic swirl generators. The swirl numbers for the TSTs in a 3.08m/s tidal (plug) flow were found to be between 0.14 and 0.28, which describes a weak or very weak swirl flow. Whilst the characteristics are in agreement with theory it also means that the swirl component of the wake is not coupled with the axial component and cannot be used to estimate the wake length. However, peak swirl number for the 4 bladed turbine is close to the threshold of 0.3 at which axial velocity starts to become coupled with tangential velocity and therefore wake recovery may be related to S for some turbine designs.

Control Port Influence on Swirl, Operating, and Flow Characteristics of a Mini-Vortex Amplifier on Glove Box Service

Abstract Vortex amplifiers (VA) use fluidic phenomena to modify flow through a containment breach, when used to protect glove box workers from exposure to the contents. The influence of control port geometry on swirl, operating characteristics, global flow, and momentum characteristics is studied experimentally. Shape and size of the control flow channels and the pressure applied at the tangential ports are critical in determining the trajectory of the jet issuing from the tangential ports and deflection of radial flow and vortex strength. Dominance of control-to-exit area ratio is confirmed. A clear improvement in performance is noted for a practical geometry derived from shaped passages of the device. Flow and momentum characteristics provide additional design data. The relationship of swirl number to output flow is demonstrated. Global flow and momentum characteristics provide insight into design and operation that is useful when avoiding back diffusion.

3D Numerical Simulation on the Variable Swirl Intake Process of Diesel Engine

To study the flow and swirl characteristics in the variable swirl intake system of a four-valve diesel engine, a numerical simulation with using the three dimensional CFD software AVL-FIRE, was calculated on the intake flow in three types of inlet of the engine. Two swirl-control valve plans are posed and a better plan was selected through the comparative study. The result shows that with a lager valve lift the flow characteristic of spiral inlet is better than that of tangential inlet, and in the opposite case the results are also opposite. The double inlets make the swirl torque increase. When a swirl-control valve is set in the spiral inlet, the variable swirl effect is better, and it ensures better flow capacity and larger swirl ratio range.

Influence of Variable Swirl Intake Manifolds for DI Diesel Engine on in-Cylinder Air Motion

This paper developed a new design of variable swirl intake manifolds for four-valve DI diesel engine by setting swirl control valves in the intake manifolds. The 3-D numerical model under the same experimental condition was established and particular flow information in intake manifolds and cylinder was achieved. Influence of variable swirl intake manifolds on intake flow characteristics and in-cylinder swirl characteristics were analyzed. The simulation results show that the swirl intensity in cylinder can be tuned by this device. The swirl intensity increases gradually with decrease flow coefficient and it can meet the requirements of swirl intensity for different operating conditions.

Swirl characterisation in steady and unsteady flows with PIV measurements

A detailed aerodynamic analysis of the swirl characteristics of an in-cylinder flow generated by a cylinder head engine is presented and that can be easily extended to the case of real in-cylinder engine flow. The article contributes to the reflection related to the pertinence to keep the characterisation of the swirl generation from the cylinder head in steady rigs.

Measured vorticity distributions in a model of tangentially fired furnace

Simultaneous three-component six-sensor hot-wire probe measurements were made in a model of tangentially fired furnace (TFF) to measure the flow properties of an isothermal flow field. The quantities measured including the spatially resolved isothermal air velocity components and their two higher order moment statistical properties, i.e., the skewness and flatness factors, and the vorticity components and their skewness and flatness factors. Detailed experimental data provided an improved understanding of the behavior of the turbulent transport in the burner zone and in the upper and central regions of the TFF. The measured velocity and vorticity fields showed the swirl characteristics of the fluid flow in the TFF interior as expected and that the flow has attached to the walls in the burner zone and central region which is not desired in an operating TFF. The solid walls in these domains, including the pendants located in the upper region, act as vortex generators. Oscillation of the velocity components, and of the other quantities measured in the experiment, may be derived from the fragmentation of the vortexes and the coherent structures existing in the furnace interior. This work helps clarity the fouling and slagging mechanisms and the flow attachment in the burner zone and central region, the flow deviation and residual swirling downstream the pendants in the upper furnace, by giving insight into the vorticity and the coherent structures in the TFF.

Numerical Study of Swirl Properties of Rotating Conical Channel with Axial Flow

This work is concerned with a numerical study of the laminar flow of a viscous fluid between two coaxial cones, with the inner one rotating on which a constant axial flow is imposed. The two cones have the same apex angle value, so that the gap width between them is constant. Two configurations of the same volume are studied: (i) divergent flow passage (Div) and (ii) convergent flow passage (Cov), which represents geometrically the reverse case of (i). Analysis with the aid of the boundary layer assumptions is carried out by the use of an implicit finite difference method. A coordinate transformation is applied to the governing equations in order to remove the explicit effect of the apex angle from the calculation process for both cases, so that the boundary conditions can be simplified. The swirl characteristics are studied in both configurations with regard to the same inlet flux and the same rotation speed of the inner cone. The competition between centrifugal and axially-transporting effects in both cases is discussed. As a result, it is found that the swirl increases in Div from the entrance for a fixed value of the apex angle, while the swirl evolution in Cov depends strongly on the apex angle value.

A study on the effects of intake port eccentricity and a partition between the two intake ports on the in-cylinder swirl characteristics in a valve diesel engine

The effects of intake port eccentricity and a partition between the two intake ports on the incylinder swirl characteristics in a 4 valve diesel engine having the two intake ports, one is a helical intake port and the other is a tangential intake port, were investigated by using the impulse swirl meter(ISM) in a steady flow test rig. Mean flow coefficient ( , swirl ratio ( ) and the mass flowrate through the two intake ports with and without intake port partition were measured. The results showed that the characteristics of in-cylinder swirl ratio formed by a 4-valve cylinder head were largely affected by valve eccentricity ratio ( ) and the existence of an intake port partition between the two intake ports. Mean flow coefficient ( ) increases and swirl ratio ( ) decreases in case of being the partition between the two intake ports. And also the mass flowrate through the tangential intake port is 19.0% and 7.7% more than that of the helical intake port in case of the two intake ports with and without partition respectively.ively.