Swirl Ratio Research Articles

Experimental Investigation on the Influence of Swirl Ratio on Tornado-like Flow Fields by Varying Updraft Radius and Inflow Angle

The swirl ratio is the most critical parameter for determining the intensity and structure of tornado-like vortex, defined as the ratio of angular momentum to radial momentum. The angle of entry flow and the updraft radius are two key parameters affecting the swirl ratio. Many laboratory simulators have studied the effect of swirl ratio by changing the angle of entry flow, but there is a lack of research on the updraft radius. Therefore, for a deep sight of the impact of the updraft radius on the swirl ratio and tornado-like vortex, a laboratory tornado simulator capable of adjusting the updraft radius was designed, built, and tested. And, the effects of various swirl ratios caused by the updraft radius and the angle of entry flow on the tornado-like vortices were investigated, in terms of the dual-celled vortex transformation and vortex wandering. It was found that the effects of the updraft radius and the angle of turning vanes on the tornado-like vortices are quite different, and the formation of the dual-celled vortex is more sensitive to the updraft radius, because a larger angular momentum and axial pressure gradient can be provided. In addition, increasing the updraft radius has a greater inhibitory effect on the vortex wandering phenomenon compared to the angle of the turning vanes due to the flow fluctuations induced by turbulence.

Cyclic Analysis of In-Cylinder Vortex Interactions Based on Data-Driven Detection and Characterization Framework

Abstract The complex vortex flow interactions are critical to affect the fuel–air mixing and combustion stability in direct-injection engine. However, due to the strong cyclic variations inside engine, the multiscale swirl flow characteristics with cyclic details are difficult to be sufficiently revealed. Therefore, a vortex detection and characterization framework, including physical and data-driven methods, is implemented to elucidate the cyclic vortex interaction process. In this study, a high-speed time-resolved particle image velocimetry is applied to record the spatiotemporal flow behavior under three different swirl ratio conditions. First, the presence of vortex motion is detected at each crank angle for each engine cycle. Results show that the vortex interaction processes under different swirl ratio conditions exhibit distinctive characteristics. The presence of multiple vortices and their interactions are found to trigger dramatic changes and variations in swirl flow behavior. Then, the individual-cycle analysis of the vortex interaction effects on flow characteristics is conducted. The vortex characteristics including vortex location, strength, and size are examined with cyclic detail using data-driven unsupervised clustering. Results indicate that the vortex merging is the main source inducing the vortex characteristics variations. Furthermore, the occurrence and duration of the vortex merging process are found to be closely related to the intake swirl ratio and valve lift profile. Increased swirl ratio and valve lift cause vortex to merge earlier and reduce the merging duration. This finding provides a potential idea to alleviate the cyclic variation issue by controlling the vortex merging process.

Pressure loss control in a rotor-stator cavity with inward throughflow

The back cavity of a centrifugal impeller is a typical rotor-stator cavity system with centripetal inflow in small or medium-sized aeroengines. In this paper, the effectiveness of using the “vortex control hole” structure to control the pressure loss in such a cavity is studied with experiment and numerical simulation. Vortex control hole refers to the passage connecting the internal and external air flow of the cavity. It distributes on the stationary casing circumferentially with a well-designed angle to produce an opposite tangential velocity to the main flow, thus reducing the tangential velocity of the main flow in the cavity. By controlling the swirl ratio, the pressure loss at cavity outlet could be decreased. The rotating Reynolds number Re φ = 6 × 105∼2.4 × 106, and turbulence parameter λt = 0.21∼0.55. Since the mainstream velocity has no tangential component at the inlet, it is considered that the inlet swirl ratio β0 is 0. The numerical simulation results were compared with the experimental results. The flow structure, the distribution of the swirl ratio, and the static pressure loss at the outlet of the cavity under different secondary air stream rates will be given. The coupling mechanism between the secondary airflow and the main flow in the cavity and the mechanism of the secondary air stream reducing the pressure loss in the disc cavity will be analyzed.

Coupling mechanism of pressure and temperature in a co-rotating cavity with radial flow

In the secondary air system (SAS) of an aeroengine, co-rotating cavities with radial flow are in charge of extracting airflow from the compressor and providing it to the turbine. In high-speed cavities, pressure and temperature have a strong coupling correlation, which had not been investigated in previous studies. Accurate monitoring of airflow quality is a prerequisite for improving its cooling efficiency. In this study, theoretical analysis and verified numerical simulation were used to investigate the flow and heat transfer in the cavities, and a coupled prediction model (CPM) was developed to study the correlation among velocity, pressure and temperature. The results revealed that density, viscosity, and swirl ratio were important mediums for coupling pressure and temperature. Furthermore, autocorrelations existed in velocity, pressure, and temperature, and their fluctuations were rapidly transmitted through the mediums and eventually backfired. The CPM, which could be used to predict aerodynamic parameters, showed a relative average error of less than 10% compared to the Reynolds stress model (RSM).

Experimental and Numerical Investigation on Finned Vortex Reducer in a Rotating Cavity with a Radial Inflow

In aero-engines, a secondary air system is used to cool the rotor discs and seal cavities between rotor and stator parts. The pressure loss caused by bleed air can be effectively reduced by setting the finned vortex reducer. Thus, the bleed system design can be optimized by researching the flow structure and pressure loss of each section in the cavity with a finned vortex reducer. In this study, the influence of different installation positions of a finned vortex reducer on the pressure loss characteristics was investigated through experimental and numerical simulation methods, focusing on the radial inflow of the secondary air system. The results indicate that the inlet and outlet positions of the fins affect the flow structure in the cavity. The aerodynamic parameters (rotational Reynolds number ReΦ and mass flow rate coefficient Cw), together with the inlet and outlet radii of the fins, influence the pressure loss in the cavity. Considering the swirl ratio β constrained by the fins, a pressure loss model was established, which showed good agreement with the experimentally measured pressure loss. This model reflects the impact of the inlet and outlet positions of the fins on the pressure loss characteristics.

Study on Effect of Piston Bowl Depth on Intake Air Flow Behaviour Using Ansys Fluent Cold Flow

Gas flow behaviour is an extremely complicated question on internal combustion engine and plays a key role in air-fuel mixing performance. A proper mixture process significantly improves the combustion performance and thus enhances the engine efficiency. This study estimates the effect of different piston bowl depths on the flow field development inside the combustion chamber of a CNG engine using Ansys Fluent. The cold flow model was utilized without considering the combustion behaviour. The three-dimensional model was developed based on a single cylinder CNG converted engine. Four different bowl heights were applied while the compression ratio was maintained as the designed value of 10. The tumble and swirl as well as the turbulent flow pattern were investigated to consider the gas flow behaviour. The simulation results indicate that the tumble and swirl ratio increase with increasing of piston bowl depth. The case of bowl height 17 mm shows better flow behaviour and higher velocity for a good mixing performance as well as turbulence dissipation.

A numerical investigation of debris initialisation in tornado-like wind fields

The process of debris initialisation is examined for two tornado-like vortices with swirl ratios (S) of 0.3 and 0.7. The vortices were modelled using Large-eddy Simulation and the motion of spherical debris were calculated using Lagrangian-particle tracking. A total of 2700 individual debris particles, corresponding to three different groups (A, B and C) with different Tachikawa numbers (K=2.5, 1.2 and 0.6 respectively) were released. The vortex S=0.7 has greater magnitude of tangential velocity (∼12.7 m/s) compared to vortex S=0.3 (∼11.7 m/s). The corresponding maximum vertical velocities in the flow when S=0.3 were approximately twice those corresponding to S=0.7; this resulted in longer flight durations for debris group A, B and C, i.e., 65%, 73% and 58% longer respectively. An analysis of the spatial displacement of the vortex centre relative to the centre of the simulator shows that both vortices have a maximum displacement of less than 0.02 m. This suggests that the low wandering motions of the vortices have minimum effect on the debris initialisation. The vertical velocity component is shown to be key for the generation and sustaining of debris flight. For example, for S=0.3, approximately 22% (group A), 5% (group B) and 10% (group C) more particles were being initialised compared to S=0.7. The ensemble averaged flow fields associated with flight initiation show the greatest difference at low elevation (less than 0.11 m) compared to non-initialising conditions. It was also found that the tangential and radial velocity components have relatively little impact on flight initialisation. The findings presented in this research provide a fundamental insight into the physics which govern debris initialisation in tornado-like flow.

Effect of vanes on vortex characteristics of a vortex ventilation system

A modified local ventilation system using vortex flows with vanes is proposed to enhance ventilation performance. The effect of the vanes on the stability of vortex generation, its structure, and ventilation performance was experimentally investigated using particle image velocimetry measurements. The mean velocity vectors and vorticity contours with and without vanes were compared for Qex = 0.129 m3/s at Vs = 1.73 m/s to investigate the effect of vanes on the vortex characteristics. The flow structures, including the mean velocity field and vortex core size, were very similar with and without the vanes. However, distinct differences were found in the vortex characteristics related to vortex stability, including turbulent kinetic energy, circulation, swirl ratio, and vortex center distances. The normalized turbulent kinetic energy with vanes was observed to be relatively low in the core region. When the vanes were attached, the value of the circulation over the core region increased from 0.151 to 0.155; furthermore, Sc/Sin also increased by 3%. The results indicate that the vortex stability improved after installing the vanes. The concentration of particulate matter was measured to quantify the improvement in the performance of the vortex ventilation system. The improvement was evaluated by the increasing ventilation rate of up to 5.5% with vanes, which is attributed to the increase in vortex strength and stability. The results can be utilized as basic information to design vortex ventilation systems for large-scale factories.

CFD investigation the combustion characteristic of ammonia in low-speed marine engine under different combustion modes

As a carbon-free hydrogen-carrying fuel, ammonia can effectively solve the problem of greenhouse gas emissions and has great application potential in marine engines. At present, low pressure and high pressure injection are the two main combustion modes of low-speed marine engine, and the former is closer to the Otto cycle, while the latter is closer to the Diesel cycle. In this study, a low pressure direct injection natural gas/diesel dual fuel engine was converted to an ammonia/diesel engine (LP). High pressure direct injection ammonia/diesel engine was converted by a diesel-only engine (HP). The application of ammonia was compared in above two combustion modes. Results show that using ammonia in HP mode can easier get high power, but LP’s IMEP, efficiency performance is better. However, LP mode has a large risk of ammonia escape (2.79%) and unburning (5.49%), and N2O in the emission is also worthy of attention and further research. In addition, due to the difference in N2O, the greenhouse effect of LP mode is also greater. For ignition, LP mode is not only affected by diesel injection, but also in-cylinder swirl and equivalent ratio due to the influence of premix mode. Currently, the HP mode has more potential for marine engine.

Numerical study of flow characteristics of tornado-like vortices considering both swirl ratio and aspect ratio

Flow characteristics of tornado-like vortices are primarily influenced by the swirl ratio and aspect ratio. This study systematically investigates effects of these two essential parameters on vortex visualization, mean flow fields, and fluctuations by large eddy simulations (LES). The geometric dimensions of a tornado-like vortex simulator are characterized by the inner cylinder radius and floor height. The former affects the core radii where maximum tangential velocities occur, as well as the vortex type which is used to separate flow structures while the latter influences the vortex type. Furthermore, the ratios of flow characteristics of tornado-like vortices, such as radial distances where the maximum tangential and radial velocities occur, to the inner cylinder radius (RV.max/r0; RU.max/r0, Rc/r0) have a high correlation with the swirl ratio. The ratios of heights where the maximum tangential and radial velocities occur to the floor heights (ZV.max/H0; ZU.max/H0) are mainly related to the aspect ratio. These parameters can be expressed by the swirl ratio and aspect ratio with high R-squared values of 0.941, 0.794, 0.984, 0.964, 0.958. Finally, vortex types can be modeled as a function of both swirl ratio and aspect ratio. This study reveals the relationship between the simulator geometry and generated vortices.

Influence of Intake Valve Structure Combined with Valve Lift Dissimilitude on Intake Performance of Diesel Engine

For diesel engines equipped with a combined spiral/tangential inlet, the main object of the valve structure and valve lift dissimilitude strategies is the valve, the changes of both will alter the motion state of the in-cylinder airflow, which has an important impact on the formation and combustion of the mixture. In order to investigate the flow performance of valve structure and valve lift dissimilitude, this paper used computational fluid dynamics (CFD) numerical simulation and multi-parameter regression methods to optimize the dual intake valve structure and obtained three valve structures with better intake performance first. Then, the optimized intake valve structure models were combined with the valve lift dissimilitude schemes to conduct steady-flow tests for the intake port. Through the reasonable combining of the two, the intake performance of the original engine was further improved. The results show that the valve structure has a relatively small influence on the intake mass, while it has a greater effect on the formation of the swirl in the cylinder, increasing the swirl ratio by 8.0%. The optimized valve structure model was combined with the valve lift dissimilitude scheme. It was found that the valve structure with optimal intake mass combined with the dissimilitude scheme of the largest valve lift of the spiral inlet could increase the flow coefficient by a maximum of 1.9%. The valve structure of the optimal swirl ratio combined with the dissimilitude scheme of the largest valve lift of the tangential inlet could increase the swirl ratio by a maximum of 9.7%. This study can guide diesel engines with combined intakes to increase the intake mass and improve the intake performance.

A novel three-dimensional analytical tornado model constructed based on force balance analysis

The analytical model for tornado vortices is crucial in both the wind field characterization and the tornado-resistant design of civil structures. The objective of this study is to derive a novel three-dimensional analytical tornado model from the vortex governing equations simplified based on the force balance analysis in tornado-like vortices (TLVs). First, TLVs with different swirl ratios are generated in a numerical simulator utilizing the large-eddy simulation. Then, the forces in the axisymmetric vortex governing equations are calculated for time-averaged TLVs. The governing equations in the single-cell TLV are simplified by ignoring some significantly small terms. Finally, a novel three-dimensional analytical tornado model, which contains the radial, tangential, and vertical velocity as well as the pressure, has been proposed and validated. The result shows that the force balance in the single-cell TLV is simpler than that in TLVs with larger swirl ratios. In the single-cell TLV, the viscous forces in the radial and vertical directions can be neglected, while the tangential viscous force remains to play an important role in the force balance. The proposed model mitigates the limitations of existing models in describing single-cell tornado vortices, such as only two-dimensional velocity being given, the neglection of the vertical shear effects near the ground, and the infinite velocity at high altitudes. It shows good agreement with the numerical and experimental TLVs as well as the real tornado.

Numerical investigation on the effects of HC geometry on the flow and heat transfer in the disk cavity system at the turbine vane root

In this study, we numerically investigate the flow and heat transfer in the sealing system at the vane root of a heavy-duty turbine with the aim of determining the optimal geometry of honeycomb cells within a certain parameter range. First, we analyze the impact of honeycomb cell geometry on flow in the sealing gaps, including flow rotation, energy dissipation in the teeth chamber and honeycomb cell, and frictional losses. Next, we examine the heat transfer capacity between the leakage flow and the surfaces of the rotor or stator, and establish the relationship between the stream function and the average heat transfer coefficient. Third, we compare the predicted core swirl ratio, the most important aerodynamic parameter in disk cavities, with those from equations in the literature. The decrease in core swirl ratio in the upstream disk cavity indicates that the use of different honeycomb cell geometries may lead to excessive axial thrust. Finally, we study the local and average heat transfer capacities on the turbine disk and introduce a correction factor (0.12–0.21) into the correlation to make it applicable to analogous turbine disks or rotor–stator cavities in other turbo machines with low radii honeycomb labyrinth seals. Based on our findings, we provide recommendations for the optimal honeycomb cell geometries for the two sealings for different targets. These results serve as a reference for designers of honeycomb labyrinth seals for gas turbines and other turbo machines.

Absolute instabilities and dynamics of helical vortices in twin annular swirling jets

Modern low-emissions gas turbine combustors commonly employ a twin annular swirling flow configuration that consists of a central annular inner jet and a surrounding annular outer jet. This paper investigates the instability dynamics of helical vortices of such a flow configuration in non-reacting laminar setting with a varying outer jet swirling ratio S. The corresponding base flow features a centerbody wake (CBW), an outer recirculation zone, and a lip recirculation zone at low swirl ratios, whereas at high swirl ratios, the CBW is replaced by a central recirculation zone (CRZ). The azimuthal mode with wavenumber m=1 is found to be absolutely unstable in the CBW region at low swirl ratios (S<0.8), though not large enough to trigger global oscillations. With further increased swirl ratio (S≥0.8), the CBW is suppressed and the CRZ supports a large region of absolute instability for both m=1 and m=2 modes. A three-dimensional nonlinear time stepping performed at S=0.8 confirms that the absolute instability of m=1 mode near the nozzle exit leads to the formation of a single-helix vortex in the near-field. Downstream of the CRZ, the m=1 mode transits to convective instability, whereas the m=2 mode is absolutely unstable. The single-helix vortex is consistently found to disappear in the far-field, where the flow dynamics is dominated by a double-helix vortex counter-winding around the tail of the CRZ.

Effect of the geometrical shapes of the helical-spiral shroud intake valve on swirl generation in cylinder of diesel engine

Improving combustion efficiency for diesel engines is an important requirement to save fuel and lower exhaust gas toxicity. In this study, the effect of the geometric shape of the helical-spiral shroud intake valve (HSSIV) for the swirl generation in a diesel engine cylinder was studied, which has important significance in improving the combustion efficiency in a diesel engine.In this study, helical-spiral shroud (HSS) are classified into convex, flat, and concave types according to the installation angle on the intake valve, and their influence on the swirl generation in the cylinder are comparatively analyzed using the computational fluid dynamics (CFD) method. As a result, it is considered that HSSIV with convex shape generates the best swirl and tumble effect in the engine cylinder. The Model 1 with convex shape has a swirl ratio value of 32.5 which is 3.8 times larger at 80CAD, and the tumble ratio value is 48.2 which is 4.5 times larger at 130CAD, compared to Model 0 with no shroud. The findings and results of this study were applied to the diesel engine, but they can also be applied to gasoline engines, and can also be applied to research subjects that need to generate a swirl in the fluid flow path without additional energy consumption and reduction in the volumetric efficiency of the fluid.

Effects of piston crown designs on in-cylinder flow and mixture formation in gasoline direct injection engine under the lean burn condition

In this study, the effects of piston shapes on in-cylinder flow characteristics and mixture formation in the lean condition was analyzed using the PIV method and CFD (CONVERGE v2.4). The four-piston geometries were concave, flat, convex, and base pistons, and the pistons were mounted on a GDI engine with transparent quartz. To quantify in-cylinder flow characteristics, the mean velocity, tumble ratio, turbulent kinetic energy, and tumble center were calculated. In addition, to analyze the effects of the difference in piston shapes in detail, the velocity fraction was calculated by dividing the cylinder area into three. In-cylinder flow was compared for the case without injection and the case with injection. There were four timed injections at C.A. 420°, 480°, 540°, and 600°, and the mixture characteristics were investigated in the cases of 480° and 600° injection. In the intake process and early compression process, there was no significant difference in the quantitative values for the shape of the piston regardless of the presence or absence of injection. However, the effects of the piston crown designs increased in the later compression process. As a result, the highest turbulent kinetic energy was found using a flat piston with a relatively high tumble ratio and swirl ratio in the absence of injection. The mixture formation was similar for all piston crown designs when injected at the crank angle of 480°. However, when the crank angle of 600° was injected, a stagnant fuel area was formed using the base-type piston, so it was difficult to secure sufficient fuel near the center of the cylinder.

Investigation on suitable swirl ratio and spray angle of a large-bore marine diesel engine using genetic algorithm

The swirl flow and spray angle are crucial to the organization of the combustion process in marine engines. In this work, to explore the suitable swirl ratio and corresponding spray angle for large-bore marine diesel engines, the artificial neural network (ANN) coupled with the genetic algorithm (GA) was used. At the same time, to increase the swirl ratio without affecting the scavenging efficiency, the cylinder gas recirculation (CGR) strategy was adopted in this manuscript. Compared with the original design, results indicate that the optimal swirl ratio is about 10 for the large-bore marine diesel engine when applying the CGR strategy. Due to the improved fuel–air mixing process and combustion process, the thermal efficiency and the output power of the optimal case increased by 4.86% and 5.2%, respectively. The present results are helpful for the design and optimization of the fuel–air mixing and combustion processes for large-bore marine diesel engines.

CFD ANALYSIS OF SECTOR COMBUSTION SIMULATION IN FOUR STROKE DIRECT INJECTION DIESEL ENGINE

In this article an attempt has been made in cylinder sector combustion CFD simulation of four stroke petrol engines using ANSYS fluent 2019 to obtain very useful results using a modelled engine. In order to improve engine quality, understanding on sector combustion properties in engine cylinder is of major importance because combustion condition significantly influences engine efficiency, Capabilities in providing optimum combustion conditions which include high optimum swirl ratio, and optimum tumble ratio in respective engine can result in enhancement of engine power and comfort, along with reduction of fuel consumption, exhaust emission and noise. The simulation is applied for a geometry with crank radius (55mm), connecting rod length (165mm), Engine speed (1800rpm), which is developed to study the effect combustion inside the cylinder. Piston starts from bottom dead center about 541degrees and the maximum pressure reaches at 716 degrees. The pressure increases from 542 crank angle degree to 716 crank angle degree and reaches its maximum value at 716 crank angle degrees. The Maximum pressure at the end of compression is 63.69Kpa and temperature is 1200K. The maximum penetration length of injection is occurred at crank angle 722 degree is 0.014mm.

Analysis of Improved In-Cylinder Combustion Characteristics with Chamber Modifications of the Diesel Engine

This study numerically analyses the effects of chamber modifications to investigate the improvement of in-cylinder combustion characteristics of the diesel engine using a computational fluid dynamics (CFD) approach. Five different modified chambers, namely, the double swirl combustion chamber (DSCC), bathtub combustion chamber (BTCC), double toroidal re-entrant combustion chamber (DTRCC), shallow depth combustion chamber (SCC), and stepped bowl combustion chamber (SBCC) were developed and compared with a reference flat combustion chamber (FCC). The effects of chamber modifications on temperature formation, velocity distribution, injection profiles, and in-cylinder turbulent motions (swirl and tumble ratio) were investigated. During the compression stroke, near top dead centre, the SCC showed a peak temperature of 970 K, followed by the FCC (968 K), SBCC (967 K), and DTRCC (748 K to 815 K). The DSCC and the SCC showed a high swirl ratio above 0.6, whereas the DTRCC and the BTCC showed a high tumble ratio of approximately 0.4. This study found that the SCC, BTCC, and DSCC have better combustion rates than the FCC in terms of temperature, heat release rate, and velocity distribution. However, the DTRCC showed poor temperature formation rates and rapid heat release rates (approx. 150 J/°CA), which can lead to rapid combustion and knocking tendencies. In conclusion, the DSCC and the SCC showed better combustion rates than the other chambers. In addition, turbulent motions inside the chambers avoided combustion in crevice regions. This study recommends avoiding chambers with wider bowls in order to prevent uneven combustion across the cylinder. Furthermore, split bowls such as the DSCC, along with adjusted injection rates, can provide better results in terms of combustion.

A Novel Design of Rim Sealing Flow for Improving Sealing Effectiveness

AbstractRim seal structures and sealing flows are essential in aero engines for preventing hot gas ingestion from mainstream to turbine disk cavities. A novel design method of rim sealing flow path based on auxiliary sealing holes and sealing air re-distributions has been proved to improve sealing effectiveness. The present paper uses this method to re-design the axial rim sealing flow in a high-pressure turbine front cavity in an engine turbine. The incidence angle of the auxiliary sealing air has been proved to have a significant influence on sealing performance. Three different incidence angles, 0-deg, 35-deg, and 70-deg, with the maximum angle close to the vane exit flow angle, are investigated using unsteady computational fluid dynamics methods validated by experimental data. Sealing effectiveness, swirl ratio, unsteady flow structures in both rim clearance and wheel space cavity are considered. The auxiliary sealing air with a swirl in the circumferential direction is proved to improve and uniform swirl ratio and suppress flow instabilities. This results in a reduction in hot gas ingestion and a considerable improvement in sealing effectiveness. The mechanisms of improving sealing effectiveness using this novel method are explained. The conclusions may support the understanding of the complex flow mechanisms near the rim seal, provide references for the design of this novel structure and give possibilities to improve rim seal performance and engine efficiency.