Inlet Swirl Research Articles

Effect of inlet rotating swirl on endwall film cooling for two representative hole arrangements

The swirl generator is widely used in lean-burn combustor to guarantee flame stability and reduce NOx emissions. Thus, the non-uniformities induced by the swirler would affect and damage film-cooling effectiveness on the turbine components, even blow-off coolant coverage, to some certain extent. The arrangement of film-cooling holes was normally designed to be perpendicular to the axial direction and in standard straight row. In this work we experimentally studied the effects of inlet swirl and mass flow ratio on traditional film cooling holes arrangement and a new arrangement pattern whose holes are located along the isobars. Results indicated that the swirl perturbation would damage film coverage. The film-cooling effect of endwall on which the holes are along the isobars, is invariably more promising than that of endwall on which hole arrangement is perpendicular to axial with the same mass flow of coolant, whether the inlet conditions is uniform or not.

The effects of swirling decaying flow towards pipe entry length and heat transfer in an annular pipe

The hydrodynamic entry length of axial pipe flow has been studied extensively over the years. Entry length is used to identify range of fully developed flows as commonly used in many practical engineering applications (e.g. Moody’s chart). For laminar axial pipe flow, the hydrodynamic entry length has been investigated by Kays, Shah and Bhatti (KSB) (Lh = 0.056 ReDh). In contrast, several approximations exist for fully turbulent flows (i.e. 10 Dh–150 Dh). Through theoretical and numerical investigations, the hydrodynamic entry length for swirling decaying pipe flow in the laminar regime is investigated. It is found that, the development length Lh for the axial velocity profile is reduced when a rotational component is added to the mean flow. The reduction in the hydrodynamic length is found to be proportional to the inlet swirl angle θ and the magnitude of the rotational component. Results indicate that a modification can be made on the KSB equation for two-dimensional swirling annular pipe flow. This research also investigates the effect of the local swirl number and Reynolds number on the steady and unsteady heat transfer inside an annular pipe. The existence of the jet effect near the exit of the swirl vane altered the behaviour of the local heat transfer coefficient in the axial direction (along the pipe) for z = 0 mm to z = 40 mm. The heat transfer coefficient for the 30° vane angle is found to increase after z = 0 mm to a maximum value before decaying nonlinearly, whereas, for the 45° and 60° vane angles, the heat transfer coefficient decreases nonlinearly starting from the vane exit. It is found that, for low Re, Ts changes linearly over the course of the cooling zone for all vane angles. With increasing Reynolds number, the behaviour of the cooling curve changes from linear to nonlinear. Overall, the cooling time is found to be inversely proportional to Re. With increasing vane angle, the overall swirl number S along the pipe decreases, thus, reducing the overall swirling momentum in the annular pipe, leading to a lower heat diffusion rate. It is found that the dependency of the temperature of the solid rod Ts on Re is decreasing as Re increases.

Effects of temperature-dependent thermo-physical properties on hydrodynamic swirl decay in microtubes

In this paper, the influence of temperature-dependent thermo-physical properties is investigated on the decay of swirl in a laminar swirling flow of liquid through a heated microtube. The conservation equations for mass, momentum, and energy are numerically solved to obtain the velocity and temperature fields. The decay of swirl is quantified by the variation of the ratio of swirl number at a section to that at the inlet ( S/ S0) along the flow. The results reveal that constant property simulations result in faster swirl decay as compared to the variable-property simulations. Further, the implications of slip length, inlet swirl number, inlet swirl velocity profile, and Reynolds number on the swirl decay are presented. The results of the present analysis bear significant technological consequences in the design of micro-heat exchangers with intrinsic rotationalities.

The Development of Swirling Decaying Laminar Flow in an Annular Pipe

Work on the hydrodynamic entry length of pipe and duct flow has been well studied over the years. The assumption of fully developed flows is commonly used in many practical engineering applications (e.g. Moody's chart). For laminar axial pipe flow, the hydrodynamic entry length can be found through the monomial proposed by Kays, Shah and Bhatti (KSB) (Lh=0.056ReDh). In contrast, several approximations exist for fully turbulent flows (i.e. 10Dh-150Dh). Through theoretical and numerical investigations, the hydrodynamic entry length for swirling decaying pipe flow in the laminar regime is investigated. It was found that, the development length Lh for the axial velocity profile changes when a tangential component is added to the mean flow. The reduction in the hydrodynamic length was found to be dependent on the inlet swirl angle θ. The results indicate that a modification can be made on the KSB equation for two-dimensional swirling annular pipe flow.

The Development of Swirling Decaying Laminar Flow in an Annular Pipe

Work on the hydrodynamic entry length of pipe and duct flow has been well studied over the years. The assumption of fully developed flows is commonly used in many practical engineering applications (e.g. Moody's chart). For laminar axial pipe flow, the hydrodynamic entry length can be found through the monomial proposed by Kays, Shah and Bhatti (KSB) (Lh=0.056ReDh). In contrast, several approximations exist for fully turbulent flows (i.e. 10Dh-150Dh). Through theoretical and numerical investigations, the hydrodynamic entry length for swirling decaying pipe flow in the laminar regime is investigated. It was found that, the development length Lh for the axial velocity profile changes when a tangential component is added to the mean flow. The reduction in the hydrodynamic length was found to be dependent on the inlet swirl angle θ. The results indicate that a modification can be made on the KSB equation for two-dimensional swirling annular pipe flow.

Acoustic Dynamics of A Swirl Premixed Combustor with Different Operating Conditions

The effects of inlet swirl and external excitation on the flow field and combustion acoustic modes in a low NOx premixed combustor are experimentally investigated using a 100kW laboratory rig. It combines different operating conditions with variations in swirl number and varying levels of external excitation which are critical factors influencing the flow- flame interaction within the combustor. Results show the formation of a vortex induced central recirculation zone (CRZ) for the two swirl conditions which increase in length and width with changes in the swirl strength and forcing. The flow structure eventually merges with the high momentum flow region, a feature common to many swirl combustors. The acoustic oscillations were observed to be affected by the variations in the swirl strength with further dynamics at different levels of excitation. Accurate combination of these conditions (swirl, and excitation) could be advantageous in suppressing the intensity of the destructive acoustic instabilities in the burner. Results of this nature provide information for the design of an active control system for the combustor.

Effect of intake swirl on the performance of single cylinder direct injection diesel engine

In the present work, the effect of inlet manifold geometry and swirl intensity on the direct injection (DI) diesel engine performance was investigated experimentally. Modifications in inlet manifold geometry have been suggested to achieve optimized swirl for the better mixing of fuel with air. The intake swirl intensities of modified cylinder head were measured in swirl test rig at different valve lifts. Later, the overall performance of 435 CC DI diesel engine was measured using modified cylinder head. In addition, the performance of engine was compared for both modified and old cylinder head. For same operating conditions, the brake power and brake specific fuel consumption was improved by 6% and 7% respectively with modified cylinder head compared to old cylinder head. The maximum brake power of 9 HP was achieved for modified cylinder head. The results revealed that the intake swirl has great influence on engine performance.

Influence of Combustor Flow With Swirl on Integrated Combustor Vane Concept Full-Stage Performance

The integrated combustor vane concept for power generation gas turbines with can combustors has been shown to have significant benefits compared to conventional nozzle guide vanes (NGV). Aerodynamic loss, heat transfer levels, and cooling requirements are reduced while stage efficiency is improved by approximately 1.5% (for a no-swirl scenario). Engine realistic combustor flow with swirl, however, leads to increased turning nonuniformity downstream of the integrated vanes. This paper thus illustrates the altered integrated vane stage performance caused by inlet swirl. The study shows a distinct performance penalty for the integrated vane rotor as a result of increased rotor incidence and the rotor's interaction with the residual swirl core. The stage efficiency advantage of the integrated combustor vane concept compared to the conventional design is thus reduced to 0.7%. It is furthermore illustrated how integrated vane profiling is suitable to reduce the turning variation across the span downstream of the vane, further improve stage efficiency (in this case by 0.23%) and thus mitigate the distinct impact of inlet swirl on integrated vane stage performance.

Mixing performance of split-and-recombine micromixer with offset inlets

This study proposes a novel 3D split-and-recombine passive micromixer with offset-inlets. The micromixer is composed of non-aligned inlets and spatially repeating mixing units with mixing chambers and sub-channels. Each repeating unit has a chamber and two sub-channels with a number of alternate bends to create chaos in the flow. The non-aligned inlets provide inlet swirl while split-and-recombine mixing units stretch interfacial area, which eventually enhance mixing efficiency of the micromixer. The numerical modeling was conducted by solving three-dimensional steady state flow equations along with the diffusion equation for several flow conditions to evaluate the parametric mixing performance. A variance-based mixing index was used to compute the degree of mixing. A characterization methodology was employed to demonstrate the effect of several design parameters, i.e., width and depth of the mixing channel, pitch, length and height of the mixing chamber on the performance. The proposed micromixer exhibited excellent performance over a wide range of Reynolds numbers covered in the present study. At low and medium Re, proposed micromixer performed much better than 3D serpentine and 3D serpentine SAR micromixers reported in the recent literature.

Proper Orthogonal Decomposition (POD) analysis of CFD data for flow in an axisymmetric sudden expansion

CFD simulations of swirling flow in a 2:1 axisymmetric sudden pipe expansion are performed and used to understand the structure of the flow. The k–ε and SAS-zonal LES models available in ANSYS CFX are used to model turbulence. Comparison of these results shows that the scale-resolving simulation captures much more detail of the flow and provides much more physical results in terms of the flow structures that are resolved. As well as conventional analysis using typical CFD post-processing techniques and Fast Fourier Transforms (FFTs), Proper Orthogonal Decomposition (POD) is used to extract reduced order models of the wall pressure data. This technique is used to extract dominant structures in the spatial domain and to investigate transient behaviour. Data from a finite set of monitor points located at the pipe wall are also examined as a potential means of detecting flow behaviour for use in flow control models that utilise differential wall pressure input data. Such models are required to control, for example, inlet swirl to minimise wall impaction in spray dryers.

Analysis of Effect of Inlet Swirl In Four Stroke Single Cylinder Diesel Engine With Different Inlet Valve Geometries Using CFD

Flow patterns are essential to ensure that the engine can produce high performance with the presence of swirl and tumble effect inside the engine cylinder. This paper provides the simulation of air is simulated in the software to predict the flow pattern. The flow pattern is simulated by using the steady state pressure based solver. The domain used for the simulations predicated on the particular engine parameters. Mistreatment the CFD problem solver ANSYS FLUENT, the CFD simulation is earned for four totally different geometries of the valve. The geometries consist of Horizontal, Vertical, curve and arc springs. In this simulation, only the intake strokes are simulated. From this results show that the velocity of the air flow is high during the sweeps the intake stroke takes place. This situation is produced more swirls and tumble effect during the compression, hence enhancing the combustion rate in a whole region of the clearance volume of the engine cylinder. This will initiate to the production of tumble and swirl in the engine cylinder.

New Understanding of Mode Switching in the Fluidic Precessing Jet Flow

We report the first systematic investigation of the phenomenon of “switching” between the two bistable axial jet (AJ) and precessing jet (PJ) flow modes in the fluidic precessing jet (FPJ) nozzle. While geometric configurations have been identified where the fractional time spent in the AJ mode is much less than that in the PJ mode, nevertheless, the phenomenon is undesirable and also remains of fundamental interest. This work was undertaken numerically using the unsteady shear stress transport (SST) model, the validation of which showed a good agreement with the experimental results. Three methods were employed in the current work to trigger the flow to switch from the AJ to the PJ modes. It is found that some asymmetry in either the inlet flow or the initial flow field is necessary to trigger the mode switching, with the time required to switch being dependent on the extent of the asymmetry. The direction and frequency of the precession were found to depend on the direction and intensity of the imposed inlet swirling, which will be conducive to the control of the FPJ flow for related industrial applications and academic research. The process with which the vortex skeleton changes within the chamber is also reported. Furthermore, both the rate of spreading and the maximum axial velocity decay of the jet within the nozzle are found to increase gradually during the switching process from the AJ to the PJ modes, consistent with the increased curvature within the local jet.

On the dynamics of the transition to vortex breakdown in axisymmetric inviscid swirling flows

This paper reports on novel features found in the dynamics of the transition to vortex breakdown in inviscid axisymmetric flows with swirl. These features are revealed by a transient simulation of an open ended pipe flow where the inlet swirl is suddenly increased from a swirl number just below the onset of vortex breakdown to a swirl number just above the onset of vortex breakdown. To eliminate the numerous parameters influencing breakdown, the axisymmetric Euler equations with swirl are used as a fluid flow model and solutions are obtained by means of numerical simulation. It is shown that as the step response has died out, the flow evolves to a quasi-static state where time derivatives of variables are negligible small. Stability analysis of this state shows that it can support standing waves in a small region of the flow domain. These standing waves are observed in the simulations as an imbalance in the axial momentum equation which slows down the flow near the central axis. The amplitude of this imbalance grows exponentially in time with a dimensionless growth rate of 0.83 scaled with the flowthrough time. Eventually, the axial velocity along the central axis becomes negative in a small part of the flow, leading to an axisymmetric recirculation zone, called vortex breakdown. To the authors knowledge, this study would be the first to reveal these features prior to breakdown and the results may help in understanding of the physical mechanisms leading to it as this is still a controversial issue in literature.

Experimental investigations of the turbulent swirl flow in straight conical diffusers with various angles

Results of experimental investigations of the turbulent swirl flow in three straight conical diffusers with various diffuser total angles are presented in this paper. All three diffusers have the inlet diameter 0.4 m and total divergence angles 8.6?, 10.5?, and 12.6?. The incompressible swirl flow field is generated by the axial fan impeller, and for each diffuser several regimes were achieved by changing rotation number. Original classical probes were used for measurements. The distributions of the average main swirl flow characteristics along the diffuser are shown. Distributions of the inlet Boussinesq number, outlet Coriolis coefficient, ratio of the swirl and completely axial flow loss coefficients at conical diffuser on the inlet swirl flow parameter are also presented.

Numerical Investigation of the Leakage and Rotordynamic Characteristic for a Short Staggered Labyrinth Seal

Short staggered labyrinth seals are widely used in high pressure cylinder shroud seals of steam turbines. They are good at restricting the leakage flow but do not respond well to rotordynamics and often lead to turbomachine instabilities. A numerical investigation into the leakage and rotordynamic characteristics of a short staggered labyrinth seal is carried out in this paper, concerning effects of pressure ratio, inlet preswirl, rotational speed, seal clearance and whirling frequency, using both the whirling rotor method and the multiple frequencies transient simulation method. The numerical model is verified by experimental data. The result shows that the staggered labyrinth seals have a similar but not identical leakage and rotordynamic performance compared with that of teeth-on-stator see-through labyrinth seals. The cross-coupled stiffness can be reduced by decrease inlet swirl with considering the factor of rotational speed, which can significantly benefit the stability of rotor system.

Turbine Blade Platform Film Cooling With Simulated Swirl Purge Flow and Slashface Leakage Conditions

The combined effects of inlet purge flow and the slashface leakage flow on the film cooling effectiveness of a turbine blade platform were studied using the pressure-sensitive paint (PSP) technique. Detailed film cooling effectiveness distributions on the endwall were obtained and analyzed. Discrete cylindrical film cooling holes were arranged to achieve an improved coverage on the endwall. Backward injection was attempted by placing backward injection holes near the pressure side leading edge portion. Experiments were done in a five-blade linear cascade with an average turbulence intensity of 10.5%. The inlet and exit Mach numbers were 0.26 and 0.43, respectively. The inlet and exit mainstream Reynolds numbers based on the axial chord length of the blade were 475,000 and 720,000, respectively. The coolant-to-mainstream mass flow ratios (MFR) were varied from 0.5% and 0.75% to 1% for the purge flow. For the endwall film cooling holes and slashface leakage flow, blowing ratios (M) of 0.5, 1.0, and 1.5 were examined. Coolant-to-mainstream density ratios (DR) that range from 1.0 (close to low temperature experiments) to 1.5 and 2.0 (close to engine conditions) were also examined. The results provide the gas turbine engine designers a better insight into improved film cooling hole configurations as well as various parametric effects on endwall film cooling when the inlet (swirl) purge flow and slashface leakage flow were incorporated.

Numerical investigation of effect of inlet swirl and total-pressure distortion on performance and stability of an axial transonic compressor

This paper represents numerical simulation of flow inside an axial transonic compressor subject to inlet flow distortion, to evaluate its effect on compressor performance and stability. Two types of inlet distortion, namely inlet swirl and total pressure distortion are investigated. To study the effect of combined distortion patterns, different combinations of inlet swirl and total pressure distortion are also studied. Results for cases with total pressure distortion indicate that hub radial distortion improves stability range of the compressor while tip radial distortion deteriorates it. An explanation for this observation is presented based on redistribution of flow parameters caused by distortion and the way it interacts with stall inception mechanisms in a transonic axial compressor. Results also show that while co-swirl patterns slightly improve stability range of the compressor, counter-swirl patterns diminish it. Study of combined distortion cases reveals that superimposition of effects of each individual pattern could predict the effect of a combined pattern on compressor’s performance within an accuracy of 1%. However, it is unable to predict the associated effect on compressor’s stability.

RANS computations for identification of 1-D cavitation model parameters: application to full load cavitation vortex rope

Due to the massive penetration of alternative renewable energies, hydropower is a key energy conversion technology for stabilizing the electrical power network by using hydraulic machines at off design operating conditions. At full load, the axisymmetric cavitation vortex rope developing in Francis turbines acts as an internal source of energy, leading to an instability commonly referred to as selfexcited surge. 1-D models are developed to predict this phenomenon and to define the range of safe operating points for a hydropower plant. These models involve several parameters that have to be calibrated using experimental and numerical data. The present work aims to identify these parameters with URANS computations with a particular focus on the fluid damping rising when the cavitation volume oscillates. Two test cases have been investigated: a cavitation flow in a Venturi geometry without inlet swirl and a reduced scale model of a Francis turbine operating at full load conditions. The cavitation volume oscillation is forced by imposing an unsteady outlet pressure conditions. By varying the frequency of the outlet pressure, the resonance frequency is determined. Then, the pressure amplitude and the resonance frequency are used as two objectives functions for the optimization process aiming to derive the 1-D model parameters.

Swirl Motion Effects on Flame Dynamic of Pulverized Olive Cake in a Vertical Furnace

ABSTRACTThis article presents the effect of inlet swirl motion on the flow behavior and combustion dynamics of pulverized olive cake (OC) in a 3D vertical furnace. The spherical OC particles are injected perpendicularly to the coaxial air inlet jets. Three cases are studied: without swirling air flow (Ja), with swirling axial jet (Js1), and with both swirling axial and coaxial jets (Js2). The numerical approach is based on Reynolds averaged Navier–Stokes (RANS) method using the k–ε turbulence model. For turbulence-chemistry interactions of the non-premixed combustion, a mixture fraction/probability density function approach is used. The OC thermal characteristics are determined experimentally by the thermogravimetric analysis. Flow topology, velocity contours, temperature distribution, and species concentrations profiles in several locations along the burner are obtained for all cases. Results show that the flame is more stabilized and close to the air inlet section for the swirling jet cases. The temperature of the burned gases reaches its maximum value of 1560 K.

Analyse the disk closed cycle MHD generator performance with the influence of channel characteristics

The enthalpy extraction ratio is one of the most significant parameter of a disk closed cycle MHD generator. There are two methods to improve the enthalpy extraction, those are the increase of channel cross-sectional area ratio and the implementation of inlet swirl. In this study, the mechanism of enthalpy extraction improvement has been confirmed by the two-dimensional numerical calculation. As a result, by increasing the channel cross-sectional area ratio of the disk MHD generator, the increase of static pressure and the velocity deceleration can be suppressed due to the Lorentz force, and it is possible to maintain a high flow velocity inside the channel and a high Hall parameter. The implemention of inlet swirl is possible to maintain a low static pressure inside the channel and the enthalpy extraction ratio rises due to the increase of Hall parameter. In addition, the channel cross-sectional area ratio increases due to the swirl implementation, the static pressure is kept low, and the channel inlet flow velocity increases. This also leads to the increase of enthalpy extraction ratio, that is the increase of output power.