Swirl Level Research Articles

Near-Field Mixing in a Coaxial Dual Swirled Injector

AbstractImproving mixing between two coaxial swirled jets is a subject of interest for the development of next generations of fuel injectors. This is particularly crucial for hydrogen injectors, where the separate introduction of fuel and oxidizer is preferred to mitigate the risk of flashback. Raman scattering is used to measure the mean compositions and to examine how mixing between fuel and air streams evolves along the axial direction in the near-field of the injector outlet. The parameters kept constant include the swirl level $$S_e = 0.67$$ S e = 0.67 in the annular channel, the injector dimensions, and the composition of the oxidizer stream, which is air. Experiments are carried out in cold flow conditions for different compositions of the central stream, including hydrogen and methane but also helium and argon. Three dimensionless mixing parameters are identified, the velocity ratio $$u_e/u_i$$ u e / u i between the external stream and internal stream, the density ratio $$\rho _e/\rho _i$$ ρ e / ρ i between the two fluids, and the inner swirl level $$S_i$$ S i in the central channel. Adding swirl to the central jet significantly enhances mixing between the two streams very close to the injector outlet. Mixing also increases with higher velocity ratios $$u_e/u_i$$ u e / u i , independently of the inner swirl. Additionally, higher density ratios $$\rho _e/\rho _i$$ ρ e / ρ i enhance mixing between the two streams only in the case without swirl conferred to the central flow. A model is proposed for coaxial swirled jets, yielding a dimensionless mixing progress parameter that only depends on the velocity ratio $$u_e/u_i$$ u e / u i and geometrical features of the swirling flow that can be determined by examining the structure of the velocity field. Comparing the model with experiments, it is shown to perform effectively across the entire range of velocity ratios $$0.6 \le u_e/u_i \le 3.8$$ 0.6 ≤ u e / u i ≤ 3.8 , density ratios $$0.7 \le \rho _e/\rho _i \le 14.4$$ 0.7 ≤ ρ e / ρ i ≤ 14.4 , and inner swirl levels $$0.0 \le S_i \le 0.9$$ 0.0 ≤ S i ≤ 0.9 . This law may be used to facilitate the design of coaxial swirled injectors.

Impact of Turbine-Strut Clocking and Turbine Outlet Swirl on the Heat Transfer and Film Cooling in an Aggressive Turbine Center Frame

Abstract This study focuses on the thermal impact of the clocking position of the high-pressure turbine (HPT) vanes with respect to the turbine center frame (TCF) struts and the thermal impact of the HPT outlet swirl. The TCF is a stationary duct equipped with nonturning airfoils (struts), and it connects the HPT to the low-pressure turbine (LPT). The heat transfer coefficient and the purge film cooling effectiveness are measured in an aggressive TCF for two turbine-strut clocking positions and two HPT outlet swirl levels. The measurements are carried out in a product-representative 1.5-stage HPT-TCF-LPT vane configuration under Mach similarity. The unshrouded HPT is fully purged with four individually adjustable purge flows, and the film cooling effectiveness of these purge flows in the downstream TCF is investigated. The biggest influence of turbine-strut clocking was found for the heat transfer coefficient on the struts. By clocking the HPT vanes by half a vane pitch from the thermally least to the most favorable position, a significant heat transfer reduction was achieved for both the nominal and the increased HPT outlet swirl. Increasing the HPT outlet swirl increased the flow incidence of the TCF struts and affected the heat transfer along the struts significantly. On the TCF hub, the averaged heat transfer coefficient and the averaged purge film cooling effectiveness responded relatively robustly to all imposed operating point deviations with differences of less than 2%. However, the effects on the local heat transfer and film cooling distributions on the hub were more significant.

Swirl-induced hysteresis in a sudden expansion flow

Swirling sudden expansion flows are complex flow fields containing several coherent structures that depend on the swirl number and can exhibit hysteresis behavior between increasing and subsequently decreasing swirl levels. While these flows have extensively been studied in simple geometries, results involving special designed nozzles are scarce. Therefore, this paper aims to provide insights into a more complex geometry, specifically a two-step conical expansion with a converging outlet. Experimental data is acquired for changing swirl numbers at a Reynolds number in the range of 35, 000. Stereoscopic Particle Image Velocimetry is employed to characterize downstream flow structures, while Laser Doppler Velocimetry is used to characterize upstream structures and to determine the inlet swirl number. Several distinct flow patterns are found as a function of the swirl number and the identified flow patterns include, in order of increasing swirl, a Closed Jet Flow, an Open Jet Flow (OJF), and a Coandã Jet Flow (CoJF). A central positive axial velocity is noted for both OJF and CoJF downstream of the expansion due to the converging outlet geometry. At higher swirl numbers, Vortex Breakdown moves upstream into the nozzle until a negative axial velocity is noted in the inlet tube. For these higher swirl numbers, no hysteresis is observed in the inlet tube between increasing and subsequently decreasing swirl. However, downstream of the nozzle, it is observed that the CoJF detaches at a lower swirl number than the swirl number required for attachment, indicating a hysteresis effect between in- and decreasing swirl.

Inlet distortion of a rear engines concept aircraft and its effect on a fan

Boundary layer ingesting technology (BLI) has been widely developed, but the relevant research on the rear engine concept (REC) still needs to be expanded, especially for the different characteristics of the total pressure distortion and the swirl distortion. The paper investigates the BLI inlet distortion of a REC aircraft and its effect on the fan performance by commercial software CFX. Numerical simulation is conducted to obtain the inlet distortions first and the impact of these distortions on the characteristics of NASA rotor 67 is evaluated. Results show that the distortion tends to increase with the increase of the fluid redistribution effect of the fuselage-propulsor fusion part. Comparatively, the inlet distortion caused by AOS has a more significant influence on the performance of the fan. The swirl distortion is concentrated in the edge region of AIP. The total pressure distortion which coupled higher level of swirl has a more significant effect and is offset in the circumferential direction with the continuation effect of distortion in other leaf channels not obvious.

Impact of Lean-Burn Combustor Flow on Nozzle Guide Vane Performance

Abstract In this paper we investigate the impact of lean-burn-representative swirl and temperature distortion on the aerothermal performance of fully-cooled high-pressure nozzle guide vanes (NGVs) from a modern aero-engine. Experiments were carried out in the Engine Component AeroThermal (ECAT) facility at the University of Oxford. This is a fully-annular warm-flow engine parts facility, designed to operate at engine-representative conditions of Reynolds and Mach number. Inlet profiles of swirl, turbulence, and non-dimensional total temperature were generated using a non-reacting combustor simulator. The NGV outlet flow was experimentally characterized at three downstream planes in experiments with and without lean-burn-representative inlet conditions. Area-survey measurements included distributions of whirl angle, kinetic energy (KE) loss, and non-dimensional total temperature. Experimental data is compared to computational fluid dynamics (CFD) simulations. Fully-featured NGV geometry (including film cooling holes and internal passages) was used, to account for internal cooling flow redistribution resulting from altered external loading. We show that lean-burn inlet conditions result in significant surface flow redistribution, relatively high levels of residual swirl in the downstream flow, and a small increase of integrated KE loss.

Laser-Doppler Anemometry Measurements of Turbulent Swirling Wakes

This study considers the development and evolution of the swirling turbulent wake and their link to the turbulence present in the wake. A wake generator produces swirling wakes with a minimum of artifacts that would complicate the flow. Four swirling wakes have been studied with swirl numbers ranging from 0.19 to 0.37, and the results are compared to those of a nonswirling wake. Two-component laser-Doppler anemometry has been used to measure mean and turbulence quantities in the wake, and the uncertainty of these quantities has been determined. Careful alignment of the laser-Doppler anemometry system and large numbers of independent samples were used to obtain second-order turbulence statistics with low uncertainty. The results indicate that swirl strength impacts wake behavior, and changes in the behavior are linked to modifications in the turbulence. Faster wake width growth and centerline velocity deficit decay have been observed for wakes with higher swirl strength. The results indicate that a minimum swirl level is required to significantly impact wake behavior, and, at some level of swirl, the enhanced wake evolution observed saturates. For the conditions tested, the swirl number that enhances wake diffusion before saturation has been determined to lie between 0.21 and 0.37.

Flow field investigation of Confined Coaxial Swirling Jets by Stereo-PIV

This work analyses the isothermal flow field of a research burner exploiting both swirl and radially staged combustion air. The burner is composed of two coaxial co-rotating swirling jets, and the swirl level of the two jets can be controlled independently of each other. The influence of the swirl levels on the flow field is experimentally investigated under isothermal conditions using the Stereo-PIV technique, and the results evidence significant differences in the mean flow field at the different swirl levels. The vortex breakdown occurs in all the investigated cases, except for the combination of the lowest outer swirl level and the intermediate inner swirl level. Besides, the central recirculating flow region shape and size are affected by the momentum ratio and swirl level of the central jet. When the swirl intensities of the two coaxial jets are at their maximum, LDV measurements evidence on the burner axis tangential velocity fluctuations at a frequency of about 86 Hz; a POD-based phase average of the PIV maps allows recognizing the presence of a Precessing Vortex Core (PVC) which induces a periodic merging of the two jets. Those results can be of significance in the design of double swirl burners and for the control of the combustion process. Nevertheless, further tests are required to extend the current analysis to combustion conditions.

Modeling of H2/air flame stabilization regime above coaxial dual swirl injectors

The prediction of the stabilization regime of partially premixed H2/air flames above an injector is a main subject of interest for the development of gas turbines powered by hydrogen. The way the flame is stabilized has an impact on NOx emissions, thermal stress on the injector, and combustion stability. A model based on the triple flame speed is revisited and improved to predict flame stabilization using information gathered at cold flow conditions. The model is called TFUP for Triple Flame Upstream Propagation. According to this model, the flame can anchor to the injector only if a zone with a flammable mixture and a sufficiently low local flow velocity exists continuously from the lifted flame to the injector lips. The TFUP model is applied to the case of a H2/air coaxial, dual swirl injector in which both the hydrogen and air streams are swirled. Fuel is injected through the central channel and oxidizer through the external channel. Particle image velocimetry and one dimensional Raman scattering measurements made at strategic locations are used to predict the edge flame speed for which a lifted flame should re-anchor to the injector. These predictions made in isothermal conditions are compared to observations of the flame stabilization regime. The central flow of hydrogen can be mixed with methane and helium and the external flow of air with nitrogen in order to prescribe different theoretical values for the triple flame speed. Predictions agree well with the observations made for all swirl levels conferred to the central fuel stream, fuel injection velocities, hydrogen contents in the fuel mixture injected in the central channel, and nitrogen contents in the oxidizer annular channel tested in the study. Validity limits are also discussed. The methodology presented in this study provides a simple framework to predict flame stabilization on coaxial injectors that can optionally be equipped with swirl vanes.

Numerical study of the impact of hydrogen addition, swirl intensity and equivalence ratio on methane-air combustion

Abstract Hydrogen-blended fuel is a promising resource for future generations of gas turbine engines, due to its capability of reducing carbon-based emissions. This paper presents a numerical study to assess hydrogen-enriched combustion in a laboratory-scale burner operating at a high turbulence level and under lean and stoichiometric burning conditions. Moreover, a wide range of H2 (up to 90 %) is used for enriching CH4-air combustion in combination with two different swirl levels. The results show that a high swirl intensity results in shorter flames, due to the increased turbulent intensity, which reduces the flame surface area and uniformness the reacting zone. Besides, increasing swirl intensity further increase flame temperature for a given H2-blended fuel. Overall, the results suggest that high swirl intensity in combination to lean mixtures is favorable when using H2-blended fuel with high H2 concentrations. The simulation results also demonstrate that considering radiation heat loss is influential, as it yields a reduction of the outlet temperature by not less than 100 K, bringing down NO x emissions by half.

Investigation of rapid flame front controlled knock combustion and its suppression in natural gas dual-fuel marine engine

In this study, a new-type knock mechanism for large-bore marine engines, which differs from the existing end-gas auto-ignition knock theory and detonation wave theory, is fully revealed, using a high time resolution dynamic pressure difference method. The results indicate that the disparate enhancement effects of the flame front on the high-pressure region and the low-pressure region result in an increasing pressure difference, eventually forming the knock. The distinctions between this knock and the conventional end-gas auto-ignition knock were examined. Subsequently, the different functions of swirl in the two knock mechanisms were investigated. The results illustrate that, increasing swirl in end-gas auto-ignition knock can accelerate the termination of flame surface propagation and reduce the end-gas temperature by shortening the end-gas heat accumulation, thereby decreasing the knock intensity. However, reducing swirl in the new-type knock can diminish the combustion intensity of the flame front, thereby reducing its enhancement of the pressure wave. Consequently, a reduction to one-fourth of the initial swirl level can reduce knock intensity by 91%. Particularly, a novel knock suppression method of positioning the jet flame in the opposite direction of the swirl is proposed, which can avoid the local rapid combustion to effectively eliminate knock while maintaining power.

Coupled 3D evolutionary reconstruction technique for multi-simultaneous measurements

An integrated approach for the three-dimensional tomographic reconstruction of multiple scalar fields in premixed gaseous non-sooting reactive flow applications is presented. Measurement of different physical quantities are combined to enable an in-depth analysis of the combustion process in premixed turbulent flames. This is achieved by utilizing a flexible and versatile evolutionary reconstruction technique, where measured chemiluminescence signals and deflections of a background-oriented schlieren tomography (BOST) setup are processed in a coupled manner for the first time. The 3D tomographic inverse problem is stated as a coupled system and is holistically solved for the chemiluminescence intensity field and the refractive index field (from BOST data) in the flow domain. The chemiluminescence field is interpreted as a pseudo flame surface density function of a progress variable field that allows the analysis of flame front curvatures. The proposed method is tested for its consistency and sensitivities on synthetically generated measurement data of different complexities. Finally, the technique is applied to experimental measurement data of turbulent stratified flames with different levels of swirl.

Modeling the presumed joint probability density function of conditioning variables in stratified turbulent flames

Experimental data from the Cambridge-Sandia burner are used to calculate the conditional average of temperature and the mass fractions of H2O, CO, and CO2 in the context of the Uniform Conditional State (UCS) model. The performance of various presumed joint PDF models are examined for this burner working with different swirl and stratification levels. All of the presented PDF models are based on a few statistical moments of the conditioning variables which are extracted from the data at each measuring point. Primarily, only mixture fraction and reaction progress variable are employed as the conditioning variables. The β function is employed for modeling the marginal PDF of mixture fraction in all cases. For the progress variable, the β function and Modified Laminar Flamelet (MLF)-PDF are tested for modeling the marginal PDF. It is shown that even though the MLF-PDF results in more accurate predictions overall for most of the cases, its superiority with respect to the β-PDF is relatively small in the stratified flames. The performance of the product, Plackett, and Gaussian copulas are also investigated for employing the cross-correlation of mixture fraction and progress variable in building their joint PDF. It is found that the Gaussian copula shows a superior performance over the other two. Next, normalized total enthalpy is employed as a third conditioning variable, and different PDF models are examined for the three-condition version of UCS. It is found that even though adding the third conditioning variable can improve the predictions by considering the effect of heat transfer on the chemistry manifold, such improvements depend on having a proper 3D PDF model for the conditioning variables. In the vicinity of the flame brush, the models employed for the 3D PDFs represent an inferior performance compared to the two-condition version with the use of a Gaussian copula due to complications in the marginal PDF of normalized total enthalpy in these regions. To benefit from considering the impact of heat transfer on chemistry while also avoiding complexities in modeling the 3D joint PDF near the reaction zone, a switch between the two- and three-conditional models which is triggered by the variance of progress variable is proposed. It is shown that the predictions obtained by the use of this switch are almost always superior to all other PDF models investigated in this study.

Experimental and numerical studies of the effects of the contraction ratios on the swirling flow characteristics of the model combustor outlet in lean gas turbines

Large Eddy Simulation (LES) is utilized in this work to study isothermal turbulent swirling flow characteristics for a lean partially premixed gas turbine model combustor. The goal is to investigate the influence of contraction ratio (CR) variation on the vortex breakdown phenomena features and the turbulence structure in these combustors. Particle image velocimetry (2D-PIV) measurements were carried out on a single-case model combustor using (air-air) phase to perform the mean flow behavior and the validation process under atmospheric conditions with CR equal to 0 (largest diameter, Dinlet = Doutlet), the equivalence ratio (φ) of 0.3, swirl number of (Sn) = 0.66 and Reynolds number of (Re) = 42,000. While five test cases with various CRs were applied in LES under the same conditions using (air-CH4) phase to predict the vortical structure and the precession vortex core (PVC). The CRs ranged as follows: 0, 50 %, 60 %, 70 % and 80 % (smallest diameter). Experimental and LES results show that there was a reasonable agreement between the PIV and LES results with maximum deviations of 2.8 % and 4.65 % for the normalized mean axial and radial velocities, respectively. As the CR was increased, the pressure drop and the mean axial velocity increased linearly at the contraction part. In addition, the downstream stagnation point and the size of the central toroidal recirculation zone (CTRZ) stabilized when CR = 60 %, 70 %, and 80 %. The swirl level was further enhanced by 40 % when CR = 60 % and 80 %. The presence of CR successfully suppressed the pressure and axial velocity fluctuations generated in the shear layer zones by 35 %. LES data was analyzed by Fast Fourier Transformation (FFT) and Proper Orthogonal Decomposition (POD) to investigate the PVC dynamics. The FFT showed four dominant frequencies as a result of the appearance of the PVC and vortex breakdown oscillation. The frequency of PVC (fpvc) decreased linearly with an increase in the CR where the fpvc was 20.8 Hz when CR = 0 and became 12.5 Hz at CR = 80 %. In contrast, the other frequencies were still constant even with increased CR at 187 Hz, 562 Hz, and 979 Hz. The POD analysis showed the first mode was more energetic and had 40 % of the total pressure fluctuations.

Stabilization of Low-NOx Hydrogen Flames on a Dual-Swirl Coaxial Injector

Abstract Hydrogen-fueled carbon-free energy is a growing prospect for the future of several industries, including the aeronautical and energy generation sectors. However, the transition to hydrogen comes with several challenges: flame stabilization due to the unique combustion properties of hydrogen compared to conventional fuels and control of nitrogen oxides (NOx) production due to the higher combustion temperature. In addition, the high flammability of hydrogen poses an increased risk of flashback in premixed configurations commonly used to generate low-NOx flames. As a consequence, research into strategies for low-NOx hydrogen combustion is developing, and several technologies are being considered for industrial use. Among these technologies, we consider here a dual swirl coaxial injector operated in nonpremixed conditions. This setup enables the stabilization of multiple types of flame structures that are parametrically investigated for their NOx emissions. The flame structure is observed using OH* chemiluminescence images collected using an intensified CCD camera equipped with a bandpass filter. Exhaust gas species mole fractions of NO, NO2, and O2 are measured using NDIR gas detectors and a paramagnetic sensor. This investigation reveals that stabilization of hydrogen-air flames on the double swirl injector is possible and that varying the flow parameters induces changes in structure that affect NOx emissions, independently of swirl level, residence time, and temperature that also play a role. The study is carried out at atmospheric pressure.

Experimental analysis and theoretical lift-off criterion for H2/air flames stabilized on a dual swirl injector

Stabilization mechanisms of partially premixed H2/air flames on a coaxial dual swirl injector are investigated at atmospheric conditions. Hydrogen is injected through a central duct, and the air by the outer annular channel. Both channels are swirled and two stabilization modes are observed depending on the geometrical configuration of the injector and on the operating conditions. In certain regimes, the H2/air flame stabilizes on the injector lips as a diffusion flame. For other operating conditions, the flame is lifted from the injector and burns mainly in partially premixed regime leading to limited NOx emissions. PIV measurements in cold flow conditions and direct observations of the flame indicate that the flame stabilization mode is mainly controlled by the inner hydrogen swirl level, the injector recess and the hydrogen velocity. For a given air flowrate, a minimum hydrogen velocity to lift the flame is determined for each combination of inner swirl level and injector recess. Assuming the flame close to the injector lips behaves like an edge flame, a model for flame stabilization based on the triple flame speed and the location of the stoichiometric mixture fraction line is built. According to this model, the flame is anchored to the injector if the triple flame can propagate to the inner injector lips, i.e., if the velocity along the stoichiometric line is lower than the triple flame speed. The model is tested using hydrogen diluted with argon and air diluted with nitrogen. Two cases producing predicted opposite trends are verified. First, the stoichiometric line is moved in the direction of lower velocity zone keeping the triple flame speed constant in order to anchor a lifted flame. Next, the stoichiometric line is kept constant and the triple flame speed is reduced in order to lift an anchored flame. The mechanisms driving flame stabilization are discussed.

Numerical Investigation on Mixing Characteristics and Mechanism of Natural Gas/Air in a Super-Large-Bore Dual-Fuel Marine Engine

Premixed combustion mode dual-fuel (DF) engines are widely used in large-bore marine engines due to their great potential to solve the problem of CO2 emissions. However, detonation is one of the main problems in the development of marine engines based on the premixed combustion mode, which affects the popularization of liquefied natural gas (LNG) engines. Due to the large bore and long stroke, marine dual-fuel engines have unique flow characteristics and a mixture mechanism of natural gas and air. Therefore, the purpose of this study is to present a simulated investigation on the influence of swirl on multiscale mixing and the concentration field, which provides a new supplement for mass transfer theory and engineering applications. It is suggested that the phenomenon of abnormal combustion occurs on account of the distribution of the mixture being uneven in a super-large-bore dual-fuel engine. Further analysis showed that the level of swirl at the late compression stage and the turbulence intensity are the decisive factors affecting the transmission process of natural gas (NG) and distribution of methane (CH4) concentration. Finally, a strategy of improving mixture quality and the distribution of the mixture was proposed.

Characterization of no-load conditions for a high head Francis turbine based on the swirl level

This paper compares the average flow topology in the draft tube cone of a high head Francis turbine operated at full-gate opening no-load (runaway) and speed-no-load (SNL). The comparison is based on the swirl level in the turbine quantified with the angular momentum parameter (RCu11) and the Swirl number. This study shows that RCu11 only depends on the flow angle at the guide vane outlet, the distributor height and the runner outlet diameter. The Swirl number has strong limitations in characterizing the flow at runaway and SNL and is unsuitable for no-load conditions.

Evaluation of a Turbulent Jet Flame Flashback Correlation Applied to Annular Flow Configurations With and Without Swirl

Abstract The adaptation of high hydrogen content fuels for low emissions gas turbines represents a potential opportunity to reduce the carbon footprint of these devices. The high flame speed of hydrogen air mixtures combined with the small quenching distances poses a challenge for using these fuels in situations where a significant premixing is desired. In particular, flashback in either the core flow or along the walls (i.e., boundary layer flashback) can be exacerbated with high hydrogen content fuels. In this work, the ability of a flashback correlation previously developed for round jet flames is evaluated for its ability to predict flashback in an annular flow. As a first step, an annular flow is generated with a centerbody located at the centerline of the original round jet flame. Next, various levels of axial swirl is added to that annular flow. Additional flashback data are obtained for various mixtures of hydrogen and methane and hydrogen and carbon monoxide for all the annular flow configurations. Pressures from 3 to 8 bar are tested with mixture temperatures up to 750 K. Flashback is induced by slowly increasing the equivalence ratio. The results obtained show that the same form of the correlation developed for round jet flames can be used to correlate flashback behavior for the annular flow case with and without swirl despite the presence of the centerbody. Adjustments to some of the constants in the original model were made to obtain the best fit, but in general, the correlation is quite similar to that developed for the round jet flame. A significant difference with the annular flow configurations is the determination of the appropriate gradient at the wall, which in the present case is determined using a cold flow computational fluid dynamics simulation.

Quasi-equilibrium states for helical vortices with swirl

We present a family of exact equilibrium solutions of the Euler equations consisting of a single helical vortex with an axial flow component along the vortex core. Relations between vorticity, velocity and streamfunction are analytically derived in the inviscid framework and constitute a generalization of relations valid for vortex rings (Batchelor, 1967 An Introduction to Fluid Dynamics. Cambridge University Press). Through Navier–Stokes simulations, it is shown that these relations hold for quasi-steady viscous solutions and become independent of the Reynolds number when sufficiently large. We also elaborate a procedure which generates a quasi-equilibrium with prescribed characteristics (circulation, helix radius, helical pitch, vortex core size, swirl level) and compare the obtained state with the results of an asymptotic theory. Finally, we illustrate how a strong axial flow jeopardizes such an evolution towards a quasi-equilibrium.

Wake rotation impacts on wake decay

This study considers the behavior of a well-conditioned swirling turbulent wake. A custom swirling wake generator was used to produce a swirling wake absent of a tower that complicates the flow regime. Four swirling wakes were studied with swirl numbers ranging from 0.19 to 0.37 and compared to a non-swirling counterpart. Two-component Laser-Doppler Anemometry was used to measure mean and turbulent quantities in the wake. Measured profiles were analyzed based on similarity theory applied to a swirling wake. The results show that wake behavior was impacted by the initial swirl strength. Generally, wake growth rate and axial deficit decay rate increased with higher levels of swirl, and tangential velocity decay rate increased with lower levels of swirl. However, the wake that diffused fastest was the case with a swirl number of 0.27.