ILASS Americas, 21st Annual Conference on Liquid Atomization and Spray Systems, Orlando, Florida, May 18-21 2008

A Study of Liquid Jets Injected Transversely into a Swirling Crossflow

S. B. Tambe*, and S. -M. Jeng Department of Aerospace Engineering and Engineering Mechanics

University of Cincinnati Cincinnati, OH 45221-0071 USA

Abstract

An experimental study has been conducted to study the effect of a swirling crossflow on transversely injected liquid jets. Three in-house designed axial swirlers with vane exit angles of 30°, 45° and 60° were used to generate the swirling crossflow. Water jets were injected from a 0.5 mm dia orifice located on a cylindrical centerbody that pro-truded through the hub of the swirler. The measurement technique used was multi-planar 2-D PIV and Mie-Scattering. The crossflow generated by the swirlers was observed to be fully-developed, axisymmetric and had a vortex structure similar to solid body rotation. Total crossflow velocities peaked at a radial location near r = 15 mm. Liquid jets injected in this crossflow were observed to spin along with the crossflow. The radial penetration of the jet continued to increase even at far downstream locations due to centrifugal forces and a reduction in crossflow velocities at high r. The radial penetration of the jet increased with an increase in the swirl strength of the crossflow and with the momentum flux ratio (q). The jet plume continued to expand as it moved downstream.

*Corresponding author

Introduction The transversely injected liquid jet in crossflow has

numerous applications including fuel injection [1], thrust vector control of rockets [2] and lubrication of the bearing chamber [3]. The injection of a liquid fuel jet into a crossflow is also one of several possible con-cepts of a premix module for lean, premixed, pre-vaporized (LPP) combustion for aviation gas turbines. The demands for higher efficiency of power production and smaller engines lead to an increase in the operating temperatures and pressures. This leads to increase in the production of effluents like oxides of nitrogen (NOx) since NOx formation rates increase with temperature [4]. With the increasingly stricter ICAO regulations on engine emissions, there is a strong emphasis on the de-velopment of low-emission combustion techniques. One technique is the LPP combustion, where a lean homogeneous fuel-air mixture is created just upstream of the combustor inlet. The presence of excess air throughout the primary zone ensures that the combus-tion temperature is low enough to suppress NOx forma-tion. The LPP model requires a premix duct where fuel and air are mixed together. To achieve a good homoge-neous mixture and to avoid coking, fine atomization and careful fuel placement are needed. The liquid-jet-in-crossflow has characteristics of rapid atomization and controllable penetration [1], which make it a good choice for LPP fuel injection.

Jet-in-crossflow is a fundamental flow field and has been the subject of numerous experimental as well as computational studies. Tambe [5] and Elshamy [6] have conducted detailed literature reviews of the work done in this area. However, most of these studies fea-ture uniform crossflows, i.e. where the crossflow veloc-ity does not change in the transverse direction. Only a few studies have reported crossflows with non-uniform velocity profiles. Becker and Hassa [7, 8] injected liq-uid jets into a counter-swirling double-annular cross-flow and studied the effect of momentum flux ratio and the air pressure on the jet behavior. Gong et al [9] pub-lished a preliminary report on studies conducted for the Lean Direct Wall Injection (LDWI) concept, where they injected liquid jets into a swirling flow at different injection angles. The authors previously conducted a study where jets were injected transversely into a cross-flow laden with a shear layer [10, 11]. The shear layer was generated in the form of a slip plane between two co-flowing airstreams and produced quasi-linear veloc-ity gradients across the height of the test chamber, with the jet being injected from a nozzle flush with the bot-tom wall. The shear layer strength and the sense of the crossflow velocity gradient had significant impact on the jet penetration and the post-breakup spray

The objective of the present work is to study the behavior of a liquid jet injected transversely into a

swirling crossflow. The effect of swirl strength on the jet penetration and droplet velocity distribution is inves-tigated. Three different axial swirlers were used to vary the swirl strength of the crossflow. The measurement technique used was 2-D Particle Image Velocimetry (PIV). The study was divided into two parts. The first part focused on characterizing the crossflow produced by the different swirlers used. In the second part, the impact of these crossflows on the jet was investigated.

Experimental Setup Test Section

In-house developed axial swirlers were used to pro-duce the swirling crossflow. The swirlers used had a hub diameter of 2.22 cm (0.875”) and a tip diameter of 7.62 cm (3”). The test chamber had a square cross sec-tion with an internal dimension of 7.62 cm (3”) and was 30.48 cm (12”) long. The walls of the test chamber were constructed of 3.175 mm (1/8”) thick acrylic ma-terial for optical access. The walls were mounted on aluminum corner struts, which also provided a chamfer to suppress corner recirculation zones (CRZ).

Jet injection was conducted through a centerbody, which protruded from the swirler hub and extended through the length of the test chamber. The centerbody was a stainless steel tube of outer diameter 1.905 cm (3/4”) and a wall thickness of 1.651 mm (0.065”). The jet was injected from a 0.5 mm orifice located 2.54 cm (1”) downstream of the swirler.

Figure 1a shows a Solidworks model of the test section, and the co-ordinate frame of reference used for the experiments. Figure 1b shows the actual test cham-ber. The origin of the coordinate frame was located on the axis of the centerbody at the streamwise location of the center of the jet orifice. X-axis is located in the

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Figure 1. Test Chamber, a) Solidworks model, b) Ac-tual chamber

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ILASS Americas, 21st Annual Conference on Liquid Atomization and Spray Systems, Orlando, Florida, May 18-21 2008

Table 1. Swirler Properties Vane Exit Angle No of vanes Mean Solidity Mean Aspect Ratio Swirl Number

30° 16 3.53 0.95 0.41 45° 12 2.83 0.85 0.71 60° 12 3.2 0.75 1.23

streamwise direction; Y-axis points vertically upwards and the Z-axis points to the left as viewed from down-stream. The centerbody was aligned so that the jet ori-fice was centered about the Y-axis.

The test chamber assembly was mounted onto the Horizontal Rig, which acts as a settling chamber for the air flow. The Horizontal Rig is a long pipe of diameter 15.24 cm (6”), equipped with an inline 72 kW heater. Air is provided from a Kaesar variable speed rotary compressor capable of flow rates up to 0.907 kg/s (2 lb/s) at pressures of up to 13 bars (175 psig), connected to a dryer and tank. A network of 10.16 cm (4”) and 5.08 cm (2”) dia pipes connects the air tank to the Hori-zontal Rig. Air flow rate is metered by a Micro Motion CMF300 coriolis flow meter and controlled by a stan-dard globe valve.

The injected liquid was water, and was housed in a water tank. A Nitrogen cylinder was used to pressurize the water tank, in order to drive the flow as well as maintain a constant flow rate. The water flow rate was measured by a Micro Motion CMF010 coriolis flow meter. A Parker metering valve was used for precise

control of the water flow rate. Figure 2 shows a sche-matic of the experimental setup. Swirlers

The axial swirlers used for the study were designed in-house and were fabricated by the Rapid Prototyping SLA technology. Three different swirlers were used, with vane exit angles of 30°, 45° and 60°. Since the focus of the experiments was on jet behavior, a smooth, non-circulating, helical flow was desired.

A swirler configuration with straight, radial vanes was chosen. The swirler streamwise length was taken to be 2.54 cm (1”). The number of vanes for the 45° and 60° swirlers was chosen to be 12. To achieve reason-able solidity, this number was increased to 16 for the 30° swirler. Then the only design parameter is the variation of vane angle, i.e. the angle formed between the vane and the corresponding radial plane, with streamwise distance (x). Figure 3 shows 3 different vane angle configurations for a swirler with a vane exit angle of 45°. The simplest vane configuration is a heli-cal vane, where the vane angle remains constant with x. However the drawback of helical vanes is the sudden change in direction of the air flow at swirler entry, which might add to the flow turbulence. This change in direction can be avoided by using a quadratic design, where the vane angle changes quadratically with x, in-creasing from 0° at inlet to the required angle at exit. From figure 3, we observe that the quadratic vane pro-duced a circumferential shift of 22.5°. A good rule of thumb to achieve circumferential flow uniformity is to ensure that the circumferential shift produced by the swirler is close to 360°/(no. of vanes), which equals 30° for the 45° swirler. To achieve the required shift, a mix-ture of quadratic and helical vane designs was imple-mented. For the 45° swirler, a quadratic design up to x = 1.778 cm (0.7”) and a helical design henceforth was implemented, which produced a circumferential shift of

Figure 2. Schematic of the setup

Figure 3 Swirler vane angle design

Figure 4 45° Swirler, a) Cutout view of the design, b) Actual swirler

a) b)

28.2°. Figure 4 shows a cutout of the final swirler de-sign and the actual swirler. Table 1 lists the detailed parameters of the swirlers. Measurement Technique

2-D Particle Image Velocimetry (PIV) was used for flow measurements. A The PIV system used is a LaVi-sion commercial PIV system. The Laser is a Double Pulsed Nd:YAG laser, NewWave Solo PIV, with a pulse energy of up to 120 mJ/pulse at a wavelength of 532 nm. The camera used is the LaVision Image In-tense camera, which is a double frame - double expo-sure CCD camera, capable of taking either two frame buffers, or two images in rapid succession. A bandpass filter at 532 ± 3 nm is used to restrict the light absorbed to the laser wavelength. PIV records two images in rapid succession with a known time difference. The images are divided into interrogation windows, and cross correlation is carried out on the two images to determine velocity vectors for each interrogation win-dow. For more details on the PIV system, please refer to Elshamy [6].

For the current experiments, the PIV laser sheet was aligned parallel to the X-Y planes. Multiple planes were measured for each test condition and the results were compiled together to create a 3-D map of the flow field. The PIV laser and camera were mounted on a three-axis Lintech traverse for precise control of loca-tion and alignment in the different planes. A Velmex VP9000 controller interfaced with a computer was used to control the traverse movement. A schematic of the PIV setup is shown in figure 5.

The results obtained from PIV were the Mie-Scattering images and the PIV vector plots. The Mie-Scattering images are sensitive to the droplet density at any location and provide information about the jet plume location. The PIV vector fields indicate the dis-tribution of droplet velocities within the jet plume. For each measurement plane, 200 images were recorded and the Mie-Scattering images and PIV vector plots were averaged over the 200 images.

The swirlers used in this study produce a clockwise swirl as viewed from downstream. Since the jet orifice is centered on the Y-axis, the measurement domain of

interest is the top, right quarter plane (y > 0, z < 0). From figures 1 and 5, we can see that the optical access to the chamber is mainly restricted by the corner strut, which limits the measurement domain to y < 32 mm and z > -32 mm. The measurement domain employed for PIV is -5 mm ≤ x ≤ 42 mm, -5 mm ≤ y ≤ 31 mm, 0 mm ≤ z ≤ -30 mm.

The laser sheet, being parallel to the X-Y plane, was incident upon the centerbody for a portion of the measurement domain (z = 0:-9.55 mm). Due to this, a part of the reflected light is incident upon the camera. To avoid saturating the CCD and to reduce the noise created by laser reflections, the centerbody was coated with Fluorescent Paint (figure 1b). The paint converts a portion of the reflected green laser light into red fluo-rescent light, which gets blocked by the bandpass filter on the camera. This alleviated the problems due to laser reflection. However, there were certain locations where the reflection intensity was too intense to be able to take good data, and these locations had to be skipped.

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Figure 7. PIV planar velocity distributions for case 2 (45°, We = 105.9), a) z = 0 mm, b) z = -25 mm

Figure 5. Schematic of the PIV setup

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Figure 6. Measurement domain, a) Crossflow studies, b) Jet injection studies

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ILASS Americas, 21st Annual Conference on Liquid Atomization and Spray Systems, Orlando, Florida, May 18-21 2008

Table 2. Test Conditions for Crossflow Studies Case No Swirler ma (kg/s) Vx (m/s) Vcf (m/s) We

1 30° 0.404 98.57 113.82 105.7 2 45° 0.347 81.15 114.76 105.9 3 45° 0.245 56.63 80.08 52.7 4 60° 0.245 56.73 113.45 105.5

Table 3. Test Conditions for Jet Studies

Case No Swirler ma (kg/s) Vx (m/s) Vcf (m/s) ml (kg/min)

Vl (m/s) We q

5 30° 0.404 97.65 112.75 0.141 12.03 104.7 9.6 6 45° 0.349 80.44 113.16 0.141 12.03 106.7 9.4 7 45° 0.245 56.41 79.78 0.1 8.53 52.5 9.6 8 45° 0.349 80.44 113.76 0.199 17.01 106.7 18.8 9 60° 0.245 57.07 114.13 0.141 12.01 106.1 9.4

Test conditions

The 45° swirler was considered as the base swirler. A base Weber number of 100 for air and base momen-tum flux ratio of 10 for the jet was chosen. For cross-flow studies, in addition to testing a We = 100 for all swirlers, and additional We = 50 was tested for the base swirler. Table 2 lists the test conditions for the cross-flow studies. For jet injection, the case of We = 100, q = 10 was tested for all swirlers. The effect of a change in We and q was also studied for the 45° swirler. Table 3 lists the test cases for the jet studies. Both We and q have been defined based upon the total air velocities. For water, a density of 996 kg/m3 and a surface tension of 0.072 N/m have been assumed.

Results and Discussion Crossflow Measurements

Initial tests were conducted to characterize the crossflow. The crossflow was seeded with olive oil droplets for these tests. 2-D PIV measurements were carried out at a plane separation of 5 mm, from z = 0 to -30 mm, as shown in figure 6a. The red line in figure 6a represents the plane at z = -5 mm, which had to be skipped due to intense reflections, so that 6 planes were measured. Figure 7 shows typical PIV results for the z = 0 mm and -25 mm planes for case 2 (45°, We = 105.9), which is the base crossflow case. For the z = 0 mm plane, the centerbody exists up to y = 9.55 mm, explaining the regions with no velocities. Even at z = -25 mm, the presence of the centerbody in the background and sec-ondary reflections were responsible for blank patches in the velocity field. From figure 7, it can be observed that there is no significant change in both the x- and y- ve-locity components with x. Similar observations for other cases led to the conclusion that the flow is fully developed in the measurement domain. As a result, it was possible to derive the velocities in the test chamber cross-section by averaging over x. Figure 8 plots the contours of Vx and Vy in the cross-section for case 2. The negative values for Vy are a result of the clockwise sense of the swirl, as viewed from downstream. The absence of valid velocity measurements in the region where the centerbody was present in the background can be clearly observed as the areas with zero veloci-ties. The trends in the velocities in figure 8 can be un-derstood clearly if the cross-section is considered as a polar frame of reference. Then Vx is observed to reduce as we move radially outwards, while the magnitudes of Vy increase as we move circumferentially away from the Y-axis.

Figure 8. Cross Sectional Velocity distributions for case 2 (45°, We = 105.9), a) Vx, b) Vy

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The absence of the z-components of the velocity hinders complete understanding of the flow. However the flow could be assumed to be axisymmetric since it originates from an axial swirler. Figure 9 tests the valid-ity of this assumption by plotting Vx along two direc-tions: along the lines z = 0 (Y-axis) and y = 0 (negative Z-axis). In spite of the difference in the number of points measured, the velocities compare very well, con-firming the validity of the assumption of axisymmetry.

It was previously seen in figure 8 that the velocities could be understood better from a polar frame of refer-ence. Since the crossflow is axisymmetric as well, the cross-section was converted into polar coordinates, as shown in figure 10, with θ increasing clockwise from the Y-axis. Then Vy along the Y- and Z-axes can be considered as the radial (Vr) and tangential (Vt) veloci-ties respectively. Figure 11 plots the radial variation of the velocity components. Vx initially increases with r, peaking around r = 12 mm and then gradually reduces with r. Vt was observed to increase with r, with a n-

parameter from the vortex equation (equation 1) of around 0.8. The n-parameter for free vortex and solid body rotation are -1 and 1 respectively, indicating that the crossflow is very close to a solid body rotation. The magnitudes of Vr are very small compared to Vx and Vt and can be neglected.

n

tV const r= ⋅ (1)[12]

An axisymmetric model was created, with the axial and tangential velocities modeled by 4th and 2nd degree polynomials respectively. Figure 12 plots the computed as well as experimental Vx and Vt values for cases 1, 2 and 4, which represent the We = 105 cases for the three swirlers. It can be seen that there is good correlation between the modeled and experimental data. The Vx and Vt standard errors were of the order of 4.5 and 3 m/s respectively, which are about 5 % of the peak veloci-ties. Thus the axisymmetric velocity model is a good representation of the crossflow.

The Vx and Vy velocities were used to compute the total crossflow velocities (Vcf), which have been plotted in figure 13. For all swirlers, Vcf values peak at radial locations near r = 15 mm and decrease on either sides.

The angle made by the total velocity vector (ψ) to the Vx vector is representative of the direction of the streamline at that location. These angles were calcu-lated using equation 2 and have been plotted in figure 14. We observe that ψ values undergo a minimum cor-responding to the location of maximum Vx (r = 12-15 mm) as expected. Average ψ values for r > 12 mm are

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Figure 9. Variation of Vx for case 2 (45°, We = 105.9)

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Figure 10. Transformation from Cartesian to polar co-ordinates

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Figure 12. Computed velocities for We = 105. a) Vx, b) Vt

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30.4°, 41.2° amd 45.4° for the 30°, 45° and the 60° swirlers respectively. We observe that the 30° swirler (ψ = 30.4°) is able to achieve flow angles close to the vane exit angle, while the 45° and 60° swirlers (ψ = 41.2° and 45.4°) do not provide enough turn, with the highest deficit being for the 60° swirler.

1tan t

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VV

ψ − ⎛ ⎞= ⎜ ⎟

⎝ ⎠ (2)

Since the test chamber used had a square cross-section, small corner recirculation zones (CRZ) will form at the intersection of the walls, though the pres-ence of chamfers at the corners is expected to reduce their extent. Due to the presence of the corner struts, no measurements could be taken near the corner of the cross-section. As a result, for cases 1-4, no CRZs were detected in the crossflow except for the 60° swirler (case 4) in the measurement domain. For case 4, the presence of CRZ could be detected as a sudden increase in the negative Vy values for y > 27.38 mm in the z = -30 mm plane.

Jet Measurements

The crossflow studies were followed by jet injec-tion studies, where a water jet was injected from the orifice on the centerbody. For jets, the separation be-tween measurement planes was reduced to 2.5 mm for better flow field resolution. Measurements were carried out from z = 0 to -30 mm, as shown in figure 6b. The

plane at z = -7.5 mm (marked red in figure 6b) had to be skipped due to excessive reflections, resulting in 12 measured planes.

The base case for the jet was case 6, i.e. We = 106.7, q = 9.4 for the 45° swirler. Figure 15 shows a 3-D view of the jet for the base case obtained from collat-ing the Mie-Scattering images from all planes. Figure 16 shows 3 views of the same jet as viewed along the Cartesian axes. From these figures, we observe that the jet emerges vertically upwards, and then starts spinning along with the crossflow. As the jet moves downstream,

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Figure 13. Variations of Vcf with r

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Figure 14. Variations of flow angle (ψ) with r

Figure 15. Base jet case, case 6 (45°, We = 106.7, q = 9.4)

Figure 16. Views of case 6 (45°, We = 106.7, q = 9.4), a) View from top, b) View from left, c) View from downstream

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even though the penetration in the y-sense seems to decrease, the radial penetration keeps increasing. This is seen more clearly in figure 16c, where the cross-section of the centerbody has been included for refer-ence. Then we can clearly see that the radial penetration kept increasing even far downstream. In fact, for all cases tested, the jets hit the wall of the test chamber well before completing half a revolution around the centerbody.

In a typical jet in crossflow flow field, for low-to-moderate q, the rate of increase of jet penetration be-comes very small at large downstream distances. How-ever, for the swirling crossflow, the jet penetration kept increasing even far downstream. One of the explana-tions for this phenomenon is the presence of centrifugal forces acting on the jet due to the rotating nature of the crossflow. These centrifugal forces aid the jet in pene-trating further. Another effect is similar to what the authors observed in their previous study on jets injected in a shear laden crossflow [11]. In cases where the crossflow had a negative velocity profile (Vcf decreased with y) the reduction in the penetration slope decreased as the jet penetrated further, allowing higher incre-mental penetration, as compared to that for a uniform crossflow. Since crossflow velocities decrease, the crossflow aerodynamic forces also decreases, allowing higher penetration. For the current study, the modeled total crossflow velocities were observed to reduce with r for r > 15, so a similar effect can be attributed towards the continually increasing jet penetration.

Figure 17 shows the 3-D and the top view for case 9 (60°, We = 106.1, q = 9.4), which had operating con-ditions identical to case 6, but for the 60° swirler. Com-paring figures 15-17, two significant differences can be deduced from the jet behavior in these two cases. The

jet for the 60° swirler hits the domain boundary at an earlier streamwise location as compared to the jet for the 45° swirler. This is expected, because of the higher turn angles generated by the 60° swirler. From figure 16a, the streamwise location where the jet centerline for case 6 hits z = -30 mm is approximately 37 mm, which corresponds to a mean jet flow path angle of 39°. For case 9, from figure 17b, the streamwise location for z = -30 mm was around 28 mm, yielding a mean jet flow path angle of approximately 47°. The mean flow angles for the corresponding crossflows were 41.2° and 45.4° respectively (table 4). Thus the jet can be seen to try to follow the crossflow. However, care should be taken to note that this was just a 1-D analogy of the flow. The jet flow is highly three-dimensional in nature, and re-quires a more detailed analysis.

The second difference between cases 6 and 9 is in the jet penetration. The radial penetration for the 60° swirler case is significantly higher than that for the base swirler. This can again be explained in terns of the cen-trifugal forces and the crossflow velocity gradients. Since the crossflow spins more sharply for the 60° swirler, the centrifugal forces experienced by the jet can be assumed to be higher than for the case of the 45° swirler. Also, the total crossflow velocity drops more sharply for the 60° swirler, leading to even lesser oppo-sition to jet penetrations at large r.

It was observed above that it makes more sense to describe the jet penetration in a radial sense. Hence the measurement domain was transformed into a cylindrical frame of reference. The cross-section of the cylindrical domain was identical to the polar domain used for the crossflow. For the analysis of the crossflow described previously, it was enough to convert the coordinates of the measured points from Cartesian to polar due to the assumption of axisymmetry. However, for the jets, there is a need to track the jet boundaries in the cylin-drical reference frame for jet penetration analysis. Hence, a true cylindrical domain was desired. This was achieved by first creating a very dense 3-D Cartesian domain by interpolating the Mie-Scattering intensities among the measured points. A cylindrical domain was then defined and the intensity at each of these points was obtained as an average of the points lying within half a cell distance in each direction. To ensure good results after averaging, the maximum cell dimension of the intermediate dense grid needed to be at least as small as the smallest cell dimension of the cylindrical grid. The final cylindrical grid had a cell size of 0.25 mm in x, 0.5 mm in r and 5° in θ. The cylindrical do-main used was -5 mm ≤ x ≤ 30 mm, 9.5 mm ≤ r ≤ 43 mm and 0° ≤ θ ≤ 100°.

Figure 18 shows representative contours of the jet in the X-R (θ = 40°), R-Θ (x = 10 mm) and X-Θ (r = 20 mm) planes. It is to be noted that both the R-Θ and X-Θ planes have been mapped onto a Cartesian grid for dis-

Figure 17. Views of jet case 9 (60°, We = 106.1, q = 9.4), a) 3-D View, b) View from top

play in figure 18. The R-Θ plane is actually a portion of an annulus of inner radius 9.5 mm and outer radius 43 mm, while the X-Θ plane from figure 18c is the curved surface of a cylinder of radius 20 mm. In each of these planes, the jet can be observed to be oblong in shape suggesting that none of them capture the true jet cross section, which is true since the path of the jet centerline is not aligned with any of the domain axes. This also suggests that it is necessary to track the mean path of the jet and predict the penetration and spread along this path to be able to compare with existing jet-in-crossflow data.

From the Mie-Scattering data in the cylindrical domain, it is possible to track the radial as well as tan-gential location of the edges of the jet periphery both in the radial as well as circumferential directions, from which we can determine the jet penetration and spread. Figure 19 shows the x-variation of the radial and circumferential locations of the upper radial edge of the jet plume for cases 5, 6 and 9, which represent the ef-fect of swirl angle with constant operating parameters (We ≈ 105, q ≈ 9.5). From figure 19a, we observe that the radial penetration increases with an increase in the

swirl angle, which has already been explained above. Also, initially, for x < 4 mm, a slightly higher penetra-tion for the 30° swirler is observed. However the radial penetration up to this location is less than r = 18 mm, which was radial location for the peak in the total cross-flow velocity for the 30° swirler (Figure 13). As soon as the jet enters this high crossflow velocity region, it bends sharply and the radial penetration stays low downstream of this location.

From figure 19b, we understand how the jet spins with the flow. Figure 19b suffers from a lack of good resolution in the circumferential direction, and hence a lot of discrete jumps can be observed. For both the 30° and 45° swirlers, the θ angle increases steadily with x. However, for the 60° swirler, after x = 15 mm, the slope of the θ-curve drops, indicating that the jet may no longer be spinning with the crossflow and may have gained enough momentum to penetrate straight on. It can be noted that at x = 15 mm, the jet for the 60° swirler has already penetrated 28.5 mm in the radial direction, where the crossflow total velocity (Vcf) is less than 70 m/s.

Figure 20 plots the circumferential width of the spray for the cases from figure 19. We observe that the spray for the 30° swirler starts narrowing after x = 8 mm, while the spray periphery for the 45° swirler is the widest. However, a higher resolution in the circumfer-ential direction is needed for a detailed analysis.

Figure 21 plots the radial jet penetrations for the cases 6 (base), 7 (We = 52.5) and 8 (q = 18.8), and demonstrates the effect of We and q on the jet penetra-

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Figure 18. Typical contours of case 6 (45°, We = 106.7,

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Figure 19. Location of the upper periphery for cases 5, 6 & 9 (We = 105, q = 9.5) a) Radial location, b) Circumferential location

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a)

b)

tion for the 45° swirler. Reducing We (case 7) leads to a minor increase in the radial jet penetration. Increasing q (case 8) leads to a significant increase in the jet penetra-tion. In the far downstream region, a sudden drop in penetration was experienced for case 8, the reason for which is not yet known. The effect of We and q are identical to what is observed in traditional jet-in-crossflow studies [1].

Figure 22 shows the droplet velocities in 4 of the measured planes for the base case, case 6 (45°, We = 106.7, q = 9.4). Here, the absence of the knowledge of the z-components does hamper the understanding of the 3-D flow since both radial and tangential velocities are important for the jet flow. At the z = 0 mm plane (Fig-ure 22a), the droplet velocities are mainly directed up-wards. At z = -15 mm (Figure 22b), the jet has moved a bit downstream. Also a large portion of droplets have negative Vy velocities, especially near the Z-axis (y = 0). Additionally, the droplets near the upper periphery still have positive Vy velocities, indicating that the jet is expanding. Similar observations can be deduced from the z = -20 and -25 mm planes. This indicates that the jet periphery is still spreading even at z = -25 mm. Also the spray coverage in the velocity plots is observed to be significantly larger than that observed in the Mie-Scattering images. This occurs because the Mie-Scattering intensities are roughly proportional to the droplet densities, so that regions with small number of droplets are not captured in the Mie-Scattering images.

The trends observed in figure 22 were similar to those observed for other cases. The largest droplet ve-locities were observed away from the centerbody (z ≤ - 15 mm) and these were mostly located near y = 0 mm with negative Vy velocities. The jet spray was observed to expand both in the vertically upward and downward directions, though the velocities at the upper peripheries were significantly smaller than those at the lower pe-riphery.

No CRZs were observed in the measurement do-main for the crossflows, except for the 60° swirler, where presence of CRZ was detected for r > 40.6 mm (z = -30 mm, y > 27.38 mm). Since the jet radial pene-trations were lower than r = 40.6 mm for all cases, the CRZs are believed to have no effect on the jet behavior.

Conclusions

An experimental study has been conducted to study the effect of a swirling crossflow on the behavior of a water jet injected transversely into it. Axial swirlers were used to generate the swirling crossflow, and jets were injected from a cylindrical centerbody protruding through the hub of the swirler.

The crossflow was observed to be fully-developed and axisymmetric, with a vortex motion similar to solid body rotation. An axisymmetric velocity model was created, which was observed to have very good agree-ment with the experimental data. The model predicted that the total crossflow velocities exhibited a peak near r = 15 mm. The flow angles predicted by the model reveal that the flow turn achieved by the swirlers lagged the vane exit angle except for the 30° swirler.

Water jets injected in the swirling crossflow were observed to spin along with the crossflow. However the radial penetration kept increasing even at large down-stream distances. This is believed to be caused by the presence of centrifugal forces acting on the jet and the reduction in crossflow total velocities at high r. The radial penetration increased with an increase in the swirl strength.

For a detailed study of the jet penetration, the measurement domain was transformed into a cylindrical domain. Analysis in the cylindrical domain verified that the jet radial penetration increased with an increasing in the swirl strength and that the jet spins along with the crossflow. However, as the jet penetrates higher into the region of decreasing crossflow velocity, the rate of circumferential movement of the jet decreases and it seems to penetrate straight on without further spinning. The jet for the 45° swirler was observed to have the largest circumferential spread. Changing the Weber number had little effect on the jet penetration; though increasing the momentum flux ratio increased the radial penetration considerably.

The droplet velocity distribution reveals that the jet plume keeps expanding even as the jet travels far down-

-5 0 5 10 15 20 25 300

5

10

15

20

25

30

35

40

x (mm)

Spra

y w

idth

(deg

)

30°45°60°

Figure 20. Variations of jet circumferential width with x

for cases 5, 6 & 9 (We = 105, q = 9.5)

-5 0 5 10 15 20 25 305

10

15

20

25

30

35

x (mm)

r (m

m)

We = 52.5, q = 9.6We = 106.7, q = 9.4We = 106.7, q = 18.8

Figure 21. Effect of We, q on radial penetration for the 45° swirler

stream. Since the jet spins clockwise with the cross-flow, high negative y-velocities were observed in the bottom half of the plume. However, positive y-velocities are observed at the top of the plume indicat-ing that some droplets still keep penetrating higher. A complete representation of the velocity field could not be generated due to the missing z-velocity components, since only 2-D measurements have been carried out.

Future Work It was observed that the missing z-components of the velocities hamper a full understanding of the 3-D flow field, especially for the jet injection cases. Repeating the tests with laser sheets aligned with Y-Z planes could alleviate these problems. Also additional PDPA testing could be carried out to investigate the droplet distribution in the spray. Nomenclature m mass flow rate q liquid-air momentum flux ratio r radial coordinate, radius V air, liquid velocity We aerodynamic Weber number x streamwise coordinate y vertical coordinate z lateral coordinate θ circumferential coordinate, polar coordinate ψ flow angle Subscripts a air

cf crossflow property (total velocity) l liquid r radial component t tangential component x x-component y y-component z z-component References 1. Becker, J., and Hassa, C., Atomization and Sprays

11:49-67 (2002) 2. Chen, T. H., Smith, C. R., Schommer, D. G., and

Nejad, A. S., 31st Aerospace Sciences Meeting and Exhibit, Reno, NV 1993

3. Birouk, M., Azzopardi, B. J., and Stäbler, T., Parti-cle and Particle Systems Characterization 20:283-289 (2003)

4. Lefebvre, A.W., Gas Turbine Combustion, McGraw-Hill, 1983, Ch 9

5. Tambe, S. B., “Liquid Jets in Subsonic Crossflow,” MS Thesis, Department of Aerospace Engineering and Engineering Mechanics, University of Cincin-nati, Cincinnati, OH (2004)

6. Elshamy, O.M., “Experimental Investigations of Steady and Dynamic Behavior of Transverse Liquid Jets,” PhD Dissertation, Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati, Cincinnati, OH (2007)

7. Becker, J., and Hassa, C., Journal of Engineering for gas turbines and Power, 125:901-908 (2003)

8. Becker, J., Heitz, D., and Hassa, C., Atomization and Sprays, 14:15-35 (2004)

Figure 22. Velocity planes for the base case, case 6 (45°, We = 106.7, q = 9.4), a) z = 0 mm, b) z = -15 mm, c) z = -20 mm, d) z = -25 mm

a)

c)

b)

d)

9. Gong et. al., Journal of Propulsion and Power, 22,1: 209-210 (2006)

10. Tambe, S. B., Elshamy, O. M., and Jeng, S.-M, 45th Aerospace Sciences Meeting and Exhibit, Reno, NV Jan 2007

11. Tambe, S. B., Elshamy, O. M., and Jeng, S.-M., 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Confer-ence & Exhibit, Cincinnati, OH, 2007

12. Gupta, A. K., Lilley, D. g., and Syred, N., Swirl Flows, Abacus Press, 1984, Ch 1