**2. Experimental setup**

Figure 3 shows a schematic of the experimental setup used to study the injection of a liquid jet from a flat surface into the cross flow of air at elevated pressure. This setup had a plenum chamber, a rectangular air supply channel, a test section with injector under investigation and a pressurized chamber with four 38mm (1.5 inch) thick windows for optical access to the spray.

Plenum chamber was 203.2 mm in diameter and 457.2mm long. Two perforated screens were installed at the entrance and at the exit of the plenum to achieve necessary level of turbulence and flow uniformity in the test section. The rectangular supply channel was 62.3mm (2.45 inch) by 43.2mm (1.7 inch) in cross-section and was 304.8mm long. It was equipped with a "bell-mouth" air intake which was connected to the bottom of the plenum chamber to smoothen the air flow. On the other end of the channel four aerodynamically shaped plates were attached to the channel creating a test section with a cross-section 31.75 x 25.4mm (1.25 x 1.00 inch).

Fuel Jet in Cross Flow – Experimental Study of Spray Characteristics 65

was ~1.4KPa (2 psi) higher than in the test section to keep temperature in its surrounding below 1000C. Mixture of the air passing the test section, injected Jet-A fuel and cooling air left the rig through the exhaust line, passing through the control valve, flow straightener and afterburner where fuel was burned in the pilot flame of natural gas to prevent fuel from

Flow conditions in the test section were monitored using 3mm (1/8inch) diameter Pitot tube and thermocouple, which were located within the 2.45" × 1.70" test channel (see Figure 4). An additional pressure transducer and thermocouple were installed just downstream of the test section. Differential pressure sensor measured pressure drop along test section to support flow velocity measurements by the Pitot tube. Axes of the coordinate system used in this study were designated as shown on the Figure 5. *X* was direction of fuel injection. *Y* –

Lateral spread of the spray and *Z* – Direction of the air flow.

Fig. 4. Instrumentation of the test section

Fig. 5. Coordinate system for spray characterization

entering the atmosphere.

Fig. 3. Schematic of the test facility

This test section has ~50mm (2.00 inch) long, 6mm (1/4 inch) thick windows on three sides for optical access to the spray zone. The fuel injectors were installed on the centerline of the plate 10mm downstream of transparent section. The whole system was fixed to a massive optical table while optical tools were installed on a traversing mechanisms, which provides precise movement (minimal step is 0.0254mm) in three mutually orthogonal directions using step motors and electronic drivers controlled using a computer. In the current study, 1mm increments of movement were typically used for characterizing the spray. Maximum possible flow conditions in the test sections were P=4.2MPa (600 psi) and T=755K (900F) which correspond to supercritical flow conditions for the Jet-A fuel. These flow conditions were achieved by supplying preheated air flow from the controllable high pressure air supply at P < 5.0Mpa (720 psi) and T < 800K (10000F) into the plenum, where it then enters the 1.25" × 1.00" test section.

Velocity in the test section was controlled by the motorized control valve in the exhaust line (see Figure 3). Cooling of the test channel, test section as well as inner and outer windows in case of the preheated air use was achieved by pressurizing of the pressure vessel with the high pressure air flow (P<5.0MPa, T~295K). This cooling air was eventually mixed with the high temperature air from the test section in the exhaust path. Pressure of this cooling air 64 Advanced Fluid Dynamics

This test section has ~50mm (2.00 inch) long, 6mm (1/4 inch) thick windows on three sides for optical access to the spray zone. The fuel injectors were installed on the centerline of the plate 10mm downstream of transparent section. The whole system was fixed to a massive optical table while optical tools were installed on a traversing mechanisms, which provides precise movement (minimal step is 0.0254mm) in three mutually orthogonal directions using step motors and electronic drivers controlled using a computer. In the current study, 1mm increments of movement were typically used for characterizing the spray. Maximum possible flow conditions in the test sections were P=4.2MPa (600 psi) and T=755K (900F) which correspond to supercritical flow conditions for the Jet-A fuel. These flow conditions were achieved by supplying preheated air flow from the controllable high pressure air supply at P < 5.0Mpa (720 psi) and T < 800K (10000F) into the plenum, where it then enters

Velocity in the test section was controlled by the motorized control valve in the exhaust line (see Figure 3). Cooling of the test channel, test section as well as inner and outer windows in case of the preheated air use was achieved by pressurizing of the pressure vessel with the high pressure air flow (P<5.0MPa, T~295K). This cooling air was eventually mixed with the high temperature air from the test section in the exhaust path. Pressure of this cooling air

Fig. 3. Schematic of the test facility

the 1.25" × 1.00" test section.

was ~1.4KPa (2 psi) higher than in the test section to keep temperature in its surrounding below 1000C. Mixture of the air passing the test section, injected Jet-A fuel and cooling air left the rig through the exhaust line, passing through the control valve, flow straightener and afterburner where fuel was burned in the pilot flame of natural gas to prevent fuel from entering the atmosphere.

Flow conditions in the test section were monitored using 3mm (1/8inch) diameter Pitot tube and thermocouple, which were located within the 2.45" × 1.70" test channel (see Figure 4). An additional pressure transducer and thermocouple were installed just downstream of the test section. Differential pressure sensor measured pressure drop along test section to support flow velocity measurements by the Pitot tube. Axes of the coordinate system used in this study were designated as shown on the Figure 5. *X* was direction of fuel injection. *Y* – Lateral spread of the spray and *Z* – Direction of the air flow.

Fig. 4. Instrumentation of the test section

Fig. 5. Coordinate system for spray characterization

Fuel Jet in Cross Flow – Experimental Study of Spray Characteristics 67

The main difference between the investigated injectors was shape of the surface between the

(a) Sharp edged injector (b) Round edged injector

One injector had sharp edge as shown on the Fig 7-a and the other one had smooth transition path from the plenum to the orifice (i.e., round edge, see Fig 7-b). Their hydraulic characteristics presented on the Fig. 8 reflect this difference in the injector's internal shape.

*d*

*Pinj*.>60psi) which is relevant to the current study.

*C*

. . 2 *inj fuel inj fuel*

of the sharp edge orifice was

*A P m*

 

relatively constant *Cd~0.75* in the tested range of *ReD* numbers while the discharge coefficient of the round edge orifice is *Cd~0.96* at the Reynolds numbers exceeding

**3.2 3.7 4.2 4.7**

**log10(ReD)**

Effect of injector geometry on jet disintegration was first demonstrated without cross flow of air. Images of the fuel jets injected from both injectors into the atmosphere are presented on the Fig. 9. It is clearly seen that the jet coming out of the sharp edged orifice disintegrated forming spray structures, ligaments and droplets (see Figure 9-a) while jet injected from the

A closer look on these fuel jets without cross flow in a near field (see Figure. 10) reveals that the jet injected from the sharp edge orifice expands and disintegrates while the jet from the round edge orifice shows the development of the hydrodynamic instabilities (see Figures 10 a and 10-b respectively). This observation suggests that internal turbulence created by the sharp edge at the entrance of the cylindrical orifice (*L/D*~10) dramatically change jet boundaries and may lead to the differences in spray creation especially when the mechanism of the jet disintegration in the cross flow at elevated Weber numbers (*We*>200) is "shearing". In fact images of the fuel jets shown on the Figure 11 clearly indicate that significant scale difference in liquid border structure on the outer edge of the jet remain

**Sharp Edge Sharp** 

*fuelDinj.Ufuel /*

*fuel)*

**Round Edge Round Edge** 

**3.2 Characteristics of injectors** 

plenum and the injection orifice.

Fig. 7. Schematics of the tested injectors

Specifically, discharge coefficient

**0.6**

Fig. 8. Hydraulic characteristics of the tested injectors (*ReD*=

round edge orifice was relatively smooth and intact (Figure 9-b).

**0.7**

**0.8**

**Discharge coeff., Cd**

**0.9**

**1.0**

*ReD=10,000 (*
