Nozzle with sweeping jet actuator and associated methods

Abstract

A nozzle (30) for a jet engine (32) is disclosed. The nozzle (30) includes at least one sweeping jet actuator (10) operatively coupled to the nozzle (30). The sweeping jet actuator (10) has an inlet opening (14) and a discharge slot (26). The inlet opening (14) is configured to receive a supply of air (40) and the discharge slot (26) is configured to discharge that supply of air in a sweeping motion (42) into and interacting with an air flow (36) moving through the nozzle (30). A jet engine (32) with a nozzle (30) and a sweeping jet actuator (10) coupled to the nozzle (30) is also disclosed. A method of operating a jet engine (32) having a nozzle (30) with a sweeping jet actuator (10) is further disclosed.

Description

NOZZLE WITH SWEEPING JET ACTUATOR AND ASSOCIATED METHODSCross Reference to Related Application

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 527,796, filed July 19, 2023, the disclosure of which is incorporated by reference herein in its entirety.Statement Regarding Federally Funded Research Or Development

[0003] This invention was made with government support under N00173-19-C- 6000 and awarded by the Naval Research Laboratory. The government has certain rights in the invention.TECHNICAL FIELD

[0004] The invention relates generally to sweeping jet actuators used on nozzles of jet engines.BACKGROUND

[0005] Sweeping Jet Actuators (SJAs) are viable flow control devices for improving the aerodynamic performance of high lift vehicles by mitigating separated flow regions. SJAs emit spatially and temporally oscillating jets without any moving parts and, instead, rely primarily on the feedback mechanism inside the SJAs. For example, SJAs placed ahead of the rudder hinge line on a full-scale Boeing 757 may increase the rudder control by using miniature sweeping jet actuators. It has been found that its performance exceeds that of the chevron technology at takeoff conditions. SJAs not only provide fluidic injections but also sweeping motionswithout the requirement of external power supply devices. The addition of the sweeping motion is shown to impact the noise reduction. The sweeping and oscillating frequency may be designed to target specific supersonic jet noise mechanisms, such as frequencies associated with the peak noise intensities associated with the large scale mixing noise and shock associated with noise. Thus, it is shown that the SJA technology has a greater potential of the noise reduction than the regular fluidic injection methods.SUMMARY OF THE INVENTION

[0006] According to one aspect of the disclosure, a nozzle for a jet engine is disclosed. The nozzle includes at least one sweeping jet actuator operatively coupled to the nozzle. The sweeping jet actuator has an inlet opening and a discharge slot. The inlet opening is configured to receive a supply of air and the discharge slot is configured to discharge that supply of air in a sweeping motion into and interacting with an air flow moving through the nozzle. The nozzle may include a shroud enclosing an exterior portion of the nozzle to form an interior section such that the sweeping jet actuator is positioned within the interior section.

[0007] In an embodiment, a longitudinal axis of the sweeping jet actuator may be substantially parallel to a longitudinal axis of the nozzle. In another embodiment, a longitudinal axis of the sweeping jet actuator may be substantially perpendicular to a longitudinal axis of the nozzle.

[0008] In an embodiment, the at least one sweeping jet actuator may include a plurality of sweeping jet actuators. That plurality of sweeping jet actuators may be equally spaced around the periphery of the interior section of the nozzle.

[0009] In an embodiment, the supply of air entering the inlet opening may be bleed air from the jet engine. In another embodiment, the supply of air entering theinlet opening may be environmental air. In yet another embodiment, the supply of air entering the inlet opening may be a combination of bleed air from the jet engine and environmental air.

[0010] According to another aspect of the disclosure, a jet engine is disclosed. The jet engine includes a nozzle and at least one sweeping jet actuator operatively coupled to the nozzle. The sweeping jet actuator has an inlet opening and a discharge slot. The inlet opening is configured to receive a supply of air and the discharge slot is configured to discharge that supply of air in a sweeping motion into and interacting with an air flow moving through the nozzle. The nozzle may include a shroud enclosing an exterior portion of the nozzle to form an interior section such that the sweeping jet actuator is positioned within the interior section.

[0011] In an embodiment, a longitudinal axis of the sweeping jet actuator may be substantially parallel to a longitudinal axis of the nozzle. In another embodiment, a longitudinal axis of the sweeping jet actuator may be substantially perpendicular to a longitudinal axis of the nozzle.

[0012] In an embodiment, the at least one sweeping jet actuator may include a plurality of sweeping jet actuators. That plurality of sweeping jet actuators may be equally spaced around the periphery of the interior section of the nozzle.

[0013] In an embodiment, the supply of air entering the inlet opening may be bleed air from the jet engine. In another embodiment, the supply of air entering the inlet opening may be environmental air. In yet another embodiment, the supply of air entering the inlet opening may be a combination of bleed air from the jet engine and environmental air.

[0014] In another aspect of the disclosure, a method of operating a jet engine is disclosed. The jet engine has a nozzle with at least one sweeping jet actuator, whichincludes an inlet opening and a discharge slot. The method includes causing a first air flow to move through the jet engine and the nozzle; causing a second air flow into the inlet opening of the sweeping jet actuator; and discharging the second air flow from the discharge slot of the sweeping jet actuator in a sweeping motion such that the discharged second air flow interacts with the first air flow moving through the nozzle.

[0015] In an embodiment, the second air flow entering the inlet opening may be bleed air from the jet engine. In another embodiment, the second air flow entering the inlet opening may be environmental air. In yet another embodiment, the second air flow entering the inlet opening may be a combination of bleed air from the jet engine and environmental air.

[0016] In an embodiment, the discharged sweeping second air flow interacts with the first air flow moving through nozzle such that a resulting thrust of the jet engine is greater than a thrust of the jet engine without the sweeping jet actuator.

[0017] In another embodiment, the discharged sweeping second air flow interacts with the first air flow moving through nozzle so as to reduce the noise level of the jet engine compared to the jet engine without the sweeping jet actuator.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. Some of the figures in the pending provisional application used color to differentiate test results and flowsimulations. Those colors were converted to black and white or grayscale to generate the figures for this application.

[0019] FIG. 1 A is a schematic representation of an exemplary SJA geometry.

[0020] FIG. 1 B is a perspective view of a jet engine with a nozzle having a plurality of SJAs according to an embodiment of the invention.

[0021] FIG. 1 C is a perspective view of the nozzle of Fig. 1 B with one SJA in partial cross section.

[0022] Fig. 1 D is a schematic representation of a nozzle with SJAs oriented perpendicular to the axial flow through the nozzle.

[0023] FIGS. 2A and 2B are schematic representations of flow motion (Mach number contours) inside an exemplary SJA at two instances in time, where the SJA injection pressure is four times of the ambient pressure and the Mach number is 1 .0 at the SJA throat.

[0024] FIGS. 3A and 3B are a pair of graphs showing how the sweeping frequency depends on the ratio L / di, where the SJA entrance width di is 0.13”.

[0025] FIG. 4 is a schematic representation of where a microphone was located in a standalone SJA test.

[0026] FIGS. 5A-5E are a series of graphs of sound data from an SJA scalability study, where L / di = 4.6-8.2.

[0027] FIGS. 6A-6D are a series of images showing SJA flow motion at the first peak frequency, i.e., the sweeping frequency.

[0028] FIG. 7 is a schematic defining the far-field noise radiation angle.

[0029] FIGS. 8A-8C is a series of graphs of experimental data showing the effect of the SJA axial location on the noise reduction performance, where D, the nozzle exit diameter, is 2.16”, the SJA length is approximately 1 ”, L / di = 7.3, the injectionpressure is four times the ambient pressure, and both the main nozzle and the SJA flows are at standard sea level temperature.

[0030] FIGS. 9A-9C is a series of graphs of experimental data showing scalability tests of nozzles implemented with SJAs, where the injection pressure is four times the ambient pressure and both the main nozzle and the SJA flows are at standard sea level temperature.

[0031] FIGS. 10A-100 is a series of graphs of experimental data showing the frequency effect on the noise reduction performance, where D, the nozzle exit diameter, is 2.16”, the SJA width di is 0.13”, the injection pressure is four times the ambient pressure, and both the main nozzle and the SJA flows are at standard sea level temperature.

[0032] FIGS. 11A-11 C is a series of graphs of experimental data showing the frequency effect on the noise reduction performance, where D, the nozzle exit diameter, is 2.8”, the SJA width di is 0.17”, the injection pressure is four times the ambient pressure, and both the main nozzle and the SJA flows are at standard sea level temperature.

[0033] FIG. 12A is a schematic representation of typical SJA configured to generate flow sweeping from one side to another.

[0034] FIG. 12B is a schematic representation of the SJA in FIG. 12A, but with square plugs positioned to eliminate the sweeping motion of the flow such that the SJA generates simple injection flow.

[0035] FIGS. 13A-13C is a series of graphs of experimental data showing the sweeping motion effect on the noise reduction, where D, the nozzle exit diameter, is 2.16”, the SJA length is approximately 1”, L / di = 7.3, the injection pressure is fourtimes the ambient pressure, and both the main nozzle and the SJA flows are at standard sea level temperature.

[0036] FIGS. 14A-14C is a series of graphs of experimental data showing noise reduction of the faceted nozzle having SJAs, where the nozzle diameter is 3.2”, L / di = 7.3, the SJA length is approximately 1 .5”, the nozzle temperature is three times the ambient temperature, i.e., the nozzle temperature ratio (NTR) is 3.0.DETAILED DESCRIPTION OF THE INVENTION

[0037] An exemplary sweeping jet actuator (SJA) 10 is shown in Fig. 1. The SJA 10 includes an inlet 12 with an inlet opening 14 and an inlet outlet 16. The SJA 10 also includes an interacting region or mixing chamber 18, feedback channels or paths 20a, 20b, control ports 22a, 22b, an outlet 24, and a discharge slot 26. The inlet opening 14 has a width, di, the inlet outlet 16 has a width, di , the outlet has width, d2, the SJA has length, L and a width, W, and the feedback channels 20a, 20B have a width, Ws.

[0038] A nozzle 30 having a plurality of the SJAs 10 incorporated therein is shown in Fig. 1 B according one aspect of the invention. The nozzle 30 is illustrated as part of a jet engine 32 of the type used on military jets, for example. SJAs 10 may, however, be incorporated into jet engines of the type used on commercial or general aviation aircraft. During operation of the jet engine 32, air flows into the front of the jet engine and moves through the interior of the jet engine 32 as indicated by arrows 34. The air flow then flows through and exits the nozzle 30 as indicated by arrows 36.

[0039] The plurality of the SJAs 10 are operatively coupled to an interior section38 of the nozzle 30. The SJAs 10 may be equally spaced around the periphery ofthe interior section 38. In an embodiment, there are an even number of SJAs 10 equally spaced around the periphery of the interior section 38. In an embodiment, there may be as few as one SJA 10 operatively coupled to the interior section 38. The maximum number of SJAs 10 spaced around the periphery of the interior section 38 is largely dictated by the diameter of the nozzle 30, where nozzles 30 with larger diameters may accommodate more SJAs 10 compared to nozzles 30 with smaller diameters. In an embodiment, the SJAs 10 may be positioned directly adjacent to one another so that there is effectively no space between them.

[0040] With reference to Figs. 1 B and 1 C, the longitudinal axis of each SJA 10 is substantially aligned with the longitudinal axis of the nozzle 30. Here substantially aligned equals 0s± 5s. As such, the inlet opening 14 of the inlet 12 is configured to receiving a source of air as indicated by arrows 40. The air flows through the SJA 10 and exits through the discharge slot 26 as indicated by arrows 42. By design, the air leaving the discharge slot 26 moves back and forth in a sweeping motion, i.e., oscillates, along the length of the discharge slot 26, whose longitudinal axis is largely tangential to the periphery of the nozzle 30. In other words, the longitudinal axis of the discharge slot 26 is substantially perpendicular to the longitudinal axis of the nozzle 30. In other embodiments, the longitudinal axis of the discharge slot 26 may be oriented at any angle relative to the longitudinal axis of the nozzle 30. The sweeping air 42 from the discharge slot 26 interacts or mixes with the airflow 36 and serves to reduction the noise level of the that airflow 36 discharged from the nozzle 30. The nozzle 30 may include a shroud 44 that extends from a discharge end 46 of the nozzle 30 to where the nozzle 30 couples to the remainder of the jet engine 32. The shroud 44 encloses the SJAs 10 in the interior section 38 such that the SJA 10is not directly exposed to the slipstream of air moving over the exterior of the jet engine 32.

[0041] The discharge slot 26 in Figs. 1 B and 1 C is oriented essentially perpendicular to the inner surface of the nozzle 30. In other embodiments, the discharge slot 26 may be oriented at angle relative to the inner surface of the nozzle 30. When the discharge slot 26 is substantially tangential to the inner surface of the nozzle 30, the sweeping air 42 may help cool the inner surface of the nozzle 30 in addition to providing noise suppression.

[0042] In an embodiment, the air flow 40 may be bleed air, i.e., air diverted from the air flow 34 flowing through the jet engine 32. In another embodiment, the air flow 40 may be environmental air, i.e., from the slipstream around the exterior of the jet engine 32, may be ducted to enter the inlet opening 14 of inlet 12. In an embodiment, the air flow 40 may be a combination of bleed air and environmental air.

[0043] In another embodiment of the invention, a plurality of SJAs 50 may be operatively coupled to a nozzle 52 such that the longitudinal axis of each SJA 50 may be tangential to the diameter of the nozzle 52 as shown in Fig. 1 D. That is, the longitudinal axis of each SJA 50 is substantially perpendicular to the longitudinal axis of the nozzle 52. In other embodiments, the longitudinal axis of the discharge slot 26 may be oriented at any angle relative to the longitudinal axis of the nozzle 52. Here substantially perpendicular equals 90s± 5s. Airflow (arrows 54) is introduced via appropriate ductwork 56 into an inlet 58 of the SJA 50. That airflow moves through the SJA 50 and exits via the discharge slot 60 as indicated by arrows 62. The longitudinal axis of the discharge slot 60 is substantially parallel to the longitudinal axis of the nozzle 52.

[0044] The discharge slot 60 in Fig. 1 D and 1 C is oriented essentially perpendicular to the inner surface of the nozzle 52. In other embodiments, the discharge slot 60 may be oriented at angle relative to the inner surface of the nozzle 52. When the discharge slot 60 is substantially tangential to the inner surface of the nozzle 52, the sweeping air 62 may help cool the inner surface of the nozzle 52 in addition to providing noise suppression.

[0045] The invention also contemplates a method for reducing exhaust noise of an operating jet engine, the jet engine having a nozzle. The method includes providing at least one SJA on the nozzle and during operation, supplying an airflow to the SJA. configuring the SJA so that the airflow exits the SJA at a discharge slot such that the exiting airflow interacts with a jet engine airflow flowing through the nozzle.

[0046] SJAs are implemented between the outer nozzle surface and the seal surfaces. The SJAs and seal surfaces are connected by the SJA exit slot. The ratio L / di is an important parameter that can greatly affect the sweeping frequency, where L is the length of the SJA chamber and the di is the width of the SJA entrance.

[0047] An extensive parametric study was conducted to assess jet noise reduction when the SJA is used on a nozzle. It was found that the sweeping frequency may be adjusted by geometry parameters and the sweeping frequency that is in the frequency range of the far-field noise is more effective. The sweeping motion improves the noise reduction and using the SJA is more promising than the fluidic injection technology that use either a steady or simple pulsating injection approaches. In addition, it is found that the axial location of the SJA installation strongly impacts the amount of noise reduction. The peak noise reduction is shown 4dB at the jet temperature of the standard sea level for some takeoff nozzle pressureratios in laboratory tests, but it is limited to the range of 2dB to 3dB in simulations at a higher nozzle temperature comparable to the maximum non-afterburning power level. However, using SJAs may increase the thrust, and the thrust increase depends on the ratio between the mass flow rate of the nozzle flow and that of the SJA injection. The supply of the SJA flow may come from the bypass cooling flow used in military engine nozzles. The SJA flow using bypass cooling flow will improve cooling effectiveness because of the sweeping motion that covers a large area.

[0048] The noise reduction of chevrons is around 2~3dB. The criteria of a promising noise reduction technology are twofold. The noise reduction performance is equivalent to or exceeds that of chevrons, especially at takeoff conditions. The induced thrust loss should be in an acceptable range, for example, within 1 .5% at the cruise condition.

[0049] The design of the baseline nozzle is based on NASA ground test data of F- 18 airplane using a General Electric F404 engine. The ground-test condition had a nozzle pressure ratio (NPR) of 2.72 and a throat temperature of 1671 .9 °R, which is approximately 929K. The nozzle pressure ratio at the cruise condition was 4.8. Two model-scale nozzles were previously designed and fabricated based on the information given by the NASA ground-test data. The equivalent nozzle diameters are 3.17” and 1 .45”. Because the large nozzle requires a much higher mass flow supply, the smaller nozzle is often preferred for an extensive parametric study in laboratory tests. However, in assessing the SJA noise reduction performance, it has been found that the smaller nozzle of 1 .45” diameter results very small SJA flow channels. The surface roughness and the flow boundary layers may significantly modify the channel width and height and greatly reduce the SJA sweeping motions. Thus, nozzles have to be sufficiently large to assess the SJA performances. In this study, two nozzle sizes,2.16” and 2.8”, were used in laboratory tests, and a reasonably good scalability was achieved.

[0050] Both numerical simulations and laboratory measurements were conducted to develop and optimize the noise reduction technology of SJAa. The flow solver is JENRE®. The far-field noise was computed by the acoustic analogy approach based on the near-field flow field predicted by Large Eddy Simulations (LES). Acoustic measurements were acquired using a model 4954 Bruel & Kjaer1 / 4 inch condenser microphone with a frequency response of 100kHz in laboratory tests. Schlieren data were recorded using a z-type configuration and a high-speed camera acquiring data at 57750Hz. The joint effort of the numerical and laboratory tests has already been used to study the noise generation of the baseline model-scale faceted nozzles and the noise reduction performances of micro-vortex generators and azimuthally varying chevrons. The past experiences have demonstrated that this joint effort is a very effective approach.

[0051] As shown in Figures 2A and 2B, the SJA generates oscillating and sweeping motions due to the SJA jet instabilities and the feedback mechanism inside the actuators. The SJA performances of standalone SJAs were first examined. When the SJAs were installed on the faceted nozzle, the effects of the axial location, the scalability, the sweeping frequency, and the sweeping motions were examined in laboratory tests at a nozzle temperature of the standard sea level. In addition, the noise reduction was further assessed at a higher nozzle temperature by large-eddy simulations. The simulation data was also used to assess the thrust performance. Characteristics of Standalone SJA Flows

[0052] As shown in Figures 2A and 2B, an SJA emits a sweeping oscillating flow because a jet has inherent flapping modes and the SJA chamber reinforces andaugments those flapping modes, resulting in strong sweeping motions. The noise sources in the jet plume have various frequencies. For example, the noise source near the nozzle has high frequencies, but in the downstream region, the source frequency is much lower. Thus, it would be beneficial to obtain sweeping frequency in a broad range so the frequency’s effect on noise reduction may be evaluated. It is known that the sweeping frequency maybe adjusted by varying the injection pressure and the mass flow rate. This approach, however, may provide only a very limited range of the sweeping frequency. Thus, a more effective way was needed.

[0053] The current work observed that the sweeping frequency is a strong function of the ratio between the SJA chamber length and the SJA entrance width, L / di (see Figure 1 A). This frequency dependence has been examined in both numerical and laboratory tests, and the results are shown in Figures 3A and 3B, where the injection pressure is three times the ambient pressure and the temperature is at the standard sea level. In laboratory tests, the ratio L / di \s adjusted by reducing the SJA length, but the range of the ratio cannot be reduced too far. In numerical tests, small ratios were further obtained by scaling down the SJA configuration, but keeping the SJA entrance and the exit areas unchanged. This approach may generate very small ratios, but still maintain the injection mass flow rate. The numerical results agreed well with the laboratory results. The data indicate that the sweeping frequency is a strong function of the ratio L / b / and it increases as the ratio L / di decreases. The rate at which the sweeping frequency increases is much larger at small L / di. This approach provides a method to obtain a broad range of sweeping frequencies.Scalability of the Sweeping and Oscillating Frequencies

[0054] Evaluating the scalability of SJA flows provides some insight as to whether SJAs would work on real-world engines. To evaluate scalability, five SJAconfigurations that have similar shapes, but different sizes were tested. The ratio L / di were 4.6, 6.5, 7.3, 7.8, and 8.2 and di =0.13” and L changed. The nearfield pressure was measured by one microphone located 1 inch away at 45 degrees from the vertical line as illustrated in Figure 4.

[0055] The results of the scalability tests are shown in Figures 5A-5E, where four injection pressure ratios were used (I PR=1 .5, 2.0, 3.0, and 4.0). These injection pressure ratios are comparable to those observed in bypass cooling flows in military flight engines and the bypass cooling flows may be used to supply the SJA flows. All these injection pressure ratios are expected to generate supersonic jets after the flow passes the SJA throat area, as shown in Figures 2A and 2B. SJA flows produce multiple peak frequencies. The overall spectral shape remain similar at all five sizes, but the frequency changes with L / di such that increasing L / di results in a decrease in the sweeping frequency to maintain a scaling law of a constant normalized frequency or Strouhal number defined as St=fL / U, where U is the mean velocity through the SJA. The test data demonstrate that the SJA performance is scalable. The motion corresponding to the first peak frequency of the SJA flow where the SJA length is 1 ” is extracted from the Schlieren images and the microphone data, and the result is shown in Figures 6A through 6D. It is clear that the first peak frequency corresponds to the sweeping motion that oscillates from one side to another. In addition, the higher peak frequencies remain unchanged as the injection pressure ratio is increased from 1 .5 to 4.The Effect of the SJA Axial Location

[0056] Previous studies have shown that the axial location of noise reduction devices implemented on the seal surfaces greatly impacts their noise reduction performance because the noise reduction devices can greatly modify the internalshock-cell structure and the modification varies with the axial location. Thus, the effect of the SJA axial location was investigated at three axial locations in laboratory tests. The SJAs are implemented at a distance X (see Figure 1 B) equal to 0.1 D, 0.3D, and 0.65D from the nozzle exit, respectively, where D is the nozzle-exit diameter (see Figure 1 B), which is 2.16”, the SJA length is approximately 1 ”, and the ratio L / di = 7.3. The definition of the far-field radiation angle is shown in Figure 7 and the noise reduction results are shown in Figures 8A-8C. Three takeoff nozzle pressure ratios were tested and the jet temperature was at the standard seal level. The reduction due to the screech elimination is not considered because screech tones are rarely observed in real-world engine tests. The test data show that the SJA noise performance is highly dependent on the SJAs axial location. The axial location of 0.3D upstream of the nozzle exit appears to be an optimal location and the noise reduction of 3dB-4dB was observed at the peak radiation at 150° at the two higher nozzle pressure ratios.The Scalability Test of the SJA Noise Reduction Performance

[0057] The scalability was first examined in standalone SJA tests as shown in Figures 5A-5E, where a reasonably good scalability is presented based on five SJA sizes. A vertical offset was added to the data for IPR=2.00, 3.00, and 4.00 to separate the individual data plots for the sake of clarity. This scalability was also examined when SJAs were installed on the faceted nozzles. The first nozzle-exit diameter is 2.16” and the SJA length is approximately 1 ” with the ratio L / di = 7.3. The geometry of the second nozzle was scaled up by 1 .3 and the nozzle-exit diameter was 2.8”. The axial location of 0.3D upstream of the nozzle exit was used. It can be seen that the difference caused by the nozzle and SJA sizes was small in the downstream direction, but there was some differences up to 2dB in the upstreamdirection. Because the noise reduction in the peak direction is the main concern, this scalability is thus acceptable.

[0058] Figures 9A-9C is a series of graphs of experimental data showing scalability tests of nozzles implemented with SJAs, where the injection pressure is four times the ambient pressure and both the main nozzle and the SJA flows are at standard sea level temperature. Figures 9A-9C show that the SJAs work better in large scale. In other words, the noise reduction is greater for D=2.8” than D=2.16”. The Sweeping Frequency Effect

[0059] As shown in Figures 3A and 3B, the sweeping frequency may be adjusted by changing the ratio L / di . Three ratios, L / di = 4.6, 7.3 and 9.7, were tested on nozzles with the aforementioned two nozzle sizes: 2.16” and 2.8”. The results are shown in Figures 10A-10C and Figures 11 A-1 1 C. The ratio L / di = 7.3 generates a sweeping frequency that has a Strouhal number between 0.13 to 0.15 at the nozzle pressure ratios shown in those figures. This Strouhal number is defined as St=Frequency*D / Uj, where D is the nozzle-exit diameter and the Uj is the jet velocity. Because the peak noise frequencies observed in downstream direction have St between 0.1 and 0.2, it is clear that the sweeping frequencies generated by the ratio L / di = 7.3 are in the peak frequency range. However, the ratio L / di = 9.7 generates sweeping frequencies that have St between 0.07 to 0.08, which are lower than the noise peak frequencies. On the other hand, the ratio L / di = 4.6 generates sweeping frequencies that have St greater than 0.4, much greater than the noise peak frequencies. The Figures 10A-10C and Figures 11 A-1 1 C show that the ratio L / d 1 = 7.3 presents the best noise reduction performances, likely because the sweeping frequencies are within the noise peak frequency range. The test results indicate that there is an optimal ratio of L / di and the noise peak frequency may be used as areference to decide this optimal ratio. In addition, the differences caused by the ratio L / di were relatively less in the larger nozzle. The possible explanation is that the flow generated by a small SJA chamber is more sensitive to changes in geometry parameters because the flow in a small SJA channel may be more easily altered by the surface roughness and boundary layers near the surfaces. Prior experiences show that the sweeping motion may be very weak when a SJA length is small, for example, near 0.5”. The test results also show that when SJAs are used in real-world applications, the noise reduction performance would be less sensitive to the change of geometry parameters because of the large sizes.The Effect of the Sweeping Motion

[0060] A prominent feature of the SJA method is that it may generate sweeping motions, which sets it apart from the conventional fluidic injection methods that have also been tested for jet noise reduction by a few research groups. Thus, it would be advantageous to examine if the presence of a sweeping motion is beneficial to the noise reduction. To that end, the noise reduction generated by a configuration that does not generate the sweeping motion was also tested and this configuration is shown in Figure 12B, where square plugs block the generation of the sweeping motion. On the other hand, the configuration in Figure 12A is a regular SJA configuration that generates an oscillating flow sweeping from one side to another. Both configurations have L / di = 7.3 and the length of the chamber is approximately 1 ”. The noise reduction performances of these two configurations are shown in Figures 13A-13C. Clearly, the configuration that generates sweeping motion presents more noise reduction, indicating that the sweeping motion is beneficial to the noise reduction. Thus, the SJA method is more promising than a conventional injection method.The Noise Reduction Performance at a Higher Nozzle Temperature

[0061] Because the temperature of a real-world jet engine exhaust is much higher than that at the standard seal level, a nozzle temperature that is three times of the ambient temperature was tested by using large-eddy simulations. This nozzle temperature ratio (NTR) is comparable to those at the non-afterburning maximum conditions. The results, shown in Figures 14A-14C, demonstrate that the SJAs increase the noise in the upstream direction, similar to the trend observed in laboratory tests at a lower nozzle temperature ratio of NTR = 1 .0. In addition, the peak noise reduction at NPR = 2.7 and NTR = 3.0 is more than those assessed in laboratory tests at the lower nozzle temperature of NTR = 1 .0, which is consistent with the trend shown in the previous assessments of noise reduction technologies of micro-vortex generators (MVGs) and chevrons. A higher nozzle temperature would see more noise reduction in the peak radiation direction. However, at the two higher nozzle pressure ratios, the peak noise reductions are lower than those observed in laboratory tests, which differs from the trend observed previously and the cause is not clear so far. The peak noise reduction at the two lower nozzle pressure ratios was between 2dB and 3dB.The Thrust Performance of SJAs

[0062] The supply for the SJA flow may come from a bypass cooling flow that has a temperature much lower than the nozzle temperature. The addition of the SJA fluid increases the mass flow rate, as shown Table 1 . The thrust and mass flow rate were assessed at the nozzle exit using the flow data predicted by large-eddy simulations at a nozzle temperature of NTR = 3.0 shown in Figures 14A-14C.Table 1 — Increases of the thrust and mass flow rate caused by a SJA configuration.

[0063] The ratios in Table 1 are the percentages of the increased amounts based on the baseline nozzle values. The ratio between the mass flow rate of the nozzle and that of SJAs decreases as the nozzle pressure ratio increases because a higher nozzle pressure ratio increases the mass flow rate of the main nozzle, but the mass flow rate of SJAs remains unchanged. It is clear that the addition of the SJA flow increases the overall thrust and this increase depends on the increase of the mass flow rate. SJAs that have approximately half of the mass flow rates were also tested (results not shown) and the thrust increase was around 0.2%. However, tests show that the noise reduction performance is not very sensitive to the SJA mass flow rate in the mass flow ranges tested in this work.

[0064] Sweeping jet actuators may generate oscillating sweeping motions at a given frequency without any moving parts. SJAs, similar to MVGs, are a viable flow control method for improving the aerodynamic performance by mitigating separated flow regions. Both technologies may be applied to aircraft engines to reduce the jet noise. The performance of MVGs is very promising and the peak noise reduction may reach to 4dB~5dB with acceptable thrust penalties. Similarly, an extensive parametric study was also conducted for the SJA technology, including standalone SJAs and faceted nozzle implemented with SJAs. It has been found that the SJA size has to be sufficient large to avoid the surface roughness effect and the small nozzle size we have used previously is not good for this test because the resulted SJA size would be too small. Thus, two larger nozzle sizes are used for this assessment. The key points learned from this assessment are as follows:A) SJA sweeping frequency is a strong function of the ratio between the SJA length (L) and the SJA entrance width (di).B) The sweeping motion improves the noise reduction. Thus, the SJA method is more promising than the conventional fluidic injection methods.C) The SJA configuration that generates the sweeping frequency comparable to the far-field peak noise frequency is more effective for noise reduction.D) The axial location of the SJA installation is strongly influences the noise reduction.E) The flow and noise reduction characteristics of SJAs present a good scalability with sizes tested in this work, indicating that what is learned in laboratory tests may be extended to larger sizes in real-world applications.F) The peak noise reduction of sweeping jet actuators is shown 4dB at a jet temperature of the standard sea level for some takeoff nozzle pressure ratios in laboratory tests, but it is limited to the range of 2dB to 3dB in simulations at a nozzle temperature comparable to the maximum nonafterburning power level.G) The SJA method reduces jet noise and also increases the thrust. This is advantageous because other noise reduction techniques have an adverse effect on engine operation by causing a reduction of thrust.

[0065] The assessment of the SJA technology is more complex than those involving micro-vortex generators and chevrons because SJAs involve many moreparameters. The current assessment indicates that this technology is promising in both noise reduction and improved thrust performance.

[0066] While the invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the Applicant’s general inventive concept.

Claims

WHAT IS CLAIMED IS:1 . A nozzle (30) for a jet engine (32) comprising: at least one sweeping jet actuator (10) operatively coupled to the nozzle (30), the sweeping jet actuator (10) having an inlet opening (14) and a discharge slot (26), wherein the inlet opening (14) is configured to receive a supply of air (40) and the discharge slot (26) is configured to discharge that supply of air in a sweeping motion (42) into and interacting with an air flow (36) moving through the nozzle (30).

2. The nozzle of claim 1 , wherein the nozzle further includes a shroud enclosing an exterior portion of the nozzle to form an interior section, the sweeping jet actuator being positioned within the interior section.

3. The nozzle of claim 1 , wherein a longitudinal axis of the sweeping jet actuator is substantially parallel to a longitudinal axis of the nozzle.

4. The nozzle of claim 1 , wherein a longitudinal axis of the sweeping jet actuator is substantially perpendicular to a longitudinal axis of the nozzle.

5. The nozzle of claim 1 , where the at least one sweeping jet actuator includes a plurality of sweeping jet actuators.

6. The nozzle of claim 5, wherein the plurality of sweeping jet actuators are equally spaced around the periphery of the interior section of the nozzle.

7. The nozzle of claim 1 , wherein the supply of air entering the inlet opening is bleed air from the jet engine.

8. The nozzle of claim 1 , wherein the supply of air entering the inlet opening is environmental air.

9. The nozzle of claim 1 , wherein the supply of air entering the inlet opening is a combination of bleed air from the jet engine and environmental air.

10. A jet engine (32) comprising: a nozzle (30); and at least one sweeping jet actuator (10) operatively coupled to the nozzle (30), the sweeping jet actuator (10) having an inlet opening (14) and a discharge slot (26), wherein the inlet opening (14) is configured to receive a supply of air (40) and the discharge slot (26) is configured to discharge that supply of air in a sweeping motion (42) into and interacting with an air flow (36) moving through the nozzle (30).11 . The jet engine of claim 10, wherein the nozzle further includes a shroud enclosing an exterior portion of the nozzle to form an interior section, the sweeping jet actuator being positioned within the interior section..

12. The jet engine of claim 10, wherein a longitudinal axis of the sweeping jet actuator is substantially parallel to a longitudinal axis of the nozzle.

13. The jet engine of claim 10, wherein a longitudinal axis of the sweeping jet actuator is substantially perpendicular to a longitudinal axis of the nozzle.

14. The jet engine of claim 10, where the at least one sweeping jet actuator includes a plurality of sweeping jet actuators.

15. The jet engine of claim 14, wherein the plurality of sweeping jet actuators are equally spaced around the periphery of the interior section of the nozzle.

16. The jet engine of claim 10, wherein the supply of air entering the inlet opening is bleed air from the jet engine.

17. The jet engine of claim 10, wherein the supply of air entering the inlet opening is environmental air.

18. The jet engine of claim 10, wherein the supply of air entering the inlet opening is a combination of bleed air from the jet engine and environmental air.

19. A method of operating a jet engine (32) having a nozzle (30), the nozzle (30) having at least one sweeping jet actuator (10) having an inlet opening (14) and a discharge slot (26), comprising: causing a first air flow (34, 36) to move through the jet engine (32) and the nozzle (30); causing a second air flow (40) into the inlet opening (14) of the sweeping jet actuator (10); anddischarging the second air flow (40) from the discharge slot (26) of the sweeping jet actuator (10) in a sweeping motion (42) such that the discharged second air flow (40) interacts with the first air flow (36) moving through the nozzle (30).

20. The method of claim 19, wherein the second air flow entering the inlet opening is bleed air from the jet engine.21 . The method of claim 19 wherein the second air flow entering the inlet opening is environmental air.

22. The method of claim 19, wherein the second air flow entering the inlet opening is a combination of bleed air from the jet engine and environmental air.

23. The method of claim 19, wherein the discharged sweeping second air flow interacts with the first air flow moving through nozzle such that a resulting thrust of the jet engine is greater than a thrust of the jet engine without the sweeping jet actuator.

24. The method of claim 19, wherein the discharged sweeping second air flow interacts with the first air flow moving through nozzle so as to reduce the noise level of the jet engine compared to the jet engine without the sweeping jet actuator.

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