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Flow Control for Enhanced Store Separation
J. Shipman*, S. Arunajatesan†, P.A. Cavallo‡, R. Birkbeck§, and N. Sinha** Combustion Research and Flow Technology, Inc., Pipersville, PA 18947
L. Ukeiliey†† University of Florida, REEF, Shalimar, FL
Farrukh Alvi‡‡ Florida State University, Tallahassee, FL
In this paper, we describe ongoing research to understand the effect of cavity flow control techniques on stores inside a non-rectangular aircraft weapons bay for supersonic conditions. While previous work has shown these techniques to be capable of effectively controlling the cavity flowfield, this study focuses primarily on the effect of cavity flow control on stores inside the cavity and their trajectories. The control concept studied is a segmented 3-slot jet, which has been shown to be effective both in experimental studies, the results of which are reported in a companion paper 1, as well as in detailed computational simulations2. Here, results of computational simulations of uncontrolled, baseline weapons bay configurations are compared with the results of controlled configurations for two different types of internal stores: an asymmetric finless store and a store with fins and control surfaces. Additional dynamic simulations were performed on the finless store involving an ejected release from the bay for both the uncontrolled baseline and controlled configurations.
I. Introduction ecent applications of flow control to cavities such as those found in aircraft weapons bay configurations have shown reductions in dynamic loads on surfaces of the bay (see Refs. 3,4 for recent reviews). In a companion paper 1, effective control using concepts employing very low mass flow rates and operating at
very reasonable pressures is presented. Recent computational work 2 involving high resolution LES calculations has focused on the underlying flow mechanisms responsible for the effectiveness of this class of flow control device for supersonic cavity flows. Due to the small mass flow rates and pressures, these represent systems that can potentially be employed on full scale configurations. At full scale, these concepts can reduce life cycle costs by reducing structural fatigue. Of equal value for military platforms is their effect on store separation. This is the subject of this paper.
The current research activities performed under AFRL’s SEAR Program (Separation Enhancement and Acoustic Reduction) involve computational and experimental analyses of the effect of these control concepts on acoustic loads and store separation from a weapons bay. The focus is on reducing the dynamic loads on the stores and improving the envelope over which effective separation can occur. With increasing emphasis on smaller munitions, the effect of the shear layer dynamics on the store trajectory is ever more important to understand. Furthermore, the relationship between reducing dynamic loads (on cavity surfaces and weapons surfaces) and store trajectories is not clear. Recent analyses 5 of this phenomenon have primarily been carried out through the use of grid testing – the effects of interaction of the store with the flow dynamics are ignored in this approach.
* Research Scientist, Combustion Research and Flow Technology, Inc., Pipersville, PA, AIAA Member. † Senior Research Scientist, Combustion Research and Flow Technology, Inc., Pipersville, PA, AIAA Member. ‡ Senior Research Scientist, Combustion Research and Flow Technology, Inc., Pipersville, PA, Senior AIAA Member. § Senior Design Engineer, Combustion Research and Flow Technology, Inc., Pipersville, PA. ** Vice Pres. & Technical Director, Combustion Research and Flow Technology, Inc., Pipersville, PA, AIAA Associate Fellow. †† Associate Professor, Department of Mechanical Engineering, U FL, and AIAA Member. ‡‡ Associate Professor, Department of Mechanical Engineering, Florida State U, and AIAA Member.
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45th AIAA Aerospace Sciences Meeting and Exhibit8 - 11 January 2007, Reno, Nevada
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Figure 1. RMS wall pressures compared to measured valued for the non-rectangular cavity.
In addition to the computational simulations presented here, wind tunnel experiments were conducted at three facilities. Small scale experiments to test various leading edge fluidic control concepts were performed at the supersonic wind tunnel at the Advanced Aero-Propulsion Laboratory (AAPL) at Florida State University and the 2”-by-2” tri-sonic wind tunnel in the Anechoic Jet Laboratory at the University of Mississippi National Center for Physical Acoustics (NCPA). Results of both of these experiments are described in the companion paper of Reference 1. Experiments were also performed at the Lockheed Martin Compressible Flow Wind Tunnel (CWFT) with the aim of testing the control concepts at a larger scale and assessing the effect of the flow control techniques on a sting mounted store. The results from these tests will be presented at a future time. Here, we present computational simulations of baseline and controlled weapons bay cavity/store configurations for Mach 1.5 flow conditions that correspond to the small-scale wind tunnel experiments. The control concept studied in the simulations is a segmented 3-slot jet located at the leading edge of the cavity. This corresponds to the most effective slot jet configuration of the NCPA and CFWT experiments. The simulations involve two different stores placed in the weapons bay cavity: an asymmetric finless store and a store with fins and control surfaces. Simulations are performed with and with out slot jet control for these stores at the lipline of the cavity, i.e. in the shear layer. Additional dynamic simulations were performed on the finless store involving an ejected release from the bay for both the uncontrolled baseline and controlled configurations.
II. Approach The simulations presented in this study are accomplished using the CRUNCH CFD® 6,7 unstructured Navier-
Stokes solver. The basic numerical framework of the CRUNCH CFD® code is a finite volume second-order Roe/TVD scheme in which the flow variables are defined at the vertices of he mesh. An edge-based data structure is employed wherein a polyhedral control volume is constructed from the union of all cells incident to a given node, and the control volume faces are associated with each edge. The inviscid flux calculation proceeds by looping over all edges in the mesh, and is grid-transparent, while a cell-based method is employed to compute the flowfield gradients at the control volume faces for evaluating the viscous fluxes 6. For these simulations, no explicit turbulence model was applied, and the code was run with the Monotone Integrated Large Eddy Simulation (MILES) method.
Early in the program a validation exercise was performed to validate the computational framework for a non-rectangular cavity geometry at Mach 2.0 flow conditions 2. The results were compared to wall pressure measurements by Alvi and co-workers 3, shown in Figure 1. Two pressure taps were used in the measurements, one on the floor and one on the back wall of the cavity, and it is seen that the computed results agree very well with the data. It is clear that the methods used here are able to capture the dynamic loads, and hence, by inference the flow characteristics of the cavity. Subsequent to this calculation, additional simulations were performed to identify the grid requirements to model the slot jet concept and ensure that the dynamics of the jet-shear layer interaction were sufficiently resolved.
For the dynamic store drop simulations, a full six-DOF module is used to handle the coupled dynamic body motion. A stress-based mesh motion solver handles the mesh movement and deformation that results 8. The mesh movement procedures within the CRUNCH CFD® code employ a stress solver in which the grid is treated as an elastic solid. The elasticity of the grid is a function of cell volume, with the smaller cells of the mesh having a greater stiffness than the larger cells. This ensures that the mesh deformation that results from a translating or rotating body occurs primarily in the regions of the mesh away from the body surfaces in coarser regions of the mesh.
Mesh quality is maintained for large deformations by coupling the flow solver with the unstructured mesh adaptation package, CRISP CFD® 8,9, a parallel mesh modification and quality improvement code for three-dimensional mixed-element unstructured meshes. Grids comprised of tetrahedral, prismatic, and hexahedral elements are modified to generate more accurate flow solutions through local refinement and coarsening. In moving body applications, these coarsening and refinement methods may also be employed to accommodate boundary
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motion, as is the case with the current store release problem. For the store drop simulations presented here, mesh adaptation was driven strictly by mesh quality sensors and did not employ flowfield gradient based features of the code.
III. Cavity Configuration and Flow Conditions The simulations described in this paper are all carried out at 1/72nd scale to correspond to the wind tunnel
experiments performed on a similar cavity configuration (see Ref. 1). The wind tunnel scale cavity that is being studied here is a non-rectangular cavity having variations in width and depth representative of an aircraft weapons bay. The geometry is shown in an aircraft frame of reference (i.e. out-of-the-bay direction is down) in Figure 2. In all subsequent figures, the cavity will be depicted in a wind tunnel frame of reference, opposite of the aircraft frame with an out-of-the-bay view facing up. The floor and side walls contain slope changes, with the aft end of the bay being deeper than the front end. Based on the depth of the cavity at the back wall, the L/D ratio is approximately 5.6. The flow Mach number is 1.5 at a static tunnel pressure of around 8 psi. Under these conditions the flow ‘Q’ or dynamic head corresponds to an altitude of 24,000 ft at Mach 1.5. As with the LES studies of this cavity 2, an approach boundary layer profile with a thickness of about 1.8 mm was applied to the inflow boundary condition, slightly more than one cavity width upstream of the leading edge. The boundary layer thickness was obtained from a previous RANS simulation of the wind tunnel nozzle and test section and verified experimentally.
The three-slot jet configuration studied in the simulations, shown in Figure 3, corresponds to the most effective of the various slot configurations studied in the NCPA Mach 1.5 experiments 1. The slots are symmetric with the centerline of the cavity and are placed about one slot width upstream of the cavity leading edge. For the jet blowing cases, the slot jets are operated under choked conditions, with a jet stagnation pressure of P0j = 20 psi representing the mass blowing conditions that achieved optimal acoustic suppression in the experiments.
w2/L = 0.331
L/D = 5.6
w1/L = 0.161D
Lw2w1
w2/L = 0.331
L/D = 5.6
w1/L = 0.161
w2/L = 0.331
L/D = 5.6
w1/L = 0.161DD
Lw2w1
Lw2w1
t
w1
l
l /w1 = 0.144 t/w1 = 0.025
t
w1
l
t
w1
l
l /w1 = 0.144 t/w1 = 0.025 l /w1 = 0.144 t/w1 = 0.025
Figure 2. Schematic Of Wind Tunnel Scale Non-
Rectangular Weapons Bay Cavity. Figure 3. Three-Slot Jet Configuration At
The Leading Edge Of The Cavity. The two stores that are studied in these simulations are shown in Figure 4 and Figure 5, which also illustrate the
multi-element grid topology employed. The stores are positioned towards the aft end of the cavity and off-centerline to represent a carriage location to one side of the weapons bay. The first store studied, shown in Figure 4, represents a simplified model of a LOCAAS twin pack, an asymmetric and aerodynamically unstable body lacking fins or other control surfaces. Both static and dynamic store drop simulations are presented for this configuration. Additionally, static baseline and jet blowing simulations are presented for a second store configuration involving a generic Paveway-like store with fins, shown in Figure 5. This is a much larger store with control surfaces that make it more responsive to the pressure and velocity fluctuations in the cavity and shear layer. The grid topology for the two configurations is similar with the majority of the cavity using a structured hexahedral topology. A channel surrounding the store and encompassing the projected path is meshed using tetrahedral cells to accommodate the geometric complexity of the store and allow for efficient mesh adaptation as the store is ejected from the cavity. In both configurations, a structured hexahedral topology is used adjacent to the store to resolve the viscous boundary layer on the store.
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For the static cases, the store is positioned with its center of gravity aligned with the lipline of the cavity, holding the store captive in the cavity shear layer for the duration of the simulation. In the moving store simulations, the store is initially positioned inside the cavity and is imparted with an initial acceleration such that a specified end-of-stroke velocity is reached. At the end of the constant acceleration ejection stroke, the body motion is handed off to the six-DOF module. At this point in the simulation, the body motion is affected by the aerodynamic forces on the store. The calculation is terminated when the store completely clears the shear layer – this is determined by visual inspection of the flow field contours.
(a) (b) Figure 4. Finless Store Configuration And Mesh Topology for the (a) front and (b) side views.
(a) (b) Figure 5. Finned Store Configuration And Mesh Topology for the (a) front and (b) side views.
IV. Results – Finless Store
A. Static Simulations The baseline and controlled simulations for the static finless store were run for a physical time span surpassing 6
ms with a time step of 1.0e-6 seconds. To illustrate the general characteristics of the cavity flowfield with and without jet blowing, a snapshot of the flowfield showing Mach number on axial and lateral planes through the c.g. point for the baseline and 20 psi jet cases is shown in Figure 6. The figure shows the fluctuations in the shear layer growing from the cavity leading edge and impinging on the nose of the store and aft wall of the cavity. The lateral plane in the figure intersects with the store-side slot jet, and the shock generated by the jet is evident for the 20 psi jet blowing case. A slight lofting of the shear layer is evident for the jet blowing case, as well as a slightly more spanwise-coherent recirculation inside the cavity. To illustrate more clearly the 3D nature of the flowfield and the impact of the jet blowing on the cavity flow structure, plots showing an isosurface of vorticity magnitude colored with Mach number are compared for the two cases in Figure 7. The signature of the jets is clearly seen in the vorticity plots. The jets retain a coherent structure for about 1.5 cavity widths downstream of the leading edge before the shear layer fluctuations become strong enough to break up the jet structures. A small recirculation region evident by the dark region upstream of the cavity leading edge is shown for the 20 psi case. In the baseline case, thin vortical structures that span the cavity width are seen that indicate spanwise coherent roll-ups in the shear layer. These structures are not evident in the jet case.
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(a) Baseline
(b) Pj = 20 psi
Figure 6. Snapshot In Time Showing Mach Number Contours On Axial And Lateral Planes Through The Store C.G. Point For the (a) Baseline, and (b) 20 psi Jet Cases.
(a) Baseline (b) Pj = 20 psi Figure 7. Isosurface Of Vorticity Magnitude Colored With Mach Number For the
(a) Baseline and (b) 20 psi Jet Cases. Probes placed along the cavity floor, back wall and surface of the store recorded pressure history for the time
span of the simulation. A comparison of the pressure spectrum of several of these points for the two cases is shown in Figure 8. Probe number 8 records the impact of the shear layer with the nose of the store. For the baseline case, most of the energy at this point is in a distinct mode that is completely suppressed in the jet blowing case. The broadband sound pressure level is also significantly reduced in the blowing case. At the back wall of the cavity, similar suppression of the dominant modes as well as the general sound pressure level across the frequency range is observed. On the cavity floor, while there is a slight suppression of the overall levels, little suppression of the cavity modes is evident. Thus, the presence of the store affects the ability of the slot jets to control the acoustic loads in the bay.
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8: nose of store
(a)
6: back wall of cavity
(b)
4: cavity floor
(c)
Figure 8. Pressure Spectra For The Baseline And 20 Psi Jet Cases For Points On The (a) Store Nose, (b) Cavity Aft Wall, And (c) Cavity Floor.
B. Dynamic Simulations The baseline and jet blowing cases for this store configuration were repeated with the store accelerating through
the ejection stroke, then traversing through the shear layer and out into the freestream flow with a body six-DOF module tracking the store trajectory. The store initially starts with a position that is representative of a carriage location inside an aircraft’s weapons bay, with the center of gravity a distance of d/D = 0.283 into the scaled cavity, where D is the cavity depth. The store is uniformly accelerated out of the bay to a speed Ve, normalized by the freestream velocity, of Ve/U∞ = 0.0215, at the end-of-stroke position. The ejection stroke spans 0.694 ms in time and places the store just into the cavity side of the shear layer. The store’s inertia gained from the forced ejection continues to carry the store out of the bay, but at this point the six-DOF module is invoked and the trajectory of the store is now affected by the aerodynamic forces.
As the store moves through the cavity, the mesh motion causes a decline in the cell quality in the tetrahedral portion of the grid that the store is traversing. Beneath the store, the cells are stretched, while above the store the cell volumes are compressed. More significantly to the mesh quality, however, is the mesh strain induced on either side of the store, creating skewed cells. This degradation in cell quality is periodically rectified by the use of mesh adaptation. The mesh adaptation is automatically triggered from cell quality thresholds that are computed and tracked during the simulation. Once the mesh has been corrected, the solution is interpolated onto the new mesh and the simulation continues. A very uniform cell quality and count is maintained in the region vacated by the store thus maintaining solution accuracy. A time series of the mesh at several positions during the ejection event illustrating mesh deformation and adaptation is shown in Figure 9.
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(a)
(b)
(c)
(d) Figure 9. Time Series Of Store Position And Mesh Motion/Adaption During The Ejection Simulation.
A time series of contours of Mach number for the ejected baseline and 20 psi jet cases is shown in Figure 10.
These snapshots are chosen to span the separation event equally. The total time for the subscale separation event is 0.002 seconds. During this time period the store is likely to experience multiple cycles of the shear layer oscillations. The dominant mode of the cavity is at a strouhal number, based on the freestream velocity and the cavity length, of about 0.7. Compared in the same non-dimensional units, the time for the ejection stroke
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corresponds to a strouhal number of 0.2. This indicates that during the smaller portion of the total separation time span that the store takes to accelerate to the ejection velocity, it has experienced only several cycles of the dominant cavity oscillation mode. This could have implications on the timing of the store release, whether the shear layer is pumping into or out of the cavity at the moment that the store enters the shear layer. For the jet blowing case, the shear layer is lofted slightly higher above the store, resulting in the store traveling further out of the bay before encountering the full momentum of the freestream flow. This is evident in Figure 10 at the 0.75 ms point by the lack of a strong shock at the nose of the store. As the store traverses the shear layer and enters the freestream, the non-axisymmetric pressure loads at the nose of the store start to pitch the nose into the bay. Because the store has such a large inertia from the initial acceleration through the ejection stroke, the trajectory of the store is affected little by the presence of leading edge blowing.
(a) T= 0 ms
(b) T=0.75 ms
(c) T=1.35 ms
(d) T=2.0 ms
Figure 10. Time Series Of Mach Number Contours For The Ejected Baseline And 20 psi Jet Cases.
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The evolution of the forces with time on the body for both cases alongside the forces recorded from the static store cases is shown in Figure 11, Figure 12 and Figure 13 for the vertical, lateral, and pitch moment, respectively. The strong variations in the forces that the store experiences directly in shear layer are clearly visible in all three force histories for the static simulations, on the right hand side of the plots. For the dynamic simulations, the force variations are smaller at the beginning of the ejection, when the store is inside the bay, and then increase to comparable values once the store reaches the shear layer. Once the store penetrates the shear layer and moves completely into the supersonic freestream, the magnitude of the force fluctuations again decreases. Also noted in all three Figures is the reduction in the magnitude of the fluctuations for the controlled case.
For the vertical force in Figure 11, a positive value is in the out-of the-bay direction. The into-the-bay vertical force is shown to increase as the store is released into the freestream and pitches into the flow for the dynamic simulations. Figure 12 shows the lateral force histories for the dynamic and static simulations. For the static simulations, both the baseline and jet blowing cases exhibit a low frequency oscillation underneath the higher frequencies. For the dynamic simulations, the lateral force on the store is highly oscillatory as long as the store is in the cavity, dropping substantially in relative magnitude when it is completely separated from the bay. The magnitude of these oscillations is lower than those for the vertical force, however. Figure 13 shows the pitch moment for the dynamic and static simulations. Again, the oscillations increase as the store moves from inside the bay into the shear layer, and the magnitude of these oscillations is reduced by the jet blowing.
Figure 11. Vertical Force Coefficients (Positive = Out Of Bay) For Baseline (Black) And 20 Psi Jet (Red)
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V. Results – Finned Store, Static Simulations The results presented above indicate that while the jet blowing substantially reduces the magnitude of
fluctuations felt by the store, at the ejection velocity imposed, the inertia of the store is too great to show a measurable affect on the trajectory. Further studies were initiated to study the 3-slot jet control configuration on a store having fins and aerodynamic control surfaces, which could cause it to be more susceptible to the dynamics of the cavity flowfield. The generic finned store shown in Figure 5 was chosen. The grid topology is similar to that of the previous cases, with the exception of a more complicated system of hexahedral blocks surrounding the store to account for the fins.
Simulations for this store held static at the cavity lipline are presented here. The mesh used in these computations is shown in Figure 14. Three cases are presented: a baseline case with no blowing, a 20 psi jet case, and a third case where the jet pressure is doubled to 40 psi. To illustrate the general characteristics of the flowfield for the three cases, snapshots of the flowfield comparing Mach number contours are shown in Figure 15. The position of the store, parallel with the lipline of the cavity, places it directly within the shear layer, and a small shock generated by the fins protruding into a portion of freestream flow is seen in the baseline case. As with the plots shown in Figure 6, a shock generated by the jets and a slight lofting of the shear layer is evident for the two jet blowing cases, both stronger for the 40 psi jet. To illustrate the 3D nature of the flowfield and the impact of the jet blowing on the cavity flow structures, plots showing an isosurface of vorticity magnitude colored with Mach number are compared for the three cases in Figure 16. For the jet blowing cases, the coherent jet flow structure breaks down at an axial station just upstream of the store nose. It is interesting to note that while the increased blowing rate causes a stronger separation upstream of and to the sides of the cavity, the coherence of the jet structures break down at a similar axial station of the cavity.
Probes placed along the cavity floor, back wall, and surface of the store recorded pressure history for the time span of the simulations as with the earlier cases. A comparison of the pressure spectrum of several of these points for the three cases is shown in Figure 17. Probe number 8 records the impact of the shear layer with the nose of the store. As with the previous cases, the dominant modes at this point are completely suppressed in the jet blowing cases. The broadband sound pressure levels are significantly reduced in the blowing cases. At the back wall of the cavity, similar suppression of the dominant modes as well as the general sound pressure level across the frequency range is observed. On the cavity floor, as observed with the previous cases, while there is a slight suppression of the overall levels, little suppression of the cavity modes is evident. While the first mode is reduced by the slot jet blowing, the second mode is completely unaffected.
(a) (b) Figure 14. Mesh Topology And Store Position For The Static Finned Store Cases for (a) front and (b) side
views.
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(a) Baseline
(b) Pj = 20 psi
(c) Pj = 40 psi
Figure 15. Snapshot In Time Showing Mach Number Contours On Axial And Lateral Planes Through The Store C.G. Point For The (a) Baseline, (b) 20 Psi Jet, And (c) 40 Psi Jet Cases.
(a) Baseline (b) Pj = 20 psi
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(c) Pj = 40 psi
Figure 16. Isosurface Of Vorticity Magnitude Colored With Mach Number For The (a) Baseline, (b) 20 Psi Jet, And (c) 40 Psi Jet Cases.
8: nose of store
6: back wall of cavity
(a) (b)
4: cavity floor
(c)
Figure 17. Pressure Spectra For The Baseline, 20 Psi Jet, and 40 Psi Jet Cases For Points On The Store (a) Nose, (b) Cavity Back Wall, and (c) Cavity Floor.
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The forces on the store recorded during the simulations are plotted in Figure 18 for the vertical and lateral forces, and the pitch moment. It is noted that for the finned store, the lateral force fluctuations are larger than that for the vertical forces, the opposite of which is true for the finless store, which has no control surfaces but a larger cross sectional area in the vertical direction. Many cycles of the shear layer fluctuations are recorded over the time span of the simulation, and a very low frequency oscillation is evident beneath the higher frequencies. The amplitude of the force fluctuations is reduced with the 20 psi jet case as compared to the baseline case for all the forces, and to a greater degree with the 40 psi jet case. This is most evident in the lateral force history shown in Figure 18b. The mean loads for the static simulations are shown in Table I, which tabulates the mean forces and moments on the store for the time sample of the simulation and represents the average forces and moments that the store is subjected to in the shear layer. In the table, the force coefficients for the axial, vertical (positive = out of the bay), and lateral (positive is towards the bay centerline) directions are denoted by CFx, CFy, and CFz, respectively. The mean yaw and pitch moments (positive = nose-into-the-bay) are also included in the table, denoted by CMy and CMz, respectively. Some important trends are noted: The mean vertical force, CFy, is negative for the baseline case, resulting in a into-the-bay mean force, but reverses sign to an out-of-the-bay direction with slot jet blowing. For the higher blowing rate, the effect is still positive, but to a smaller extent. Similarly, with the mean pitching moment, CMz, the slot jet blowing corrects a positive, nose into-the-bay moment to a nose out-of-the-bay direction, and no additional gain is obtained by the higher blowing rate. The mean lateral force, CFz, is reduced only by a small amount for the 20 psi slot case while for the 40 psi slots, the mean lateral force is reduced by a much larger extent. These trends are seen as favorably affecting the loads on the store for the current position at the lipline of the cavity, where the flow environment is the most severe, due to the pressure and velocity fluctuations of the shear layer.
(a) (b)
(c)
Figure 18. Force History For The Baseline (Black), 20 psi Jet (Red), And 40 psi Jet (Blue) Cases For The (a) Vertical Force, (b) Lateral Force, And (c) Pitch Moment.
VI. Conclusion Unsteady CFD simulations of both static and dynamic store configurations have been performed to study the
effects of cavity flow control techniques, which have been previously shown to effectively control the cavity flowfields 1,2, on stores inside the cavity and their trajectories. The cavity studied here corresponds to wind tunnel 1 studies of a non-rectangular cavity representative of an aircraft weapons bay. The control concept focused on in this study is a segmented 3-slot jet, which was shown to be effective in the experimental wind tunnel studies. Results of calculations of uncontrolled, baseline configurations have been compared to with the results of controlled configurations for two different types of stores, an asymmetric finless store and one with fins and control surfaces, held static at the lipline of the cavity. Additional dynamic simulations were performed on the finless store involving an ejected release from the bay for both an uncontrolled baseline and a controlled configuration.
The slot jet blowing is effective in reducing the acoustic loads present in the cavity as shown by the results of these cases. This is consistent with the experimental results in Reference 1. The forces and moments on the store in the shear layer are shown to be affected by the slot blowing configuration in a favorable direction. The magnitude of the force fluctuations that the store is subjected to is reduced for the controlled cases. The mean vertical forces are reversed to an out-of-the-bay direction, the mean lateral forces are reduced, and a nose-into-the-bay mean pitching moment corrected with the controlled configuration. With the large ejection velocity, the dynamic simulations illustrate that the trajectory is affected little by the slot blowing. Additional studies are underway to investigate the affect of control on a store ejected with a much smaller velocity.
The above calculations illustrate the importance of understanding the effects of flow control on the store. If the oscillations of the forces on the store can be reduced, the store can potentially be ejected with a smaller ejector. This will reduce the overall weight of the ejection system and free up valuable space in the bay. Additionally, allowing for a smaller ejection force will benefit smaller munitions.
Acknowledgments Funding was provided through the AFRL VAAI Separation Enhancement and Acoustic Reduction (SEAR)
Program, Mr. James Grove, Technical Monitor. Technical discussions and HPC computer time is gratefully acknowledged.
References 1 .Ukeiley, L., Coiffet, F., Sheeha, M., Alvi, F., Arunajatesan, S., and Jansen, B., "Control of Pressure Loads in Complex
Cavity Configurations," AIAA Paper 2007-1238, 2007. 2 Arunajatesan, S., Kannepalli, C. and Sinha, N. “Analysis of Control Concepts for Cavity Flows”, AIAA-2006-2427. 3 Cattafesta, L.; Williams, D.; Rowley, C.; & Alvi, F. (2003) “Review of Active Control of Flow-Induced Cavity
Resonance.” AIAA, Paper 2003–3567. 4 Rowley, C. & Williams, D. (2006) “Dynamics and Control of High-Reynolds Number Flow over Open Cavities.” Annual
Review of Fluid Mechanics, Vol. 38, pp. 251–276. 5 Bower, W.W. et al., “High-Frequency Excitation Active Flow Control for High-Speed Weapon Release (HiFEX)”, AIAA-
2004-2513. 6 Hosangadi, A., Lee, R.A., Cavallo, P.A., Sinha, N., and York, B.J., “Hybrid, Viscous, Unstructured Mesh Solver for
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Combusting Flows", Journal of Propulsion and Power, Vol. 12, No. 3, 1996, pp. 494-503. 8 Cavallo, P.A., and Grismer, M.J., “A Parallel Adaptation Package for Three-Dimensional Mixed-Element Unstructured
Meshes,” Journal of Aerospace Computing, Information, and Communications, Vol. 2, No. 11, 2005, pp. 433-451. 9 Cavallo, P.A., Sinha, N., and Feldman, G.M., “Parallel Mesh Adaptation Method for Moving Body Applications,” AIAA
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