Weapons Bay Research Articles

Fluid and aero-acoustic analysis of internal bays: Geometric length-to-depth effects

Weapon bays are essential for any bomber, Next Generation Fighter Aircraft, and unmanned combat air vehicles (UCAVs). As flow approaches the leading edge of such cavity, it separates and forms a shear layer. The structure of bays and residing stores thus become prone to intense acoustic and aerodynamic loading– a major design concern. Cavity flow shows significant dependence on its shape. This makes flow actuation possible by only changing the geometric variable of length-to-depth (L/D) ratio. This study compares two bays with an L/D ratio of 5 (deep) and 10 (shallow) in terms of acoustics and affiliated aerodynamic drag. A transient RANS formulation obtained overall sound pressure levels (OASPL) on bay ceilings. An integral-based method was also used to predict far-field noise propagation due to flow fields of both cavities. It is argued that at Mach 0.6, the character of bays changes remarkably when its L/D is altered. Deeper bays show a smoother pressure profile and significantly less drag while operating in shear mode. Shallow bays, on the other hand, show bluff body type drag with uneven pressure distribution, having the potential of causing downwash on residing stores. At the same time, acoustic loads on the ceiling and acoustic signatures in the far-field are comparable for both cavities.

Influence of Door Gap on Aeroacoustics and Structural Response of a Cavity

Numerical aeroacoustic analysis using the Shear Stress Transport–Scale Adaptive Simulation turbulence model was conducted on a weapon bay model based on the M219 geometry with doors incorporating radar cross-section reduction features. The effect of the introduction of a gap between the doors and the cavity edge on the aeroacoustic and structural response of the cavity was analyzed at Mach 0.85. The effect of introducing 3 deg of sideslip was also investigated. Both mean and unsteady flow analyses were conducted. The results showed a strong palliative effect of the door gap with and without sideslips. The overall analysis of the spectral signature on the forces and moments acting on the doors indicated the possibility of fluid–acoustic coupling, as all acoustic spectra showed a predominant tone located at the same frequency of the first structural mode.

Detached Eddy Simulations of Cavity-Store Interactions at Subsonic Turbulent Flow

Weapons bays have gained much attraction in the last decade, mainly in the context of next-generation aircraft. Although internal store carriage provides numerous advantages, aero-mechanical challenges still exist, particularly for safe store separation. Therefore, it is essential to gain fundamental knowledge of the flow field within weapons bays, which can be achieved by studying the flow within a more simplified geometry of a cavity. In this study, detached eddy simulations are performed using the Elastic-Zonal-Navier–Stokes-Solver (EZNSS) to characterize the unsteady turbulent flow within NASA’s benchmark rectangular cavity with a store model located at various positions. Simulations are performed at a Mach number of 0.4 and a Reynolds number of 7 million to form a transitional cavity flow, which is common in jet-fighter weapons bays. The numerical results are validated with experimental data for the empty cavity and cavity-with-store configurations. The effect of the store’s position on the cavity flow characteristics is analyzed and verified, as well as the aerodynamic loads exerted on the store. Results show a complex interaction between the store model and the cavity flow field, manifested by distortion of the wall pressure fluctuations and mean flow structures and large amplitude fluctuations of the loads exerted on the store. The insights reported herein can serve future development efforts of more accurate numerical frameworks for cavity-with-store configurations towards improving their applicability for weapons bays store separation in certification procedures.

Visualization of pressure fluctuation characteristics of weapon bay on unmanned aerial vehicle using delayed detached eddy simulation

In the present study CFD simulation with delayed detached eddy simulation (DDES) are performed to investigate pressure fluctuation environment on an open cavity and weapon bay of UAV. The main purpose of this study is to explore the aerodynamic noise level of complex cavities with slant ceiling and irregular length–depth ratio. First, two cases on an open cavity at Ma 0.85 are analyzed to determine the slant ceiling influence, which shows that the sound pressure levels increase by 1 dB due to the transverse flow effect. Then, a typical weapon bay on unmanned aerial vehicle is simulated to investigate the aerodynamic noise environment. The overall sound pressure level in the weapon bay is up to 157 dB, and when the Mach number turns from 0.6 to 0.8, the amplitude of all modes increases about 16–23 dB. The main focuses of this investigation are to discuss the mechanism of noise generation in a slant ceiling cavity and determine the pressure fluctuation characteristic of a typical weapon bay on unmanned aerial vehicle.Graphical abstract

Numerical Simulation and Computational Fluid Dynamics Analysis of Two-Dimensional Lid-Driven Cavity Flow Within the Weapon Bay of an Autonomous Fighter Drone

The efficient deployment of weapons in military operations is critical for mission success, and the flow of air within the weapon bay of an autonomous fighter drone plays a vital role in achieving this objective. In this paper, we present a comprehensive numerical simulation and computational fluid dynamics (CFD) analysis of the three-dimensional lid-driven cavity flow within the weapon bay of an autonomous fighter drone. To address this challenging problem, we employ CFD analysis and a multigrid approach to solve the Navier-Stokes equations for the aerodynamic problem. Our simulations include high Reynolds numbers of up to 10,000, which demonstrates the potential of CFD analysis in optimizing the design of autonomous fighter drones for military operations. We evaluate the effectiveness of the linked strongly implicit multigrid technique in estimating high-Re fine-mesh flow solutions using the vorticity-stream function formulation of the two-dimensional incompressible Navier-Stokes equations. The model issue is the driven flow in a square cavity, and we consider meshes up to 1024 x 1024 points and combinations with Reynolds numbers as high as 1000. To further improve the accuracy of our simulations, we employ one-dimensional grid clustering coordinate transformations instead of uniform mesh refinement, as the flow field exhibits one or more secondary vortices. Our findings demonstrate that CFD analysis can provide valuable insights into the complex flow dynamics within the weapon bay of autonomous fighter drones, which can lead to the optimization of their design for enhanced mission capabilities. Overall, our study highlights the significance of numerical simulations and CFD analysis in the design and optimization of autonomous fighter drones for military applications. Our results can serve as a basis for future research in the field of UAV aerodynamics and contribute to the development of more efficient and effective military operations.

Parallel aeroacoustic computation of unsteady transonic weapon bay using detached‐eddy simulation via open computational fluid dynamics source codes

SummaryCavity flow research has been ongoing experimentally since the 1940s, especially for weapon bay use in fighter aircraft. Technology advancement has led to the beginning of simulations of experimental studies. The success of these simulations has increased with the emergence of High‐Performance Clusters, and simulation studies have started to take the role of experimental studies. In this paper, an open rectangular, unsteady transonic cavity with a length to depth ratio of 5, Mach number 0.85 and Reynolds number of approximately 6.5 × 106 is simulated using Computational Fluid Dynamics (CFD) on a High‐Performance Cluster. Likewise, cavity door is used to model a real weapon bay. Detached‐Eddy Simulation is used to resolve turbulent properties in the flow domain. Results compatible with experimental data are obtained with OpenFOAM, an open‐source CFD code based on the finite volume method. Additionally, computational costs are given in the clock‐time analysis section, and the necessity of high‐performance clusters for CFD and Computational Aeroacoustics studies is emphasized.

Time-efficient simulations of fighter aircraft weapon bay

A cavity flow exhibits aero-acoustic coupling between the separated shear layer and reflecting waves within the walls of the cavity, which leads to emergence of dominant modes. It is of primary importance that this flow mechanism inside the cavity is understood to provide insights and control the relevant parameters and that it can be properly predicted using state-of-the-art CFD tools. In this study, an open-cavity configuration with doors attached on the sides and a length-to-depth ratio of mathbf{5}.7 have been studied numerically using the TAU code developed by the German Aerospace Center for transonic flows with three simulation methods such as DES with wall functions and SST-SAS with resolved wall flow or wall function techniques. The free-stream conditions investigated are Mach number (Ma) mathbf{0}.8 with Reynolds number (Re) mathbf{12} times mathbf{10} ^mathbf{6 }. The Rossiter modes occurring in the cavity due to the acoustic feedback mechanism have been numerically computed and validated. The SST-SAS model is around 90% more computationally efficient compared to the hybrid RANS-LES model providing excellent accuracy in predicting the Rossiter modes. The SST-SAS model with wall functions is 50% more computationally efficient than wall-resolving SAS simulations showing good behaviour in predicting modal frequencies and shapes, with further scope for improvement in the spectral magnitude levels.

Improved Delayed Detached-Eddy Investigations on the Flow Control of the Leading-Edge Flat Spoiler of the Cavity in the Low-Aspect-Ratio Aircraft

The internal weapon bay is widely used in modern aircraft; however, because the unsteady flows of the cavity would cause dangerous store separation and intense aerodynamic noise, the leading-edge spoiler is an easy and efficient passive flow-control method. The flow control of the leading-edge flat spoiler before the cavity of a low-aspect-ratio flying-wing aircraft is investigated based on numerical simulation. Numerical results show that the leading-edge flat spoiler completely changes the cavity flow; it obviously lifts up the shear layer and reduces the pressure inside the cavity. For the store separation from the weapon bay, the leading-edge flat spoiler is a very good passive flow-control method that curbs the nose-up trend of the store and produces a safe and stable store separation. Besides, the leading-edge spoiler reduces the noise in the rear of the cavity (max 8.2 dB), but increases the noise in the middle of the cavity (max 11.3 dB). In addition, the leading-edge spoiler brings in a large drag increase to the aircraft (39.41% when the height of spoiler is 0.2 m), which would affect the operational stability of the aircraft. The results of this paper could provide a reference for the flow control of weapon bays and the design of aircraft.

Effect of a Jet Control Device on the Process of Missile and Internal Weapons Bay Separation

To ensure that the missile is safely separated from the internal weapons bay, the jet is used to control the process of missile separation, which is mounted on the front edge of the bay. The length-to-depth ratio of the bay was L/D=8, the diameter of the missile was d1 =0.178 m, the diameter of the jet was d2 =0.05 m . The FLUENT software was combined with our group-developed code under the platform of a user-defined function (UDF) to solve the flow field and the six-degrees-of-freedom (6DOF) of missile. The detached eddy simulation method and dynamic mesh technology were used in the numerical calculations. The boundary condition of missile, bay, and aircraft was no-slip wall condition. The boundary condition of the jet was the pressure-inlet. The pressure far-field boundary was selected as other boundaries. The constraint of the ejection device on the missile was considered. It was found that the jet control device thickens the shear layer, so the shear layer with more gradual velocity gradients, which is beneficial to the separation of missile. The distance between the internal weapons bay and the missile in the positive z-direction with the jet is 1.74 times that without the jet at t=0.5 s. In the case of the jet control device, the pitching angle of the missile ranged from 0.93° to -3.94° , the angular motion range of the missile with the jet is smaller than that without. The jet can make the characteristics of the flow field friendly, and enable the missile to separate from the bay quickly, stably, and safely.

RETRACTED: Active aerodynamic noise control research for supersonic aircraft cavity by nonlinear numerical simulation

Prediction of aerodynamic noise is the key technology for the internal weapon bay of supersonic aircraft. Nonlinear numerical simulation is proposed as a new method to analyze noise recently. The Non-Linear Acoustic Solver (NLAS) is employed to study the cavity noise in supersonic combined with Reynolds-averaged Navier-Stokes (RANS) equation. It is shown by the comparison between the calculated results and the WICS wind tunnel tests when the Mach number is 2, the sound pressure level of every monitoring point is in good agreement with experiments. It indicates that the NLAS method which is based on turbulence reconstruction could well simulate the cavity noise in supersonic and reduce mesh numbers. Based on this, the contribution to aerodynamic noise suppression made by active control measure such as adding jet screen at the leading edge of cavity is investigated. It is found that jet screen improves flow condition and increases cavity safety, therefore, it is suitable for suppression of aerodynamic noise under supersonic condition.

The effect of angle of attack on the aeroacoustic environment within the weapons bay of a generic UCAV

Cavity flow studies are generally concerned with observing the effect of geometry changes whilst maintaining a fixed zero angle of attack. Cavities employed as weapons bays will, however, experience a range of angles of attack. This paper presents the first known results showing the effect of flight angle of attack on the aeroacoustic characteristics of an internal weapons bay installed in an uninhabited combat air vehicle (UCAV). The UCAV geometry consisted of a Boeing M219-type cavity in a Boeing UCAV1303 airframe. Numerical simulation was conducted using a full-scale detached eddy simulation model and representative transonic flight conditions. As well as the reference case of zero degrees, data for angles of attack of 3.0, 4.5 and 6.0 degrees were analysed. Experimental data was used to validate the reference computational model, which agreed with the overall fluctuating sound pressure level (OAFPL) to within the experimental uncertainty of 4 dB. Data from the computational model was post-processed with frequency-domain and time-frequency-domain techniques showing that the flow structure within the weapons bay was altered significantly by the angle of attack changes, affecting the mean pressure distribution, frequency spectra and resonant modes. Overall, increasing the angle of attack from 0.0 to 3.0 degrees produced an increment in the acoustic load whilst a further increase tended to affect the resonance mechanism and thereby reduce the coherence and the temporal footprints of the resonant modes.

Simulation of the Store Separation from Internal Weapons Bay Using M_SST DES Model

The internal carriage of stores on an aircraft’s merit is especially importance for attack aircraft. For the safe carriage and separation of stores, it is important to know the flow field environment the store experiences during flight. A CFD investigation was conducted to determine cavity flow characteristics. M-SST DES Method are used as numerical simulate method. Compared with the wind tunnel test results, the open cavity flows are studied. The numerical simulation results are in good agreement with the wind tunnel test results, thus verifying the credibleness of the M-SST DES Method. As a typical research model, AEDC’s ‘Wing-Pylon-Finned Store’ wind tunnel test model is computed in this paper. Last, this paper investigates the store’s separation characteristic, which is internal carriage on and release from aircraft. Those results are also indicated that the DES method of numerical simulation flow-filed can embody the unsteady aerodynamic random factors of the store separation from internal weapons bay.

Cavity Resonance Suppression Using Fluidic Spoilers

This paper examines experimentally the use of a fluidic spoiler to suppress the resonance within a partially closed cylindrical cavity subject to a grazing flow. The relative movement of aircraft and high-speed land-based vehicles through air often results in structural cavities in these vehicles being subject to shear-layer-driven resonance. This can lead to high-amplitude pressure fluctuations within the cavity volume, causing damage to stores or equipment found within landing-gear wheel or weapon bays, for example, or else significant discomfort to the passengers of cars or trains. This large-scale buffeting can also cause vehicle stability problems and can increase drag. This work presents a novel method, in which passive flow control consisting of an upstream fluidic spoiler is used to redirect the upstream flow so that the cavity orifice is shielded. As a result, the grazing flow can no longer detach from the upstream leading edge of the cavity, and thus, vortex shedding is suppressed. The scope of the study includes an examination of higher-order azimuthal acoustic modes excited in the cylindrical cavity: modes which have received little attention in the literature, but which can be readily excited for many flow configurations for partially covered cavities.

Numerical Investigations on Wedge Control of Separation of a Missile from an Aircraft

To make the missile safely separate from the internal weapons bay, a wedge flow control device is mounted on the front of the bay to control the variation of flow during the separation. The numerical simulations of missile separation without and with wedge flow control device under different sizes are carried out. The flow fields of different separation processes are obtained and discussed; the aerodynamic parameters and trajectory parameters of missile of different cases are illustrated and compared. Results show that, the wedge flow control device can accelerate the missile separation and has the effect of regulating the angular motion of missile. The influence of the wedge height is stronger than that of its length on the center of gravity motion and angular motion of missile.

Flow Field Characteristic Research on Buried Weapon Bay in Different Mach Numbers

Actually, besides the missile, some complex surface such as the surface of missile, accessories and opening and closing mechanism for the missile bay etc. will have obvious influence on flow in the bay. In order to study the steady flow characteristics of the missile bay, the calculation model is established and simplified according to the research needs. The working condition is that a missile model is carried in the middle of the missile bay. The characteristics of the flow field in the bay at Mach 1.5 and Mach 3.5 are calculated and analysed under the above working condition.

Numerical Study on a 2-D Simplified Missile Separation from High Speed Aircrafts

In this paper, 2D numerical simulations are carried out on the symmetric plane of a full size missile separation from high speed aircrafts at the conditions of Ma=5 and AOA=0°. Aerodynamics and typical flow field characteristics of the missile at different distances away from the cavity bottom are predicted via a steady RANS solver. Results show that the flow of the missile separation from high speed aircrafts with an embedded weapon bay can be divided into four stages, which are dominated separately by the flow around the missile in the deep cavity, compressed incoming flow by the lower surface of the missile, strong interacting flow between the shear flow and the upper surface of the missile and wall effect flow of the missile. For Stage I, the flow field mode of the cavity is determined by the effective length depth ratio of the cavity, however, the effective length depth ratio is decreasing with the fall of the missile. For stage II, the incoming flow will be firstly compressed by the lower surface of the missile since it’s protruding from the embedded weapon bay. After that, i.e. on the stage III, when the axis line of the missile is beyond the surface of the aircraft, the strong shear layer induced by the incoming high speed flow and the non-high speed flow in the cavity will act on the lower incoming flow, which leads to the shock wave interaction at the missile nose. Simultaneously, the strong shear layer will significantly increase the pressure on the upper surface of the missile. For stage IV, i.e. the embedded weapon bay is closed, the reflection times of the shock waves between the missile and the aircraft decrease with the increasing distance between the missile and the aircraft. In addition, the pressure on the upper surface of the missile decreases gradually. The large negative lift of the missile formed due to the extreme wall effect is beneficial to the missile separation from high speed aircrafts in some degree.

Multi-disciplinary simulations of stores in weapon bays using scale adaptive simulation

This paper presents cavity flow calculations using the scale-adaptive simulation method involving door opening, store release and aeroelasticity. For established bay flows, the structural excitation showed a directional dependence, and the structures were responding to the flow frequency content. Maximum store deformations were of about 2% of the store diameter during store release. This is the first time where such effects are quantified for stores released from within bays. The store deformation, the role of the shear layer, and the store trajectory variability are also quantified.

Investigations on the influence of control devices to the separation characteristics of a missile from the internal weapons bay

To ensure the safe separation process of a missile from internal weapons bay, the control device is mounted in front of the internal weapons bay to control the separation process. Based on the coupling of Navier-Stokes (N-S) equations and six-degrees-of-freedom (6DOF) rigid-body motion equations, the separation process of missile under four different conditions (free separation, and rectangle, prism and wedge control) was numerically simulated. The separation process and flow fields were obtained, the aerodynamic parameters and trajectory parameters of four cases compared. Our results show that, the control device can improve the aerodynamic characteristics of the flow field, enhancing the safety of the missile separation. The wedge control device has the best control effect and makes the missile stable, the rectangular and prism control devices have strong bow shock wave and make the pitch angle of the missile large.

Store Release Trajectory Variability from Weapon Bays Using Scale-Adaptive Simulations

In this paper, scale-adaptive simulation is used to study store trajectory variability for releases from transonic weapon bays. The scale-adaptive simulation captures the essential physics of the flow in the weapon bay, and its speed of computation allows for several trajectories to be computed within reasonable time. The results of the simulations are treated as a statistical set and a metric is put forward to decide the minimum number of simulations necessary to establish the mean and the standard deviation of the releases. Averaging the results of all trajectories was useful in developing an overall understanding of the bay pressure field role on the store trajectories. Filtering the obtained trajectories provided insight in the flow frequencies affecting the forces acting on the store and the coordinates of its center of gravity during releases. For the store employed in this study, less than one month of CPU time is needed for the complete set of simulations to be obtained, making this method promising as a further test before flight testing.

Cavity Flow over a Transonic Weapons Bay During Door Operation

This paper considers a transonic, idealized, weapons bay. The doors are either fixed or opened in a dynamic way. The flow evolves in three stages during door opening, corresponding to closed-cavity flow, transitional flow, and (finally) open-cavity flow. The transition needs to be taken into account to design structures, as the bay wall loads are amplified, as well as the noise. The flow fluctuations are also larger than for the fully established flow. The doors limit the development of the shear layer at the early stage of the door opening.