Subsonic Conditions Research Articles

Solving the Small Disturbance Equation and Numerical Method Optimization in Subsonic and Supersonic Flows

This paper addresses the solution of the Small Disturbance Equation (SDE) under subsonic and supersonic flow conditions using Successive Over-Relaxation (SOR) techniques. The study implements and validates numerical methods tailored to the unique dynamics of these regimes by setting precise boundary conditions, adjusting computational stencils, and managing the Mach number ( M∞ ) across the solution domain. A detailed comparison of streamline patterns between the regimes illustrates the efficacy of the applied numerical strategies. In the subsonic domain, the flow demonstrates uniform and smooth characteristics, conducive to standard SOR techniques, as evidenced by the rapid decline in residual errors, confirming the method’s efficiency for accurate solutions. Conversely, the supersonic regime presents increased complexity where standard finite difference methods encounter notable challenges, necessitating more sophisticated approaches to capture the intricate flow behaviors effectively. Conversely, in the supersonic regime, where the flow behavior exhibits more complex characteristics, the standard finite difference method faces challenges.

Acoustic flow resonances in installed rectangular jets

Zonal Large Eddy Simulations (LES) of complex installed rectangular jet flows are performed for subsonic jet conditions of the Central Institute for Aviation Motors (CIAM) experiment, where a strong tone was reported. For far-field noise modelling, the zonal LES solutions are coupled with the permeable formulation of the Ffowcs Williams and Hawkings (FW-H) method. The obtained noise spectra predictions are compared with the acoustic measurements in the CIAM facility. To reduce statistical noise of the relatively short LES time series, contributions due to several dominant low frequency tones and the remaining broadband signal are computed separately, using a tailored Fourier transform technique for each signal type. For cross-validation, noise spectra measurements of an equivalent isolated round jet in the CIAM facility are compared with the empirical sJet model calibrated on the NASA Small Hot Jet Acoustic Rig (SHJAR) jet noise database. While the two datasets agree reasonably well for mid to high frequencies, larger discrepancies are observed for low frequencies, which are attributed to acoustic reflections in the non-anechoic CIAM facility. The differences in noise levels between the CIAM dataset and the sJet model representing the NASA jet noise data are used to determine the experimental uncertainty of the CIAM noise measurements for each frequency and observer angle. For the installed rectangular jet, it is shown that far-field noise spectra predictions of the zonal LES-FW-H method for both the fundamental tone, its sixth harmonic corresponding to the jet Strouhal number of around 1, and the broadband component are broadly within the experimental error bar for most observer angles. Some discrepancies between predictions of the zonal LES method and the CIAM measurements for the main low frequency tone for the 30° and 90°, where the experimental uncertainty at low frequencies is largest are also noted. After validating the acoustic solutions, spectral and conditional averaging analysis methods are applied to elucidate mechanisms of the acoustic-flow resonance in the installed rectangular jet flow. The numerical dispersion relation is obtained to analyse phase velocities of the upstream and downstream travelling pressure waves in the stream-wise direction. The conditional analysis of pressure fluctuations inside the jet reveals the emergence of internal reflection points corresponding to a rapid change of the acoustic wave phase as well as the saddle points interpreted as localised zones of vorticity shed from the side-wall edges. To independently investigate the effect of trailing edges and corner points of the jet embodiment geometry on closing the acoustic-flow resonance cycle, several modifications of the baseline rectangular nozzle are considered, such as introducing chevron-like lobes and cuts on the trailing edges of the side walls as well as smoothing the sharp corner points of the wall edges. Following the series of additional zonal LES runs with the modified installed nozzle geometries, an optimized tone-less modification of the original installed nozzle was obtained, in broad agreement with the conditional analysis results. The obtained tone-less modification of the installed rectangular jet is further analyzed to provide insights into its similarity and differences from the aeroacoustics of the reference isolated round jet in the same CIAM facility.

Shock wave structures and vortex unsteadiness in the tip region of a transonic turbine cascade under different conditions

The tip region of transonic turbine blades (exit Mach number of 0.95) exhibits complex flow characteristics with the coexistence of multiple shock wave systems and multiscale vortices. Based on a validated detached Eddy simulation method, unsteady flow features such as the spatial-temporal dynamic evolution of tip leakage vortices (TLV) and the periodic buffet/oscillation of shock trains inside the tip gap are revealed and discussed systematically under different incidence angles (i) and heights of tip clearance. Moreover, the distinction of tip flow structures between the subsonic and transonic conditions is also manifested. Results indicate that the wandering behavior of the TLV is influenced by both the swirling strength of the vortex itself and the interaction of adjacent secondary vortices. The TLV under a tip gap of 5% blade height (h) exhibits “binary and bimodal” wandering characteristics both along the pitchwise and spanwise direction, whereas under the 1%h case, only the pitchwise wandering is prominent. The dominant characteristic frequency of the TLV wandering under different conditions falls within the spectrum range of 2.2–2.4 kHz. As for the shock trains inside the tip clearance (τ), coherently movement back and forth along the pitchwise direction with varying amplitudes can be observed, where the magnitude within the τ=1%h exceeds that observed in the τ=5%h, depending on the intensity of the shock waves. Notably, significant shock wave oscillations are present throughout the range of the chord length (c) within the τ=1%h, whereas within the tip gap of 5%h, shock wave systems exhibit more pronounced oscillations predominantly near the trailing edge.

A stochastic and analytical model of hierarchical fragmentation

Context. Molecular clouds are the most important incubators of young stars clustered in various stellar structures whose spatial extension can vary from a few AU to several thousand AU. Although the reality of these stellar systems has been established, the physical origin of their multiplicity remains an open question. Aims. Our aim was to characterise these stellar groups at the onset of their formation by quantifying both the number of stars they contain and their mass using a hierarchical fragmentation model of the natal molecular cloud. Methods. We developed a stochastic and predictive model that reconciles the continuous multi-scale structure of a fragmenting molecular cloud with the discrete nature of the stars that are the products of this fragmentation. In this model a gas structure is defined as a multi-scale object associated with a subregion of a cloud. Such a structure undergoes quasi-static subfragmentation until star formation. This model was implemented within a gravo-turbulent fragmentation framework to analytically follow the fragmentation properties along spatial scales using an isothermal and adiabatic equations of state (EOSs). Results. We highlighted three fragmentation modes depending on the amount of fragments produced by a collapsing gas structure, namely a hierarchical mode, a monolithic mode, and a mass dispersal mode. Using an adiabatic EOS we determined a characteristic spatial scale where further fragmentation is prevented, around a few tens of AU. We show that fragmentation is a self-regulated process as fragments tend to become marginally unstable following a M ∝ R Bonnor–Ebert-like mass-size profile. Supersonic turbulent fragmentation structures the cloud down to R ≈ 0.1 pc, and gradually turns into a less productive Jeans-type fragmentation under subsonic conditions so hierarchical fragmentation is a scale dependant process. Conclusions. Our work suggests that pre-stellar objects resulting from gas fragmentation, have to progressively increase their accretion rate in order to form stars. A hierarchical fragmentation scenario is compatible with both the multiplicity of stellar systems identified in Taurus and the multi-scale structure extracted within NGC 2264 molecular cloud. This work suggests that hierarchical fragmentation is one of the main mechanisms explaining the presence of primordial structures of stellar clusters in molecular clouds.

Comparison of fluid structure downstream of an evaporative flameholder with subsonic uniform and subsonic-supersonic inflows

Subsonic uniform and supersonic mixing flows are widely present in the combustion chamber of a multi-mode combined scramjet engine, where the significant pressure, velocity, and temperature gradients of the two impose severe limitations on flame propagation. The vortex structures downstream of an evaporative flameholder were experimentally measured under subsonic-supersonic mixing inflow and subsonic uniform inflow. Results indicate that, under subsonic-supersonic mixing inflow conditions, an asymmetric vortex structure in the recirculation zone is formed due to the presence of a subsonic-supersonic shear layer, which exerts compressive or stretching effects on the recirculation zone downstream of the flameholder, in contrast to the symmetric dual-vortex structure observed under subsonic uniform inflow conditions. The asymmetric recirculation zone displays fluid being entrained from one vortex to another, with the degree and direction of entrainment dependent on the supersonic expansion state. Additionally, a simplified flow field structure is proposed for comparing the differences between the subsonic-supersonic mixing inflow and subsonic uniform inflow, along with the introduction of five regions and two stages to describe the flow field structure downstream of the flameholder under subsonic-supersonic mixing inflow. Analysis of the flow characteristics downstream of the flameholder under subsonic-supersonic mixing inflow and subsonic uniform inflow conditions can offer design insights for the combustion scheme of aerospace-integrated propulsion systems.

On the measurement of the aerodynamic features of composite structures under subsonic airflow using mathematical modeling and machine learning method

This study investigates the aerodynamic features of functionally graded triply periodic minimal surface (FG-TPMS) structures under subsonic airflow using a combination of mathematical modeling and machine learning methods. The modified supersonic piston theory of Krumhaar is used to quantify the aerodynamic stiffness and damping matrices. Using characteristics and six distinct patterns of volume distribution of FG-TPMS materials in terms of their mechanical qualities, Hamilton’s principle, and parabolic shear deformation theory are used to extract the governing equations of the presented composite structure. After that, the differential quadrature method at the discrete places and Lagrange interpolated polynomials and Kronecker product are used to solve the governing equations in the numerical domain. This study highlights the potential of integrating advanced computational techniques with machine learning to address complex engineering problems. The findings provide valuable insights into the aerodynamic optimization of sandwich structures, paving the way for their more efficient and effective design in aerospace engineering. As an important outcome for related industries, the displacement field along with the Z direction increases by increasing the angle of airflow by approximately 9 % while this value for the X, and Y directions are 7 %, and 6 %, respectively. The proposed methodology offers a powerful tool for engineers and researchers seeking to optimize the performance of advanced composite materials under subsonic airflow conditions.

Influence of the swirl vanes in convergent-divergent nozzle on screech tones and mixing efficiency at subsonic and supersonic jet flow

PurposeThe purpose of this study is to investigate the effect of coaxial swirlers on acoustic emission and reduction of potential core length in jet engines.Design/methodology/approachThe swirlers are introduced in the form of curved vanes with angles varied from 0° to 130°, corresponding to swirl numbers of 0–1.5. These swirlers are fixed in the annular chamber and tested at different nozzle pressure ratios of 2, 4 and 6.FindingsThe study finds that transonic tones exist for the nonswirl jet, creating an unfavorable effect. However, these screech tones are eliminated by introducing a swirl jet at the nozzle exit. Weak swirl shows a greater reduction in noise than strong swirl at subsonic conditions. In addition, the introduction of swirl jets at all pressure ratios significantly reduces jet noise and core length in supersonic conditions, mitigating the noise created by shockwaves and leading to screech tone-free jet mixing.Originality/valueThe paper provides valuable insights into the use of coaxial swirlers for noise reduction and core length reduction in jet engines, particularly in supersonic conditions.

Aerodynamic Stability Derivative Calculations Using the Compressible Source and Doublet Panel Method

This work presents the development of closed-form expressions for the aerodynamic stability derivatives of wings and aircraft flying at subsonic compressible conditions using the unsteady subsonic 3D source and doublet panel method (SDPM). The stability derivatives are obtained directly from the frequency domain version of the nonlinear unsteady subsonic Bernoulli equation and can be calculated for negligible additional computational cost around the true geometry of the wing or aircraft for each frequency of interest. The methodology is validated by applying it to an experimental test case of a swept wing oscillating in yaw and sideslip in the wind tunnel, demonstrating that the values of the aerodynamic stability derivatives obtained from the SDPM are in good agreement with the experimental data at low and moderate angles of attack. Then, the methodology is applied to a blended-wing–body unmanned aerial vehicle configuration and the SDPM stability derivative predictions are compared to estimates obtained from both steady computational fluid dynamics calculations and the USAF DATCOM methodology. It is shown that the SDPM approach is accurate and can yield more information about the stability of the aircraft than the DATCOM, given that the latter was developed for conventional aircraft configurations.

Emergence of high-mass stars in complex fiber networks (EMERGE)

Context. Recent molecular surveys have revealed the rich gas organization of sonic-like filaments at small scales (so-called fibers) in all types of environments prior to the formation of low- and high-mass stars. These fibers form at the end of the turbulent cascade and are identified as the fine substructure within the hierarchical nature of the gas in the interstellar medium (ISM). Aims. Isolated fibers provide the subsonic conditions for the formation of low-mass stars. This paper introduces the Emergence of high-mass stars in complex fiber networks (EMERGE) project, which investigates whether complex fiber arrangements (networks) can also explain the origin of high-mass stars and clusters. Methods. We analyzed the EMERGE Early ALMA Survey including seven star-forming regions in Orion (OMC-1,2,3, and 4 South, LDN 1641N, NGC 2023, and the Flame Nebula) that were homogeneously surveyed in three molecular lines (N2H+ J = 1–0, HNC J = 1–0, and HC3N J = 10–9) and in the 3 mm continuum using a combination of interferometric ALMA mosaics and IRAM-30 m single-dish (SD) maps, together with a series of Herschel, Spitzer, and WISE archival data. We also developed a systematic data reduction framework allowing the massive data processing of ALMA observations. Results. We obtained independent continuum maps and spectral cubes for all our targets and molecular lines at different (SD and interferometric) resolutions, and we explored multiple data combination techniques. Based on our low-resolution (SD) observations (30″ or ~12 000 au), we describe the global properties of our sample, which covers a wide range of physical conditions, including low-(OMC-4 South and NGC 2023), intermediate (OMC-2, OMC-3, and LDN 1641N), and high-mass (OMC-1 and Flame Nebula) star-forming regions in different evolutionary stages. The comparison between our single-dish maps and ancillary YSO catalogs denotes N2H+ (1–0) as the best proxy for the dense, star-forming gas in our targets, which show a constant star formation efficiency and a fast time evolution of ≲1 Myr. While apparently clumpy and filamentary in our SD data, all targets show a much more complex fibrous substructure at the enhanced resolution of our combined ALMA+IRAM-30 m maps (4″.5 or ~2000 au). A large number of filamentary features at subparsec scales are clearly recognized in the high-density gas (≳ 105 cm−3) that is traced by N2H+ (1–0) directly connected to the formation of individual protostars. Surprisingly, this complex gas organization appears to extend farther into the more diffuse gas (~103−104 cm−3) traced by HNC (1–0). Conclusions. This paper presents the EMERGE Early ALMA Survey, which includes a first data release of continuum maps and spectral products for this project that are to be analysed in future papers of this series. A first look at these results illustrates the need of advanced data combination techniques between high-resolution interferometric (ALMA) and high-sensitivity, low-resolution single-dish (IRAM-30 m) datasets to investigate the intrinsic multiscale, gas structure of the ISM.

Mathematical analysis of acoustic wave interaction of vibrating rigid plates with subsonic flows

This research article investigates the effects of object's vibration and fluid movement on the acoustics of subsonic flows, specifically focusing on the scattering of acoustic waves by a vibrating rigid plate submerged in uniform flow. The acoustic plane wave that impacts the plate, coupled with its oscillatory motion, causes a disruption in the fluid medium. This disturbance, in turn, gives rise to a Rayleigh wave that propagates along the boundary separating the plate and the fluid. The study uses the Wiener‐Hopf technique to analytically model the acoustic scattering by a rigid barrier of finite dimensions and analyze the relationship between acoustics and structures. The method involves applying Fourier transformations to the governing boundary value problem and resolving the Wiener‐Hopf equations using the factorization theorem, Liouville's theorem, and analytical continuation. The integral equations of scattered potential computed asymptotically are used to describe the acoustic characteristics of structures and their interaction with fluid flow in subsonic conditions. The findings of the study reveal the sharp peaks of the scattered potential at certain angles with more oscillation in high subsonic flow. Also, increasing the frequency of the vibrating plate increases the amplitude of the scattered potential but is attenuated in mean flow whereas enhancing plate vibrations amplifies the scattered sound, and it is more vibrant in high subsonic flow than mean flow and no fluid flow. This research has applications in noise reduction, aeronautical engineering, and the detection of underwater structures using acoustic waves and micropolar elastic media.

Numerical modeling of air ejectors covering supersonic, subsonic and closed-port operations

The physics and modeling of air ejectors in on- and off-design conditions have been extensively addressed in the past, reaching a good level of maturity. However, to achieve a robust model at system scale integrating an ejector, there is a need for developing 0D models suitable to tackle abnormal functioning modes, such as cases where the ejector works in subsonic conditions, reverse flows, or closed ports. Based on state-of-the-art models, a new 0D model has been built in the current work, where proper subroutine implementations allow covering normal and abnormal operations of convergent nozzle ejectors. The current research also focuses on understanding the physical behavior of air ejectors for aeronautical applications. In this regard, CFD-RANS simulations are used to perform model verification and calibration as well as to gain knowledge of the whole operational envelope. The regimes reproduced by the 0D model, and validated by CFD, cover the normal operating mode with different choking regimes, the occurrence of a subsonic primary flow, and the closed secondary port case. Additional cases are run to assess other features of the ejector behavior, such as the influence of geometrical properties on the choking mechanism and the impact of thermal effects.

Experimental investigation of a Y-shaped engine inlet at subsonic flow conditions

Abstract In this paper, the results of an experimental investigation for a Y-shaped engine inlet are presented. The experiment is performed at subsonic flow conditions. The main focus is given to time-dependent total pressures measured at the aerodynamic interface plane. Distinctive frequencies carrying high energy contents of the fluctuating total pressures are given and the relation between time-dependent and time-average performance parameters is presented. The cross-correlation coefficients of the high frequency probe readings distributed through the aerodynamic interface plane are also investigated.

A Comparative Study of Scarfed Nozzle for Jet-Installation Noise Reduction

The experimental investigation of the effects of scarfed nozzles on jet-installation noise was conducted using unheated subsonic jets in an anechoic jet noise facility. Four different types of scarfed nozzles with increasing nozzle lip angles were examined to study the installation effects at various plate distances away from the jet. Mach numbers ranging from 0.3 to 0.8 were investigated in the experiments. The use of scarfed nozzles is known to result in the deflection of flow away from the centre axis, inducing asymmetry in the jet shears, leading to azimuthal variation in the spectra, and ultimately, noise reduction. This study aims to explore the possibility of reducing jet-installation noise using scarfed nozzles at subsonic flow conditions. The characteristics of jet hydrodynamic pressure fluctuations were investigated in the axial direction using far-field measurements. The near-field flow features were studied using surface pressure transducers installed on the flat plate for the installed configurations. Detailed spectral, coherence, and correlation analyses were carried out to determine the noise reduction mechanisms associated with scarfed nozzles in the proximity of a flat plate. The results of the study showed that the use of scarfed nozzles significantly reduced the jet-installation noise. The reduction was attributed to the generation of an asymmetric flow field induced by the nozzle geometry. The reduction in noise levels was also observed to increase with increasing nozzle lip angle. The detailed analyses revealed that the noise reduction mechanism was associated with a decrease in the acoustic power generated by the jet. Overall, the results suggest that scarfed nozzles can be an effective means of reducing jet-installation noise in subsonic flow conditions.

Study of the Energy Efficiency of Compressed Air Storage Tanks

This study focusses on the energy efficiency of compressed air storage tanks (CASTs), which are used as small-scale compressed air energy storage (CAES) and renewable energy sources (RES). The objectives of this study are to develop a mathematical model of the CAST system and its original numerical solutions using experimental parameters that consider polytropic charging and discharging processes, changes in the time of the temperature, flow parameters of the inlet and outlet valves under choked and subsonic conditions, and the characteristics of the air motor. This model is used to select CAST as an energy storage system for compressed air generated by compressors and recycling, as well as an energy source to drive DC generators and a pneumatic propulsion system (PPS). A measuring test rig is built to verify the polytropic pressure and temperature variations during CAST charging and discharging obtained from numerical solutions. The topic of discussion is the functional model of a high-pressure air system (HPAS) that contains a CAST connected to an air motor coupled to a mechanical drive for a DC generator or PPS. Such a system is used in small-scale CASTs, which currently respond to socio-economic demands. The presented CAST energy efficiency indicators are used to justify the storage of compressed air energy on a small scale. Small-scale compressed air storage in CASTs is currently important and relevant due to the balance between peak electricity demand and the development of wind energy, photovoltaics, and other renewable energy sources.

Aerodynamic Shape Optimization of Subsonic/Supersonic Flows Integrating Variable-Fidelity Longitudinal Trim Analysis

Most existing studies on aerodynamic shape optimization have not considered longitudinal trim under control surface deflection, typically achieving self-trim through a constraint of zero pitching moment or adjusting the optimized configuration for longitudinal trim. However, adjustments to the optimized configuration might introduce additional drag, reducing overall optimization benefits. In this paper, a novel approach of incorporating control surface deflection for longitudinal trim in aerodynamic optimization is proposed. Firstly, an aerodynamic computation program based on the high-order panel method was developed, introducing velocity perturbations on specific mesh surfaces to simulate actual control surface deflections. Subsequently, a comprehensive optimization framework was established, encompassing parametric modeling, aerodynamic computation, and variable-fidelity control surface deflection analysis. Finally, aerodynamic optimization analysis was conducted under both subsonic and supersonic conditions. Thirty-one design variables were selected with the trimmed lift-to-drag ratio in cruising condition as the objective function and the control surface deflection angle as the constraint. The results indicated an 8.52% increase in the trimmed lift-to-drag ratio compared to the baseline model under subsonic conditions and an 8.1% increase under supersonic conditions.

Numerical Investigation on the Effect of Fuel-Rich Degree in the RBCC Engine under the Ejector Mode

The ejector mode of the Rocket-Based Combined-Cycle (RBCC) engine is characterized by high fuel consumption. This study is aimed at investigating the influence of the rocket fuel-rich degree on the RBCC engine’s performance under the ejector mode combined with simultaneous mixing and combustion (SMC). Numerical simulations were conducted for various rocket mixing ratios (Φ=1.6~3.2) under subsonic (Maf=0.9) and supersonic (Maf=1.8) flight conditions. It was observed that a high fuel-rich degree in the rocket plume negatively impacts the eject performance under all conditions. However, it improves the overall performance (Isp) at high flight Mach numbers (Maf). For supersonic conditions, increasing the fuel-rich degree promotes greater fuel participation in combustion, thereby enhancing RBCC engine performance. Nevertheless, the subsonic-supersonic mixing layer exhibits low evolution, resulting in a decrease in reaction efficiency from 29.2% to 12.0% as the Φ decreases from 3.2 to 1.6. Consequently, there is an inefficient utilization of fuel. To optimize RBCC engine performance, the rocket fuel-rich degree can be appropriately increased. However, this increase should be limited to prevent fuel wastage arising from low reaction efficiency. Under subsonic conditions (Maf=0.9), the low kinetic energy of captured air leads to the occurrence of “negative thrust surface” and “wall impact” phenomena, which hinder the efficient and stable operation of the RBCC engine. Consequently, adjusting the fuel-rich degree alone cannot promote specific impulse (Isp), and a low fuel-rich degree is considered an ideal strategy when combined with adjustable nozzle technology.

Analysis of stall characteristics of the cuspidal waverider at subsonic conditions

The stall characteristics of the cuspidal waverider under subsonic conditions were studied at M = 0.4 and H = 0 km incoming flow. The stall characteristics were compared with those of delta wing models with the same leading-edge swept angle and the same aspect ratio. It can be found that the flow field changes of the cuspidal waverider are similar to those of Model 1 and Model 2. The critical angle of attack of the cuspidal waverider is more influenced by the aspect ratio, but less related to the leading-edge swept angle. The lift change of the cuspidal waverider is closely related to the vortex structure on the leeward side. As the angle of attack increases, the vortex structure becomes thicker and stronger, and moves toward the middle of the model under the action of the overflowing high pressure gas on the lower surface. Under the same angle of attack, the vortex structure under the effect of the adverse pressure gradient, the intensity along the flow direction decreases while the vortex continues to move away from the wall. Besides, the possible splitting of large vortex into smaller ones will be another result of the effect of the inverse pressure gradient. The smaller the overall aspect ratio of the model, the greater actual swept angle and the greater effective swept angel of the vortex structure, which allows the vortex to exist at higher angles of attack. When the vortex structure is broken to form a larger recirculation area in the leeward area, the negative pressure at the leeward surface decreases, the lift coefficient decreases, and a stall occurs.

The effect of Flow Speed and Angle of Attack on the Aerodynamic Noise of NACA 0012 Airfoil

Wind energy is one of the main sources of renewable energy in the market today. The influence of the wind speed and the angle of attack on the aerodynamic noise was investigated in this study. Four different samples of airfoils were used. Three speeds (5, 10, 15 m/s) were employed. The results revealed that the aerodynamic noise was associated directly with the flow speed. The data showed that when the velocity increases by (5 m/s), the noise gets louder by an average amount of (10 dB). As the increase of flow velocity increased the velocity shear, this eventually increased the aerodynamic noise. As for the angle of attack, it had an effect on the aerodynamic noise as well. The results showed an increase in the overall sound pressure level between (1-4 dBA) when the angle of attack increased from (5 degrees) to (10 degrees), while there was an increase (1-6 dBA) when the angle of attack increased from (10 degrees) to (15 degrees). This study was conducted under subsonic flow condition and Reynolds number (3.3×104).

Numerical study on the influence of fabric permeability on the inflation process and aerodynamic characteristics of disk-gap-band parachute

Supersonic parachute plays a crucial role in Mars exploration missions. The disk-gap-band (DGB) parachute he been used in all the successful Mars exploration missions. The parachute is fabricated from different porous fabric materials, and the fabric permeability is an important design and performance parameter, now it has been proved that the fabric permeability of porous canopy has important effects on the complicated flow fields around the parachute and in turn effects the nonlinear deformation and aerodynamic performances of the flexible canopy. However, till now, the influence mechanism of fabric permeability on the fluid-structure interaction mechanism and aerodynamic performance of supersonic flexible porous parachute in the inflation process still remain unknown. Therefore, in this study, a fluid-structure coupling method was used to numerically simulate the inflation process of disk-gap-band parachute with different fabric permeability (i.e., different fabric materials), and the effect of fabric permeability on the aerodynamic performance of disk-gap-band parachute was also analyzed. The results showed that the fabric permeability has a significant effect on the inflation process of DGB parachute with different fabric materials. During the inflation process, the oscillation angle and drag coefficients of the parachute both gradually decreased with the increase of fabric permeability, while the stability performance of the parachute became more complicated. Furthermore, it was also found that the influence of fabric permeability was different under subsonic and supersonic conditions. The K5836-3 fabric used as canopy material has better stability under subsonic conditions, and the 42105 fabric material has the best stability under supersonic conditions.

Aerodynamic drag of axisymmetric models with different boattail angles under subsonic and supersonic flow conditions

Aerodynamic drag of axisymmetric models with different boattail angles under subsonic and supersonic flow conditions