Supersonic Regime Research Articles

Application of Supersonic Air Plasma Torch for Metallic Nickel-Based Alloys Spraying

This paper presents the preliminary results of the supersonic air plasma torch development for powder materials spraying. The pilot experiments on measurement the particles velocity of the disperse phase of high-temperature heterogeneous flow showed that the use of supersonic regime of the thermal plasma flow enabled more than a 1.5 increase in the average velocity of the sprayed particles. We also compare the properties of nickel-based coatings sprayed at subsonic and supersonic modes.

Characteristic-Based Flux Splitting to Solve Compressible Flow over an Airfoil

Current paper presents the Characteristics-based Flux Splitting to improve the numerical behaviour for the inviscid compressible flows. NACA 0012 airfoil is chosen as the test case at angles of attack in the steady state for subsonic, transonic, and supersonic regimes. To calculate the convective fluxes of the Euler equations by the finite volume approach, the Characteristics-based Flux Splitting (CFS) based on the local Mach number is introduced and compared with the conventional Jameson Averaging Method (JAM). To overcome the numerical oscillations especially at the shocked region, artificial dissipation is implemented for the JAM scheme while there is no need to such dissipations for the CFS scheme. For the time integration the Runge–Kutta method is applied. Consistent boundary condition based on characteristics is employed. The results prove the excellence of the CFS scheme regarding the accuracy, stability and convergence. The results are validated and compared with those of others available in the literature.

Pressure Bifurcation Phenomenon on Supersonic Blowing Trailing Edges

Turbine blades operating in transonic–supersonic regime develop a complex shock wave system at the trailing edge: a phenomenon that leads to unfavorable pressure perturbations downstream and can interact with other turbine stages. Understanding the fluid behavior of the area adjacent to the trailing edge is essential in order to determine the parameters that have influence on these pressure fluctuations. Colder flow, bled from the high-pressure compressor, is often purged at the trailing edge to cool the thin blade edges, affecting the flow behavior and modulating the intensity and angle of the shock waves system. However, this purge flow can sometimes generate nonsymmetrical configurations due to a pressure difference that is provoked by the injected flow. In this work, a combination of Reynolds-averaged Navier–Stokes simulations and a global stability analysis is employed to explain the physical reasons of this flow bifurcation. By analyzing the features that naturally appear in the flow and become dominant for some value of the parameters involved in the problem, an antisymmetrical global mode, which is related to the sudden geometrical expansion of the trailing-edge slot, is identified as the main mechanism that forces the changes in the flow topology.

Study of base pressure behavior in a suddenly expanded duct at supersonic Mach number regimes using statistical analysis

Journal of Applied Mathematics and Computational Mechanics, Prace Naukowe Instytutu Matematyki i Informatyki, Politechnika Częstochowska, Scientific Research of the Institute of Mathematics and Computer Science, Czestochowa University of Technology

Base Pressure Behaviour in a Suddenly Expanded Duct at Supersonic Mach Number Regimes using Taguchi Design of Experiments

Abstract Experimental investigations are carried out to study the control of base pressure without and with the use of micro-jets through suddenly expanded axi-symmetric passage in the supersonic regime. Four micro jets having an orifice diameter of 1mm were located at 90° intervals. In the base area, active controls jets have been placed on a pitch of a circle diameter that is 1.3 times the exit diameter of the nozzle. The jets were dispensed abruptly into the axi-symmetric tube maintained at a cross-sectional area of 4.84 times the exit nozzle area. The variation of base pressure as a function of flow control parameters namely Mach number, nozzle pressure ratio (NPR) and length to diameter) ratio (L/D) are evaluated experimentally. This study also assesses the impact of flow control variables on base pressure for two cases viz. with control and without control respectively. An L 9 orthogonal array of Taguchi and the analysis of variance were employed to investigate the percentage of contribution of these parameters and their interactions affecting the base pressure. The correlations between the various factors affecting the base pressure were obtained by using multiple linear regression equations. Confirmation tests were conducted in order to test the developed linear regression equations for their practical significance. Both the regression models were found to be significant and reliable with a percentage deviation lying in the range of − 6.12% to 10.26% for base pressure without control and −13.92% to 6.58% for base pressure with control. Analysis of variance was also performed in order to determine the statistical significance of each parameter on the total variability of base pressure. The study concluded that Mach number is the most influential parameter affecting base pressure followed by NPR and L/D.

Air Vehicle Management with Integrated Thrust-Vector Control

Vectored thrust is a powerful flow control technology that has long been used in rockets, launch vehicles, and other space systems. The technology has been more recently applied to atmospheric flight in conjunction with airbreathing propulsion systems. When fully integrated with other aerodynamic controls, vectored thrust has been shown to enable air vehicle management under unconventional flight conditions ranging from vertical takeoff or landing to agile maneuvering flight well beyond the aerodynamic stall boundary, the latter enabling close-in air-combat advantage. Capabilities demonstrated in several previously developed high-performance thrust-vectored experimental aircraft are reviewed and explored to illustrate the value and versatility of integrated thrust-vector (ITV) control technology. These capabilities include enhanced control authority at low airspeeds; deep, poststall maneuverability; tailless flight in both subsonic and supersonic flight regimes; extremely short takeoff and landing capability; as well as other benefits that can accrue from ITV implementation. Applications of this technology to contemporary aircraft are also discussed, and ITV nozzle concepts intended for use in conjunction with gas-turbine engines, including both mechanical and fluidic approaches, are briefly reviewed. A vision and rationale for incorporating ITV control on future civil and commercial aircraft designs are discussed, as are the likely areas of research needed for realization of the full potential of the ITV concept.

Thermodynamic Analysis of the Limit Cycles of a Device for Gas Flow Stratification

For the first time the limit conditional cycles in P-V and T-S coordinates of the device implementing the stratification effect (TL) for subsonic and supersonic flow regimes have been presented. The analysis of energy efficiency of heat exchange processes in TL on the basis of the developed limit cycles is carried out. As one of the integrative criteria of the device functioning the indicator of power exchange efficiency of the flow machine is offered.

Spectral analysis of jet turbulence

Informed by large-eddy simulation (LES) data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. The educed structures are generally well predicted by the resolvent analysis. Over a range of low frequencies and the first few azimuthal mode numbers, these jets exhibit a low-rank response characterized by Kelvin–Helmholtz (KH) type wavepackets associated with the annular shear layer up to the end of the potential core and that are excited by forcing in the very-near-nozzle shear layer. These modes too have been experimentally observed before and predicted by quasi-parallel stability theory and other approximations – they comprise a considerable portion of the total turbulent energy. At still lower frequencies, particularly for the axisymmetric mode, and again at high frequencies for all azimuthal wavenumbers, the response is not low-rank, but consists of a family of similarly amplified modes. These modes, which are primarily active downstream of the potential core, are associated with the Orr mechanism. They occur also as subdominant modes in the range of frequencies dominated by the KH response. Our global analysis helps tie together previous observations based on local spatial stability theory, and explains why quasi-parallel predictions were successful at some frequencies and azimuthal wavenumbers, but failed at others.

An experimental study of binary lateral jets on a standard model in subsonic, transonic, and supersonic cross-flows

There are numerous aerodynamic and nonaerodynamic methods to control flying devices, one of which is lateral jets, i.e. a high-speed method with convenient operation at low speeds or high altitudes. In this research, a new arrangement of lateral jets is examined by testing in a wind tunnel. The test is conducted on the Basic Finner model. In this design, the jets at the top and bottom of the model are arranged in pairs and parallel to each other. This combination, in addition to controlling pitch channel, provides the necessary conditions to control the roll channel. In this paper, pressure distribution is examined in the upstream and downstream areas as well as middle of jets. The flow visualization method is also used. The results are provided for subsonic, transonic, and supersonic free flow regime at the positive and negative angles of attacks. In the subsonic and supersonic flows, the achievements of the binary jets are the further pressure reduction on the middle line of jets compared with the same position at downstream of a single jet, and maintaining a high-pressure area of a single jet at the upstream of jets compared with the upstream area. However, the pressure reduction rate is lower in the transonic regime and the effectiveness of the angle of attack is greater than the subsonic and supersonic flows. Finally, a comparison with numerical result is accomplished.

Spectral analysis of jet turbulence and radiated sound

Informed by LES data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic, and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. We demonstrate that two distinct mechanisms, which can be distinguished by their characteristic frequency scaling and spatial support, lead to the formation of wavepackets—coherent structures that are known for their acoustic importance in the aft-angle radiation of high subsonic and supersonic jets. We compare these characteristics to acoustic source features extracted from hologram sound pressure measurements in a recent publication. The evidence strongly suggests that both mechanisms are active in full-scale jets and comprise the experimentally educed sources of sound.

Trapping Low-mass Planets at the Inner Edge of the Protostellar Disk

Abstract The formation of multiple close-in low-mass exoplanets is still a mystery. The challenge is to build a system wherein the outermost planet is beyond 0.2 au from the star. Here, we investigate how the prescription for type I planet migration affects the ability to trap multiple planets in a resonant chain near the inner edge of the protostellar disk. A sharp edge modeled as a hyperbolic tangent function coupled with supersonic corrections to the classical type I migration torques results in the innermost planets being pushed inside the cavity through resonant interaction with farther planets because migration is starward at slightly supersonic eccentricities. Planets below a few Earth masses are generally trapped in a resonant chain with the outermost planet near the disk edge, but long-term stability is not guaranteed. For more massive planets the migration is so fast that the eccentricity of the innermost resonant pair is excited to highly supersonic levels due to decreased damping on the innermost planet as it is pushed inside the cavity; collisions frequently occur, and the system consists of one or two intermediate-mass planets residing closer to the star than the disk’s inner edge. We found a neat pileup of resonant planets outside the disk edge only if the corotation torque does not rapidly diminish at high eccentricity. We call for detailed studies on planet migration near the disk’s inner edge, which is still uncertain, and for an improved understanding of eccentricity damping and disk torques in the supersonic regime.

Wake effects of a stationary charged grain in streaming magnetized ions.

A systematic numerical study of wake potential and ion density distribution of a single grain in flowing ions under the influence of a magnetic field applied along the flow is presented. A strong magnetic field introduces ion focus depletion behind grains, facilitating the entrance of electrons far in the downstream towards the grain. It is shown that the magnetic field suppresses the amplitude of the wake potential and modifies the ion density distribution substantially. The wake peak potential and position characteristics and density distribution of plasma constituents in the presence of a magnetic field and charge-exchange collisions for the subsonic, sonic, and supersonic regime are also delineated. In the subsonic regime, simulations demonstrate the accumulation of ions near the dust grain in the transverse direction, while complete suppression of oscillations in the transverse direction takes place for the sonic and supersonic regime.

Conceptual Design of a Reusable Unmanned Space Vehicle Using Multidisciplinary Optimization

In this paper, a conceptual design for a reusable unmanned space vehicle was studied with multiple objective functions. To achieve this goal, a multi-objective genetic algorithm was used, and the performance of the space vehicle was evaluated based on weight, propulsion, aerothermodynamics, and trajectory analysis. Minimization of weight and landing speed and maximization of the highest CL in the supersonic flight regime were selected as the objective functions. The maximum limits in the dynamic pressure and the heat flux were applied as constraints. All objective functions are in trade-off relationships with each other. The geometry that produced the smallest weight had a very small wing size. Also, the vehicle that had the maximum CL in the supersonic flight regime had a closer angle between the flow and the lower surface of the wing, which showed the highest CL on the flat surface. The vehicle design with the lowest landing speed had the largest wing, which generated sufficient lift.

Experimental study of the noise radiated by an air flow discharge through diaphragms and perforated plates

An experimental analysis of the noise radiated by a high pressure flow discharge through diaphragms and perforated plates is carried out for a large range of subsonic and supersonic operating conditions (nozzle pressure ratio (NPR) from 1 to 3.6). A parametric study of the geometrical parameters is also achieved to characterize their influence onto the acoustic radiation and ways to reduce it. This reaches from single diaphragms to multi-perforated plates with variable hole diameters and arrangements that are placed at the exit of a duct. Different acoustic behaviors are observed: in all cases the far-field acoustic radiation is dominated by a broadband contribution associated with the turbulent mixing in shear layers. In the diaphragm cases, this broadband noise has similar characteristics as the mixing noise of classical unheated jets while in the multi-perforated plates cases, it is composed of two distinct humps associated with different parts of the jets development. For supersonic regimes, in addition to this broadband radiation, shock associated noise (screech and broadband shock associated noise) appears for all diaphragm cases and for the perforated plate with the closest holes. Finally for the smallest NPR, a high frequency tonal noise has been observed in most of the multi-perforated cases and for the smallest diaphragm. Different regimes of this radiation have also been observed with a possible amplitude modulation of the dominant tone. This radiation may be attributed to vortex shedding due to the sharp section reduction that would trigger a flow resonance between the small ducts of the holes and their sharp edges.

X-ray binaries with neutron stars at different accretion stages

Abstract. Different accretion regimes onto magnetized NSs in HMXBs are considered: wind-fed supersonic (Bondi) regime at high accretion rates <math/> g s-1, subsonic settling regime at lower <math/> and supercritical disc accretion during Roche lobe overflow. In wind-fed stage, NSs in HMXBs reach equilibrium spin periods P* proportional to binary orbital period Pb. At supercritical accretion stage, the system may appear as a pulsating ULX. Population synthesis of Galactic HMXBs using standard assumptions on the binary evolution and NS formation is presented. Comparison of the model P* – Pb (the Corbet diagram), P* – Lx and Pb – Lx distributions with those for the observed HMXBs (including Be X-ray binaries) and pulsating ULXs suggests the importance of the reduction of P* in non-circular orbits, explaining the location of Be X-ray binaries in the model Corbet diagram, and the universal parameters of pulsating ULXs depending only on the NS magnetic fields.

The resonant drag instability (RDI): acoustic modes

Recently, Squire & Hopkins (2017) showed any coupled dust-gas mixture is subject to a class of linear 'resonant drag instabilities' (RDI). These can drive large dust-to-gas ratio fluctuations even at arbitrarily small dust-to-gas mass ratios. Here, we identify and study both resonant and new non-resonant instabilities, in the simple case where the gas satisfies neutral hydrodynamics and supports acoustic waves ($\omega^{2}=c_{s}^{2}\,k^{2}$). The gas and dust are coupled via an arbitrary drag law and subject to external accelerations (e.g. gravity, radiation pressure). If there is any dust drift velocity, the system is unstable. The instabilities exist for {\em all} dust-to-gas ratios $\mu$ and their growth rates depend only weakly on $\mu$ around resonance, as $\sim\mu^{1/3}$ or $\sim \mu^{1/2}$ (depending on wavenumber). The behavior changes depending on whether the drift velocity is larger or smaller than the sound speed $c_{s}$. In the supersonic regime a 'resonant' instability appears with growth rate increasing without limit with wavenumber, even for vanishingly small $\mu$ and values of the coupling strength ('stopping time'). In the subsonic regime non-resonant instabilities always exist, but their growth rates no longer increase indefinitely towards small wavelengths. The dimensional scalings and qualitative behavior of the instability do not depend sensitively on the drag law or equation-of-state of the gas. The instabilities directly drive exponentially growing dust-to-gas-ratio fluctuations, which can be large even when the modes are otherwise weak. We discuss physical implications for cool-star winds, AGN-driven winds and torii, and starburst winds: the instabilities alter the character of these outflows and could drive clumping and/or turbulence in the dust and gas.

Nonlinear plasma waves in an electron gas

The nature of traveling wave solutions to equations of hydrodynamics of a 3D electron gas with parabolic dispersion law depends on whether the motion is subsonic or supersonic. Solitons representing localized depressions of the electrostatic potential and electron density are predicted to exist in the subsonic regime: at rest the solitons are dark while in motion they are grey. Two types of periodic waves are found in the supersonic regime: (i) smooth waves whose small amplitude limit is described by harmonic theory, and (ii) waves with sharp troughs and smooth crests of the potential with the electrons accumulating in the troughs.

A Priori Tests of RANS Models for Turbulent Channel Flows of a Dense Gas

Dense gas effects, encountered in many engineering applications, lead to unconventional variations of the thermodynamic and transport properties in the supersonic flow regime, which in turn are responsible for considerable modifications of turbulent flow behavior with respect to perfect gases. The most striking differences for wall-bounded turbulence are the decoupling of dynamic and thermal effects for gases with high specific heats, the liquid-like behavior of the viscosity and thermal conductivity, which tend to decrease away from the wall, and the increase of density fluctuations in the near wall region. The present work represents a first attempt of quantifying the influence of such dense gas effects on modeling assumptions employed for the closure of the Reynolds-averaged Navier–Stokes equations, with focus on the eddy viscosity and turbulent Prandtl number models. For that purpose, we use recent direct numerical simulation results for supersonic turbulent channel flows of PP11 (a heavy fluorocarbon representative of dense gases) at various bulk Mach and Reynolds numbers to carry out a priori tests of the validity of some currently-used models for the turbulent stresses and heat flux. More specifically, we examine the behavior of the modeled eddy viscosity for some low-Reynolds variants of the $k-\varepsilon $ model and compare the results with those found for a perfect gas at similar conditions. We also investigate the behavior of the turbulent Prandtl number in dense gas flow and compare the results with the predictions of two well-established turbulent Prandtl number models.

Comparative Flow Field Analysis of Boundary Layer Diverter Intake and Diverterless Supersonic Intake Configuration

In this paper comparative flow field analysis of two intake configuration i.e. Boundary Layer Diverter Intake and Diverterless Supersonic Intake is carried out based on dimensionless parameters under various flow conditions. Numerical analysis of aircraft intake is a complex phenomenon which involves both external and internal flow analysis. In this research, both external and internal flow characteristics of intake duct are analyzed in detail. A comprehensive mesh scheme is devised and implemented to accurately capture the flow behavior in external surrounding of intake duct and flow passing through the intake duct. The analysis is carried out at different flow conditions to analyze the flow behavior in subsonic and supersonic regimes. Engine design mass flow rate is used for accurate intake analysis and results are validated with available literature. Boundary layer diversion and pressure recovery are examined for each intake configuration and comparative analysis based on pressure recovery is carried out subsequently. The analysis reveals that at subsonic and transonic regimes, Boundary Layer Diverter intake is much more effective than Diverter less Supersonic Intake, however, in supersonic regime Diverter less Supersonic Intake is found be to more effective. The research can further help in modifying/ improving the design of an existing intake configuration for enhanced intake efficiency.

A stabilized Powell–Sabin finite-element method for the 2D Euler equations in supersonic regime

In this paper a Powell–Sabin finite-element (PS-FEM) scheme is presented for the solution of the 2D Euler equations in supersonic regime. The spatial discretization is based on PS splines, that are piecewise quadratic polynomials with a global C1 continuity, defined on conforming triangulations.Some geometrical issues related to the practical construction of the PS elements are discussed, in particular, the generation of the control triangles and the imposition of the boundary conditions. A stabilized formulation is considered, and a novel shock-capturing technique in the context of continuous finite-elements is proposed to reduce oscillations around the discontinuity, and compared with the classical technique proposed by Tezduyar and Senga (2006). The code is verified using manufactured solutions and validated using two challenging numerical examples, which allows to evaluate the performance of the PS discretization in capturing the shocks.