Decrease In Mach Number Research Articles

Investigation of transonic flows through an idealized ORC turbine vane using Delayed Detached Eddy simulations

An idealized transonic blade configuration is studied using Delayed Detached Eddy Simulations (DDES), with focus on the loss mechanisms associated with the base pressure and turbulent wake development. The working fluid is Novec649, which is commonly used in low temperature Organic Rankine Cycle (ORC) power plants. Due to the molecular complexity of the fluid, a lower pressure ratio and exit Mach number are achieved compared to an air flow through the same geometry, a phenomenon that becomes more pronounced when considering thermodynamic operating conditions that lead to stronger non-ideal gas behavior, and which is well captured by models of standard use in ORC design and analysis, such as Reynolds-Averaged Navier–Stokes (RANS) models. Overall, as the fluid isentropic exponent and the exit Mach number decrease, the losses tend to increase. When performing a breakdown of the losses, the wake region provides the dominant contribution. Unlike RANS models, the DDES resolves the largest turbulent scales in the wake region, allowing fine-detail analysis of the unsteady wake dynamics, namely vortex shedding, and its influence on the loss coefficients. In the low supersonic Mach number range considered (M2∼1–2), the vortex shedding exhibits a flapping motion in the reattachment region behind the trailing edge. The Strouhal number, classically formed with the diameter of the trailing edge, is found to increase with increasing outlet Mach number. However, when introducing a new scaling based on the neck width of the reattachment region, directly related to the shape of the recirculation bubble and the associated reattachment shocks, the Strouhal number collapses to a relatively constant value of about 0.3 in all cases. DDES also shows that, due to the large heat capacity of Novec649, temperature fluctuations in the wake are greatly reduced, leading to the suppression of the so-called energy separation phenomenon occurring in air flows. While RANS simulations capture satisfactorily the main features and global quantities of the flow, they fail in describing the flow around the trailing edge. This results in inaccurate estimates of the back pressure, which ultimately leads to an underestimation of the losses by about 20%. Unsteady RANS simulations can predict the wake unsteadiness, but do not capture the couplings between large coherent structures, the recirculation, and the shocks, also resulting in inaccurate performance predictions. Thus, the present result showcase the importance of using advanced scale-resolving simulations for improved analysis and design of ORC turbines.

Shock waves characteristics and losses estimation of non-equilibrium condensation flow in nozzle and steam turbine cascade

The investigation of transonic non-equilibrium condensation is paramount due to its profound influence on the shock patterns and the distribution of losses. This study numerically investigates the shock wave morphology, evolution, and quantitative loss calculation under the influence of non-equilibrium condensation within the Moses-Stein nozzle and Dykas cascade. The results indicate that the vapor near the nozzle wall undergoes phase transition first and forms “X-shaped” condensation shock, which impervious to back pressure variations. Conversely, the “λ-shaped” aerodynamic shock moves towards the throat with increasing back pressure, triggering boundary layer separation. The entropy generation of “λ-shocks” accounts for over 98% and represents the primary source of shock losses. Strong pressure side shock induces shock wave-boundary layer interactions with the blade suction wall, resulting in reflected shocks. However, the latent heat released by non-equilibrium condensation mitigates this effect, increasing the total pressure loss coefficient by 0.188. The decrease in Mach number under high back pressure causes a notable increase in the trailing edge shock angle, with the wave foot shifting upstream. Notably, the proportion of shock losses attributed to the suction side of trailing edge exceeds 80%, significantly surpassing other regions, which progressively increases with rising back pressure. Therefore, it is crucial for cascade optimization. The findings can provide references for the optimization design of low-pressure steam turbine blade profiles. The results can serve as a guide for optimizing the blade profiles of low-pressure steam turbine.

Effect of the arrangement of the injectors on the flow quantities in water injection into the hot supersonic crossflow inside the cylinder

In this study, the effect of different arrangements of injectors on the injection of liquid water into the hot supersonic crossflow of cylindrical geometry on the performance and the rate of evaporation has been studied using a numerical method. The crossflow has a Mach of about 2 and a total temperature of 800[Formula: see text]K. At first, the penetration height and droplets produced by atomization in the supersonic flow are validated using the Lagrangian technique, and the results have been compared with the experiments. The usage of heat transfer equations and the evaporation model for the spray evaporation of droplets in the hot flow is also performed in the validation process, and the results are compared with the experimental results. Then, the injection into the examined geometry with four, six and eight injectors in three different arrangements was evaluated. The results indicate that employing an arrangement of eight injectors leads to the most significant reduction in total temperature, with average total temperatures decreasing to below 550[Formula: see text]K. The results demonstrate a 40% decrease in total pressure, with a decrease in Mach number to about 1 at the end of the cylinder. Additionally, the evaporation rate shows higher evaporation of water in the eight-injector arrangement compared to other arrangements.

Numerical solution of steady nonlinear differential equations for compressible flow through a spinning convergent divergent nozzle

Many projectiles tend to spin about their longitudinal axis while progressing in the forward direction. It helps in providing stability and a reference direction for guidance during their run. Many different projectiles employ a supersonic convergent-divergent nozzle to produce thrust for their forward motion; hence, the nozzle and overall whole propulsion system tend to spin about its axis of rotation. The main aim of this study is to observe the effect of spin on the nozzle. In this research, a converging bell-shaped diverging nozzle is numerically designed using a method of characteristics (MOC) for exit Mach number 3.21. Viscous simulations are performed for both two- and three-dimensional cases. The analysis is then performed with nozzle spinning about its axis of symmetry with a constant angular velocity of 10 revolutions per second. The analysis is repeated for the value of constant angular velocities to be 15 and 20 revolutions per second, and the behavior of flow with increasing angular velocity is examined. It has been observed that the exit Mach number and velocity decrease due to the radial protrusion of the boundary layer, and it has a negative impact on the performance of the nozzle. Moreover, the decrease of exit Mach number is in direct relation to increasing angular velocity.

Study of Two-Fluid Effects in Weakly Ionized Plasma Under Electromagnetic Fields

The multifluid effects caused by the relative motion and interaction between plasma components have a significant effect on electromagnetohydrodynamic wave propagation and the related mass and energy transport of flows. In this work, the charged particle (ion and electron)–neutral two-fluid model is analyzed and employed to study the two-fluid effects (e.g., velocity drift and thermodynamic nonequilibrium between plasma components) of the weakly ionized plasma flows under the electromagnetic fields. In a hypersonic E×B crossed-field configuration acceleration problem, the increased electromagnetic field strength significantly enhances the two-fluid effects. When the load factor equals 3, which measures the strength of the electrode voltage and induced electromotive force, the relative velocity difference between the charged particles and neutrals can reach 28%. The influences of two-fluid effects appreciably increase with the Mach number and Knudsen number but decrease with the degree of ionization. This suggests that, as the vehicle speed and altitude increase, the two-fluid effects become more significant.

Characterization of internal discharge shock waves of gas‐insulated switchgears using shadowgraphy

AbstractThe gas‐insulated switchgear (GIS) is a vital component of a power system, and understanding the shock wave characteristics of its internal discharge is crucial to ensure the safe and stable operation of the entire system. In this study, a high‐speed shadowing technique is employed to obtain the shadowgraphs of a typical flow‐field evolution of sulfur hexafluoride (SF6) gas following the breakdown of a pin–plate gap inside a GIS. Experimental data were used to derive parameters, including the Mach number, propagation speed, distance of the discharge shock wave, and the temperature, pressure, density, and velocity of the SF6 gas after wave generation. With a 0.2‐mm discharge gap and 0.4‐MPa pressure, the discharge generates a spherical shock wave, centred at the contact between the discharge channel and electrodes, that propagates in all directions. The shock wave gradually weakens after 20 μs, propagating at near‐sonic speed, and its Mach number decreases from 2.92 to 1.15; similarly, its post‐wave parameters sharply decrease during the first 20 μs. Additionally, a significant reflection occurs when the shock wave propagates to the metal wall. The authors’ findings provide a valuable reference for detecting and diagnosing the internal discharge in GISs.

Computational study of lateral jet interaction in hypersonic thermochemical non-equilibrium flows using nonlinear coupled constitutive relations

The present study reports the numerical analyses of lateral jet interaction around a Terminal High Altitude Area Defense-type (THAAD-type) model in hypersonic rarefied flows, with the real gas effect incorporated. The computation approach employed is the recently developed thermochemical non-equilibrium nonlinear coupled constitutive relations (NCCR) model. Regarding the simulation conditions, the flight velocity and height are set to 20 Ma and 80 km, respectively. To disclose the flow mechanism of lateral jet interaction, the complex flowfield characteristics and surface pressure distributions are discussed at length. Additionally, the research explores the impact of two key factors, namely, the jet pressure ratio and the jet Mach number, on the control performance of an in-flight vehicle's reaction control system (RCS). The results demonstrate that the complicated flowfield structures in lateral jet interaction are successfully reproduced by the NCCR model. With an increase in either the jet pressure ratio or the jet Mach number, the force and moment amplification factors decrease, while the absolute value of the normal force coefficient increases. Notably, it is found that the rarefied gas effect captured by the NCCR model against the Navier–Stokes–Fourier solution affects the lateral jet interaction flowfield, e.g., weakening the compressibility of the barrel shock and the expansibility of the Prandtl–Meyer expansion fan, as well as strengthening the jet wraparound effect. Importantly, the rarefied gas effect also exerts a prominent influence on the performance of RCS, with the degree of influence diminishing as the jet Mach number or the jet pressure ratio increases.

Study on the flow field of a kerosene-fueled integrated inlet-combustor-nozzle oblique detonation engine

In this study, a large-scale kerosene-fueled oblique detonation engine with a design point of Mach 10 is proposed. The flow combustion characteristics and the propulsive performance considering the wall viscous drag of the detonation engine are investigated using numerical simulation methods with a detailed combustion mechanism. The accuracy of the numerical results is verified by comparing it with the detonation wave pole curve of kerosene fuel. The result demonstrates that the combined injection method consisting of wall and center-strut injectors can meet the requirements of fuel mixing in the oblique detonation engine and a stabilized oblique detonation wave is successfully formed in the combustor. The decrease in the fuel equivalent ratio leads to an increase in the non-uniformity of the temperature distribution behind the detonation wave and the decrease in the wave angle. The advantage of the oblique detonation wave in hypersonic propulsion is its easy adjustment and can achieve flight over a wide-speed range. The combustion heat release behind the wave is closer to the upper part of the wave surface as the incoming Mach number decreases. The oblique detonation engine proposed in this study can still generate stable net specific impulse at non-design point flow Mach numbers. The net specific impulse can reach 715 s at a non-design point speed of Mach 8. It proves the feasibility of wide-speed range flight applications of oblique detonation engines.

Highly structured turbulence in high-mass star formation: An evolved infrared-dark cloud G35.20-0.74 N

Context. Massive stars are generally believed to form in environments characterized by supersonic turbulence. However, recent observations challenge this traditional view. High-spatial- and spectral-resolution observations of the Orion Molecular Cloud (OMC, the closest massive star formation region) and an infrared-dark cloud (IRDC) G35.39 (a typical distant massive star formation region) show a resolution-dependent turbulence, and that high-mass stars are forming exclusively in subsonic to transonic cores in those clouds. These studies demand a re-evaluation of the role of turbulence in massive star formation. Aims. We aim to study the turbulence in a typical massive-star-forming region G35.20-0.74 N (G35.20 in short) with sufficient spatial resolution to resolve the thermal Jeans length, and sufficient spectral resolution to resolve the thermal line width. Methods. We use the Atacama Large Millimeter/submillimeter Array (ALMA) dust continuum emission to resolve fragmentation, the Karl G. Jansky Very Large Array (JVLA) 1.2 cm continuum to trace ionized gas, and JVLA NH3 (1,1) to (7,7) inversion transition lines to trace line width, temperature, and dynamics. We fit those lines and remove line broadening due to channel width, thermal pressure, and velocity gradient to obtain a clean map of intrinsic turbulence. Results. We find that (1) the turbulence in G35.20 is overall supersonic, with mean and median Mach numbers 3.7 and 2.8, respectively. (2) Mach number decreases from 6–7 at a 0.1 pc scale to less than 3 toward the central cores at a 0.01 pc scale. (3) The central ALMA cores appear to be decoupled from the host filament, which is made evident by an opposite velocity gradient and significantly reduced turbulence. Because of intense star-formation activity in G35.20 (as compared to the relatively young and quiescent IRDC G35.39), the supersonic turbulence is likely replenished by protostellar outflows. G35.20 is therefore representative of an evolved form of IRDC G35.39. More observations of a sample of IRDCs are highly demanded in order to further investigate the role of turbulence in the initial conditions required for massive-star formation.

INVESTIGATING THE EFFECTS OF OUTLET PRESSURE FROM STEAM TURBINE BLADE ON WETNESS AND ENTROPY GENERATION WITH CONSIDERATION OF NON-EQUILIBRIUM CONDENSATION

Steam turbines are one of the main elements of a power plant that steam thermal energy turns into rotational energy. Due to condenser pressure changes, the pressure at the end of steam turbines changes. In this study, the Bakhtar blade is used, and the effects of changes in the pressure outlet of the blade on the flow behavior are investigated. In this research, 62.56 kPa, 72.56 kPa, 82.56 kPa, 92.56 kPa, and 102.56 kPa are considered for the pressure at the end of the steam turbine blade. First, the CFD solution results are compared with the laboratory data of the Bakhtar turbine's blade. Then, the effect of outlet pressure is examined. Regarding obtained results, the proposed numerical solution can properly predict the experimental data. By the growth of the outlet pressure of the steam turbine blade, the Mach number decreases and the pressure and temperature distribution increase. As the pressure increases from 62.56 kPa to 102.56 kPa, the average Mach number decreases by 29.8% at the outlet, and the average temperature at the outlet increases by 3.9%. The nucleation rate does not have a noticeable change. However, liquid mass fraction decreases with the increase in outlet pressure. By increasing the pressure from 62.56 kPa to 102.56 kPa, the average wetness decreases by 39.5% at the outlet. This study shows that condenser pressure changes affect the liquid phase produced in the end blade of the steam turbine.

Research on the influence of supersonic phenomena on the gas film flow field of micron-groove-orifice aerostatic journal bearings under high gas supply pressure

To solve the problem of performance degradation caused by supersonic phenomena under high gas supply pressures in orifice-compensated aerostatic journal bearings (OCAJBs), a double-row gas supply micron-groove-orifice aerostatic journal bearing (MGOAJB) is designed, and the SST k- ω turbulence model is used to analyze the influences of the supersonic phenomena on the gas film flow field under different gas supply pressures, gas film thicknesses and orifice diameters. Compared with traditional OCAJBs, under high gas supply pressure, supersonic phenomena occur near the gas film inlet in both the MGOAJB and the OCAJB. The Mach number, maximum pressure, temperature and Reynolds number of the OCAJB are higher than those of the MGOAJB, but the MGOAJB has a more stable gas film pressure due to pressure equalization. As the gas film thickness of the MGOAJB increases, the Mach number, Reynolds number and temperature near the gas film inlet increase, but the pressure decreases, the recovery of the pressure and temperature becomes more obvious when the gas velocity drops to a subsonic speed. With increases in the MGOAJB orifice diameter, the pressure, temperature and Reynolds number increase, the Mach number decreases, and the recovery of the pressure and gas temperature becomes more obvious.

3-D global hybrid simulations of magnetospheric response to foreshock processes

It has been suggested that ion foreshock waves originating in the solar wind upstream of the quasi-parallel (Q-||) shock can impact the planetary magnetosphere leading to standing shear Alfvén waves, i.e., the field line resonances (FLRs). In this paper, we carry out simulations of interaction between the solar wind and terrestrial magnetosphere under radial interplanetary magnetic field conditions by using a 3-D global hybrid model, and show the properties of self-consistently generated field line resonances through direct mode conversion in magnetospheric response to the foreshock disturbances for the first time. The simulation results show that the foreshock disturbances from the Q-|| shock can excite magnetospheric ultralow-frequency waves, among which the toroidal Alfvén waves are examined. It is found that the foreshock wave spectrum covers a wide frequency range and matches the band of FLR harmonics after excluding the Doppler shift effects. The fundamental harmonic of field line resonances dominates and has the strongest wave power, and the higher the harmonic order, the weaker the corresponding wave power. The nodes and anti-nodes of the odd and even harmonics in the equatorial plane are also presented. In addition, as the local Alfvén speed increases earthward, the corresponding frequency of each harmonic increases. The field-aligned current in the cusp region indicative of the possibly observable aurora is found to be a result of magnetopause perturbation which is caused by the foreshock disturbances, and a global view substantiating this scenario is given. Finally, it is found that when the solar wind Mach number decreases, the strength of both field line resonance and field-aligned current decreases accordingly.

Comparative studies of shock-wave boundary-layer interactions in Earth and Mars atmospheres

Investigations of ramp-induced shock-wave boundary-layer interaction have been carried out for real gas flows of air and carbon dioxide through hypersonic laminar flow simulations corresponding to Earth and Mars atmospheres. An in-house-developed solver, which accounts for the real gas effects, has been employed for these studies. Effects of various parameters like wall temperature, freestream stagnation enthalpy, freestream Mach number, and blunt leading edge are explored on the intensity of shock-wave boundary-layer interaction (SWBLI). In either case, an increase in separation length is observed with an increase in wall temperature and a decrease in Mach number as well as freestream stagnation enthalpy. Here, the intensity of alteration is always noted to have a higher percentage for the Mars gas model. Further, separation length is found to be almost equal for the same wall to total temperature ratio in both of the flow mediums. The present study also affirms the fact that the leading edge bluntness can be used as a tool to reduce the size of the separation region in these planetary atmospheres. Revised correlations have been proposed for hypersonic Earth atmospheric flow with real gas effects to predict the extent of upstream influence and separation bubble size. The outcomes of simulations have also helped to device new correlations for these flow features of SWBLI for Mars atmospheric conditions. In all, the need for consideration of real gas effects and an exclusive real gas flow solver for the Mars atmosphere are the prominent recommendations of current studies.

Design and operational assessment of a low-boom low-drag supersonic business jet

There has been a worldwide interest to develop a supersonic business jet (SSBJ) for a minimum range of 4000 nm with low sonic boom intensity and high fuel efficiency. An SSBJ design model is developed in the GENUS aircraft conceptual design environment. With the design model, a low-boom low-drag SSBJ concept is designed and optimized. This article studies the design concept for its operational performances. The sustained supersonic cruise flight is studied to find out the fuel-efficient Mach number and altitude combinations. The combined supersonic and subsonic cruise flight scenarios are studied to evaluate the feasibility of boom-free flight routes. The one-stop supersonic cruise flight scenario is studied to compare the fuel consumption and time advantage over subsonic airliners. The off-design sonic boom intensity is studied to explore the operational space assuming there would be a sonic boom intensity limit in the future. Through the studies, it is revealed that there is a corresponding most fuel-efficient operating altitude for a specific cruise Mach number. To operate the aircraft near the cutoff Mach number leads to both increases in the fuel consumption (6.3%–8.1%) and the mission time (11.7%–13.1%). The business-class supersonic transport (231 g/PAX/km) consumes nearly three times fuel as the economic-class supersonic transport (77 g/PAX/km), which is still far more than the economic-class subsonic transport (20 g/PAX/km). Off-design sonic boom intensity studies reveal different trends against the common understanding: the sonic boom intensity does not necessarily decrease as the altitude increases; the sonic boom intensity does not necessarily decrease as the Mach number decreases.

Efficient Highly Subsonic Turbulent Dynamo and Growth of Primordial Magnetic Fields.

We present the first study on the amplification of magnetic fields by the turbulent dynamo in the highly subsonic regime, with Mach numbers ranging from 10^{-3} to 0.4. We find that for the lower Mach numbers the saturation efficiency of the dynamo (E_{mag}/E_{kin})_{sat} increases as the Mach number decreases. Even in the case when injection of energy is purely through longitudinal forcing modes, (E_{mag}/E_{kin})_{sat}≳10^{-2} at a Mach number of 10^{-3}. We apply our results to magnetic field amplification in the early Universe and predict that a turbulent dynamo can amplify primordial magnetic fields to ≳10^{-16} G on scales up to 0.1pc and ≳10^{-13} G on scales up to 100pc. This produces fields compatible with lower limits of the intergalactic magnetic field inferred from blazar γ-ray observations.

Research on the Adjustable Guide Vane in a Compressor Sector Cascade

In order to simulate the inlet flow angle and Mach number of the tested blade, a row of guide vanes is set before the tested blade during the sector cascade experiment. In this paper, a kind of adjustable guide vane (AGV) is designed, which can rotate continuously and change the inlet flow angle of the tested blade conveniently and quickly. The variation rule of the clearance between the AGV and the end wall is introduced. The influence of the clearance on the flow field structure under different Mach number and incidence angle is studied by numerical and experimental methods. It is found that the clearance of the leading edge is small at the top and the root, and the leakage vortex is mixed with the passage vortex. The interaction between the leakage vortex and the passage vortex in the trailing edge results in the decrease of Mach number and the increase of flow angle at the AGV outlet. The clearance has little effect on the span of 20% - 80%. At the same incidence angle condition, with the increase of Mach number, the influence range of leakage vortex is expanded, and the variation magnitude of flow angle and Mach number at the top and root position is increased; At the same Mach number condition, with the decrease of the AGV rotation angle from positive to negative, the top clearance is increased gradually, and the root clearance is decreased gradually. The separation range at the top is expanded gradually, which results in the variation magnitude of flow angle and Mach number is increased, but the effect is opposite at the root of the AGV.

Infrared signature of NEPE, HTPB rocket plume under varying flight conditions and motor size

In this study, radiation signatures of rocket plumes based on HTPB and NEPE propellants are simulated under varying altitudes, flight Mach numbers, and motor size. The flow field of plume is calculated by computational fluid dynamics, and the infrared signature is predicted using a Ludwig model. To verify the numerical method, experiments were conducted using small rocket motors and radiometric FTIR. The acceptable agreement between numerical calculation and the experiment was obtained in 2–5 μm wavelength region. The total radiance decreases with increasing altitude whether afterburning exists or not. A decreasing rate in the radiance of the plume with strong afterburning is larger than that of the plume with weak afterburning. The change in total intensity according to altitude depends on the afterburning and is directly affected by the radiating area. As the flight Mach number increases, total radiance, total intensity, and radiating area decrease. The motor size makes radiation intensity increase exponentially; exponent value is from 2.6 to 2.7. As the motor size increases, the effect of altitude increases, while the effect of flight Mach number decreases.

Asymmetries in the Earth's dayside magnetosheath: results from global hybrid-Vlasov simulations

Abstract. Bounded by the bow shock and the magnetopause, the magnetosheath forms the interface between solar wind and magnetospheric plasmas and regulates solar wind–magnetosphere coupling. Previous works have revealed pronounced dawn–dusk asymmetries in the magnetosheath properties. The dependence of these asymmetries on the upstream parameters remains however largely unknown. One of the main sources of these asymmetries is the bow shock configuration, which is typically quasi-parallel on the dawn side and quasi-perpendicular on the dusk side of the terrestrial magnetosheath because of the Parker spiral orientation of the interplanetary magnetic field (IMF) at Earth. Most of these previous studies rely on collections of spacecraft measurements associated with a wide range of upstream conditions which are processed in order to obtain average values of the magnetosheath parameters. In this work, we use a different approach and quantify the magnetosheath asymmetries in global hybrid-Vlasov simulations performed with the Vlasiator model. We concentrate on three parameters: the magnetic field strength, the plasma density, and the flow velocity. We find that the Vlasiator model reproduces the polarity of the asymmetries accurately but that their level tends to be higher than in spacecraft measurements, probably because the magnetosheath parameters are obtained from a single set of upstream conditions in the simulation, making the asymmetries more prominent. A set of three runs with different upstream conditions allows us to investigate for the first time how the asymmetries change when the angle between the IMF and the Sun–Earth line is reduced and when the Alfvén Mach number decreases. We find that a more radial IMF results in a stronger magnetic field asymmetry and a larger variability of the magnetosheath density. In contrast, a lower Alfvén Mach number leads to a reduced magnetic field asymmetry and a decrease in the variability of the magnetosheath density, the latter likely due to weaker foreshock processes. Our results highlight the strong impact of the quasi-parallel shock and its associated foreshock on global magnetosheath properties, in particular on the magnetosheath density, which is extremely sensitive to transient quasi-parallel shock processes, even with the perfectly steady upstream conditions in our simulations. This could explain the large variability of the density asymmetry levels obtained from spacecraft measurements in previous studies.

Experiment and numerical investigation of flow control on a supersonic inlet diffuser

Design of a two-dimensional supersonic inlet was developed. Numerical simulation and wind tunnel experiment were carried out to investigate the aerodynamic performance and variable geometric rules of the inlet. The result indicates that the variable geometry scheme adopted solves the contradiction between starting performance at low Mach number and aerodynamic performance at high Mach number. Inlet works normally and stably over a wide speed range. Compared with the diffuser without suction, the performance of the diffuser with suction is higher. Total pressure recovery coefficient σe improves by 2%-3% while outlet Mach number decreases by about 0.03 under different inflow Mach numbers. During the process of shock train moving upstream, the propagation gradually transforms from up and down mode to left and right mode. Flow separation caused by the shock train is mainly concentrated on the sidewall in the upstream of the diffuser. Sidewall suction case is more effective to eliminates the low-energy flow and stabilize the terminal shock wave. As backpressure increases, shock train changes from weak λ-type to strong λ-type and finally to X-type near the suction slots.

The thermochemical non-equilibrium scale effects of the high enthalpy nozzle

The high enthalpy nozzle converts the high enthalpy stagnation gas into the hypervelocity free flow. The flow region of the high enthalpy nozzle consists of three parts: an equilibrium region upstream of the throat, a non-equilibrium region near the throat, and a frozen region downstream of the throat. Here we propose to consider the thermochemical non-equilibrium scale effects in the high enthalpy nozzle. By numerically solving axisymmetric compressible Navier-Stokes equations coupling with Park’s two-temperature model, the fully non-equilibrium solution is employed throughout the entire nozzle. Calculations are performed at different stagnation conditions with the different absolute scales and expansion ratio. The results of this study are twofold. Firstly, as the absolute scale and expansion ratio increase, the freezing position is delayed, and the flow approaches equilibrium. Secondly, the vibrational temperature and Mach number decrease with the increase in the nozzle scale and expansion ratio, while the speed of sound, static pressure, and translational temperature increase as the nozzle scale and expansion ratio increase.