Decrease In Mach Number Research Articles

Experimental research on collector effect on operating characteristics of high-speed free-jet wind tunnel

Collector is one of the key parts of the high-speed free-jet wind tunnel, which directly affects the performance of wind tunnel. In this paper, a small high-speed free-jet wind tunnel is used as the test platform to carry out the start-up and operation characteristics test of wind tunnel. Start-up pressure characteristics were obtained at various Mach number, and the influence of the collector throat heights and collector positions on start-up pressure and matching pressure was preliminarily studied. The results show that the high collector throat height can meet the requirements of wind tunnel start-up and pressure matching. The closer the collector is to the nozzle, the smaller the corresponding starting pressure and matching pressure. However, this trend weakens with the decrease of Mach number, which lays a foundation for the development of large high-speed free jet equipment.

Experimental Investigation of the Effects of Magnetic Mirrors on Plasma Transport in the Prototype Material Plasma Exposure Experiment

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory is developing a helicon radio frequency (RF) source for plasma production along with microwave electron heating and RF ion heating. Proto-MPEX has several magnetic mirrors that affect plasma transport. The magnetic field near the helicon source is ~ 0.05 T, and the peak magnetic field in Proto-MPEX is ~ 1.8 T, which results in a large magnetic well for particles sourced at the helicon transporting toward the target region. Keeping the helicon source field and the target field constant, experiments have been conducted by methodically changing the magnetic field, at a local axial location, within the source and the target. Plasma flow measurements using Mach probes have shown a decrease in the flow as a function of the magnetic mirror ratio. Plasma flows were further investigated with ion cyclotron resonant heating (ICH). Results with the addition of ICH measured upstream of the antenna have shown a decrease in Mach number as a function of mirror ratio when compared to helicon discharges. Such flow behavior demonstrated slowing down of the plasma due to the increased reverse plasma flow toward the helicon plasma source. However, in high magnetic fields, when the resonant magnetic field moved away from the ICH antenna, no effects on the plasma flow due to ICH were observed.

Investigating the effect of water nano-droplets injection into the convergent-divergent nozzle inlet on the wet steam flow using entropy generation analysis

In many industrial pieces of equipment, such as ejectors, thermo-compressors, supersonic separators, etc., in which the condensation phenomenon occurs spontaneously, steam enters the nozzle in a saturated condition. Liquid droplets are likely to be present in the saturated vapor. In the present paper, the effect of the existence of a number (9 cases) of liquid droplets (with a fixed size of 20 nm in all cases) on the saturation steam has been studied. The results demonstrate that with the increase in the number of droplets at the nozzle inlet; pressure, temperature, liquid mass fraction, mass-generated rate and entropy increase in the convergent part. However, the growth of droplets and Mach number decrease. Furthermore, due to steam condensation and latent heat transfers to steam, the degree of supercooling, the supersaturation ratio and the flow rate at the nozzle inlet are decreased, the intensity of condensation shock is reduced, and shock occurs with delays. With an increase in the number of droplets, condensation shock and the nucleation phenomenon will not occur. The amount of entropy production decreases with the surge in the number of droplets at first, and then begins to increase. The results demonstrate that in the presence of 3 × 10+14 droplets, compared to the absence of water droplets at the nozzle inlet, generated entropy, liquid mass fraction and the mass flow rate will decrease by 9.4%, 12.5%, and 1.7%, respectively.

THE EFFECT OF CONVERGENT-DIVERGENT NOZZLE PROFILE ON ITS PERFORMANCE

The paper presents the effect of convergent-divergent nozzles profile across specified inlet pressures values from (1.5 bar-4 bar), with constant back pressure of (1 bar). The flow of air through three convergent-divergent nozzles was studied theoretically. The flow was assumed to be one-dimensional, adiabatic and reversible (isentropic). The flow parameters like static pressure ratio and Mach number were analyzed. The flow parameters were obtained in term of area ratio along the nozzle. MATLAB code was built in order to find the Mach number along the nozzles, by using Newton-Raphson method. The shockwave position inside the nozzles was determined, using "analytic method". ANSYS fluent 18 was used to simulate the flow through the three nozzles. Two- dimensional, turbulent and viscous models were utilized to solve the governing equations. K-? model was used to model the turbulent effect. The results concluded that, reduction in inlet pressure can not affect the flow upstream the throat. Also the shockwave appearance can be noticed by a sudden rise in static pressure associated with a sharp decrease in Mach number. Shockwave moves toward the throat by reduction the inlet total pressure .By comparison the static pressure distribution along the three nozzles where can be deduced that the profile has an effect on the flow character i.e. (static pressure Mach no).The best performance among the nozzles is the performance of nozzle (N1), which (75%) of its length work as nozzle at the lowest inlet pressure of (1.5bar) while (44% and 60%) of the nozzles length for (N2 and N3) respectively work as the nozzle.

Effect of Thermal Barrier Coating and Gas Radiation on Film Cooling of a Corrugated Surface

In this work, a numerical study is conducted to investigate film cooling of a corrugated surface. A conjugate heat transfer analysis is carried out, accounting for the presence of thermal barrier coating (TBC) and gas radiation. The Mach number of mainstream flow is maintained at Ma = 0.6, while cold stream Mach number is varied from 0.3 to 0.58, and density ratio is kept 4. From this study, it is observed that the overall film cooling effectiveness increases by a value ranging from 0.10 to 0.15 with the use of TBC. The hot side metallic wall temperature increases in the range of 100–150 °C when the effect of gas radiation is considered. It is also found that the film cooling effectiveness decreases with decrease in the cold side Mach number.

Experimental research on the effect of shock wave on the evolution of high-pressure diesel spray

With the increase in the diesel injection pressure in modern diesel engines, the velocity of the diesel spray increases accordingly, and shock waves are induced when the spray is supersonic. To better understand the effect of shock waves on the spray development, the evolution of the high-pressure diesel spray and shock wave under different diesel injection pressures and ambient pressure has been investigated using the Schlieren imaging method. The results show that the shock wave affects the development of the spray and the mixing effect between the spray and surrounding air. The shock wave promotes development of the spray tip penetration and enhances the gas entrainment effect. However, the shock wave has an inhibitory effect on the spray development in the radial direction. In addition, the shock wave angle determines the range of influence on the ambient air, which affects atomization of the spray. The shock wave angle increases with the decrease in the spray front Mach number. An empirical correlation of the shock wave angle and spray front Mach number was proposed in this paper. The calculated results are in good agreement with the experimental data. In addition, a diagram of the shock wave generation and classification in a diesel engine is proposed.

The responses of the earth’s magnetopause and bow shock to the IMF Bz and the solar wind dynamic pressure: a parametric study using the AMR-CESE-MHD model

We have used the AMR-CESE-MHD model to investigate the influences of the IMF Bz and the upstream solar wind dynamic pressure (Dp) on Earth’s magnetopause and bow shock. Our results present that the earthward displacement of the magnetopause increases with the intensity of the IMF Bz. The increase of the northward IMF Bz also brings the magnetopause closer to the Earth even though with a small distance. Our simulation results show that the subsolar bow shock during the southward IMF is much closer to the Earth than during the northward IMF. As the intensity of IMF Bz increases (also the total field strength), the subsolar bow shock moves sunward as the solar wind magnetosonic Mach number decreases. The sunward movement of the subsolar bow shock during southward IMF are much smaller than that during northward IMF, which indicates that the decrease of solar wind magnetosonic Mach number hardly changes the subsolar bow shock location during southward IMF. Our simulations also show that the effects of upstream solar wind dynamic pressure (Dp) changes on both the subsolar magnetopause and bow shock locations are much more significant than those due to the IMF changes, which is consistent with previous studies. However, in our simulations the earthward displacement of the subsolar magnetopause during high solar wind Dp is greater than that predicted by the empirical models.

Longitudinal Aerodynamic Performance of the Apollo Entry Capsule near Transonic Speeds

A complex dynamic behavior exists in the flow structures surrounding blunt atmospheric entry capsules as they decelerate from supersonic to subsonic speeds during a lifting reentry. In the current study, unsteady simulations of the Apollo capsule undergoing pitch oscillations were carried out applying the DLR (German Aerospace Center) TAU code to predict the static and dynamic aerodynamic derivatives. Numerical results for static analysis show that the capsule, with its given center of gravity, is predicted to be statically stable both in the super- and subsonic regimes. The dynamic analysis was then performed, indicating that the capsule will turn dynamically unstable when the trim angle of attack is close to zero or if the freestream Mach number decreases. The unsteadiness of wake vortices and the influence of wake pressure on the moment coefficient appear to be the primary factors affecting the dynamic behavior. A time lag between the capsule oscillations and the moments acting on the backcone is shown to be the source of the observed dynamic instabilities.

A New Approach to Energy Integral for Investigation of Dust—Ion Acoustic (DIA) Waves in Multi-Component Plasmas with Quantum Effects in Inertia Less Electrons

Dust-ion acoustic waves are investigated in this model of plasma consisting of negatively charged dusts, cold ions and inertia less quantum effected electrons with the help of a typical energy integral. In this case, a new technique is applied formulating a differential equation to establish the energy integral in case of multi-component plasmas which is not possible in general. Dust-ion acoustic (DIA) compressive and rarefactive, supersonic and subsonic solitons of various amplitudes are established. The consideration of smaller order nonlinearity in support of the newly established quantum plasma model is observed to generate small amplitude solitons at the decrease of Mach number. The growths of soliton amplitudes and potential depths are found more sensitive to the density of quantum electrons. The small density ratio r(= 1 − f) with a little quantized electrons supplemented by the dust charges Zd and the in-deterministic new quantum parameter C2 are found responsible to finally support the generation of small amplitude solitons admissible for the model.

Analytical and Numerical Investigations of Wedge-Induced Oblique Detonation Waves at Low Inflow Mach Number

The wedge-induced oblique detonation wave (ODW) at low inflow Mach number is investigated via Rankine–Hugoniot analysis and numerical simulations. The results show that the Chapman–Jouguet oblique detonation wave (CJ ODW) plays a significant role in the structure of the ODW. And the influence of the CJ ODW is the reason why an attached ODW can propagate upstream. Both the analytical and numerical results show that the decrease of inflow Mach number and the increase of wedge angle are conducive to the upstream propagation of ODW. In the upstream propagation process, a Mach reflection wave configuration is always established on the wedge surface. For the upstream propagating ODW that cannot detach from the wedge surface by itself, it will stabilize at a point on the wedge surface with an induction region, which is a few times the length of the induction zone of an ideal Zeldovich–von Neumann–Döring (ZND) detonation. Benefiting from the short induction region, the stabilized upstream propagating ODW has extraordinary stability.

FULL PARTICLE ELECTROMAGNETIC SIMULATIONS OF ENTROPY GENERATION ACROSS A COLLISIONLESS SHOCK

Experimental data from Cluster have shown that entropy density can be generated across Earth's bow shock. These new observations are a starting point for a more sophisticated analysis that includes computer modeling of a collisionless shock using observed shock parameters as input. In this Letter, we present the first comparison between observations and particle-in-cell simulations of such entropy generation across a collisionless shock. The ion heating at the shock is dominated by the phase mixing of reflected and directly transmitted ions, which are separated from the incident ions. The electron heating is a nearly thermal process due to the conservation of their angular momentum. For both species, we calculate the entropy density across the shock, and obtain good consistency between observations and simulations on entropy generation across the shock. We also find that the entropy generation rate is reduced as the shock Mach number decreases.

Magnetic ramp scale at supercritical perpendicular collisionless shocks: Full particle electromagnetic simulations

Supercritical perpendicular collisionless shocks are known to exhibit foot, ramp, and overshoot structures. The shock ramp structure is in a smaller scale in contrast to other microstructures (foot and overshoot) within the shock front. One-dimensional full particle simulations of strictly perpendicular shocks over wide ranges of ion beta βi, Alfvén Mach number MA, and ion-to-electron mass ratio mi/me are presented to investigate the impact of plasma parameters on the shock ramp scale. Main results are (1) the ramp scale can be as small as several electron inertial length. (2) The simulations suggest that in a regime below the critical ion beta value, the shock front undergoes a periodic self-reformation and the shock ramp scale is time-varying. At higher ion beta values, the shock front self-reformation is smeared. At still higher ion beta value, the motion of reflected ions is quite diffuse so that they can lead to a quasi-steady shock ramp. Throughout the above three conditions, the shock ramp thickness increases with βi. (3) The increase (decrease) in Mach number and the decrease (increase) in the beta value have almost equivalent impact on the state (i.e., stationary or nonstationary) of the shock ramp. Both of front and ramp thicknesses are increased with MA.

Numerical study of unsteady starting characteristics of a hypersonic inlet

The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics (CFD) method. The full Navier–Stokes equations are solved with the assumption of viscous perfect gas model, and the shear-stress transport (SST) k–ω two-equation Reynolds averaged Navier–Stokes (RANS) model is used for turbulence modeling. Results indicate that during impulse starting, the flow field is divided into three zones with different aerodynamic parameters by primary shock and upstream-facing shock. The separation bubble on the shoulder of ramp undergoes a generating, growing, swallowing and disappearing process in sequence. But a separation bubble at the entrance of inlet exists until the freestream velocity is accelerated to the starting Mach number during self starting. The mass flux distribution of flow field is non-uniform because of the interaction between shock and boundary layer, so that the mass flow rate at throat is unsteady during impulse starting. The duration of impulse starting process increases almost linearly with the decrease of freestream Mach number but rises abruptly when the freestream Mach number approaches the starting Mach number. The accelerating performance of booster almost has no influence on the self starting ability of hypersonic inlet.

Effect of the Axial Spacing between Vanes and Blades on a Transonic Gas Turbine Performance and Blade Loading

Unsteady numerical simulations have been conducted to investigate the effect of axial spacing between the stator vanes and the rotor blades on the performance of a transonic, single-stage, high-pressure, axial turbine. Three cases were considered, the normal case, which is based on the geometry of a commercial jet engine and has an axial spacing at 50% blade span equal to 42% of the vane axial chord, as well as two other cases with axial spacings equal to 31 and 52% vane axial chords, respectively. Present interest has focused on the effect of axial gap size on the instantaneous and time-averaged flows as well as on the blade loading and the turbine performance. Decreasing the gap size reduced the pressure and increased the Mach number in the core flows in the gap region. However, the flows near the two endwalls did not follow monotonic trends with the gap size change; instead, the Mach numbers for both the small gap and the large gap cases were lower than that for the normal case. This Mach number decrease was attributed to increased turbulence due to the increased wake strength for the small gap case and an increased wake width for the large gap case. In all considered cases, large pressure fluctuations were observed in the front region of the blade suction side. These pressure fluctuations were strongest for the smaller spacing. The turbine efficiencies of the cases with the larger and smaller spacings were essentially the same, but both were lower than that of the normal case. The stator loss for the smaller spacing case was lower than the one for the larger spacing case, whereas the opposite was true for the rotor loss.

Momentum losses by charge exchange with neutral particles in H-mode discharges at JET

The effect of a neutral density background on the toroidal angular momentum and kinetic energy profiles has been investigated in JET. Under equivalent conditions but with increasing gas fuelling during the flat top phase, it has been observed that both the edge rotation and temperature decrease. The increase in electron density was not sufficient to compensate the rotation and temperature loss such that both energy and momentum confinement times are significantly reduced. The edge localized mode behaviour is observed to be significantly affected by the increased neutral influx. A simple 1.5D fluid model has been used to qualitative capture the neutral transport response within the plasma, followed by a forward model of the passive charge-exchange (CX) emission of carbon to obtain a corrected radial neutral density profile. It has been found that the neutral density is sharply attenuated over the edge region, with similar edge magnitudes in both the non-fuelled (Γ0/ne ∼ 1.2 m s−1) and maximum fuelled case (Γ0/ne ∼ 2.5 m s−1). Discharges with reversed-B operation exhibited even higher normalized neutral fluxes related to first orbit effects and increased wall interactions. Over the full neutral influx range, a decrease in pedestal thermal Mach number from 0.25 to 0.14 was observed. Increased neutral penetration up to the pedestal top (r/a ∼ 0.9) due to multiple CX interactions is obtained from the interpretive model. Under these multiple neutral–ion interactions, the impact on the CX loss of angular momentum is larger compared with the CX energy loss. The drag torque was seen to increase up to 10% of the total applied torque, while energy losses appeared to be smaller. The accuracy of this global approach method is unfortunately limited; however, the estimated momentum sink was found comparable to the torque required to explain the discrepancy between observed global energy and momentum confinement.

Flow characteristics of a cold helium arc‐jet plasma along open field lines

AbstractWe experimentally study plasma parameters including ion acoustic Mach number of expanding cold helium plasma jet with an electron temperature of less than 1 eV flowing along open field lines. It is experimentally found that the ion Mach number increases from 1 to 3, and that the plasma potential decreases by about 1 V. We discuss the experimental results based on a quasi one‐dimensional flow model in which the plasma is assumed to be quasi‐neutral and in a state of thermodynamic equilibrium. Our model describes the ion acceleration, the axial profiles of the potential drop, and the electron temperature/density. The model also shows that the helium ions are accelerated both by the electric field and by the increasing cross‐sectional area of the transonic flow. After the ion acceleration, the ion Mach number decreases and the electron temperature increases. These phenomena are discussed in terms of a shock wave. It is noted that the electron density decreases even in the shock wave. This is discussed in terms of rapid recombination because of the low electron temperature. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Electron acoustic solitary waves in unmagnetized two electron population dense plasmas

The electron acoustic solitary waves are studied in unmagnetized two population electron quantum plasmas. The quantum hydrodynamic model is employed with the Sagdeev potential approach to describe the arbitrary amplitude electron acoustic waves in a two electron population dense Fermi plasma. It is found that hot electron density hump structures are formed in the subsonic region in such type of quantum plasmas. The wave amplitude as well as the width of the soliton are increased with the increase of percentage presence of cold (thinly populated) electrons in a multicomponent quantum plasma. It is found that an increase in quantum diffraction parameter broadens the nonlinear structure. Furthermore, the amplitude of the nonlinear electron acoustic wave is found to increase with the decrease in Mach number. The numerical results are also presented to understand the formation of solitons in two electron population Fermi plasmas.

예조건화 오일러 방정식의 계산 오차 문제

예조건화 오일러 방정식의 수렴특성에 미치는 계산 오차의 영향을 해석하였다. 다양한 마하수의 원형 턱이 있는 이차원 관내 유동을 계산하였다. 마하수가 감소함에 따라 차분오차는 증가하는데, 에너지 방정식의 계산 오차는 다른 방정식의 계산 오차보다 빠르게 증가하는 것으로 나타났다. 그리고 예조건 행렬의 역행렬을 곱하여 변형된 지배방정식 형태를 이용하면 계산 오차 문제를 완화할 수 있음을 보였다 The effects of cancellation errors on the convergence characteristics of preconditioned Euler equations at low Mach numbers are analyzed. Flows in a two-dimensional channel with a circular bump are calculated at different Mach numbers. It is shown that the cancellation error in the energy equation grows faster than those in the other equations as the Mach number decreases. It is also shown that the cancellation problem of the energy equation can be alleviated by multiplying the inversion of the preconditioner.

Cancellation problem of preconditioning method at low Mach numbers

The effects of cancellation errors on the convergence characteristics of preconditioned Navier–Stokes equations at low Mach numbers are analyzed. Laminar viscous flows around a circular cylinder are calculated at different Mach numbers. It is shown that the cancellation error in the energy equation grows faster than those in the other equations, as the Mach number decreases. It is also shown that the cancellation problem of the energy equation is due to the off-diagonal element that is related to a pressure change in the preconditioner.

Coronal mass transfer in interbinary loops

We consider the transfer of coronal mass between the members of a detached binary system along interconnecting rigid magnetic loops. We show that the asymmetry in the gravitational potential drives a flow from the star closer to fill its Roche lobe towards the other star. The loop base pressures, flow velocities and mass fluxes are not externally imposed but are a result of the heating rate along the loop. As the loop heating increases, the base pressures and mass transfer rates increase and the Mach number decreases. If the heating is not uniformly distributed along the loop, but is instead concentrated near one of the stars, then the mass transfer rate either increases or it decreases, and even changes direction, depending on which star the heating is concentrated on. We also discuss the effect of choosing different boundary conditions. Our model predicts mass transfer rates in reasonable agreement with existing observational estimates, but fails to explain the presence of chromospheric material detected between the stars. Additionally, the differential emission measure profile of the loop models is calculated and it is found to be higher in the loop leg close to the secondary star.