Supersonic Stage Research Articles

Sensors Layout Optimization Design of Rocket Sled Test System.

The rocket sled, as a ground dynamic test system, combines the characteristics of the wind tunnel test and the flight test. However, some practical factors, such as shock wave interference, ground effect, and high-intensity aerodynamic noise will cause serious interference and even failure of the uniformly distributed sensors during horizontal sliding in a wide speed range. The AGARD HB-2 standard model is employed as the payload to simulate the aerodynamic and aeroacoustic characteristics during the variable acceleration period, aiming to optimize the test sensors layout. It is observed that in the high Mach number flow fields, strong coupling behaviors among complex waves will occur. The peak of wake vortex strength will appear at 1.5 s and gradually diminish over time. In addition, when the vortex between the load and the booster is monitored, its position shifts forward in the subsonic stage, then gradually moves backward and expands in the supersonic stage. Acoustic directivity is pronounced at subsonic and transonic speeds, pointing towards 75° and 135° relative to the sliding speed, respectively. These results can provide technical support for sensor layout and high-precision testing in rocket sled tests.

Aerodynamic analysis of a 1.5 kW two-stage counter-rotating partial-admission impulse turbine for small-scale power system with a high expansion pressure ratio

Partial-admission impulse turbine is suitable for small-scale power cycles with a high expansion pressure ratio (EPR) and a low mass flow rate. However, the exit velocity of a single-stage turbine is very high, leading to a large exit loss. A new two-stage counter-rotating impulse turbine has been developed to recover the exit loss, which has a novel structure without stator between the two rotors. However, the internal flow characteristic of such a turbine is still unclear. In this study, the aerodynamic performance of the two-stage counter-rotating partial-admission impulse turbine is analyzed. The internal aerodynamic characteristics are estimated via CFD simulation. First, the geometric parameters are determined based on the mean-line model. Then, the characteristic line method is adopted to design the blade profile of the first supersonic stage based on the vortex flow theory. Subsequently, the performances are estimated under the design and off-design conditions via 3D CFD simulation. The results indicate that the modified convergent-divergent supersonic nozzle exhibits a better adaption with the impellers. The load is principally imposed on the upper zone of the blades. The power output of the turbine reaches 1501.3 W with an EPR of 52 and an efficiency of 45.99 % at the design point and the power of the first impeller accounts for 76.5 %. The mass flow rate increases almost linearly with the augmentation of the turbine inlet pressure. The power output proportion of the second impeller may arrive at 27.63 % under off-design conditions, showing the addition of the second stage can improve the turbine performance evidently.

УЧЕТ ТРЕНИЯ НА НАЧАЛЬНОМ ЭТАПЕ ВЕРТИКАЛЬНОГО ВНЕДРЕНИЯ ВЫПУКЛОГО УДАРНИКА В УПРУГУЮ ПОЛУПЛОСКОСТЬ

The initial stage of indentation of a convex rigid punch into isotropic elastic half-plane with friction is considered. A closed mathematical formulation in Cartesian coordinates is presented by equations of motion in the absence of a body force for homogeneous isotropic elastic medium in terms of displacement potentials, Cauchy equations for deformations, Hooke law and translational equation for the punch. Initial conditions are homogeneous. Outside of contact region surface is free from stresses. Inside contact region normal displacements of the surface of a half-space and the surface of a punch are taken to be equal and the relation between tangential and normal stresses in a form of Coulomb friction law is given. Due to the short duration of the supersonic stage and smallness of the contact region radius the tangential stress direction is considered to be point independent. Resolving functional equations are given in a form of convolutions with influence functions. The latter is the solution the original problem for half-plane with a special boundary condition in a form of the Dirac delta function. This solution is obtained in the domain of Laplace transform by time and Fourier transform by spatial coordinate. The original is constructed with the combined Fourier–Laplace inversion method. Solution is given with consideration to the initial stage characteristic property of supersonic velocity of contact region expansion (no smaller than propagation velocity of expansion-compression waves). It is shown that kinematic parameters of the punch, resulting force and discontinuities of the first kind on boundaries of the contact region are independent of friction unlike contact pressure. Calculation examples for different values of friction coefficient are presented.

An Effective Simulation Scheme for Predicting the Aerodynamic Heat of a Scramjet-Propelled Vehicle

Currently, aerothermal research into scramjet-propelled vehicles characterized by a wedge-shaped section is relatively sparse. Based on the Mach number, grid strategy, and numerical method, an effective simulation scheme for predicting the aerodynamic heat of a scramjet-propelled vehicle during flight is proposed in this paper. At different Mach numbers, the appropriate grid strategy and numerical method were determined by validation tests. Two-dimensional external flow field models based on wedge sections were established and, unlike in blunt bodies, the tests showed that at the high supersonic stage, the ideal cell Reynolds number should be no larger than 16. At the hypersonic stage, the ideal cell Reynolds number and aspect ratio of wall cells near the shock should be no larger than 40, and the AUSM+ flux type performs better than Roe’s FDS flux type at the above stages. The aerothermal prediction indicates that during a flight time of about 34 s, the temperature change reaches about 1913.35 °C, and the maximum average temperature change rate reaches 115 °C/s.

Numerical simulation of flow field in a Laval nozzle based on one-dimensional Euler equation

Numerical simulation refers to a computer research method which runs calculation based on a specific mathematical model to simulate actual physical processes. It is a powerful tool to analyse complex engineering problems. In this paper, a numerical method for solving the steady one-dimensional Euler equations using a two-step second-order difference scheme is developed. The method is implemented by a Python code. The method is applied to numerical simulation of flows in a Laval nozzle and used to investigate the influence of shapes of Laval nozzle. It is found that the physical quantities of the nozzle flow show a positive correlation trend with different throat positions. In terms of the temperature, density, and pressure, they increase during the initial evolutions, then reach the maximum point and produce significant fluctuations, indicating the flow flows into the transonic stage. Subsequently, those physical properties gradually tend to a stable value during the supersonic stage. Moreover, it is observed that the closer the throat is to the exit, the lower the Mach number at which it eventually stabilizes. Finally, a suggestion about the best shape of the nozzle which can realize the max efficiency is concluded. Despite using an inviscid flow model, the steady pressures are quite satisfactorily predicted over the range of frequencies studied.

Mechanism of remote vacancy emergence by a supersonic crowdion cluster in a 2D Morse lattice

The supersonic M×N-crowdions are excited in a two-dimensional lattice by giving sufficiently large initial velocity v to the M×N block of atoms along a close-packed direction, where N is the number of neighboring atoms in one close-packed row and M is the number of neighboring rows. In this study, dynamics of a pair of quasi-1D supersonic 1×2-crowdions moving in parallel close- packed atomic rows separated by one non-excited atomic row (middle row) are investigated in 2D triangular Morse lattice by means of molecular dynamics simulations. It is shown that when a certain threshold excitation energy value is exceeded, the motion of these two 1×2-crowdions leads to creation of a remote vacancy in the middle row at a significantly long distance from the initiation point at the moment, when the supersonic stage of the crowdion propagation turns into subsonic one. This distance is directly proportional to the excitation energy of the 1×2-crowdion pair. The mechanism of vacancy formation is related to appearance of a Frenkel pair in the middle row, namely an immobile vacancy and an interstitial atom, which, together with the two interstitials in the outermost rows, forms the stable subsonic 3×1-crowdion cluster. It is concluded that the crowdion propagation can be accompanied by not only mass transfer but also plays a role in the formation of atomic vacancies inside crystal lattices.

Aerotunelska verifikacija efekata isticanja mlaza na aerodinamičke karakteristike osnosimetričnog projektila

Experimental verification of base-bleed effects on aerodynamic characteristics for the supersonic flight stages was requested during the development of an axi-symmetric projectile. The experimental setup for testing base-bleed configurations of the projectile was designed, built and tested in the T-38 trisonic blowdown wind tunnel of the Military Technical Institute (VTI), Belgrade. Gas-generator was formed from a simple chamber with a single manifold pneumatically connected to a high-pressure air supply. Wind tunnel tests comprised measurement of aerodynamic forces and moments of the projectile with active base-bleed. Flow visualization was performed using the Schlieren method. It was of interest to verify the base drag reduction in the wind tunnel tests and to compare it with numerical predictions. In addition, the experience gained during these tests has been found to be helpful in the design of the future similar wind tunnel setups

Studies on high efficiency in the supersonic turbine stage for rocket employing scarfed nozzle

Studies on high efficiency in the supersonic turbine stage for rocket employing scarfed nozzle

THE POSSIBILITY OF STUDYING SUPERSONIC FLOW PROFILE CLOSE TO THE SCREEN BY THE METHOD OF HYDRAULIC ANALOG MODELING

Supersonic flow around the system of bodies (lattice wings, a wing near the shielding surface, blades of supersonic stages of the compressor, etc.) is accompanied by complex pictures of shock waves, which depend on several parameters characterizing the mutual arrangement, the bodies of their external shapes and sizes, as well as the Mach number. These patterns are determined by the nature of the interaction of the head shock wave and the shock wave on the lower surface of the profile, caused by a change in the flow direction as a result of deflection of the flap. The paper presents the results of an investigation of supersonic flow around a profile with a flap near the screen, obtained using the method of hydraulic analog simulation (the method of gas-hydraulic analogy). This method is based on the analogy of the equations of motion describing a planar gas flow and a thin liquid layer and is used in solving a large class of plane problems of stationary and nonstationary gas dynamics. The parameters that affect the structure of the flow around the profile near the screen are: the Mach number of the profile movement with the values M ∞ = 1.4 ÷ 1.9; relative distance of the profile from the screen with the values Н з = 0.2 ÷ 1.0; angle of flap deflection with values δ з = 0 ÷ 40°. In the course of the experimental investigation, the changes in the structure of shock waves were determined and the influence of the above-mentioned parameters on the process was revealed. The results of the experimental study are presented in the form of graphical dependencies of the relative position of the shock wave on the lower surface of the profile for different Mach numbers, the relative position of the profile from the screen, and the angle of deflection of the flap Δ = f (М ∞ ,Н з , δ з ). On the basis of the analysis of the obtained dependences, a generalized parameter is derived, which makes it possible to determine the boundaries of changes in the structure of shock waves in a given type of problem.

Design criteria for novel supersonic nozzles with high pitch-chord ratio

High pitch-chord ratio turbine stages are a novel class of high enthalpy drop impulse turbines. Significant limitation of traditional design approach for such turbines is a low partial admission rate due to low volumetric flow rates. The main idea of high pitch-chord ratio design is in increase of the stage load coefficient with decrease of the flow angles. The latter allows to provide higher partial admission rate and, hence, higher stage efficiency compared with the traditional design approach. As a consequence, efficiency of the high pitch-chord ratio stages varies between 65% and 75%, whereas partially admitted stages efficiency tend not to exceed 60%. High pitch-chord ratio nozzles have a rectangular cross section. This feature leads to a vortex pair occurrence in a nozzle flow path. An interaction of these vortices for transand supersonic stages leads to additional losses and comparably low nozzle efficiency. The present paper aimed at first, establishing the design criteria which are essential for the nozzle efficiency, and, second, finding the optimal ratios of the proposed criteria. CFD simulation approach is used for the study. The gained deliverables are helpful for increasing of the nozzle velocity ratio.

Аэродинамическая оптимизация формы лопаток направляющего аппарата сверхзвуковой компрессорной ступени

Аэродинамическая оптимизация формы лопаток направляющего аппарата сверхзвуковой компрессорной ступени

О влиянии тангенциального навала лопаток на энергетические характеристики рабочего колеса сверхзвуковой компрессорной ступени

О влиянии тангенциального навала лопаток на энергетические характеристики рабочего колеса сверхзвуковой компрессорной ступени

Resolution of the threshold fracture energy paradox for solid particle erosion

Previous models of a single erosion impact, for a rigid axisymmetric indenter defined by the shape function , have shown that a critical shape parameter exists which determines the behaviour of the threshold fracture energy. However, repeated investigations into this parameter have found no physical explanation for its value. Again utilising the notion of incubation time prior to fracture, this paper attempts to provide a physical explanation of this phenomena by introducing a supersonic stage into the model. The final scheme allows for the effect of waves along the indenters contact area to be taken into account. The effect of this physical characteristic of the impact on the threshold fracture energy and critical shape parameter are investigated and discussed.

Characterization of the supersonic wake of a generic space launcher

The wake flow of a generic axisymmetric space-launcher model is investigated experimentally for flow cases with and without propulsive jet to gain insight into the wake-flow phenomena at a supersonic stage of the flight trajectory which is especially critical with respect to dynamic loads on the structure. Measurements are performed at Mach 2.9 and a Reynolds number Re D = 1.3 × 106 based on model diameter D. The nozzle exit velocity of the jet is at Mach 2.5, and the flow is moderately underexpanded (p e/p ∞ = 5.7). The flow topology is described based on velocity measurements in the wake by means of particle image velocimetry and schlieren visualizations. Mean and fluctuating mass-flux profiles are obtained from hot-wire measurements, and unsteady wall-pressure measurements on the main-body base are performed simultaneously. This way, the evolution of the wake flow and its spectral content can be observed along with the footprint of this highly dynamic flow on the launcher main-body base. For the case without propulsive jet, a large separated zone is forming downstream of the main body shoulder, and the flow is reattaching further downstream on the afterbody. The afterexpanding propulsive jet (air) causes a displacement of the shear layer away from the wall, preventing the reattachment of the flow. In the spectral analysis of the baseline case, a dominant frequency around St D = 0.25 is found in the pressure-fluctuation signal at the main-body base of the launcher. This frequency is related to the shedding of the separation bubble and is less pronounced in the presence of the propulsive jet. In the shear layer itself, the spectra obtained from the hot-wire signal have a more broadband low-frequency content, which also reflects the characteristic frequency of turbulent structures convected in the shear layer, a swinging motion (St D = 0.6), as well as the radial flapping motion of the shear layer (St D = 0.85), respectively. Moving downstream along the shear layer, spectral content at slightly higher frequencies (St D < 4) gets more pronounced and can be related to the shear layer instability process and the signature of smaller turbulent structures that appear in the wake.

Self-organized shocks in the sedimentation of a granular gas.

A granular gas in gravity heated from below develops a certain stationary density profile. When the heating is switched off, the granular gas collapses. We investigate the process of sedimentation using computational hydrodynamics, based on the Jenkins-Richman theory, and find that the process is significantly more complex than generally acknowledged. In particular, during its evolution, the system passes several stages which reveal distinct spatial regions of inertial (supersonic) and diffusive (subsonic) dynamics. During the supersonic stages, characterized by Mach>1, the system develops supersonic shocks which are followed by a steep front of the hydrodynamic fields of temperature and density, traveling upward.

Investigation of the effect of roughness of duct surfaces of a supersonic high-pressure stage of an axial compressor on its characteristics

Results of calculations and experimental investigations of characteristics of a supersonic high-pressure wide-chord stage of an axial compressor are presented. The influence of surface roughness on the characteristics of this stage are analyzed. A method of identification of aerodynamic flow parameters in the compressor duct is described.

Исследование влияния шероховатости поверхностей проточной части сверхзвуковой высоконапорной ступени осевого компрессора на ее характеристики

Исследование влияния шероховатости поверхностей проточной части сверхзвуковой высоконапорной ступени осевого компрессора на ее характеристики

108 超音速部分挿入タービン段の非定常数値解析による損失生成機構の考察

108 超音速部分挿入タービン段の非定常数値解析による損失生成機構の考察

Nonstationary axisymmetric problem of the impact of a spherical shell on an elastic half-space (initial stage of interaction)

The supersonic stage of interaction (where the rate of expansion of the contact region is no less than the speed of compression waves) between a Timoshenko-type spherical shell (indenter) and an elastic half-space (foundation) is studied. The expansion of the desired functions in series in Legendre polynomials and their derivatives are used to construct a system of resolving equations. An analytical-numerical algorithm for solving this system is developed. A similar problem was considered in [1], where the original problem was replaced by a problem with a periodic system of indenters.

Asymptotic theory of liquid–solid impact

The liquid–solid impact problem is analysed with the help of the method of matched asymptotic expansions. This method allows us to estimate the roles of different effects (viscosity of the liquid, surface tension, compressibility, nonlinearity, geometry) on the impact, to distinguish the regions of the flow and the stages of the impact, where and when each of these effects is of major significance, to present a complete picture of the flow, and describe approximately such phenomena as jetting, escape of the shock onto the liquid–free surface and cavitation. Five stages of the impact are distinguished: supersonic stage, transonic stage, subsonic stage, inertia stage and the stage of developed liquid flow. The asymptotic analysis of each stage is based on general principles of hydrodynamics and will be helpful to design experiments on liquid impact and to develop an adequate computational algorithm, as well as to understand the dynamics of the process.