External Flow Mach Numbers Research Articles

The Influence of External Flow Field on the Flow Separation of Overexpanded Single-Expansion Ramp Nozzle

Flow separation and transitions of separation patterns are common phenomena of nozzles working with a wide Mach range. The maximum thrust method is applied to design the single-expansion ramp nozzle (SERN) for specific operating conditions. The nozzle is used to numerically simulate the transition processes of separation patterns under the linear change in the external flow Mach number and the actual trajectory take-off condition of a rocket-based combined cycle (RBCC), to investigate the mechanism through which the external flow field influences the separation pattern transition during acceleration. The computational fluid dynamics (CFD) method is briefly introduced, followed by experimental validation. Then, the design procedure of SERN is described in detail. The simulation results indicate that as the external Mach number increases, the flow field in the nozzle undergoes transitions from RSS (ramp) to FSS, and finally exhibits a no-flow separation pattern. The rate at which the external Mach number varies has little effect on the transition principle of the nozzle flow separation patterns, but it has a significant effect on the critical Mach number of the transition points. The external flow field of the nozzle has an airflow accumulation effect during acceleration, which can delay the transition of the flow separation pattern.

Re-entry vehicle performance analysis under the control of lateral jet

AbstractLateral jets are used to control the missiles and re-entry vehicles at high altitudes. The objective of the research paper is to investigate the effect of lateral jet interaction with the external flow on a blunted nose cone re-entry vehicle configuration and its flight speed. Structured mesh is used for the simulations, and the computational analysis is carried out by Ansys Fluent solver. The simulation results are validated, and the same methodology used for the parametric analysis. Simulations have been carried out at an external flow Mach number 6, 8.1, 12 and 16 at five degree angle-of-attack for jet-off and jet-on conditions. At 8.1 Mach number, the normal force coefficient is decreased by 45.6% due to jet interaction. The lateral jet interaction effectively reduces the nose down pitching moment. At 8.1 Mach number, the pitching moment coefficient was reduced by 48% with the jet-on condition compared to the jet-off condition.

Interaction of external flow with linear cluster plug nozzle jet

Plug nozzle flow in the presence of external flow is experimentally investigated at free-stream Mach numbers of 0.0, 0.7, 0.9, 1.1, and 1.5. The internal nozzle is operated in overexpanded and underexpanded regimes for these external flow Mach numbers. For the subsonic external flow, slight changes in the plug jet flow are observed as compared to the no-external-flow case. The supersonic external flow introduces substantial changes to plug flow jet structure as well as the wave interactions within it, as compared to the no-external-flow case. For the overexpanded internal nozzle operation, the oblique shock waves are asymmetric within the plug core jet. For underexpanded internal nozzle operation, an oblique shock formation is noticed on the plug surface which induces flow separation downstream. The RMS of the pressure fluctuations indicates a distinct peak corresponding to the foot of the overexpansion shock on the plug surface. These peaks are observed at consistent pressure ratios for all the external flow conditions considered. Regarding the cluster plug nozzle flow field, three-dimensional flow features are noticed because of the intermodule interactions. For both the overexpanded and underexpanded internal jet conditions, the interactions between the modules are predominantly compression waves in the spanwise direction. The RMS of the pressure fluctuations measured along the intermodule centreline suggests that the spanwise wave interactions have considerable influence on the flow unsteadiness.

Mathematical modeling of jet interaction with a high-enthalpy flow in an expanding channel

Results of modeling the interaction of a plane supersonic jet with a supersonic turbulent high-enthalpy flow in a channel are reported. The problem is solved in a two-dimensional formulation at external flow Mach numbers M∞ = 2.6 and 2.8 and at high values of the total temperature of the flow T0 = 1800–2000 K. The mathematical model includes full averaged Navier-Stokes equations supplemented with a two-equation turbulence model and an equation that describes the transportation of the injected substance. The computations are performed by using the ANSYS Fluent 12.1 software package. Verification of the computational technique is performed against available experimental results on transverse injection of nitrogen and helium jets. The computed and experimental results are demonstrated to agree well. For the examined problems, in addition to surface distributions of characteristics, fields of flow parameters are obtained, which allow one to reproduce specific features that can be hardly captured in experiments. Parametric studies show that an increase in the angle of inclination and the mass flow rate of the jet leads to an increase in the depth of jet penetration into the flow, but more intense separated flows and shock waves are observed in this case.

Computation of Noise Radiation from Fan Inlet and Aft Ducts

This paper examines turbofan noise radiation characteristics of both the inlet and the aft exhaust ducts using solutions obtained from a finite element code. The far-field principal lobe peak angle variations with mode cutoff ratio, duct Mach number, and external flow Mach number are examined. The predicted far-field principal lobe peak angle variations compare very well with the available analytical results. It is found that the principal lobe peak angle of the inlet radiation is insensitive to the duct and external flow Mach numbers. In the case of the aft duct, an increase in duct Mach number moves the principal lobe away from the aft duct axis, whereas an increase in external flow Mach number moves the principal lobe toward the aft axis. The solutions (for both inlet and exhaust duct radiation) also show that the far-field radiation principal lobe peak angle is only a function of cutoff ratio and nearly independent of the mode number. The ability of the code to handle ducts with acoustic treatments is also demonstrated.

Two-dimensional jet interaction studies at large values of Reynolds and Mach numbers

The situation chosen for study is a gaseous jet that is injected through a transverse slot nozzle in a wall and into a supersonic external flow which is uniform outside of a turbulent boundary layer. Experiments were conducted with normal, sonic jets and forward-facing steps at external flow Mach numbers of 2.5 to 13, and Reynolds numbers based on running length of 7.5 X 10 to 5.5 x 10. The amplification factor (the upstream interaction force plus the jet thrust normalized by the vacuum thrust of a sonic jet) is relatively insensitive to variations in external flow Mach number and Reynolds number. The effect of pressure ratio on amplification factor is very small when the external flow properties and jet mass flow rate are held constant. Plateau pressures associated with separation upstream of the jet or step, and wall static pressure distributions near the separation line are in good agreement with existing correlations.

Supersonic laminar boundary layer near the plane of symmetry of a cone at incidence

Supersonic laminar boundary-layer equations near the plane of symmetry of a cone at incidence are treated by the similarity method. Numerical integration of differential equations governing such a flow is performed, taking into consideration the temperature dependence of the Prandtl numberPrand viscosity μ throughout the boundary layer. On the leeward side, a detailed consideration of the solutions shows the existence of two solutions up to a critical incidence beyond which it appears that no solution may be found. Calculations carried out for a set of values of the external flow Mach number show up a significant effect of this parameter on the behaviour of the boundary layer.

A study of the interaction of gaseous jets from transverse slots with supersonic external flows.

The paper describes a study concerning the sonic injection of a gaseous jet through a transverse slot nozzle in a wall into an external flow which is uniform outside of a turbulent boundary layer. An analytic model of the flowfield has been constructed in which conservation of momentum is applied to a control volume at the jet nozzle exit. A series of flat-plate experiments was conducted with normal, sonic jets at external flow Mach numbers of 2.61, 3.50, and 4.54. Pressure data near separation and the plateau were in agreement with existing correlations. Comparisons of the trends predicted by the analysis with two-dimensional force data from these experiments and from other sources showed good agreement. Values of amplification factor, the upstream interaction force plus the jet thrust divided by the vacuum thrust of a sonic jet, of 2.9 to 3.2 were measured. The amplification factor is relatively insensitive to variations in external flow Mach number and variations in injectant gas properties. A correlation of data obtained from experiments with finite-span slots demonstrates that the effective jet penetration height and the slot span are the important characteristic dimensions of such flowfields.

The Mixing of Turbulent Supersonic Fuel-Air Streams

SummaryAn integral part of the study of supersonic combustion is the investigation of supersonic turbulent mixing of dissimilar fluids. Experimental results obtained in the course of investigating the turbulent mixing zone between supersonic streams of CO3 and air are presented. Good correlation between observation and available theories has been obtained in terms of the parameter ξ=σy/x. The correlating parameter σ defines the spreading rate of the mixing zone. The available theories, though not developed for these specific conditions, are shown to be applicable to the turbulent mixing of supersonic streams.The correlating parameter σ was determined for three different combinations of internal and external flow Mach numbers. The values found for σ were 18, 16·3, 15·3 for constant external Mach number 1·62 and internal Mach number 1·62, 1·53, 1·47 respectively. The magnitudes of σ showed the expected trend, that is the higher value implies the least divergence of the mixing boundaries.The reasonable agreement with experiment and the simplicity of application of the momentum integral form of solution would appear to favour the use of this approach for the theoretical prediction of the mixing conditions.