CFD-Based Simulation of Inlet Unstart Phenomena: Toward Supersonic Inlet Flow Control Techniques

2003 ◽  
Author(s):  
Daniel N. Miller ◽  
Brian R. Smith
Keyword(s):  
Steady State ◽  
Flow Control ◽  
High Speed ◽  
Steady State Solution ◽  
Accurate Solution ◽  
Back Pressure ◽  
Inlet Flow ◽  
Control Techniques ◽  
Contour Plots ◽  
Inlet Unstart

A time-accurate, full Navier-Stokes, Computational Fluid Dynamics (CFD) analysis of a back-pressure-induced, high-speed inlet unstart event was conducted. The objective was to identify visible and quantitative flowfield characteristics prior to and during an unstart event. The CFD-based investigation was conducted on a 2-D wind-tunnel model geometry of a forebody and inlet at a freestream Mach number of 5. A sequence of steady-state solutions were run to map the inlet flowfield response to subsequent increases in back-pressure from a design value up to the point of imminent unstart. A time-accurate solution commenced, using the final steady-state solution as the initial condition. The CFD-derived inlet flowfield contour plots compared well with test-derived color schlieren images, while predictions for steady-state and transient wall pressure compared reasonably with test data. A CFD-based study of inlet flow control techniques will follow.

An Efficient Algorithm for Computing the Steady-State Dynamic Response of High-Speed Mechanisms

1994 ◽  
Author(s):  
Tyler J. Selstad ◽  
Kambiz Farhang
Keyword(s):  
Steady State ◽  
High Speed ◽  
Steady State Solution ◽  
Time Varying ◽  
Initial Condition ◽  
Steady State Response ◽  
Periodicity Condition ◽  
Varying Coefficients ◽  
State Response ◽  
Time Varying Coefficients

Abstract An efficient method for obtaining the steady-state response of linear systems with periodically time varying coefficients is developed. The steady-state solution is obtained by dividing the fundamental period into a number of intervals and establishing, based on a fourth-order Rung-Kutta formulation, the relation between the response at the start and end of the period. Imposition of periodicity condition upon the response facilitates computation of the initial condition that yields the steady-state values in a single pass; i.e. integration over only one period. Through a practical example, the method is shown to be more accurate and computationally more efficient than other known methods for computing the steady-state response.

An Experimental and Numerical Study of the Isothermal Flowfield Behind a Bluff Body Flameholder

1997 ◽  
Vol 119 (2) ◽  
pp. 328-339 ◽  
Author(s):  
C. N. Raffoul ◽  
A. S. Nejad ◽  
R. D. Gould ◽  
S. A. Spring
Keyword(s):  
Steady State ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Steady State Solution ◽  
Accurate Solution ◽  
State Solution ◽  
Laser Doppler Velocimeter ◽  
Two Dimensional ◽  
Reynolds Stresses

An experimental and numerical investigation was conducted to study the turbulent velocities and stresses behind a two-dimensional bluff body. Simultaneous three-component laser-Doppler velocimeter (LDV) measurements were made in the isothermal incompressible turbulent flowfield downstream of a bluff body placed at midstream in a rectangular test section. Mean velocities and Reynolds stresses were measured at various axial positions. Spanwise velocity measurements indicated that the flow is three dimensional in the recirculation zone of the bluff body. Confidence in the accuracy of the data was gained by calculating the mass fluxes at each axial station. These were found to agree with each other to within ±3 percent. A parallel Computational Fluid Dynamics (CFD) study was initiated to gage the predictive accuracy of currently available CFD techniques. Three solutions were computed: a two-dimensional steady-state solution using the standard k-ε model, a two-dimensional time-accurate solution using the standard k-ε model, and a two-dimensional time-accurate solution using a Renormalized-Group (RNG) k-ε turbulence model. The steady-state solution matched poorly with the data, severely underpredicting the Reynolds stresses in the recirculation zone. The time-accurate solutions captured the unsteady vortex shedding from the base of the bluff body, providing a source for the higher Reynolds stresses. The RNG k-ε solution provided the best match to the data.

scholarly journals Theory of Intrinsic Variability in Hot-Star Winds

1991 ◽  
Vol 143 ◽  
pp. 155-166
Author(s):  
Stanley P. Owocki
Keyword(s):  
Steady State ◽  
High Speed ◽  
Direct Consequence ◽  
Steady State Solution ◽  
Driving Mechanism ◽  
Intrinsic Variability ◽  
Rarefied Flow ◽  
Root Cause ◽  
Wind Variability ◽  
Scattering Effects

The winds of the hot, luminous, O, B, and WR stars are driven by the line-scattering of the star's continuum radiation flux. Several kinds of observational evidence indicate that such winds are highly structured and variable, and it seems likely that a root cause of this variability is the known strong instability of the line-driving mechanism. Initial dynamical models of the nonlinear evolution of this instability confirm that the wind indeed becomes highly structured, with large amplitude (~500 – 1000 km/s) shocks that separate high-speed rarefied flow from lower speed, dense shells. Remarkably, such variability can often have an intrinsic character, persisting even in the absence of explicit perturbation, and it now appears that this is a direct consequence of a degeneracy in the steady-state solutions for such models. However, recent work indicates that including scattering effects, which have so far been ignored in these pure-absorption models, might reduce or even break this steady-state solution degeneracy; through the “line-drag” effect, scattering can also reduce the strength of the instability, possibly rendering it an advective character for which wind variability now requires explicit perturbation from below. This review will examine the consequences of these ideas for understanding the likely nature of wind variability among the various kinds of early-type stars.

An Experimental and Numerical Study of the Isothermal Flowfield Behind a Bluff Body Flameholder

1995 ◽  
Author(s):  
Charbel N. Raffoul ◽  
Abdollah S. Nejad ◽  
Richard D. Gould ◽  
S. Alan Spring
Keyword(s):  
Steady State ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Predictive Accuracy ◽  
Numerical Study ◽  
Steady State Solution ◽  
Accurate Solution ◽  
State Solution ◽  
Laser Doppler Velocimeter ◽  
Reynolds Stresses

An experimental and numerical investigation was conducted to study the turbulent velocities and stresses behind a 2-D bluff body. Simultaneous three-component laser Doppler velocimeter (LDV) measurements were made in the isothermal incompressible turbulent flowfield downstream of a bluff body placed at midstream in a rectangular test section. Mean velocities and Reynolds stresses were measured at various axial positions. Spanwise velocity measurements indicated that the flow is three dimensional in the recirculation zone of the bluff body. Confidence in the accuracy of the data was gained by calculating the mass fluxes at each axial station. These were found to agree with each other to within ±3%. A parallel Computational Fluid Dynamics (CFD) study was initiated to gauge the predictive accuracy of currently available CFD techniques. Three solutions were computed: a 2-D steady-state solution using the standard k-ε model, a 2-D time-accurate solution using the standard k-ε model, and a 2-D time-accurate solution using a Renormalized-Group (RNG) k-ε turbulence model. The steady-state solution matched poorly with the data, severely underpredicting the Reynolds stresses in the recirculation zone. The time-accurate solutions captured the unsteady vortex shedding from the base of the bluff body, providing a source for the higher Reynolds stresses. The RNG k-ε solution provided the best match to the data.

Flow Diagnostics in Shock Wave-Boundary Layer Interaction Experiments in Hypersonic Flow

2014 ◽  
Vol 660 ◽  
pp. 669-673
Author(s):  
Mohd Rashdan Saad ◽  
Azam Che Idris ◽  
Konstantinos Kontis
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flow Control ◽  
High Speed ◽  
Vortex Generators ◽  
Flow Diagnostics ◽  
Control Techniques ◽  
Layer Interaction ◽  
Boundary Layer Interaction ◽  
Wave Boundary

Shock Wave-Boundary Layer Interaction (SBLI) is a phenomenon occurring in high-speed propulsion systems that is highly undesirable. Numerous methods have been tested to manipulate and control SBLI which includes both active and passive flow control techniques. To determine the improvements brought by the flow control techniques, advanced and state-of the-art flow diagnostics and experimental techniques are required, especially when it involves high-speed flows. In this study, a number of advanced flow diagnostics were employed to investigate the effect of micro-vortex generators in controlling SBLI in Mach 5 such as Pressure Sensitive Paints (PSP), Particle Image Velocimetry (PIV), schlieren photography and oil-flow visualization. The flow diagnostics successfully visualized the boundary layer separation and also the improvements brought by the micro-vortex generators.

A Method for Evaluating the Effect of Circumferential Inlet Distortion on the Aerodynamic Stability of Multi-Stage Axial-Flow Compressors

2010 ◽  
Author(s):  
Tsuguji Nakano ◽  
Andy Breeze-Stringfellow
Keyword(s):  
Steady State ◽  
High Speed ◽  
Axial Flow ◽  
Pressure Rise ◽  
Stability Limit ◽  
Rotating Stall ◽  
Classical Dynamic ◽  
Inlet Flow ◽  
Inlet Distortion ◽  
Multi Stage

A simple engineering parameter to evaluate the stability of high-speed multi-stage compressors with distorted inlet flow has been derived based on a simplified semi-compressible linear stability model. The parameter consists of steady-state flow quantities and geometric parameters of the compressor and it indicates that the circumferential integral of the slope of the steady-state individual blade row static pressure rise characteristics is important in the determination of the compressor stability limit in the presence of distortion. The parameter reduces to the author’s rotating stall inception parameter in the limit of non-distorted inlet flow. Since the model includes a downstream plenum and throttle, a condition for pure surge inception with undistorted inlet flow has been deduced. The pure surge conditions can be reduced to the classical dynamic and static instability conditions in the limit of a constant annulus area incompressible compressor. The results indicate that rotating stall always precedes surge instability, as many engineers and researchers would expect from experience. The parameter for instability with inlet distortion was calculated using test data measured in a high-speed 5-stage compressor with two different types of circumferential inlet distortion, and the results show that the parameter has a strong correlation with the data and is an improvement over the classical incompressible stability parameter. The results demonstrate that the parameter captures much of the physics important during the instability inception in a high-speed multi-stage compressor subjected to circumferential inlet distortion. The parameter clearly shows how each compressor component’s characteristics contribute to the overall stability in a high speed axial multi-stage compressor, therefore, it will aid engineers and designers in their understanding and prediction of the aerodynamic instability inception phenomena.

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