Effects of Unforced Bounday Layer Transition on the Performance of a Two-Dimensional Hypersonic Inlet

2013 ◽  
Vol 275-277 ◽  
pp. 466-471
Author(s):  
Hai Feng Miao ◽  
Lv Rong Xie ◽  
Weng Xiao Chai
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Two Dimensional ◽  
Layer Transition ◽  
Recovery Coefficient ◽  
Static Pressure Distribution ◽  
Hypersonic Inlet ◽  
Flow Rate Increase ◽  
Compression Ramp ◽  
Onset Location

Numerical investigation was conducted on a typical two-dimensional hypersonic inlet to study the influence of unforced boundary layer transition affected by compression ramp geometric parameters on the inlet performance. The numerical results show that the transition onset location on the compression ramp can be delayed by filleting the ramp intersection, and also the inlet's performance obviously improves when the transition onset location is delayed. Compared with full turbulent situation, when the boundary layer transition occurs, the unstart of the inlet is significantly mitigated, the heat transfer rate on the compression ramp decreases, both the total pressure recovery coefficient and mass flow rate increase at both design and off-design points. But the static pressure distribution along the ramp is fairly independent of the varieties of boundary layer.

Numerical simulation of boundary-layer transition and transition control

1989 ◽  
Vol 199 ◽  
pp. 403-440 ◽  
Author(s):  
E. Laurien ◽  
L. Kleiser
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Transition Process ◽  
Numerical Results ◽  
Boundary Layer Transition ◽  
Two Dimensional ◽  
Layer Transition ◽  
Longitudinal Vortices ◽  
Tollmien Schlichting

The laminar-turbulent transition process in a parallel boundary-layer with Blasius profile is simulated by numerical integration of the three-dimensional incompressible Navier-Stokes equations using a spectral method. The model of spatially periodic disturbances developing in time is used. Both the classical Klebanoff-type and the subharmonic type of transition are simulated. Maps of the three-dimensional velocity and vorticity fields and visualizations by integrated fluid markers are obtained. The numerical results are compared with experimental measurements and flow visualizations by other authors. Good qualitative and quantitative agreement is found at corresponding stages of development up to the one-spike stage. After the appearance of two-dimensional Tollmien-Schlichting waves of sufficiently large amplitude an increasing three-dimensionality is observed. In particular, a peak-valley structure of the velocity fluctuations, mean longitudinal vortices and sharp spike-like instantaneous velocity signals are formed. The flow field is dominated by a three-dimensional horseshoe vortex system connected with free high-shear layers. Visualizations by time-lines show the formation of A-structures. Our numerical results connect various observations obtained with different experimental techniques. The initial three-dimensional steps of the transition process are consistent with the linear theory of secondary instability. In the later stages nonlinear interactions of the disturbance modes and the production of higher harmonics are essential.We also study the control of transition by local two-dimensional suction and blowing at the wall. It is shown that transition can be delayed or accelerated by superposing disturbances which are out of phase or in phase with oncoming Tollmien-Schlichting instability waves, respectively. Control is only effective if applied at an early, two-dimensional stage of transition. Mean longitudinal vortices remain even after successful control of the fluctuations.

Criteria for Boundary Layer Transition

2011 ◽  
Author(s):  
Stefan Becker ◽  
Donald M. McEligot ◽  
Edmond Walsh ◽  
Eckart Laurien
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Layer Flow

New results are deduced to assess the validity of proposed transition indicators when applied to situations other than boundary layers on smooth surfaces. The geometry employed utilizes a two-dimensional square rib to disrupt the boundary layer flow. The objective is to determine whether some available criteria are consistent with the present measurements of laminar recovery and transition for the flow downstream of this rib. For the present data — the proposed values of thresholds for transition in existing literature that are based on the freestream turbulence level at the leading edge are not reached in the recovering laminar run but they are not exceeded in the transitioning run either. Of the pointwise proposals examined, values of the suggested quantity were consistent for three of the criteria; that is, they were less than the threshold in laminar recovery and greater than it in the transitioning case.

Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss — Part I: Methodology and Computational Results

2021 ◽  
Author(s):  
Jinwook Lee ◽  
Zoltán S. Spakovszky ◽  
Edward M. Greitzer ◽  
Mark Drela ◽  
Jérôme Talbotec
Keyword(s):  
Boundary Layer ◽  
Acoustic Noise ◽  
Transition Process ◽  
Boundary Layer Transition ◽  
Wavy Surface ◽  
Computational Results ◽  
Surface Waviness ◽  
Layer Transition ◽  
Fan Blade ◽  
Onset Location

Abstract This two-part paper describes a new approach to determine the effect of surface waviness, arising from manufacture of composite fan blades, on transition onset location movement and hence fan profile losses. The approach includes analysis and computations of unsteady disturbances in boundary layers over a wavy surface, assessed and supported by wind tunnel measurements of these disturbances and the transition location. An integrated framework is developed for analysis of surface waviness effects on natural transition. The framework, referred to as the extended eN method, traces the evolution of disturbance energy transfer in flow over a wavy surface, from external acoustic noise through exponential growth of Tollmien-Schlichting (TS) waves, to the start and end of the transition process. The computational results show that surface waviness affects the transition onset location due to the interaction between the surface waviness and the TS boundary layer instability, and that the interaction is strongest when the geometric and TS wavelengths match. The condition at which this occurs, and the initial amplitude of the boundary layer disturbances that grow to create the transition onset is maximized, is called receptivity amplification. The results provide first-of-a-kind descriptions of the mechanism for the changes in transition onset location as well as quantitative calculations for the effects of surface waviness on fan performance due to changes in surface wavelength, surface wave amplitude, and the location at which the waviness is initiated on the fan blade.

scholarly journals On the Effects of an Installed Propeller Slipstream on Wing Aerodynamic Characteristics

10.14311/562 ◽  
2004 ◽  
Vol 44 (3) ◽  
Author(s):  
F. M. Catalano
Keyword(s):  
Boundary Layer ◽  
Relative Position ◽  
Aerodynamic Characteristics ◽  
Boundary Layer Transition ◽  
Flow Visualisation ◽  
Two Dimensional ◽  
Wind Tunnel Experiments ◽  
Layer Transition ◽  
Laminar Separation ◽  
Turbulent Separation

This work presents an experimental study of the effect of an installed propeller slipstream on a wing boundary layer. The main objective was to analyse through wind tunnel experiments the effect of the propeller slipstream on the wing boundary layer characteristics such as: laminar flow extension and transition, laminar separation bubbles and reattachment and turbulent separation. Two propeller/wing configurations were studied: pusher and tractor. Experimental work was performed using two different models: a two-dimensional wing with a central cylindrical nacelle for the tractor configuration, and a simple two-dimensional wing with a downstream propeller for the pusher tests. The relative position between propeller and wing could be changed in the pusher model, and a total of 7 positions were analysed. For the tractor tests the relative propeller/wing was fixed, but three different propellers: two, three and four bladed were tested. Measurements included pressure distribution, hot wire anemometry and boundary layer characteristics by flow visualisation. The results showed that the pusher propeller inflow affects the wing characteristics by changing the lift, drag, and also delays the boundary layer transition and separation. These effects are highly dependent on the relative position of the wing/propeller. On the other hand, the tractor propeller slipstream induces transition and its effect is dependent on the number of blades.

Large-eddy simulation of boundary-layer separation and transition at a change of surface curvature

2001 ◽  
Vol 439 ◽  
pp. 305-333 ◽  
Author(s):  
ZHIYIN YANG ◽  
PETER R. VOKE
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Two Dimensional ◽  
Layer Transition ◽  
Transition Mechanism ◽  
The Mean ◽  
Dimensional Instability

Transition arising from a separated region of flow is quite common and plays an important role in engineering. It is difficult to predict using conventional models and the transition mechanism is still not fully understood. We report the results of a numerical simulation to study the physics of separated boundary-layer transition induced by a change of curvature of the surface. The geometry is a flat plate with a semicircular leading edge. The Reynolds number based on the uniform inlet velocity and the leading-edge diameter is 3450. The simulated mean and turbulence quantities compare well with the available experimental data.The numerical data have been comprehensively analysed to elucidate the entire transition process leading to breakdown to turbulence. It is evident from the simulation that the primary two-dimensional instability originates from the free shear in the bubble as the free shear layer is inviscidly unstable via the Kelvin–Helmholtz mechanism. These initial two-dimensional instability waves grow downstream with a amplification rate usually larger than that of Tollmien–Schlichting waves. Three-dimensional motions start to develop slowly under any small spanwise disturbance via a secondary instability mechanism associated with distortion of two-dimensional spanwise vortices and the formation of a spanwise peak–valley wave structure. Further downstream the distorted spanwise two-dimensional vortices roll up, leading to streamwise vorticity formation. Significant growth of three-dimensional motions occurs at about half the mean bubble length with hairpin vortices appearing at this stage, leading eventually to full breakdown to turbulence around the mean reattachment point. Vortex shedding from the separated shear layer is also observed and the ‘instantaneous reattachment’ position moves over a distance up to 50% of the mean reattachment length. Following reattachment, a turbulent boundary layer is established very quickly, but it is different from an equilibrium boundary layer.

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