Strong Viscous-inviscid Interaction Research Articles

Aerodynamic Heating of a Blunted Plate in the Regime of Strong Viscous–Inviscid Interaction

Aerodynamic Heating of a Blunted Plate in the Regime of Strong Viscous–Inviscid Interaction

The Effect of Pressure Disturbances on the Heating of the Plate Surface in the Strong Interaction Regime

The results of an experimental wind-tunnel investigation of the plate surface heating in the strong viscous-inviscid interaction regime are presented. It is shown that In the presence of a wedge mounted in the vicinity of the trailing edge of the plate the temperature distribution over the plate surface ahead of the wedge considerably changes up to the leading edge, as compared with the case of flow past the same plate in the absence of the wedge. The boundary layer flow is not steady, since during the run the surface temperature grows continuously, the temperature distribution itself along the plate surface being variable. It is established that in an unsteady boundary layer the upwind propagation of pressure disturbances produced by a thin wedge is fundamentally different in nature from the disturbance propagation in the case of flow past a plate with a constant surface temperature.

Investigation of the hypersonic flow around a thermally insulated sliding plate in the regime of strongviscous-inviscid interaction under variable conditions at the trailing edge

Investigation of the hypersonic flow around a thermally insulated sliding plate in the regime of strongviscous-inviscid interaction under variable conditions at the trailing edge

Methods of Controlling Flows under the Strong Hypersonic Interaction Conditions

The methods of the flow control in a laminar boundary layer at local surface cooling are studied. The dependence of the velocity of disturbance propagation upstream on the temperature factor of the body surface is obtained. The methods of controlling the boundary layer flow under the strong viscous-inviscid interaction conditions by means of suppressing the upstream disturbance propagation are investigated.

Управление течением в гиперзвуковом пограничном слое

A method of flow control in a two-dimensional hypersonic boundary layer under strong viscous-inviscid interaction is considered. The effect of blocking the process of transferring disturbances upstream due to a decrease in the propagation velocity of disturbances with a decrease in the temperature factor of the surface area is shown.

Temperature Factor Effect on the Disturbance Propagation in Hypersonic Flow past a Yawed Flat Plate

The flow in the three-dimensional laminar boundary layer on a yawed flat plate of finite length is studied in the regime of strong viscous-inviscid interaction with a hypersonic flow. In the vicinity of the leading edge the flow functions are expanded in series under the assumption that the base pressure dependent on the transverse coordinate is given at the trailing edge of the plate. It is established that the expansions obtained include an indefinite function and its derivative with respect to the transverse coordinate. The corresponding boundary value problems are formulated and numerically solved, the eigenvalues are found, and it is shown that the exponent in the third term of the expansion differs from that in the second term only by one. The plate surface temperature effect on the flow parameters and the initiation of three-dimensional disturbances is investigated.

Assessment of a numerical design tool for pitching airfoils

The aim of this study was to assess the applicability of a numerical design tool for pitching airfoils; by evaluating their aerodynamic performance comparing experimental and numerical data at different levels of complexity. Experimental findings of non-harmonically pitching airfoil configurations in a water tunnel at medium Reynolds numbers are compared to solutions of a modified double-wake vortex-panel method with boundary-layer formulation and unsteady Reynolds-averaged Navier–Stokes simulations. For steady-state airfoil configurations at high angle of attack, large eddy simulation data are also considered. Rigorous analysis of the sources of error and uncertainty in numerical methods and measurements proves that from an engineering point of view, a low-cost double-wake model is well suited for the design process of, for example, wind-turbine blades. That is, the overall first-order error and uncertainty of the double-wake panel method with a strong viscous-inviscid interaction model are in a reasonable range against the measurements and the much more expensive numerical methods. Thus, the low computational costs plus the accuracy make the unsteady panel-boundary-layer method a useful and reliable tool to analyze the aerodynamics of pitching airfoils in the design process.

Flow past a delta wing in the strong viscous-inviscid interaction regime

Three-dimensional laminar boundary layer flow over a planar delta wing with the span of the order of unity is investigated in the strong interaction regime. The flow functions are expanded in power series in the transverse coordinate in the vicinities of the plane of symmetry of the wing and its leading edge. The induced pressure over the wing span is determined by matching the expansions obtained and compared with the results of the numerical finite-difference solution of the boundary layer equations in partial derivatives.

Simulations of the Yawed MEXICO Rotor Using a Viscous-Inviscid Panel Method

In the present work the viscous-inviscid interactive model MIRAS is used to simulate flows past the MEXICO rotor in yawed conditions. The solver is based on an unsteady three-dimensional free wake panel method which uses a strong viscous-inviscid interaction technique to account for the viscous effects inside the boundary layer. Calculated wake velocities have been benchmarked against field PIV measurements, while computed blade aerodynamic characteristics are compared against the load calculated from pressure measurements at different locations along the blade span. Predicted and measured aerodynamic forces are in overall good agreement, however discrepancies appear in the root region which could be related to an underestimation of the rotational effects arising from Coriolis and centrifugal forces. The predicted wake velocities are generally in good agreement with measurements along the radial as well as the axial traverses performed during the experimental campaign.

Disturbances Propagation in Supersonic Boundary Layers

Disturbances propagation processes are investigated in two-dimensional boundary layers for the case of strong viscous-inviscid interaction. The speed of upstream disturbances propagation as a function of specific heat ratio and Prandtl number is determined. Formula for speed propagation is developed on the basis of characteristics and subcharacteristics analysis corresponding to the gasdynamic wave processes and processes of convection and diffusion.

A strong viscous-inviscid interaction model for rotating airfoils

A strong viscous-inviscid interaction model for rotating airfoils

Dynamic stall modelling on airfoils based on strong viscous–inviscid interaction coupling

AbstractThe prediction of the aerodynamic performance of pitching airfoils in stall conditions is considered in the context of strong viscous–inviscid interaction modelling. The aim of the work is to demonstrate the capabilities of a low‐cost dynamic stall model well suited for engineering applications. The model is formulated on the basis of a standard panel method combined with a vortex blob approximation of the wake. The development of the boundary layer over the airfoil and the evolution of the shear layer in the wake are taken into account by means of strong viscous–inviscid interaction coupling. To this end a transpiration layer is added to the inviscid formulation which represents the displacement effect viscosity results in the flow while the non‐linear coupled equations are solved simultaneously. Separation is modelled by introducing a second wake originating from the separation point (‘double‐wake’ concept) which is provided as part of the boundary layer solution. The theoretical presentation of the model is supported with favourable comparisons to four sets of wind tunnel measurements. Copyright © 2007 John Wiley & Sons, Ltd.

Formation of Supercritical Flow Regions on Low-Aspect-Ratio Wings

The flow over a planar low-aspect-ratio delta wing is considered in the strong viscous-inviscid interaction regime. The study is carried out for Newtonian passage to limit, when the adiabatic exponent tends to unity, while the Mach and Reynolds numbers increase without bound. For the flow over a cold wing, an analytical expression for the coordinate of supercritical-to-subcritical transition in the boundary layer is derived. The aspect ratios for which the flow in the three-dimensional boundary layer is subcritical over the entire wing are derived. The approximate formula for the transition coordinate is compared with the results of a numerical solution of the system of differential equations in the case in which the Prandtl number is equal to unity.

Unsteady Separation Processes at High Reynolds Number and Their Control

Physical situations where a viscous boundary layer breaks down and interacts strongly with an effectively inviscid external flow are common place. For large Reynolds numbers, viscous effects are normally confined to thin boundary layers on all solid surfaces for the majority of any observation time. In most practical situations, exposure of such layers to an adverse pressure gradient is inevitable and in this circumstance, a sequence of events commences near the wall that culminates in an eruption and a strong viscous-inviscid interaction with the external flow. The events leading up to eruption are known as the Van Dommelen–Shen process and the eruption itself is referred to as boundary-layer separation; here the term ‘separation’ denotes the first process of interaction between a hitherto thin boundary layer and the external flow. The event is sufficiently complicated that extraordinary measures are needed to compute its evolution. In most situations, the onset of separation is subtle and hard to detect and thus development of rational control procedures is a challenging task. Here recent calculations of unsteady separation events are discussed for two- and three-dimensional flows. The phenomena involved are generic but leading-edge separation on airfoils and rotorcraft blades is emphasized. Recent studies on various control mechanisms are described, which are found to have the effect of slowing down and/or weakening the separation process. For some control processes, it has proved possible to eliminate separation entirely.

Mass transfer on a delta wing in a hypersonic flow

The effect of mass transfer on the parameters of the laminar boundary layer flow on a cold delta wing in a hypersonic viscous perfect-gas flow is investigated for the case of a strong viscous-inviscid interaction regime. The influence of the mass transfer intensity on the supercritical-subcritical transition coordinate and the local and total aerodynamic parameters of a delta wing with a power-law cross-section is numerically determined.

Gas injection from the surface of a triangular plate in a hypersonic flow

The flow formed as a result of gas injection through the permeable surface of a triangular plate is investigated in the regime of strong viscous-inviscid interaction between the hypersonic flow and the laminar boundary layer. The features of the flow past strongly cooled surfaces with the formation of supercritical and subcritical flow regions in the boundary layer are studied. The injected gas distribution ensuring the existence of self-similar solutions in the supercritical flow regions is obtained.

Influence of intense surface cooling on hypersonic viscous flow past a delta wing

The influence of intense surface cooling on the parameters of a laminar boundary layer flow on a thin delta wing in a hypersonic viscous perfect-gas stream is studied for the strong viscous-inviscid interaction regime. The effect of the power-law shape of the wing cross-section and the wing thickness to boundary-layer displacement thickness ratio on the local and total aerodynamic characteristics is numerically investigated.

A contribution to the physical analysis of separated flows past three-dimensional humps

The aim of this article is to present a few improvements in the understanding of both mathematical and physical aspects of three-dimensional separated flows past a protuberance on a flat plate. Only steady laminar incompressible flows are considered here. The asymptotic structure of boundary-layer flows with strong viscous-inviscid interaction has been extensively studied by several authors, mainly with the triple-deck theory. The first part of this paper presents the results of a systematic analysis of the asymptotic structure when the obstacle's dimensions vary. This work explains why the triple-deck properties are so much characteristic. The three-dimensional boundary-layer equations are then solved with a quasi-simultaneous interacting technique, and the results are examined in order to describe the three-dimensional topology of the flow. Two types of flows are described, corresponding to a dent and a hump, that exhibit completely different behaviours.

COMPUTATION OF NON-STATIONARY SHOCK-WAVE/CYLINDER INTERACTION USING ADAPTIVE-GRID METHODS

A numerical study of shock wave propagation over a cylinder is presented. Hybrid, structured-unstructured adaptive grids are employed for the numerical solution of the Euler and Navier-Stokes equations. A second-order Godunov-type scheme is employed for the discretization of the inviscid fluxes, while central differences are used for the viscous terms. The time integration is obtained by a second-order prediction-corrector scheme. Simulation of the unsteady gasdynamic phenomena around the cylinder is obtained at different incident-shock Mach numbers. The shock-wave diffraction over the cylinder is investigated by means of various contour plots, as well as pressure and skin friction distributions. The calculations reveal that the Euler solutions are very close to the Navier-Stokes ones in the first half of the cylinder, but large differences between the two solutions exist in the second half of the cylinder and the wake of the flow field, where strong viscous-inviscid interaction occurs.

Effect of a hump on the stability of subsonic boundary layers over an airfoil

The effect of a hump on the stability of subsonic boundary layers over an airfoil is investigated. The mean flow is calculated using an interacting boundary-layer solver which accounts or strong viscous-inviscid interaction and separation bubbles. The two-dimensional stability of the calculated two-dimensional mean flows is determined. The growth rates are integrated along a prescribed path to yield the amplification factor (i.e. N-factor), which is used to predict transition from laminar to turbulent flow. The analysis is performed for different heights and locations of the hump and for different Mach numbers. The results show that increasing the Mach number enhances separation, which partially offsets the stabilizing influence of compressibility. The most dangerous frequency decreases as the Mach number increases for a fixed hump location or the hump is moved downstream for a fixed Mach number. Moreover, the amplification factor increases as the hump height increases and the peak amplification factor increases and moves further downstream as the hump is moved downstream. The influence of suction and heat-transfer strips on controlling the destabilizing influence of the hump is investigated. The results show that cooling and suction strips stabilize the flow and therefore delay transition from laminar to turbulent flow, whereas, a heating strip destabilizes the flow. Applying suction through multiple strips can be as effective as suction through a single strip. Also the total flow rate required using multiple strips may be less than that required using a single strip. Moreover, cooling through multiple strips is as effective as cooling through a single strip. We investigate optimal locations of suction and cooling strips for a certain hump location.