Hydromagnetic boundary layer flow around an oscillating axisymmetric body

Boundary layer flow due to rotational oscillations of an axisymmetric body in the presence of a constant magnetic field is analysed by a process of successive approximations. The induced steady flow is confined only to the meridian place. The effect of the magnetic field is to decrease this steady flow.     

Laminar boundary layer in a swirling flow

The spatial non-self-similar boundary layer in a compressible gas in a swirling flow is studied. Boundary-layer equations are written in variables ensuring constancy of the coefficients of first derivatives and are solved by the finite-difference method. Boundary-layer peculiarities in the presence of a return circulation region in the channel are clarified.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 43–49, January–February, 1976.     

Stability of a spanwise nonuniform boundary layer flow

The linear stability of a boundary layer flow with a spanwise-periodic nonuniformity in the velocity profile is investigated. This flow can be considered as a model of a streaky structure occurring in the boundary layer at a high freestream turbulence level. It is shown that for a small nonuniformity amplitude symmetric modes similar to Tollmien-Schlichting waves are the most unstable. At higher nonuniformity amplitudes, antisymmetric modes, qualitatively different from Tollmien-Schlichting waves and having a larger phase velocity, are the most amplified. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 54–63, November–December, 1998. The study was carried out with the support of the International Scientific and Technical Center (project No. 199-95) and the Russian Foundation for Basic Research (project No. 95-01-01201a).     

Stability of a disperse-mixture flow in a boundary layer

The hydrodynamic stability of a dilute disperse mixture flow in a quasi-equilibrium region of a boundary layer with a significantly nonuniform particle concentration profile is investigated. The mixture is described by a two-fluid model with an incompressible viscous carrier phase. In addition to the Stokes drag, the Saffman lifting force is taken into account in the interphase momentum exchange. On the basis of a numerical solution of the boundary-value problem for a modified Orr-Sommerfeld equation, neutral stability curves are analyzed and the dependence of the critical Reynolds number on the governing parameters is studied. It is shown that taking into account the particle concentration nonuniformity in the main flow and the Saffman lifting force significantly changes the stability limits of the two-phase laminar boundary layer flow. The effect of these factors on the boundary layer stability is considered for the first time.     

Vortex stretching in a laminar boundary layer flow

 A new technique to produce controlled stretched vortices is presented. The initial vorticity comes from a laminar boundary layer flow and the stretching is parallel to the initial vorticity. This low velocity flow enables direct observations of the formation and destabilization of vortices. Visualizations are combined with quasi-instantaneous measurements of a full velocity profile obtained with an ultra-sonic pulsed Doppler velocimeter. Several modes of destabilization are observed and include pairing of two vortices, hairpin deformation, and vortex breakdown into a coil shape. Received: 3 April 1996/ Accepted: 4 October 1996     

Laminarization of boundary layer flow on a vibrating wing

A new type of Tollmien-Schlichting wave excitation, experimentally detected in [6] in investigating the unsteady perturbation field downstream from roughness on the surface of a vibrating wing, is studied. It is shown that the generation mechanism consists in the nonlinear interaction between the unsteady disturbance produced by the vibrations of the smooth wall and the steady nonuniformity of the boundary layer above the roughness.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 26–34, March–April, 1993.     

Passive control of cavitating flow around an axisymmetric projectile by using a trip bar

Quasi-periodical evolutions such as shedding and collapsing of unsteady cloud cavitating flow, induce strong pressure fluctuations, what may deteriorate maneuvering stability and corrode surfaces of underwater vehicles. This paper analyzed effects on cavitation stability of a trip bar arranged on high-speed underwater projectile. Small scale water tank experiment and large eddy simulation using the open source software Open FOAM were used, and the results agree well with each other. Results also indicate that trip bar can obstruct downstream re-entrant jet and pressure wave propagation caused by collapse, resulting in a relatively stable sheet cavity between trip bar and shoulder of projectiles.     

Local heat transfer around a wall-mounted cube at 45° to flow in a turbulent boundary layer

The flow and local heat transfer around a wall-mounted cube oriented 45° to the flow is investigated experimentally in the range of Reynolds number 4.2 × 10³–3.3 × 10⁴ based on the cube height. The distribution of local heat transfer on the cube and its base wall are examined, and it is clarified that the heat transfer distribution under the angled condition differs markedly to that for cube oriented perpendicular to the flow, particularly on the top face of the cube. The surface pressure distribution is also investigated, revealing a well-formed pair of leading-edge vortices extending from the front corner of the top face downstream along both front edges for Re>(1−2)×10⁴. Regions of high heat transfer and low pressure are formed along the flow reattachment and separation lines caused by these vortices. In particular, near the front corner of the top face, pressure suction and heat transfer enhancement are pronounced. The average heat transfer on the top face is enhanced at Re>(1−2)×10⁴ over that of a cube aligned perpendicular to the flow.     

The unsteady boundary layer flow in a convergent channel

An incompressible fluid is at rest in a converging channel between intersecting planes when, at some moment of time, the flow towards a sink at the point of intersection is set up impulsively. The motion is taken to be of the boundary layer type, and it is found that the transient part of the flow decays algebraically as the steady state motion becomes dominant. The final decay takes place at the edge of the boundary layer, with the viscous forces affecting the unsteady flow in a region that eventually lies outside the steady state boundary layer.     

Stability of two-phase gas-solid particle flow in a boundary layer

The stability of a boundary layer above a flat plate with a pressure gradient in the case when a gas flow carries suspended particles of an admixture is considered on the basis of the equations for the aeromechanics of heterogeneous media [1, 2]. The investigation is carried out in the framework of the same assumptions as in [3], where the stability of Poiseuille flow in a channel was studied. The velocity profile of the unperturbed flow is selected from the Falkner-Skan family. The Chebyshev spectral element method is used for the calculations.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 60–64, March–April, 1987.     

Laminar boundary layer in flow of a nonequilibrium ionized gas

The motion of a hypersonic body is accompanied by an increase in the gas temperature in the boundary layer up to tens of thousands of degrees, which causes the gas to ionize. Under these conditions there are problems in calculating coefficients of viscosity, diffusion, and heat conduction. Investigations have shown that it is invalid to extrapolate the widely used approximations for transport coefficients in the high temperature region [1–3]. This paper considers the laminar boundary layer in the vicinity of the stagnation point of a blunt body in a stream of monatomic nonequilibrium ionized gas. The main thrust is a more accurate calculation of transport coefficients and an investigation of their effect on profiles of the gasdynamic parameters. A specific calculation is performed for argon by way of example.     

On the wave-cancelling nature of boundary layer flow control

This work deals with the feedforward active control of Tollmien–Schlichting instability waves over incompressible 2D and 3D boundary layers. Through an extensive numerical study, two strategies are evaluated; the optimal linear–quadratic–Gaussian (LQG) controller, designed using the Eigensystem realization algorithm, is compared to a wave-cancellation scheme, which is obtained using the direct inversion of frequency-domain transfer functions of the system. For the evaluated cases, it is shown that LQG leads to a similar control law and presents a comparable performance to the simpler, wave-cancellation scheme, indicating that the former acts via a destructive interference of the incoming wavepacket downstream of actuation. The results allow further insight into the physics behind flow control of convectively unstable flows permitting, for instance, the optimization of the transverse position for actuation. Using concepts of linear stability theory and the derived transfer function, a more efficient actuation for flow control is chosen, leading to similar attenuation of Tollmien–Schlichting waves with only about 10% of the actuation power in the baseline case.     

Numerical simulation of thermal boundary layer profile measurement

Heat transfer rates from a surface can be determined from the slope of the temperature profile measured with a thermocouple wire traversing within a boundary layer. However, accuracy of such measurement can suffer due to flow distortion and conduction through the thermocouple wire. The present numerical study consists of two parts—a 2D simulation of flow distortion due to a cylinder in cross flow near a solid wall and a 3D simulation defined as a fin problem to calculate the thermal profile measurement error due to conduction through the thermocouple wires. Results show that the measured temperature is lower than the true temperature resulting in a 5% under-prediction of local heat transfer coefficient. A parametric study shows that low thermal conductivity thermocouple (E type) with a small wire diameter (76 micron) is desirable to reduce the measurement error in local Nusselt number.