Computations of instability and turbulent mixing by Nikiforov’s modelRazin, A. N.;Bolshakov, I. V.
2014 Thermophysics and Aeromechanics
doi: 10.1134/S0869864314040027
Abstract The results of modeling several laboratory experiments, including a large class of advanced experimental studies of turbulent flows, are presented. The results of the Meshkov’s “cylindrical” and “planar” experiments on the confluence of two zones of turbulent mixing, the experiments of Poggi, Barre, and Uberoi have been carried out using the Nikiforov’s model. The presented results attest that the Nikiforov’s model qualitatively describes the considered class of flows if the mean gas-dynamic quantities are computed with a high accuracy in the technique, and the width of the front of the finite-difference shock wave does not depend on the size of the computational grid cell.
Formation of the turbulent boundary layer at air blowing through a wall with an abrupt change in boundary conditionsKornilov, V. I.;Boiko, A. V.
2014 Thermophysics and Aeromechanics
doi: 10.1134/S0869864314040039
Abstract Development of an incompressible turbulent boundary layer with air blowing through a finely perforated flat surface, consisting of a permeable region and impermeable region behind, was studied experimentally. The mass flow rate of injected air Q per an area unit was varied from 0 to 0.2 (kg/s)/m2. Detailed data about the internal structure of the boundary layer in the flow region, characterized by an abrupt change in the flow conditions at the boundary of permeable and impermeable regions, were obtained. A consistent decrease in the local values of skin friction coefficient along a permeable sample and with an increase in the values of Q, reaching 90% at maximal Q, is shown. The role of the flow region behind the zone with an abrupt change in the boundary conditions, essential from the viewpoint of skin friction reduction, is revealed.
Determination of true temperature of opaque materials via spectral distribution of thermal radiation intensity: application of Wien’s displacement lawRusin, S. P.
2014 Thermophysics and Aeromechanics
doi: 10.1134/S0869864314040052
Abstract The equation for the derivative connecting surface spectral emissivity, wavelength, and thermodynamic (true) temperature of an opaque heated body at the point of spectral maximum of thermal radiation was obtained. It is suggested to solve the problem of determining the true temperature of an opaque surface in two stages. At the first stage, the spectral range, most comfortable for approximation of body emissivity, is distinguished using a special function (relative emissivity), and the true temperature is determined. At the second stage, the true temperature is determined again using the resulting equation for the derivative. The dimensionless parameter that connects the radiative properties of material with the peak wavelength and characterizes deviation from Wien’s displacement law was found. If the absolute value of this parameter is low, the value of true temperature obtained at the first step can be specified at the second stage. This approach is illustrated by experimental data obtained at comparison of spectral radiance of the temperature lamps.
Heat transfer characteristics for disk fansPrikhodko, Yu. M.;Chekhov, V. P.;Fomichev, V. P.
2014 Thermophysics and Aeromechanics
doi: 10.1134/S0869864314040064
Abstract Multiple-disk fans belong to the class of friction machines; they can be designed in two variants: centrifugal disk fans and diametrical disk fans. Flow patterns in these two types of machines are different, and they possess different heat transfer characteristics. The paper presents results of experimental study for a centrifugal disk fan under atmospheric pressure with air taken as working gas. The radial temperature distribution for a disk was obtained at different rotation speed of the rotor and different heating of the disks. Heat transfer characteristics of a centrifugal disk fan and a diametrical disk fan were compared. The research results demonstrate a higher heat transfer efficiency for centrifugal design versus diametrical disk design.
In-water gas combustion in linear and annular gas bubblesTeslenko, V. S.;Drozhzhin, A. P.;Medvedev, R. N.;Batraev, I. S.
2014 Thermophysics and Aeromechanics
doi: 10.1134/S0869864314040088
Abstract A new pulsed-cyclic method of in-water gas combustion was developed with separate feed of fuel gas and oxygen with the focus on development of new technologies for heat generators and submerged propellers. The results of calorimetric and hydrodynamic measurements are presented. In-water combustion of acetylene, hydrogen, and propane was tested with the operation frequency of 2–2.5 Hz and with a linear injector. The combustion dynamics of combustion of stoichiometric mixture with propane (C3H8+5O2) was studied for a bubble near a solid wall; the produced gas bubble continues expansion and oscillations (for the case of linear and annular bubbles). It was demonstrated that gas combustion in annular bubbles produces two same-magnitude pulses of force acting on the wall. The first pulse is produced due to expansion of combustion products, and the second pulse is produced due to axial cumulative processes after bubble collapse. This process shapes an annular vortex which facilitates high-speed convective processes between combustion products and liquid; and this convection produces small-size bubbles.
Characteristics of dual-combustion ramjetGounko, Yu. P.;Shumskiy, V. V.
2014 Thermophysics and Aeromechanics
doi: 10.1134/S0869864314040106
Abstract The authors discuss a possibility to use a diverging dual-combustion chamber as applied to high-supersonic boost ramjets operating at flight Mach numbers up to Mf = 8–10. Due to diverging, this chamber allows beginning the ramjet operation from flight Mach numbers Mf ini = 2–3. The diverging combustion chamber is characterized by a ratio of its exit cross-sectional area relative to the cross-sectional area of air-intake throat. This expansion area ratio is determined at Mf = Mf ini, but it should be the same at all flight Mach numbers Mf ⇒ Mf ini, and depends on two factors: the location of a normal shock in the air-intake throat and the condition of reaching the critical velocity at the chamber exit. The dual-combustion chamber provides heat supply in its alone channel first to the subsonic flow and then, along with acceleration of the flying vehicle, to the supersonic flow, which is bound with a decrease in relative heating of working gas. Calculations of characteristics of an exemplified dual-combustion ramjet considered with a twodimensional air-intake were performed in the range of Mf = 3–7.