Methods of experimental investigations of the Görtler instability in boundary layers (review)Gimon, T. A.; Lukashevich, S. V.; Morozov, S. O.; Shiplyuk, A. N.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s0869864322020019
The paper presents a review of the methods of experimental investigations of the Görtler vortices in boundary layers. The proposed models are used in experiments for the analysis of the Görtler instability; the major methods of Görtler vortex generation are described. It has been revealed that spontaneous uncontrolled emergence of the Görtler vortices is caused by the roughness of model surfaces (especially in the area of the leading edge of a plane model) and free-stream disturbances. Effective methods of generation of controlled stationary and nonstationary disturbances generating the Görtler vortices in the boundary layer are described. The methods of experimental measurements of boundary layer parameters in the presence of the Görtler vortices are presented; the diagnostic capabilities of these methods are demonstrated, and the major scientific results obtained by these methods are reported.
Control of mixing of gas flowsLatypov, A. F.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s0869864322020032
The present study shows that enhancement of the mixing efficiency (increasing the total pressure of the mixture) requires expansion of the cross section of the high-pressure gas flow. It is found that the parameters of the mixtures are identical in the cases of distributed and one-step mixing of the perfect gas flows. However, distributed mixing (multistep mixing as a finite-dimensional analog) is more reasonable because it ensures flow control to provide conditions to satisfy the existence of a steady flow in the channel.
Investigating the possibility of using the turbo-expander for natural gas pressure reduction stationsMoghadam Dezfouli, A.; Saffarian, M. R.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s0869864322020044
Using a turbo-expander instead of a regulator, the output temperature will be reduced. Reducing the gas temperature to the freezing temperature of the water within gas can damage the station equipment. In the present work, the gas flow is simulated in a turbo-expander under the real conditions of natural gas pressure reduction stations and the amount of gas temperature reduction during this process is predicted. The equations of continuity, Navier-Stokes, energy, and k−ε turbulence model are solved with the help of CFD. Simulation results for twelve real cases, including three different input pressures, two different output pressures, and two different input temperatures are obtained. Results show that almost for every 9 psi pressure reduction, the temperature decreases by 1 °C. Also, the highest temperature drop occurs in the middle part of the outlet. Results show that due to a very low temperature of outlet gas, using a turbo-expander in the case of high-pressure stations is not recommended. In the case of medium pressure stations, a turbo-expander may be used with a heater. In the case of low-pressure stations, as the temperature at the center of outlet is lower than at the other points, installing a flow mixer can solve the freezing problem.
Using the resonance phenomenon for a high efficiency of a pulse-operating ejectorVoevodin, A. V.; Petrov, A. S.; Soudakov, G. G.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s0869864322020056
The paper presents the results of computational and experimental study for parameters of the innovative pulse-mode ejector used as a flow control device for flight vehicles. The ejector comprises a Helmholtz resonator adjusted to a certain resonant frequency. The computational and experimental results revealed the existence of resonant modes in ejector operation providing a higher efficiency. Simulation for internal aerodynamics for the pulse-mode ejector can explain a high efficiency calculated by the high-pressure gas flow rate, as well as advantages/shortcomings in other metrics (compared to the steady operation mode). The margins of efficient operation of this resonance-operating ejector in the metrics of gas flow rate are calculated. The perspectives for using the ejector as a flow control devices are discussed.
Analytical analysis on g-jitter induced natural convection flow behaviour in existence of Lorentz force in a vertical micro-channelAina, B.; Pius, T.; Kamaluddin, S.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s0869864322020068
In this paper, analytical analysis on g-jitter induced natural convection flow in microgravity behavior is theoretically examined in the existence of Lorentz forces in a vertical micro-channel. Effects of velocity slip and temperature jump are also taken into account. A single component of time harmonic g-jitter is considered. Solutions are obtained for the velocity and temperature profile with a combined effect of oscillating g-jitter driving force and induced Lorentz force, the latter resulting from an application of a transverse magnetic field. Four limiting cases are studied based on the solutions. Numerical procedures are under see for various active parameters namely: g-jitter induced frequency, fluid-wall interaction, rarefaction, and Hartmann number. The results of the research unveiled that the amplitude of the velocity decreases at a rate inversely proportional to the g-jitter induced frequency and with increase in the Hartmann number. The induced flow oscillates at the same frequency as the affecting g-jitter. Furthermore, a magnetic field can be applied to suppress oscillating flows joined with g-jitter, it is more effective in damping low frequency flows but only has a moderate damping effect on the flow induced by high frequency g-jitter. Also, the temperature jump condition induced by the effects of rarefaction and fluid-wall interaction parameter plays relevant impact in slip-flow natural convection.
An impact of thermal boundary conditions on characteristics of a non-Newtonian fluid flowing through a sudden pipe contractionRyltseva, K. E.; Shrager, G. R.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s086986432202007x
A physical-mathematical model of a laminar axisymmetric flow of a power-law fluid through a sudden pipe contraction under non-isothermal conditions is presented with allowance for dissipative effects. The rheology of the liquid medium is determined by the Ostwald — de Waele law. The apparent viscosity is specified as a temperature-dependent function. Two options for setting the temperature boundary conditions on a solid wall are considered: the first implies invariable temperature along the pipe wall; and the second assumes a constant temperature value on the wall except for the area in the contraction plane vicinity, where the boundary is exposed to a zero-heat flux. The process is studied numerically using the finite-difference method. The main characteristics of the flow are calculated and visualized. The effect of thermal boundary conditions on the fluid flow structure and local pressure losses is analyzed.
Prediction of heat transfer and fluid flow in a cross-corrugated tube using numerical methods, artificial neural networks and genetic algorithmsEiamsa-ard, S.; Chuwattanakul, V.; Safikhani, H.; Promthaisong, P.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s0869864322020081
In this paper, multi-objective optimization of geometric parameters of spirally-cross-corrugated (SCC) tubes is carried out using numerical methods, genetic algorithms (GAs), and artificial neural networks (ANNs). First, the turbulent flow is numerically characterized in various SCC tube geometries using a finite volume method with the realizable k−ε turbulence model. In this approach, the heat transfer coefficient and friction factor f in tubes are calculated. First, two parameters (corrugation pitch-to-diameter ratio (PR = p/D) and corrugation depth-to-diameter ratio (DR = e/D)) are examined in a turbulent flow regime that affects the strength of quadruple longitudinal vortex flows and thermal characteristics. At the final step, using the obtained polynomials for neural networks, multi-objective genetic algorithms (NSGA II) are employed for Pareto based multi-objective optimization of flow parameters in such tubes. This analysis considers two conflicting parameters, f Re and Nusselt number Nu with respect to three design variables, Reynolds number Re, values of PR and DR. Some interesting and important relationships between the parameters and variables mentioned above emerge as useful optimal design principles involved in the heat transfer of such tubes through Pareto based multi-objective optimization. Such important optimal principles would not have been obtained without the use of a combination of numerical techniques, ANN modeling, and the Pareto optimization.
Simulation of a pulsating flow in a pipe with local constrictions as applied to hemodynamics of blood vesselsMazo, A. B.; Kalinin, E. I.; Molochnikov, V. M.; Dushina, O. A.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s0869864322020093
The oscillating flow of a viscous incompressible fluid in a rigid circular pipe with local constriction has been studied numerically. Fluid viscosity and density, channel diameter and constriction, as well as amplitude-frequency characteristics of the flow rate are identical to those of the blood flow in the human popliteal artery with stenosis. Reynolds number in the area of stenosis is Re ≈ 5·103, dimensionless pulsation frequency is Sh = 0.43·10−3, and normalized constriction of the channel is δ = d/D = 0.4. The flow under consideration is characterized by the fact that during one oscillation period, the fluid flow rate changes direction four times. This contributes to laminar-turbulent transition when the jet discharges from a constriction throat into the main flow. Qualitative features and quantitative parameters of pulsating flow have been determined including distribution of friction stresses along the channel wall.
Transient Taylor—Dean flow in a composite annulus partially filled with porous materialJha, B. K.; Yusuf, T. S.
2022 Thermophysics and Aeromechanics
doi: 10.1134/s086986432202010x
A semi-analytical study is performed to examine transient Taylor-Dean flow in a composite annulus within two concentric cylinders partially filled with porous material. In the present model, the circumferential flow is set up as a result of azimuthal pressure gradient as well as the rotation of the two concentric cylinders. The equation governing the flow is rendered non-dimensional and transformed into ordinary differential equation using the well-known Laplace transform technique. The solution is then transformed back to the time domain using the Riemann-sum approximation (RSA) approach. The solution of the steady-state of the present model including the implicit finite difference (IFD) is also computed to validate the result obtained from the RSA approach. It is important to note that the surface resistant force can be controlled by choosing suitable values of β.