The aim of this study is
to investigate the effect of mass flow rate on film cooling effectiveness
and heat transfer over a gas turbine rotor blade with three staggered rows
of shower-head holes which are inclined at 30° to the spanwise direction,
and are normal to the streamwise direction on the blade. To improve
film cooling effectiveness, the standard cylindrical
holes, located on the leading edge region, are replaced with
the converging slot holes (console). The ANSYS CFX has been
used for this computational simulation.
The turbulence is approximated by a k-e model. Detailed film effectiveness distributions
are presented for different mass flow rate. The numerical results are
compared with experimental data.
Results of an
experimental study of the excitation of high-intensity disturbances by a weak
external shock wave in laminar boundary layer on flat-plate models with sharp
and blunted leading edges at М = 2.5 are reported. The field of disturbances produced by a 2D sticker
in turbulent boundary layer on the wall of wind-tunnel test section in the free
stream is shown to have the form of an
N-wave. It is found that, on the blunted plate, the intensity of pulsations
produced by weak external shock waves in boundary layer several times exceeds
the intensity of pulsations produced in boundary layer on the model with a
sharp leading edge.
A possible influence of the deflection of control surfaces on the aerodynamics of an axisymmetric slender configuration at supersonic flow speeds is considered. A classical configuration consisting from the fuselage in the form of a body of revolution and having cross frontal fins and six-blade trailing stabilizers is considered as the investigation object. The physical flow pattern at the deflection of horizontal fin consoles is investigated and the estimates are obtained for the influence of this deflection on both the characteristics of elements (the body and stabilizers) as well as on the integral aerodynamic characteristics of the entire configuration. Numerical computations of the flow have been done at the freestream Mach number М = 3 in the range of attack angles α = 0-10° and the angles of the control surfaces deflection δcs = ±5° on the basis of the averaged Navier-Stokes equations and the SST k-ω turbulence model.
The numerical model of
momentumless turbulent wake in a horizontally homogeneous shear flow of
linearly stratified medium has been constructed. Based on this model,
the investigation of the wake dynamics has been performed. The obtained data demonstrate
the transformation of the zone of turbulent perturbations and
internal waves generated by the wake under the action of shear flow,
which leads to the deceleration of turbulence decay at large time values
after the body passage.
This article presents an investigation on heat transfer enhancement in a round tube inserted with a helically twisted tape. The effects of a helically twisted tape with alternate axis (HTT-A) on heat transfer, friction factor, and thermal performance factor behaviours are reported for the turbulent regime. HTT-A geometries are tape pitch to tube diameter, P/D = 1.0, 1.5, and 2.0; alternate length to pitch length, l/P = 1.0, 1.5, and 2.0; twisted length to tape width, y/W = 3.0; and tape width to tube diameter, w/D
= 0.2. The experiment has been performed by varying the volumetric air flow rate in order to adjust Reynolds number ranging from 6 000 to 20 000. The wall of the testing tube is uniformly heated as a constant heat flux while the tests are covered with thermal insulations to reduce heat loss to surroundings. Thermal performance is evaluated by comparing the present experimental results with the results of the modified HTT-A and also those obtained from previous study (conventional helically twisted tape, HTT). The thermal performance of tested tube with HTT-A is evaluated to obtain the degree of heat transfer enhancement and friction factor induced by HTT-A with respect to the plain tube under the same test conditions. Evenly, it is interesting to observe that the tube with HTT-A consistently possesses higher heat transfer and thermal performance factor than those with the HTT around 14.1% and 1.9%, respectively. The HTT-A with the smaller pitch ratio and adjacent twist length provides higher heat transfer rate and friction factor than the one with larger pitch ratio and alternate length as a result of a larger contact surface area, stronger swirl intensity and, thus, better fluid mixing near the tube wall. In the range determined, the tubes with the largest pitch ratio (P/D
= 2.0) and smallest alternate length (l/P = 1.0) give the highest thermal performance factor
at around 1.35. In
addition, the empirical correlations of the Nusselt number, friction
factor, and thermal performance factor are also described.
The analysis and evaluation of the forces acting on
the particle in a linear shear flow of power-law fluid (PLF) in the presence of the wall were performed. Using the
results of a series of computations for a model problem with a spherical particle near a flat wall in the Reynolds number range of 0-200 and the distance to the wall from 0 to 20
particle diameters, the correlation formulas for calculating the coefficients
of drag force and lift force were obtained. Special attention was paid to the
behavior of the forces acting on the particle approaching the wall.
The paper presents an investigation of the influence of thermophoresis on MHD mixed convective heat and mass transfer of a viscous, incompressible and electrically conducting fluid along a vertical flat plate with radiation effects. The plate is permeable and embedded in a porous medium. To describe the deviation from the Darcy model the Forchheimer flow model is used. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing partial differential equations are transformed into a system of ordinary differential equations using similarity transformation. The nonlinear ordinary differential equations are linearized by using quasi-linearization technique and then solved numerically by using implicit finite difference scheme. The numerical results are analyzed for the effects of various physical parameters such as magnetic parameter Ha, mixed convection parameter Rad/Ped, Reynolds number Red, radiation parameter R, thermophoretic parameter τ, Prandtl number Pr, and
Schmidt number Sc. The heat transfer coefficient is also tabulated for
different values of physical parameters.
The thermal state of
a translucent selectively absorbing medium was studied by the methods
of numerical simulation at different values of the optical properties of
boundaries and heat transfer from the left surface in approximation of
one-phase Stefan problem. The temperature fields and densities of
resultant radiation fluxes as well as the thermal state of the left
boundary and dynamics of layer reduction in the melting process were
analyzed. The processes of phase transition in a flat layer of
selective and gray absorbing media and emitting media were compared, and their
fundamental differences were shown.
Plasma technology was developed to create
protective-decorative coatings on the wood surfaces. Experimental investigation on applying the protective
coating using the low-temperature plasma energy as well as studies of the distribution of
temperature fields over the section of the treated workpiece have
been carried out, and the calculated results have been compared with
the experimental data.
The computational experiments using the “Overfire Air” (OFA) technology at the coal dust torch combustion in the combustor of the BKZ-160 boiler of the heat power plant No. 2 in Almaty have been conducted. The results show a possibility of reaching a reduction of the emission of noxious nitrogen oxides NOx and minimizing the energy losses. The results
of numerical experiments on the influence of the additional air supply on
the main characteristics of heat and mass transfer are presented. A
comparison with the base regime of the solid fuel combustion when there is no
supply of the additional air (OFA = 0 %) has been made.
