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To provide an analysis of turbulent flow in plane diffusers for graduate and postgraduate students (researchers) which can help them to understand turbulent flows and turbulence modelling.

Steady, incompressible, turbulent flow in two‐dimensional plane diffusers, where Reynolds averaged Navier‐Stokes (RANS) equations were simplified using the theory of turbulent boundary layers in integral form adjusted for the internal flow. To close the RANS equations, the mixing length model proposed by Michel et al., which was previously used for the calculation of turbulent flow in a straight channel with a uniform cross section, is applied for the calculation of the turbulent flow in plane diffusers. Also, in this paper, the velocity profile is approximated in every cross‐section of the diffuser by a six‐order polynomial, whose coefficients depend upon the three form parameters. Using this transformation, the system of governing equations was reduced to the three ordinary differential equations which were solved numerically.

A comparison between results obtained (velocity profiles) and experimental data obtained using HWA and LDA shows very good agreement. The method of integral equations of boundary layer is a relatively old method and tends to be forgotten since more advanced methods have been introduced. However, the results obtained using this method for the calculation of turbulent flow in a plane diffuser show a very good agreement with experimental data. Therefore, in engineering applications when simplicity and low‐cpu times are required, the integral method can still be applied successfully.

This paper offers practical help to an individual starting his/her research in the computational fluid dynamics (turbulence modelling).

OVER A QUARTER of a century ago, in September 1938, we published a review of diffuser behaviour by G. N. Patterson which, together with one of its main information sources by Gibson, has formed the accepted guide to diffuser design. Patterson's paper was broad in scope and made clear reference to the effect of parameters which were not fully investigated until much later. It is the purpose of this paper to review experimental work, much of it being along the lines formulated by Patterson, and to indicate the improved analytical understanding of diffusers.

The purpose of this paper is to find the optimum design of diffuser of supersonic wind tunnel in order to access the minimum overall pressure drop in wind tunnel, using evolutionary algorithm.

The authors developed a genetic algorithm (GA) code to calculate the shape of a diffuser with flexible walls in order to have the maximum pressure recovery. The two-dimensional turbulent and compressible flow was analyzed numerically using shear-stress transport and Advection Upstream Splitting Method (AUSM)+ turbulence models and its optimization with GA.

The results of this study indicate that elitist GA promises a powerful method for optimization of the wind tunnel diffuser. Separation zone is reduced by 22.2 percent at the convergent part of diffuser and 56 percent at the divergent part of diffuser. The efficiency of new optimized wind tunnel diffuser increased by 83 percent in comparison to the sample of supersonic wind tunnel.

It has been observed that AUSM+ method and shape design optimization using GA are robust and efficient technique to optimize wind tunnel diffuser.

In this paper, the performance simulation of a vortex controlled diffuser (VCD) has been carried out in low Reynolds number regime. The two‐dimensional steady differential equations for conservation of mass and momentum has been solved for the Reynolds number ranging from 20 to 100, aspect ratio for 2 and 4, and bleed fraction for 2 per cent, 5 per cent and 10 per cent. The effect of each variable on the diffuser efficiency and the stagnation pressure has been studied in detail. From the study, it has been revealed that when the bleed is incorporated, the VCD behaves in a completely different manner from that of a sudden expansion as far as the variation of total pressure along the diffuser is concerned. For a given Reynolds number and aspect ratio, the diffuser efficiency has been noted to be increasing with increase in bleed fraction. VCD with an area ratio of around two has been found to be most suitable. The top corner has been noted to be the most desirable location of the bleed slot for the best performance of the VCD for the considered Reynolds number regime.

ONE of tin: most important causes of low efficiency in duel systems is tin; large loss which accompanies a transformation from kinetic energy to pressure. The exit cones of wind tunnels and turbines and the expanding entries to cooling duets and air‐intakes on aircraft are some of the duct systems which lvcpiirc ellicient expansions of the flow.

A QUARTER of a century ago, in September 1938, this journal published a review of diffuser behaviour by G. N. Patterson1 which, together with one of. its main information sources by Gibson,2 has formed the accepted guide to diffuser design. Patterson's paper was broad in scope and made clear reference to the effect of parameters which were not fully investigated until much later. It is the purpose of this paper to review experimental work, much of it being along the lines formulated by Patterson, and to indicate the improved analytical understanding of diffusers.

The purpose of this study is to evaluate the effect of the perimeter heating load about the air diffusion performance index (ADPI) and propose a selection guide for proper line diffuser when perimeter heating load exists.

A high sidewall line diffuser was installed into a test room following the ISO standard 5219. The velocity and temperature distributions and the ADPI values are obtained numerically with 12 cases when the air flow rates are 425, 730 and 950 CMH and the heating loads are 0, 25, 50 and 75 percent of the total heating load, 2,143 W.

The ADPI decreases according to the increases of the flow rate on every heat load ratio of the present study except 0.75 with the line diffuser installed at the high sidewall. And we produced ADPI curves when the sidewall heating load exists or not in the same air flow rate and supply conditions. From that, it is possible to assume that the throw length guarantees more than 80 percent of ADPI with heating load on the wall.

Further work by the authors is focusing on making of database of various other diffusers which are generally used in the field.

This paper provides a modified selection guide for proper sidewall line diffusers to field engineers when perimeter heating load exists on the walls.

A solution to increase the energy production rate of the wind turbine is proposed by forcing more air to move through the turbine working section. This can be achieved by equipping the rotor with a diffusing channel ended with a brim (diffuser augmented wind turbine – DAWT). The purpose of this paper is to design an experimental stand and perform the measurements of velocity vector fields through the diffuser and power characteristic of the wind turbine.

The experiments were carried out in a small subsonic wind tunnel at the Institute of Turbomachinery, Lodz University of Technology. An experimental stand design process as well as measurement results are presented. Model size sensitivity study was performed at the beginning. The experimental campaign consisted of velocity measurements by means of particle image velocimetry (PIV) and pneumatic pitot probe as well as torque and rotational velocity measurements.

Characteristics (power coefficient vs tip speed ratio) of the bare and shrouded wind turbine were obtained. The results show an increase in the wind turbine power up to 70-75 per cent by shrouding the rotor with a diffuser. The mechanisms responsible for such a power increase were well explained by the PIV and pneumatic measurement results revealing the nature of the flow through the diffuser.

Experimental stand for wind turbine rotor testing is of a preliminary character. Most optimal methodology for obtaining power characteristic should be determined now. Presented results can serve as good input for choice of stable and reliable control system of wind turbine operational parameters.

A 3 kW DAWT is being developed at the Institute of Turbomachinery, Lodz University of Technology. Aim of the study is to design a compact and smart wind turbine optimised for low wind speed conditions. Developed wind turbine has a potential to be used as an effective element within a net of distributed generation, e.g. for domestic use.

Research carried out is the continuation of theoretical study began in 1970s. It was also inspired by practical solutions proposed by Japanese researchers few years ago. Presented paper is the summary of work devoted to optimisation of the DAWT for wind conditions in the region. Original solution has been applied, e.g. for experimental stand design (3D printing application).

The purpose of this study is to determine the best vaned diffuser design that can generate higher pressure output at a predetermined speed.

Several vaned diffusers of thin, flat-type design with different number of blades and blade angle were fabricated. The vaned diffusers were fitted inside the turbocharger compressor and test on a cold-flow turbocharger test rig. A Taguchi L₂₇ orthogonal array is selected for analysis of the data. Influence of number of blades, blade angle and rotational speed on output pressure is studied using the analysis of variance (ANOVA) technique. Finally, confirmation tests are conducted to validate the experimental results.

The optimum design parameters of the vaned diffuser using signal-to-noise ratio analysis were six blades type, blade angle of 18° and rotational speed of 70,000 rpm. Results from ANOVA showed that the speed has the highest influence on output pressure. The number of blades and blade angle produced the least effect on the pressure output.

The study used the turbocharger with the impeller size 60 mm and adapted vaned diffuser to increase the output pressure.

The purpose of this paper is to examine the initial mixing of wastewater discharged from submerged outfall diffusers and the influence of port configurations on wastewater distribution based on computational results.

Marine wastewater discharges from multiport diffusers are investigated by numerically solving three-dimensional and uncompressible two-phase flow fields. A mixture model simulates this flow and the standard k-e model to resolve flow turbulence; inter-phase interactions were described in terms of relative slip velocity between phases. Computations were performed for two values of the port spacings s/H with different current Froude numbers F.

Computational results compared well with previous laboratory measurements. Numerical results reveal that for both the closely spaced (s/H=0.21) and widely spaced (s/H=3.0) ports, the normalized dilution Sn becomes independent of F; further, the length of the near field xn and the spreading layer thickness hn are functions of F. For the closely spaced ports, the wastewater discharge behaves like a line plume, the Coanda effect is obvious, quasi-bifurcation is present, horseshoe structures of the jets in the planes are rapidly produced and then squashed and elongated, and the jet trajectories based on maximum velocity precede those based on maximum concentration. For the widely spaced ports, the wastewater discharge behaves like a point plume, the Coanda effect is not obvious, bifurcation is present, horseshoe structures of the jets in the planes are gradually produced and become ellipses, and the jet trajectories based on maximum velocity are similar to those based on maximum concentration.

Semi-empirical equations are presented to predict major near field characteristics. These provide guidance for designing multiport diffusers and assessing environmental impact.