Decreasing pressure losses in microtubes is an important subject, especially when an increase in the flow capacity is required. In the same pumping power, decreasing the pressure drops coincides with increasing the fluid flow rate passing through a microtube. The current study aims to examine how the water pressure drop across a microtube can be affected by the addition of small concentrations of different drag-reducing polymeric agents. A kind of the laminarization behaviour was found by the addition of the selected polymer to the turbulent flow. The effect of the concentration of the drag-reducing agent (DRA) on the observed viscosity and drag values are reported. Moreover, the effects of different types of drag-reducing agents on the friction factor are obtained at the best concentration in the range of examined concentrations. Under this condition the percentage of the drag reduction and increase in the capacity of the flow were respectively 33 % and 36 %. The obtained results show that more drag reduction occurs at a higher flow rate for 20 ppm of the polyacrylamide with a high molecular weight.

We calculated the drag force for asymptotically Lifshitz space times in (d+ 2)-dimensions with the arbitrary dynamical exponent z. We find that at zero and finite temperature, the drag force has a non-zero value. Using the drag force calculations, we investigate the DC conductivity of the strange metals.

The paper presents the results of an experimental investigation wherein the bullet form drag force as a function of oscillating actuator frequency, various voltage and for different orifice/slot configuration are studied. In order to perform the experiment, an axisymmetric bullet shape model with ellipsoidal nose was used in wind tunnel. The synthetic jet actuator was used to flow control at sharp cut end. The experiment was conducted in a wind tunnel with a working diameter of 1000 mm and a maximum velocity of 45 m/s. The measurements were carried out for the Reynolds number from 88000 to 352000 and for relatively large Strouhal numbers up to St = 4. 5 based on model external diameter and free stream velocity. While synthetic jet was switched on, drag coefficient has been reduced by-6% and increased by +22% in relation to the case with the synthetic jet was switched off. The synthetic jet has more impact for relatively low free stream velocity and for single axisymmetric orifice.

Drag force is one of the aerodynamic properties of Chickpea that is used extensively in the pneumatic separation and conveying systems in agricultural machinery and process engineering. Based on dimension eight samples of Chickpea were chosen. In order to hold Chickpeas in the wind tunnel 450 mm length comb was used. There are needles on the comb with 30 mm intervals.The experiment was done at three different moisture levels (42%, 46%, 52% wet basis) and at three different air velocities (10m/s, 12m/s, 15m/s) for eight dimension and at eight replications. Factorial experiment based on completely randomized design was used to analyze data.Effect of dimension moisture content and air velocity on the drag force at α=1% were more significant and their interactions did too. The mean of drag force was 7.923× 10-3 N the highest and the lowest were 18.8× 10-3 N, and 3.91 ×10-3 N, respectively. Drag force increases with increasing dimension moisture content and air velocity.Finally the results are shown based on the regression analysis with the related equations and tables.

The objective of this paper is to examine the effectiveness of wall oscillation as a control scheme of drag reduction. Two flow configurations are considered: constant flow rate and constant mean pressure gradient. The Navier-Stokes equations are solved using Fourier-Chebyshev spectral methods and the oscillation in sinusoidal form is enforced on the walls through boundary conditions for the spanwise and streamwise (for the case of inclination cycle) velocity components. Results include the effects of oscillation frequency, amplitude, oscillation orientation, and peak wall speed on drag reduction at a Reynolds number of 180 based on wall-shear velocity and channel half-width as well as the Reynolds number dependency in both flow configurations. Drag reduction as a function of peak wall speed is compared with both experimental and numerical data and the agreement is good in the trend and in the quantity. Comparison between these two flow configurations in the transient response to the sudden start of wall oscillation, turbulence statistics, and instantaneous flow fields is detailed and differences are clearly shown. This analysis and comparison have allowed some light to be shed on the way that oscillations interact with wall turbulence.

In this paper, the applicability of polymeric coatings to reduce the drag experienced by submerged ax symmetric bodies was investigated experimentally. Two different commercial polymeric coatings were used for this study: 1) Polyacrylamide (PAA), and 2) Polydemethyl siloxane (PDS). Whereas the first polymer is water-soluble; in contrast, the second polymer is hydrophobic. Drag measurements were conducted on a model of the body of interest with a geometrical scale of 1/10. A home-made water column device was used to obtain drag data at Reynolds numbers up to 20,000 (large enough for the annular flow between the exterior of the model and the interior wall of the test cell to be taken as turbulent). Extensive test results obtained using this device revealed that both polymers are effective in reducing the drag coefficient in the range of 20-30 %. The effectiveness of PAA coating, however, was realized not to be steady apparently because of its being washed away by the flowing water. In contrast, steady drag reduction was found to be achievable using the PDS coating.

When the body is running at fully immersed condition in viscous fluid, there are two components of resistance, i.e. frictional resistance and form drag. When it is near the free surface, the additional drag encountered to the body which is wave-making drag. This paper is presents the hydrodynamic performance of high-speed Unmanned Underwater Vehicle (UUV) in fully immersed condition.We did 1000000 (cells) fluid mesh around the body using Navier Stokes (N-S) equations and appropriate boundary conditions. The calculations of drag and lift have been obtained at various speeds and attack angle. The k-e model is used to solve the N-S equations. We firstly calculated for the sphere and the results of pressure distributions and drag are very good and satisfactory with the experimental data. The calculations are extended to the UUV and the pressure distributions and drag are shown in good agreement with data.

This paper is presents the computation of the wave-making drag of underwater vehicle by boundary element method (BEM). The method is employed constant strength doublet and source distributions on each quadrilateral element representing the body and free surface. Using Green's function, boundary integral equation is constituted for all elements by a matrix form to determine the potential on each element, and then calculate the pressure and wave-making drag at different vehicle speeds and water depths. The computed results indicate that the present method is in good agreement with other results and, its results are shown that the method is more capable and powerful tool for prediction and analysis of wave-making drag of underwater (UV11) vehicle.