JOURNAL OF MECHANICAL ENGINEERING AMIRKABIR (AMIRKABIR)
Year:2012 | Volume:44 | Issue:1|Papers Count:9

An experimental investigation is conducted to study the effect of vertical distance and inclination angle of a S-shaped channel on two-phase flow patterns. Five flow patterns of vortex plug, vortex slug, vortex wavy-annular, churn and mist packet annular were observed. Flow pattern maps were obtained for each case and then compared based on the different vertical distance and inclination angle to perform a parametric study. Increasing mid-section length and inclination angle cause the transition to vortex plug flow pattern to occur at higher liquid velocities as well as a greater area of churn flow pattern at the expense of smaller vortex slug flow pattern area. However, increasing mid-section length and decreasing inclination angle, ends in smaller area of mist packet annular area. It is revealed that for higher midsection lengths, effect of increasing inclination on shifting transition lines between flow patterns is more determining.

In this study, the effect of acoustic streaming on heat transfer enhancement of a down-ward-facing horizontal heating surface in a closed cylindrical enclosure filled with water was investigated experimentally. Standing waves were generated between the heating source as a reflector and vibrating lower plate. Acoustic streaming is a steady circular flow induced by this standing waves field. The upper plate was heated with a constant heat flux and side-walls were kept at the constant temperature.Therefore, the gravitational effects were negligible and the heat transfer enhancement was due to ultrasonic vibrations. In order to find out the best range of ultrasonic power, the acoustic pressure was measured. The results show that the enhancement of the heat transfer can be up to 400% by the ultrasonic vibrations. The increase in the transducer power and the decrease in the height of the heater cause the higher heat transfer coefficient in the enclosure. In addition, the increase in cavitation phenomenon severely weakens the increase in heat transfer coefficient.

Increase of environmental pollution and stricted emission legislations has forced companies to produce automobiles with the lower air pollutants. In this respect, discharge of blowby gases into the environment is prohibited and recirculating the gases into the combustion chamber and burning them is used as the accepted solution. In addition, using EGR technique to control and reduce nitrogen oxides in internal combustion engines has been quite effective. An important common feature of these two methods is that if they have not employed correctly the increase of other pollutants and significant engine power reduction may occur which is mostly due to maldistribution of recirculated gases in the manifold. Besides the injection position that has significant role in distribution of injected gas, it seems that other parameters such as the engine speed, the velocity and angle of injection may play a great role on the distribution of injected gases. In this numerical study the effect of these parameters on distribution of injected EGR or blowby gases into the EF7 intake manifold are determined. Results show inject-ion angle and engine speed have the least and the most effect on injected gases distribution, respectively.

In this paper, the performance of a metal porous radiant burner is investigated experimentally. To study the effect of firing rate and equivalence ratio, some tests have been carried out in five different firing rates and in a range of equivalence ratios which the flame is stable in the porous media. These parameters have been investigated on three porous media, which are formed from fine and coarse meshes. The results show that the surface temperature increases with increasing firing rate. In each firing rate, the equivalence ratio corresponding to the maximum temperature is determined. The maximum temperature occurs in equivalence ratios less than one (0.7-1) and Radiation efficiency of the burner decreases with increasing firing rate. The maximum radiation efficiency takes place in equivalence ratio corresponding to the maximum surface temperature. In a specific firing rate, the maximum temperature for the combined porous media (two layers of fine mesh and one layer of coarse mesh) occurs in an equivalence ratio less than that of the other porous media. The obtained results are in a good agreement with the other studies.

Smoke and toxic gases created by fire accidents in tunnel are very harmful for tunnel users health and safety .So fresh air supply for fire smoke control in the fire upstream, is important. Thus, the critical velocity is a most important factor for this. In order to determine the critical velocity during fire in the Alborz tunnel 3dimensional model of the tunnel and fire was created by FDS software. Fire with 100 mw size for 960second in model with 500m length was simulated. Fire and Smoke was modeled by HRR and heptanes’ combustions. Unsteady flow and combustions was simulated by LES and Eddy break up model. Model was meshed by 50 cm cell. Finally, simulation result was validated by experimental equation. simulation predicted value for critical velocity is 3.5 m/s which have good agreement with Oka and Atkinson experimental equation so we propose 3.5 m/s as critical velocity for fire with 100 mw in Alborz Tunnel.

In this study, a design cycle of strap on booster is presented. This procedure, based on conceptual design of solid rocket motor and statistical studies of strap on booster, is derived. The conceptual design, usages the collaborative design that enables the user interfaces to affection the design parameters. Afterwards, the software of solid rocket design and simulation of missile flight has been produced.

Computational hydrodynamics method was formulated and implemented for marine propellers. In this paper, a design methodology for predicting steady hydrodynamic performance of contra rotating propeller (CRP) has been developed based on boundary element method. The potential flow around fore propeller and aft propeller has been analyzed. In addition, with computation of induced wake distribution, interaction between fore and aft propellers are contemplated. This method for a typical contra-rotating propeller is applied. The results include hydrodynamic performance coefficients, overall force and torque on the CRP, circulation distributions and comparison of induced wake at position of distance between two propellers and induced wake at position of downstream of aft propeller. Numerical results show that the hydrodynamic performance predictions agree well with the experiment data.

Damage of a ship may cause flooding of some compartment. In extreme case it may result in the total loss of the vessel. As far as the probability of damage of a ship in seaway is concerned, there is no confidence for not happening damage of a ship. In a case of damaged ship, motion in wave is coupled with mass of flooded water where the rate of flooding itself is also coupled with the damaged ship motions. Normally damage is happening in harsh sea conditions where sea waves are the main feature of such environment. On that basis, it is needed to analyze damaged ship motions in waves. In this article, an attempt has been made to analyze a damaged ship motions in sea wave focusing on three motions, heave, pitch and roll. A mathematical model is developed in which the equation of ship motions and mass of flooding are solved simultaneously in time domain. A computer code is developed and validated by comparing with some published results. A damaged naval ship behaviors in sea waves are calculated and results are discussed.

The sound produced by the engine penetrates into the airplane through the structure and fuselage is still a grave concern for turboprop plane designers. The engine's propellers rotation is the main source of the sound in this kind of planes, the sound is transmitted to the fuselage through the structure and air so makes it vibrated. The decrease of noise made in the planes by dampers such as rubber, visco-elastic, and other non-dynamic absorber is not possible due to frequency low level. The present study investigates the designing of dynamic absorber for installing on the fuselage to absorb vibration and damping of the sound energy in the structure of the plane which makes the transmission way of vibration and sound possible in the structure. In the beginning, the theoretical relationship to design tunable dynamic absorber is gained, then the finite element model of the absorber is analyzed by ANSYS, and at the end, structuring and examining it for turboprop Antonov-140 is carried out.