Abstract:A method for simultaneously visualizing the two-dimensional distributions of temperature and soot volume fraction in an ethylene flame was presented. A single-color charge-coupled device (CCD) camera was used to capture the flame image in the visible spectrum considering the broad-response spectrum of the R and G bands of the camera. The directional emissive power of the R and G bands were calibrated and used for measurement. Slightly increased temperatures and reduced soot concentration were predicted in the central flame without self-absorption effects considered, an iterative algorithm was used for eliminating the effect of self-absorption. Nine different cases were presented in the experiment to demonstrate the effects of fuel mass flow rate and oxygen concentration on temperature and soot concentration in three different atmospheres. For ethylene combustion in pure-air atmosphere, as the fuel mass flow rate increased, the maximum temperature slightly decreased, and the maximum soot volume fraction slightly increased. For oxygen fractions of 30%, 40%, and 50% combustion in O 2 /N 2 oxygen-enhanced atmospheres, the maximum flame temperatures were 2276, 2451, and 2678 K, whereas combustion in O 2 /CO 2 atmospheres were 1916, 2322, and 2535 K. The maximum soot volume fractions were 4.5, 7.0, and 9.5 ppm in oxygen-enriched O 2 /N 2 atmosphere and 13.6, 15.3, and 14.8 ppm in oxygen-enriched O 2 /CO 2 atmosphere. Compared with the O 2 /CO 2 atmosphere, combustion in the oxygen-enriched O 2 /N 2 atmosphere produced higher flame temperature and larger soot volume fraction. Preliminary results indicated that this technique is reliable and can be used for combustion diagnosis.
The technology of scavenging ambient energy to realize self-powered of wireless sensor has an important value in practice. In order to investigate the effects of piezoelectric-patch length and the shape of front bluff body on energy conversion of the wind energy harvester by flow-induced vibration, the characteristics of a piezoelectric wind energy harvester based on bluff body are experimentally studied in this work. Four different section shapes of the bluff body, including triangular cylinder, trapezoidal cylinder, reverse trapezoidal cylinder, and square cylinder, are tested. The piezoelectric patch is attached on the leeward side of the bluff body. The lengths of piezoelectric patch are considered as 1.0D–1.4D (D is the characteristic length of the bluff body). It is found that the length of the piezoelectric patch and the shape of the front bluff body play a vital role in improving the performance of wind energy harvester. For the reverse trapezoidal cylinder and square cylinder, the back-to-back vortex-induced vibration (VIV) and galloping phenomenon can be observed. In addition, the energy harvesting performance of the reverse trapezoidal cylinder piezoelectric harvester is the best. The maximum average peak voltage of 1.806 V and the output power of P=16.3 μW can be obtained when external resistance and the length of piezoelectric patch are 100 KΩ and 1.1D, respectively.
In order to understand the gap flow between two cylinders, the characteristics of flow around two stationary cylinders and the flow-induced vibration of two staggered cylinders with roughness strips are numerically studied. The lift-drag responses, Strouhal number (St) and wake structure of two stationary cylinders in tandem, as well as the vibration response and vortex pattern of two oscillating staggered cylinders are analyzed. The results indicate that the spacing d c of two stationary cylinders at which the gap flow can be observed is different for different Re, and d c is 3D when Re = 2000 and d c = 2.5D at Re = 6000~14,000. When the distance d = d c , the force coefficient and St of two cylinders increase sharply. For the two oscillating staggered cylinders, there is a critical reduced velocity U c * = 7, which makes the amplitude magnitude relationship of the two cylinders change. With the change of the reduced velocity, the vibration frequencies of the two cylinders are consistent. When the staggered distance increases, the frequency difference of the two cylinders decreases. At the same inflow velocity, with the increase of staggered distance, a gap flow is formed between the two cylinders. When T > 0.6D and U* < 8, the gap flow becomes the main factor affecting the vibration of the two cylinders, which can be divided into the dominant region of gap flow.The FIV of a bluff body is a very complicated fluid-solid coupling process. Many studies have been done in this field, mainly focusing on the FIV characteristics and vibration control of the bluff body. The representative reviews of FIV of cylinders are by Williamson [5] and Bearman [6]. The control of FIV is embodied in two aspects. On the one hand, it is the suppression of vibration. Canpolat [7] found that rectangular grooves on a cylinder can effectively control flow through PIV experiments. Feng [8] used a water tunnel experimentation study and found that a synthetic jet can significantly change the scale of eddy current and wake mode. Lam [9] discussed the flow around a corrugated cylinder by large eddy simulation and experiment, and they controlled the vibration of the tube bundle in a heat exchanger by adding a corrugated cylinder to the tube bundle array. Zhu [10] and Song [11] studied the inhibition effect of small control rods on vortex-induced vibration (VIV). The former compared the VIV characteristics under different rod numbers, diameter ratios and gap ratios. It was found that when the attachment had nine control rods, the diameter ratio was 0.15, and the clearance ratio was 0.6, the inhibition effect of VIV was the best. The latter simulated the VIV characteristics of a cylinder with three small control rods at different angles of attack and clearance ratios. It was found that the inhibition effect was the best when the angle of attack was 45 and the clearance ratio was 0.9. Wu et al. [12] found a new method to control VIV: A twisted cylinder, which was applied to a semi-submersible offshore platform. Compared with a square cylinder, the...
Fig. I Stru cture of cycloid ball planetary transmission.and hypocycloid groove simultaneously is established , and the loads are applied on finite element models according to the different engagement positions. The simulation of stress distribution of CBPT is completed using the finite element method (FEM). The results offer an available method to intensity analysis and structural optimization of CBPT.II. STRUCT URE AN D TRANSMISSION PRI NCIPL E Fig. 1 shows the structure of CBPT. 1 is eccentric input shaft, 2 is central disc, 3 are balls, 4 is planetary disc, 5 is equal velocity output device, 6 is output shaft, 7 is clearance adjustment screw. The epicycloid groove is milled on the right side of central disc, of which tooth number is Z]. The hypocycloid groove is milled on the left side of planetary disc, of which tooth number is Z2' The balls are installed in the stagger zone of epicycloid groove and hypocycloid groove, of which number is Z3. They form the cycloid ball engagement pair. The necessary relationship of tooth number is Z2"Z] =2,The eccentric input shaft drives the planetary disc to do a planetary motion, and the hypocycloid groove on planetary disc pushes the balls to move. As the same time, the balls are restricted by the epicycloid groove on central disc, so they thrust the planetary disc to rotate with a lower angle speed reversely. At last, the rotation angle speed of planetary disc is outputted by the equal velocity output device, the velocity variation is completed. Fig. 2 shows the structure of engagement pair. In the transmission process, the relative motion between ball and cycloid groove is true rolling, so the influence of friction can Abstract -Based on the engagement principle of cycloid ball planetary transmission (CBPT), the load distribution mechanical model of engagement pair is established in condition of multiteeth engagement, and the coefficient of load distribution of teeth is presented. The finite element model of engagement pair is established in condition of four points contact. The stress distribution of engagement pair in transmission process is simulated using the finite element method (FEM), and the effect of cycloidal curtate ratio to contact stress is analyzed. The results show that the tooth profiles which transfer force alternate with different engagement positions. The maximal stress location is at the contact place that the ball meshes with the outboard tooth profile of hypocycloid groove. The oversize cycloidal curtate ratio could bring the root amputation of cycloid groove and augment the contact stress abruptly. III. LOAD DISTRIB UTIO N OF ENGAGE MENT PAIR A. Mechanical Model
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