Effect Of Side Flow Research Articles

Optimal shape design of an airship based on geometrical aerodynamic parameters

BackgroundConventional airship mathematical modeling usually involves six coupled degrees of freedom and two inputs, namely tail and thrust. The current study focuses on aerodynamic modeling. The aerodynamic model is developed in 3D-space based on plane semi-empirical model of a symmetric airship. The model depends on the main geometrical parameters of the airship. The study introduces an optimal shape design of the airship. The objective function is established to reduce drag and the effect of side flow and increases both lift force and pitching moment. Three types of airship shape construction are investigated, namely NPL, GNVR, and Wang.ResultsMATLAB genetic algorithm toolbox is used to obtain the optimal shape. The population size is 50 and the number of generations is also 50 for NPL, GNVR and Wang shapes at each corresponding angle of attack (alpha =left[ -20^circ ,20^circ right] ) and side-slip angle (beta =left[ -20^circ ,20^circ right] ). The shapes are compared to select the best fit within the operating range. To get the optimal shape, weighted averaging is performed on the optimal solution.ConclusionThe GNVR geometric construction technique is the best method to generate the optimum shape of the airship in the presence of side-slip angle effect with the utilized objective function that reduces drag and side flow and increases lift and pitching moment.

Characterization of the material-induced elastic–plastic deformations in ultra-precision diamond cutting

Ultra-precision cutting (UPC) technology can directly achieve freeform surfaces with form accuracy in sub-micrometer and surface finishing in nanometer, and the achieved surface quality affects the functionalities of the components. Different from the conventional machining process, the effects of workpiece material properties on surface generation in UPC are ignorable. The influences of plastic side flow and elastic recovery are very important for the surface quality in UPC, while few studies were found to evaluate the extent of the two phenomena. This paper makes theoretical and experimental studies on the factors affecting the side flow and recovery and proposed a method to characterize the extent of plastic side flow and recovery by studying the deviation of the groove radius in single ruling. Experiments are conducted to machine grooves with different cutting parameters on different workpiece materials. The experiment results agree well with the theoretical analyses and show that under the combined effect of side flow and recovery, the generated groove radius may be larger or smaller than the theoretical one. Moreover, the proposed method makes effective evaluation on extend of swelling and recovery in UPC.

Revisit on natural convection from vertical isothermal plate arrays II—3-D plume buoyancy effects

The three-dimensional characteristics of natural convection from isothermal vertical plate arrays with finite lengths are numerically analyzed. Studied are single- and multi-channel plate arrays with different plate length/height (L/H) ratios. To account for the extra plume buoyancy and the entrance flow resistance, extended computation domains encompassing the whole plate arrays are arranged. Highly non-uniform distributions of heat transfer coefficient exhibit along the plate, with the highest value at the plate end due to the effect of side flow. Inward, the heat transfer coefficient decreases drastically with boundary layer development but re-rises over the inner region as a result of higher plume buoyancy therein. As L/H increases, the stronger plume buoyancy promotes the overall heat transfer coefficient to approach the 2-D value with a difference of less than 4% when L/H ≥ 2. The extra plume buoyancy varies in different channels, weakest in the edge channel, leading to complex flow above the outermost channels. The plume-buoyancy enhancement on the overall heat transfer coefficient is less pronounced for arrays with finite L/H ratios than for a 2-D array due to the plume shrinkage associated with the side flow.

Natural convection of two staggered cylinders for various prandtl numbers and vertical and horizontal pitches

Natural convection heat transfer phenomena of two staggered cylinders were investigated for laminar flows. Numerical simulations were carried out to examine the effect of varying the Prandtl number and the vertical and horizontal pitch-to-diameter ratios for a Rayleigh number of 1.5 × 108 using FLUENT. This study focused on phenomena related to very small vertical pitch. The heat transfer rates of the upper cylinders were influenced by plumes from the lower cylinders, exhibiting preheating, velocity, sweep, and side flow effects. The heat transfer rates of the lower cylinders were not affected by the upper cylinders at moderate vertical pitches. However, when the vertical pitch was very small, they were affected by stagnant flow, sweep, and side flow effects.

Influences of vertical and horizontal pitches on the natural convection of two staggered cylinders

Natural convection heat transfer phenomena for two vertically staggered cylinders were investigated experimentally and numerically for both laminar and turbulent flows. Experiments were performed for the Rayleigh numbers 1.5×108 and 2.5×1010 and the Prandtl number 2014, varying the vertical and horizontal pitch-to-diameter ratios using a copper electroplating system. Numerical studies were carried out to investigate the effect of the Prandtl number. The heat transfer rates of the lower cylinders were in close agreement with those of single cylinders. However, the heat transfer rates of the upper cylinders were influenced by the plumes from the lower cylinders, exhibiting preheating, velocity, and side-flow effects. At a very small pitch, the preheating effect was dominant, whereas at a larger pitch, the velocity effect became dominant. Both effects weakened with increasing horizontal pitch-to-diameter ratio. Under turbulent flow conditions, it was visually and experimentally confirmed that laminarization occurs on the top part of the upper cylinder, due to buoyancy-aided mixed convective turbulent flow.

엇갈리게 배열된 두 개의 수평관에서 수평 피치-직경비에 따른 자연대류 열전달 영향

엇갈리게 배열된 두 개의 수평관의 수직 이격거리(Pv/D)와 수평 이격거리(Ph/D)를 변화시키며 자연대류 열전달을 실험적으로 측정하였다. 열/물질전달의 상사성을 이용하여 물질전달 실험을 수행하였고 난류영역까지 확장하였다. Pr 수 2,014, RaD 수 1.5×10?~2.5×10<SUP>10</SUP>, Pv/D는 1.02~5, Ph/D는 0~2 범위에서 수행하였다. 하단 수평관의 물질전달은 단일 수평관 상관식의 예측치와 일치하였다. 상단 수평관의 물질전달은 Pv/D가 작을 때, 하단 수평관에서 상승하는 플룸의 예열영향(Preheating effect)으로 인해 감소하였고, Ph/D가 증가하면 급격히 상승하였다. 그러나 Pv/D가 클 때, 상단 수평관의 물질전달은 하단 수평관의 플룸 속도영향으로 인하여 단일 수평관보다 컸고, Ph/D가 증가함에 따라 완만하게 감소하였다. Ph/D가 매우 증가하여도 굴뚝효과(Chimney effect)와 측면유동효과(Side flow effect) 인하여 상단 수평관의 열전달이 하단 수평관의 열전달보다 크게 나타났다.

SURFACE FINISH AND TOOL WEAR CHARACTERIZATION IN HARD TURNING USING A MATHEMATICAL CUTTING TOOL REPRESENTATION

The development of a general 3D model for a corner-radiused, chamfered, edge-honed cutting worn tool is elaborated. The surface of the cutting tool was constructed using one angular scalar specifying location on the corner radius and leading/trailing edges and another non-dimensional scalar for specifying location on the relief, edge-hone, chamfer and tool-top. Then, for given geometric parameters and cutting conditions, the angular extremities of contact on the corner radius and leading/trailing edges was obtained and validated. The kinematic surface finish on the workpiece surface including the Brammertz and sideflow effects was then simulated in typical hard turning. The model was expanded to allow wiper edges and flank wear. A simplified crater wear model was adopted for continuous hard turning to allow virtual cross-sectioning. Accurate estimation of flank and crater wear volume was also enabled. The model results for the fresh tool agreed with well-known trends from 2D modeling. Preliminary results indicate that there exists a geometric basis for higher Ra and Rt for a worn tool. The Brammertz effect simulation, though not in agreement with the data of Knuefermann (2003) corroborated the modification proposed therein.

Hydrodynamic Lubrication of the Rib-Roller End Contact of a Tapered Roller Bearing

The behavior of the lubricated rib-roller end contact of a tapered roller bearing is studied both theoretically and experimentally. A theoretical hydrodynamic approach was first developed for smooth and rigid surfaces for the particular geometry and kinematic conditions found in this contact. Simultaneous measurements of traction forces and film thicknesses by optical interferometry are performed in a special device made of a flat glass disk and a steel toric specimen which simulates this contact, lubricated with a mineral oil at ambient temperature. Good argeement is noted for both film thickness and traction forces between the hydrodynamic theoretical and experimental results. The experiments which are extended to the elasto-hydrodynamic regime show that central and minimum film thicknesses are lower than the calculated values using classical fully flooded and starved elastohydrodynamic theories. This departure is attributed to side flow effects. Traction curves obtained in this regime, under moderate pressures, show that the oil behavior remains newtonian.

Effect of side flow on the straightness of the ridge and the surface roughness

Side flow, Spanzipfel and tearing are responsible for the variation of the actual profile of a machined surface from an ideal one. The effect of side flow on the straightness of the ridge and the roughness have been studied. The correlation between the straightness of the ridge and the surface roughness at different cutting speeds, feeds and rake angle has been given.