The aerodynamic interaction between the contralateral wings and between the body and wings of a model insect are studied, by using the method of numerically solving the Navier-Stokes equations over moving overset grid...The aerodynamic interaction between the contralateral wings and between the body and wings of a model insect are studied, by using the method of numerically solving the Navier-Stokes equations over moving overset grids, under typical hovering and forward flight conditions. Both the interaction between the contralateral wings and the interaction between the body and wings are very weak, e.g. at hovering, changes in aerodynamic forces of a wing due to the present of the other wing are less than 3% and changes in aerodynamic forces of the wings due to presence of the body are less than 2%. The reason for this is as following. During each down- or up-stroke, a wing produces a vortex ring, which induces a relatively large jet-like flow inside the ring but very small flow outside the ring. The vortex rings of the left and right wings are on the two sides of the body. Thus one wing is outside vortex ring of the other wing and the body is outside the vortex rings of the left and right wings, resulting in the weak interactions.展开更多
Background: Geographic variation in body size is assumed to reflect adaptation to local environmental conditions. Although Bergmann's rule is usually sufficient to explain such variation in homeotherms, some excep...Background: Geographic variation in body size is assumed to reflect adaptation to local environmental conditions. Although Bergmann's rule is usually sufficient to explain such variation in homeotherms, some exceptions have been documented. The relationship between altitude, latitude and body size, has been well documented for some vertebrate taxa during the past decades. However, relatively little information is available on the effects of climate variables on body size in birds.Methods: We collected the data of 267 adult Eurasian Tree Sparrow(Passer montanus) specimens sampled at 48 localities in China's mainland, and further investigated the relationships between two response variables, body mass and wing length, as well as a suit of explanatory variables, i.e. altitude, latitude, mean annual temperature(MAT), annual precipitation(PRC), annual sunshine hours(SUN), average annual wind speed(WS), air pressure(AP) and relative humidity(RH).Results: Our study showed that(1) although the sexes did not differ significantly in body mass, males had longer wings than females;(2) body mass and wing length were positively correlated with altitude but not with latitude;(3) body mass and wing length were negatively correlated with AP and RH, but not significantly correlated with WS. Body mass was positively correlated with SUN and inversely correlated with MAT. Wing length was not correlated with MAT in either sex, but was positively correlated with SUN and negatively correlated with PRC in male sparrows;(4) variation in body mass could be best explained by AP and SUN, whereas variation in wing length could be explained by RH and AP in both sexes. In addition, variation in male sparrows can be explained by SUN, WS and PRC but not in females.Conclusions: Two different proxies of body size, body mass and wing length, correlated with same geographic factors and different climate factors. These differences may reflect selection for heat conservation in the case of body mass, and for efficient flight in the case of wing length.展开更多
In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using Based on the meas...In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using Based on the measured data, high-speed video techniques. inertia force acting on the insect was computed and aerodynamic force and moment of the wings were calculated by the method of computational fluid dynamics. Subtracting the aerodynamic force and the weight from the inertia force gave the leg force. The following has been shown. In its voluntary takeoff, a fruitfly jumps during the first wingbeat and becomes airborne at the end of the first wingbeat. When it is in the air, the fly has a relatively large ＂initial＂ pitch-up rotational velocity （more than 5 000~/s） resulting from the jumping, but in about 5 wingbeats, the pitch-up rotation is stopped and the fly goes into a quasi-hovering flight. The fly mainly uses the force of jumping legs to lift itself into the air （the force from the flapping wings during the jumping is only about 5%-10% of the leg force）. The main role played by the flapping wings in the takeoff is to produce a pitch-down moment to nullify the large ＂initial＂ pitch-up rotational velocity （otherwise, the fly would have kept pitching-up and quickly fallen down）.展开更多
The experiments on wing-body junction and wake flow were carried cul in alow-turbulence level wind tunnel. Intensive measurements of various flow parameters,such as the distributions of the pressure on the surfaces of...The experiments on wing-body junction and wake flow were carried cul in alow-turbulence level wind tunnel. Intensive measurements of various flow parameters,such as the distributions of the pressure on the surfaces of the airfoil and the plate wall,the mean and the fluctuating velocities, as well as the turbulent kinetic energy, u'v' andu'w'etc., were performed. The results indicate that the secondary flow entrains the highvelocity low-turbulence fluid into the boundary layer and the wake vortex dominates thewake flow. Some regions of negative eddy viscosity are also found in the wake flow.展开更多
基金supported by the National Natural Science Foundation of China(10732030)the 111 Project (B 07009)
文摘The aerodynamic interaction between the contralateral wings and between the body and wings of a model insect are studied, by using the method of numerically solving the Navier-Stokes equations over moving overset grids, under typical hovering and forward flight conditions. Both the interaction between the contralateral wings and the interaction between the body and wings are very weak, e.g. at hovering, changes in aerodynamic forces of a wing due to the present of the other wing are less than 3% and changes in aerodynamic forces of the wings due to presence of the body are less than 2%. The reason for this is as following. During each down- or up-stroke, a wing produces a vortex ring, which induces a relatively large jet-like flow inside the ring but very small flow outside the ring. The vortex rings of the left and right wings are on the two sides of the body. Thus one wing is outside vortex ring of the other wing and the body is outside the vortex rings of the left and right wings, resulting in the weak interactions.
基金supported by grants from the National Natural Science Foundation of China (NSFC, 31330073, 31672292)the Natural Science Foundation of the Department of Education, Hebei Province (YQ2014024)
文摘Background: Geographic variation in body size is assumed to reflect adaptation to local environmental conditions. Although Bergmann's rule is usually sufficient to explain such variation in homeotherms, some exceptions have been documented. The relationship between altitude, latitude and body size, has been well documented for some vertebrate taxa during the past decades. However, relatively little information is available on the effects of climate variables on body size in birds.Methods: We collected the data of 267 adult Eurasian Tree Sparrow(Passer montanus) specimens sampled at 48 localities in China's mainland, and further investigated the relationships between two response variables, body mass and wing length, as well as a suit of explanatory variables, i.e. altitude, latitude, mean annual temperature(MAT), annual precipitation(PRC), annual sunshine hours(SUN), average annual wind speed(WS), air pressure(AP) and relative humidity(RH).Results: Our study showed that(1) although the sexes did not differ significantly in body mass, males had longer wings than females;(2) body mass and wing length were positively correlated with altitude but not with latitude;(3) body mass and wing length were negatively correlated with AP and RH, but not significantly correlated with WS. Body mass was positively correlated with SUN and inversely correlated with MAT. Wing length was not correlated with MAT in either sex, but was positively correlated with SUN and negatively correlated with PRC in male sparrows;(4) variation in body mass could be best explained by AP and SUN, whereas variation in wing length could be explained by RH and AP in both sexes. In addition, variation in male sparrows can be explained by SUN, WS and PRC but not in females.Conclusions: Two different proxies of body size, body mass and wing length, correlated with same geographic factors and different climate factors. These differences may reflect selection for heat conservation in the case of body mass, and for efficient flight in the case of wing length.
基金supported by the National Natural Science Foundation of China(11232002)the 111 Project(B07009)
文摘In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using Based on the measured data, high-speed video techniques. inertia force acting on the insect was computed and aerodynamic force and moment of the wings were calculated by the method of computational fluid dynamics. Subtracting the aerodynamic force and the weight from the inertia force gave the leg force. The following has been shown. In its voluntary takeoff, a fruitfly jumps during the first wingbeat and becomes airborne at the end of the first wingbeat. When it is in the air, the fly has a relatively large ＂initial＂ pitch-up rotational velocity （more than 5 000~/s） resulting from the jumping, but in about 5 wingbeats, the pitch-up rotation is stopped and the fly goes into a quasi-hovering flight. The fly mainly uses the force of jumping legs to lift itself into the air （the force from the flapping wings during the jumping is only about 5%-10% of the leg force）. The main role played by the flapping wings in the takeoff is to produce a pitch-down moment to nullify the large ＂initial＂ pitch-up rotational velocity （otherwise, the fly would have kept pitching-up and quickly fallen down）.
文摘The experiments on wing-body junction and wake flow were carried cul in alow-turbulence level wind tunnel. Intensive measurements of various flow parameters,such as the distributions of the pressure on the surfaces of the airfoil and the plate wall,the mean and the fluctuating velocities, as well as the turbulent kinetic energy, u'v' andu'w'etc., were performed. The results indicate that the secondary flow entrains the highvelocity low-turbulence fluid into the boundary layer and the wake vortex dominates thewake flow. Some regions of negative eddy viscosity are also found in the wake flow.
