| With the development of Chinese economics, there were more and more good quality highways. Transportation on the highway was a huge contributiveness for Chinese economic development. With the increasing of fuel price, the cost of transportation vehicle also increased. How to decrease the aerodynamic drag and improve the aerodynamic characteristics of transportation vehicle became one of the most important research projects.The paper described the aerodynamic characteristics of heavy-duty truck by numerical simulations and wind tunnel experiments. The research included the flow field of heavy-duty truck, the influence of the gap length between cab and trailer, and the impact of aerodynamic interference on the different tail part shapes. According to the research, the dissertation found out the rules of aerodynamic characteristics of heavy-duty truck, and brought forward some aerodynamic drag decreasing devices on the heavy-duty truck.In Chapter I, both domestic and international current progresses were analyzed. Methods features and insufficients of their research were also summarized. The signification of this dissertation was illustrated. The research methods and contents of this subject were put forward. The outline of this dissertation was provided.In Chapter II, the basis simulation theories of hydrodynamics were discussed. First, the features of flow field were recapitulated. Second, the governing equation and solution methods were provided. Among these turbulence models and solution methods, the differential RSM of the RANS(Reynolds Average Navier-Stokes) method was illustrated in detail. The Wall Function method, dealing with the flow near wall were introduced in brief. The differential RSM of the RANS method was selected as the numerical simulation equation of this dissertation.In chapter III, the basis experiment theories of wind tuunel were introduced in brief. Experiments in wind tunnel have important values for watching the state of flow field and analyzing the changing rules of aerodynamic characteristics of vehicle model. Automobile wind tunnel experiments include balance, surface press, thread tuft, oil flow visualization, smoke thread and laser flow feature. PIV(Particle Image Velocimetry)is a new flow field analyse method, it can display instantaneous and time-averaged flow feature of automobile by laser pulse. It has a high accuracy. In this dissertation, the balance, surface press, thread tuft, oil flow visualization and PIV were tested for the flow field of Heavy-duty truck model in wind tunnell.GTS model (Ground Transportation System) was selected as heavy-duty truck simple model. It was a standard research model and be recommended by Sandian national laboratory of U.S.A. in 1996. The length of 1:1 GTS model is 19.6m, it is too long to be used in wind tunnell. So that, 1:16 and 1:8 GTS models were made.By analyzing the results of numerical simulation and wind tunnel, the rules of aerodyanmic characteristics of GTS model were found out. Such As, air flow was blocked by the front side of the cab, a stagnant zone was appearance there. Flow was separated on the edges of the cab left and right sides, and clinged on the streamline curve surface of the cab. Using balance measure, surface press measure, thread tuft and oil flow visualization, the flow field around the GTS model was displayed qualitatively. Using PIV, the experiment displayed the wake of GTS model. The results of numerical simulation and wind tunnel experiments were matching very much, it indicated that the method of numeriacal simulation of flow field around GTS model was truth.In chapter IV, being changed the length of gap between the cab and trailer of GTS model, there were 8 intervals, G=25%, 35%, 45%, 50%, 55%, 65%, 75% and 100%.By numerical simulation, the influence of the different length of gap between cab and trailer could be found. When the length of the gap was less than G=50%, the aerodynamic drag of cab and trailer enhance slowly. As the length of the gap was beyond G=50%, the aerodynamic drag of cab increase a little, but the drag of trailer increase quickly. So, G=50% is an important point for the flow field of GTS model. When G<50%, the aerodynamic drag of GTS model keep a steady value. If G>50%, the drag would increase quickly, amplitude more than 30%, as G>100%, the value of drag would keep a new steady state again.In the wind tunnel, the experiments including balance measure, surface press measure, smoke thread, oil flow visualization and PIV were tested on 1:16 GTS models. That was a series of GTS models which have different lengths of gap between cab and trailer. Form the experiment results, it can be found that when G<50%, the influence of gap is little on flow field of GTS model; when G>50%, the influence is large. When the length exceeding G=100%, the influence on flow field keeped a steady state again.The results of numerical simulation matched that of wind tunnel experiments very much. So, the flow fields of different length of gap of GTS model were truth.In chapter V, the transfigurations of the body of GTS were researched, one was cowl that was installed on the cab, There were two kinds of gap length, G=65% and G=75%. The increments of aerodynamic drag of cab were less than that of GTS model (G=50%), the value was 15%. The wake structure was very important for flow field of heavy-duty truck. The research put forwards transfigurations of the tail part shape. The transfigurations were blend (six changes, obliquity was 5o ,10 o ,15 o ,20 o , 30 o , 45 o, blend length was 1/10w, w was body width).From results of simulation and wind tunnel, the results of numerical simulation were matched by those of wind tunnel experiments. The best shape was the blend 15 which obliquity was 15o, drag coefficient was decreased 7.6%. The better tail part transfiguration was blend blend 20o,drag coefficents was decreased 7.09%. The conclusion illuminated that tail part shape of blend can decreased aerodynamic drag effectively.When cowl and tail blend were installed on the GTS model together, drag coefficient would be decreased 20%.In chapter VI, the transfigurations of the body of a real truck were researched by numerical simulation with RSM. The cowl which was installed cab could meliorate the fluid field of the really truck, the drag coefficient was decreased to 8.76%. The cowl also ameliorated the aerodynamic characteristics of gap between cab and trailer, it could extend the length of gap and not increase the drag coefficient. The blends which were installed on the tail of trailer could decreased the drag coefficient, the blend 20 which obliquity was 20o, drag coefficient was decreased 7.64%. The result of numerical simulation of the blends of real truck was matched by those of the blends of GTS, If the cowl of cab and blend of tail of trailer were installed on the real truck, the drag ciefficent could be decreased by 20% mostly. Such a value of decreased drag coefficient was very important for projects of actually engineering application. If the results of the dissertation would be applied on actually heavy-duty truck, they would reduce the cost of transportation, decrease air pollution and meliorate the environment.The research of the aerodynamic characteristics of heavy-duty truck could obtain aerodynamic characteristics changing trends. The conclusion could be applied in decreasing aerodynamic drag, improving the vehicle's economy and saving fuel. |
PDF Full Text Request