Drag Reduction Devices Research Articles

Research and Application of Aerodynamic Drag Reduction Devices on Commercial Vehicle

Reducing aerodynamic drag of commercial vehicle is an important way to realize energy saving and consumption reduction for vehicle.Hereby,all kinds of factors influencing the aerodynamic drag of commercial vehicle are researched by using computational fluid dynamics(CFD) analysis and wind tunnel test,including the influence of dome style,distance between cabin and loading platform,and side aprons.According to the above research,the drag reducing mechanism is analyzed.The research results indicate that using various aerodynamic drag reduction measures properly on commercial vehicle with loading platform can reduce aerodynamic drag significantly,and realize energy saving and consumption reduction effectively.All the proposed drag reduction measures are practically used in the products,and their effectiveness of drag reduction and energy saving is validated.

Computational simulation of model and full scale Class 8 trucks with drag reduction devices

Numerical solutions of the unsteady Reynolds-averaged Navier–Stokes equations using a parallel implicit flow solver are given to investigate unsteady aerodynamic flows affecting the fuel economy of Class 8 trucks. Both compressible and incompressible forms of the equations are solved using a finite-volume discretization for unstructured grids and using Riemann-based interfacial fluxes and characteristic-variable numerical boundary conditions. A preconditioned primitive-variable formulation is used for compressible solutions, and the incompressible solutions employ artificial compressibility. Detached eddy simulation (DES) versions of the one-equation Menter SAS and the two-equation k − ϵ/ k − ω hybrid turbulence models are used. A fully nonlinear implicit backward-time approximation is solved using a parallel Newton-iterative algorithm with numerically computed flux Jacobians. Unsteady three-dimensional aerodynamic simulations with grids of 18–20 million points and 50,000 time steps are given for the Generic Conventional Model (GCM), a 1:8 scale tractor–trailer model that was tested in the NASA Ames 7 × 10 tunnel. Computed pressure coefficients and drag force are in good agreement with measurements for a zero-incidence case. Similar computations for a case with 10° yaw gave reasonable agreement for drag force, while the pressure distributions suggested the need for tighter grid resolution or possibly improved turbulence models. Unsteady incompressible flow simulations were performed for a modified full scale version of the GCM geometry to evaluate drag reduction devices. All of these simulations were performed with a moving ground plane and rotating rear wheels. A simulation with trailer base flaps is compared with drag reduction data from wind tunnels and track and road tests. A front spoiler and three mud-flap designs with modest drag reduction potential are also evaluated.

Fuel savings on a heavy vehicle via aerodynamic drag reduction

In this numerical study, the fuel-saving potentials of drag-reducing devices retrofitted on heavy vehicles are analysed. Realistic on-road operations are taken into account by simulating typical driving routes on long-haul and urban distributions; variations in vehicle weight are also considered. Results show that the performance of these aerodynamic devices depend both on their functions and how the vehicles are operated. Vehicles on long-haul routes generally save twice as much fuel as those driven in urban areas. The fuel reductions from using selected devices individually on a large truck range from less than 1% to almost 9% of the fuel cost of a vehicle doing an annual mileage is 80,000 miles.

Numerical simulation of hypersonic flow over highly blunted cones with spike

In this paper, effectiveness of aerodisk/aerospike assemblies as retractable drag-reduction devices for large-angle blunt cones flying at hypersonic Mach numbers is simulated numerically at various angles of attack. Different lengths of spike have been chosen to investigate the effect of the aerospike on the surrounding flowfield of nose cone. The compressible, 3-D full Navier–Stokes equations are solved with k − ω (SST) turbulence model for free stream Mach number of 5.75 and different angles of attack namely 3, 7, 10, and 12. The visualized shock structure and the computed drag on the blunt cone with aerospike agree well with the experimental result. The effect of reattachment of point on the surface convective heat-load reduction is investigated for different kind of spikes with varying length to diameter ratio. Additional modifications to the tip of the spike are examined in order to obtain different bow shocks, including a cut spike, and a flat and hemispherical aerodisk mounted on the tip of the spike. The numerical results presented the pressure distributions and the surface heat reduction for different type of spike. Some discrepancies existed, especially on the length of the recirculation region.

An improved immersed boundary method for curvilinear grids

In the present paper we propose an extension of the direct-forcing immersed boundary technique, recently developed and employed by Verzicco and co-authors [Fadlun EA, Verzicco R, Orlandi P, Mohd-Yusof J. Combined immersed-boundary finite-difference methods for three-dimensional complex flow simulations. J Comput Phys 2000;161:35–60; Verzicco R, Fatica M, Iaccarino G, Moin P, Khalighi B. Large eddy simulation of a road vehicle with drag-reduction devices. AIAA J 2002;40(12):2447–55; Cristallo A, Verzicco R. Combined immersed boundary/large-eddy-simulations of incompressible three-dimensional complex flows. Flow Turbul Combust 2006;77(1–4):3–26.] and successively improved by Balaras and co-authors [Gilmanov A, Sotiropoulos F, Balaras E. A general reconstruction algorithm for simulating flows with complex 3D immersed boundaries on Cartesian grids. J Comput Phys 2003;191:660–9; Balaras E. Modeling complex boundaries using an external force field on fixed Cartesian grids in large-eddy simulations. Comput Fluids 2004;33:375–404]. We extend the aforementioned technique to curvilinear-coordinate, structured grid, Navier–Stokes solvers. This improved technique allows for more flexibility and efficiency when compared to standard methods in which the technique is coupled with orthogonal-grid solvers. Additional modifications are also proposed with respect to the state-of-art, which allow to deal with general shaped, multiple-body immersed surfaces and to make the interpolation of the velocity field off the body suitable for curvilinear grids. Several tests have been carried out to check the reliability of the proposed technique: first we have considered the three-dimensional Stokes flow around a sphere, and compared the numerical results with the analytical ones. Second we have considered the two-dimensional unsteady flow around a circular cylinder placed between two parallel solid walls and compared the results with those of the database of the Priority Research Program ‘Flow Simulation on High Performance Computers’ of the German Research Association (DFG). Third, we have considered the two-dimensional flow within a S-shaped duct containing an elliptical valve. Finally, we have applied the technique to the study of a practical high-Reynolds number industrial problem. The geometrical configuration of the first two test cases is suited for both Cartesian and curvilinear algorithms. The geometry of the third test case is suited for curvilinear meshes and makes the use of Cartesian grids very inefficient and less accurate than the curvilinear ones. In these cases Cartesian – as well as curvilinear – mesh simulations have been carried out. Finally, the geometry of the high-Reynolds industrial problem is suited for curvilinear grids. The proposed technique has shown to preserve at least the same level of accuracy of its Cartesian counterpart allowing to reduce in a considerable way the computational cost of the simulations. When the geometry is better suited for curvilinear meshes, the reduction of the computational cost is accompanied by an increased accuracy with respect to the Cartesian counterpart. We also propose a simplified direct-forcing, semi-implicit method, allowing reduced computational cost with respect to the literature techniques. We have checked the accuracy of the technique and shown that when the Reynolds number is large enough, the present simplified technique allows the use of time steps much larger than those allowed by the explicit time-advancement scheme, preserving the accuracy of the results.

Aerodynamic simulation on the drag reduction device of a large-sized bus model

In this study, a numerical simulation has been carried out for three-dimensional turbulent flows around a bluff-based bus-like body and actual bus body. The first step of this study is to verify the effectiveness of the CFD analysis. In the second step, to reduce the drag of the actual bus model, parameter studies are performed with attention to effective utilisation of the rear-spoiler equipped at the roof-end of upper body. From the results of this study, it is clear that the adoption of RNG k-ε turbulence model and nonlinear quadratic turbulence model with the second order accurate discretisation scheme predicts, fairly well, the aerodynamic coefficients. The results also show that the aerodynamic drag for a commercial bus can be reduced by 14% with the use of a drag reduction device.

B113 セメント運搬船を用いたマイクロバブルの実船実験における気泡観測

The reduction of the frictional resistance can be possible by injecting micro bubbles along ship hull. So far, we have carried out many experiments of drag reduction due to micro-bubbles using a small high speed water channel and 50m-long flat bottom ship towed in 400m towing tank, and the drag reduction is surely obtained.Based on these experiments, we carried out a full-scale ship experiment of micro-bubbles as a promising drag reduction device. In the paper, we introduce the outline of the experiment and show the behaviors of injected micro-bubbles observed through totally 12 underwater cameras set around the ship.

Experimental Investigations of Hypersonic Flow over Highly Blunted Cones with Aerospikes

Effectiveness of aerospikes/aerodisk assemblies as retractable drag-reduction devices for large-angle blunt cones flying at hypersonic Mach numbers is investigated experimentally in hypersonic shock tunnel HST2 using a 120-deg apex-angle blunt cone. An internally mounted accelerometer balance system has been used for measuring the aerodynamic drag on the blunt cone with and without forward-facing aerospikes at various angles of attack. The measurements indicate around 55% reduction in drag for the blunt cone with flat-disk spike at zero degree angle of attack for a freestream Mach number of 5.75. Surface convective heat-transfer rate measurements have been carried out on the blunt cone with a flat-disk tipped spike of varying length in order to locate the shock reattachment point on the blunt-cone surface. The measured heat-transfer rates fluctuate by about ±20% in the separated flow region as well as near the reattachment point indicating the unsteady flowfleld around the spiked blunt cone. The shock structure around the 120-deg apex-angle blunt cone with a 12-mm-long flat-tipped aerospike has also been visualized using the electric discharge technique. The visualized shock structure and the measured drag on the blunt cone with aerospikes agree well with the axisymmetric numerical simulations

Large Eddy Simulation of a Road Vehicle with Drag-Reduction Devices

The e ow around an idealized road vehicle at Reynolds numbers up to 10 5 has been simulated using large eddy simulation; the numerical technique is based on the immersed boundary approach, which allows efe cient calculations to be carried out on a Cartesian grid. The effect of the Reynolds number and the wake modie cations produced by drag reduction devices attached to the base have been analyzed and compared with available experimental data. Averaged drag coefe cient and mean velocity proe les are in good agreement with measurement. The effect of subgrid-scale modeling (Smagorinsky and dynamic model ) has also been studied.

Effects of a splitter plate in the near wake of a divergent trailing edge.

This paper discusses experimental research aimed at defining a base drag reduction device based on splitter plates. The unsteady three-dimensional nature of the flow is studied by Schlieren photography, particle image velocimetry, and measurement of the total unsteady lift and drag loads.

Theoretical Analysis of Lift Force Acting on a Bubble Rising Parallel to the Wall.

The prediction of the behavior of a rising bubble near a wall is very important to control a bubbly flow in chemical reactor, or to develop the drag reduction devices using micro bubbles etc. In the present study, theoretical analysis of a deformed bubble rising near the wall is conducted. In the former experimental studies, there is a qualitative discrepancy between the theory for a spherical bubble and experimental results in the low Reynolds number cases. It is well-known that there is no lift force acting on spherical bubble under the creeping now approximation due to the kinematic reversibility. Therefore, in case of the theory of a spherical bubble, weak inertia effect must be taken into account to obtain a lift force. However, there is another possibility to have a lift force, that is, a deformation of bubble. In the present study, to estimate the effect of deformation, we conduct the donlaln perturbation analysis using Lamb's general solution for Stokes flow. The expression for the lift force due to the deformation is shown with the higher order extension. It is also shown that the slight deformation effect becomes more important as a bubble rises closer to the wall and the effect will become larger than that of small inertia below a certain distance from the wall.

The Effect of Blade Manipulator in Fully Developed Pipe Flow

Experiments were carried out in applying the concept of passive device called BLADEs (boundary-layer alteration devices) to fully developed pipe flow to assess its feasibility as a drag reduction device. The results of both the volumetric flow rate measurement and the pipe wall pressure distribution taken far downstream show that there is a net increase in drag with the device. With BLADES in tandem arrangement, there is a further net increase in drag which is contrary to its counterpart in boundary layer flow. Although the wall shear stress measurement following the device indicates some reduction in local drag, its magnitude of reduction is much smaller than that seen in the equivalent boundary flow. All these results suggest little possibility of any useful application of BLADEs to pipe flow.

Base drag reduction by control of the three-dimensional unsteady vortical structures

The present paper deals with the wake of a 2D body equipped with a drag reduction device. The device is a 3D trailing edge consisting of alternate segments of blunt base and spanwise cavity. The aerodynamic mechanisms acting on the near wake are studied in a water tunnel from schlieren observations by thermally marking large scale structures. The results show that the efficiency of the device is directly related to the presence of longitudinal vortices. An optimization of the shapes in subsonic compressible flow had led to a decrease of more than 40% of the total drag of the profile.

On the problems of riblets as a drag reduction device

AbstractSome recent experiments have shown that it is possible to reduce the drag of a body in a uniform flow by digging tiny ribs or ‘riblets’ on its skin. This paper deals with (i) the formulation of the problem into a distributed parameter optimum design problem and (ii) with its numerical solution by the finite element method and the techniques of optimal control. Some numerically optimal riblets are presented.

Boat-tailed afterbodies of square section as drag-reduction devices

Measurement have been made in a wind tunnel at low Mach number in order to determine the effects of various boat-tailed afterbodies on the drag of a long body of square section at zero incidence. With boat-tailing only on two opposite sides the best obtainable drag reduction is quite small, and for some cases there is a large increase of drag. With boat-tailing on all four sides a substantial reduction of drag can be obtained even with a short boat-tail, as for an axisymmetric body. This indicates that useful reductions of drag should be obtainable on lorries, containers and coaches by quite short fairings at the near end.

Aerodynamic drag and pressure measurements on a simplified tractor-trailer model

The results of wind-tunnel tests on two boxes in tandem are reported. The front box represents the cab of a tractor-trailer road vehicle and the rear box represents the load. Measurements of the aerodynamic drag on the tandem model (which is always less than the sum of the two drag forces on the boxes taken in isolation) and its variation with ground proximity are given. Extensive pressure measurements on the forward- and reaward-facing surfaces of the boxes revealed the variations in the drag contributions from each face and also located regions of high pressure and of high suction. The oncoming flow separates at the forward edges of the front box. When these edges are square the flow does not re-attach onto the top or sides of the front box. As the width of the gap between the boxes is increased from zero to a value greater than is generally used in practice, the drag increases by less than 20%. When all the edges of the front-box front face are radiused such that the flow re-attaches ahead of the gap then the drag at a representative gap width may not be significantly altered. However, at zero gap the drag is well below the value for the square-edged model and it increases more rapidly with increasing gap width. At larger but still practical gap widths the drag of the radiused model is well above that of the square-edged model and reaches almost twice its zero-gap value. The performances of two drag-reducing devices were examined; these are a flat plate mounted vertically on the roof of the cab box and a horizontal plate extending reawards from the cab roof to the front face of the rear box. Neither device had any effect on the drag of the square-edged model at the chosen representative gap width, but the two devices reduced the drag on the radiused model by 11% and 41% respectively.

Development of container-mounted devices for reducing the aerodynamic drag of commercial vehicles

Aerodynamic drag coefficients are presented from a series of wind-tunnel tests carried out to determine the effectiveness of various container-mounted mouldings as drag-reducing devices. A 1 6th scale Ford D1614 cab/chassis model was fitted with a movable container in order that the cab-container gap could be varied to simulate either a rigid or an articulated vehicle. Mouldings were mounted on the container forebody and took the form of: (1) convex fairings of various external radii; (2) deflector vanes mounted both forward of and around the container's leading edges, with varying “air-gap”; and (3) semicircular and quadrant sections around the container's edges. All tests were carried out in the Cranfield Department of Aerodynamics 8 ft. × 6 ft. low-speed wind tunnel using a “ground plate” simulation technique, at tunnel speeds giving 1/3 full-scale Reynolds numbers at typical motorway cruise speeds of 50 m.p.h. Zero-yaw reductions in drag coefficient by 33% for rigid and 23% for articulated vehicles were achieved, and the corresponding figures at 20° yaw were 21% and 11% for rigid and articulated vehicles, respectively. Surface oil-flow and smoke-filament flow visualisation studies were included among the tests.

Commercial vehicle fuel economy — The correlation between aerodynamic drag and fuel consumption of a typical truck

In a programme designed to demonstrate the benefits of reducing the aerodynamic drag of commercial vehicles a number of tests were made in the MIRA 7.9 m × 4.4 m wind tunnel using a full-scale truck fitted with a number of proprietary drag-reducing devices. Then, to establish a relationship between the indicated drag reduction and fuel savings, steady-speed fuel consumption measurements were made on a test track using the vehicle fitted with many of the devices tested earlier in the wind tunnel. The highest measured reduction in drag coefficient, 36%, which was achieved with two devices used together, resulted in a fuel saving of 16% at a steady speed of 80 km h −1 and of 13% at a constant 50 km h −1. Further measurements, made on a 365 km road test route, and using one of the more efficient single devices, indicated a fuel saving of 13.2% under normal road conditions. A good correlation was established between the wind-tunnel measurements of aerodynamic drag and the steady-speed fuel consumption measurements.

Fuel Savings from Truck Aerodynamic Drag Reducers and Correlation with Wind-Tunnel Data

A 9347 km (5809 mi) cross-country fuel economy experiment was conducted to demonstrate typical fuel savings that can be obtained using drag-reducing devices on tractor-trail er trucks, and to ascertain the degree of correlation of the experimentally determined fuel savings with the fuel savings that could be predicted using data from drag reduction experiments on models in a wind-tunnel. Three trucks were used in the experiment. One truck was equipped with a commerically available wind deflector/vortex stabilizer system, another was equipped with a prototype streamline fairing/gap seal system developed at the University of Maryland, and the remaining vehicle was operated without any drag-reducing devices in order to obtain a basis from which to determine the fuel savings. The fuel savings per unit distance that resulted from use of the commerical drag reducing system was 0.029±.006 liter/km (0.012±.002 gal/mi), while that realized with the University-of-Maryland-developed prototype system was 0.057±.003 liter/km (0.024±.001 gal/mi). An analysis of the conditions under which these results were obtained indicated that they were conservative estimates of the fuel savings that would be realized with long-term operating of the vehicles and devices used in the experiment. Fuel savings predictions were performed using wind-tunnel drag reduction data, and relative airspeed and yaw angle data continuously measured in the fuel economy experiments. The measured fuel savings due to the commercial system was 75 ± 15% of the predicted value, and that due to the University of Maryland system was 78 ±4% of the predicted value. The differences obtained appear related to the nonsimulation of wind turbulence in the wind-tunnel experiments.