Shock Control Bumps Research Articles

Adapting Three-Dimensional Shock Control Bumps for Swept Flows

Shock control bumps offer the potential to reduce wave drag on transonic aircraft wings. However, most studies to date have only considered unswept flow conditions, leaving uncertain their applicability to realistic finite swept wings. This paper uses a swept infinite-wing model as an intermediate step, and it presents a computational study of the design drag performance of three-dimensional bumps. A new geometric parameter, termed bump orientation, is introduced and found to be crucial to the performance under swept flows. Classic shock control bumps aligned approximately with the local to freestream flow direction can offer drag reductions comparable to those from similar but unoriented devices in unswept flows, whereas badly misaligned bumps see severe performance degradation. For appropriately aligned classic bumps, the relationships between performance and selected geometric parameters (height, streamwise position, and isolation) are found to be somewhat similar to those observed in unswept studies.

Using a shock control bump to improve the performance of an axial compressor blade section

Here, we use numerical analysis to study the effects of a shock control bump (SCB) on the performance of a transonic axial compressor blade section and to optimize its shape and location to improve the compressor performance. A section of the NASA rotor 67 blade is used for this study. Two Bezier curves, each consisting of seven control points, are used to model the suction and pressure surfaces of the blade section. The SCB is modeled with the Hicks–Henne function and, using five design parameters, is added to the suction side. The total pressure loss through a cascade of blade sections is selected as the cost function. A continuous adjoint optimization method is used along with a RANS solver to find a new blade section shape. A grid independence study is performed, and all optimization and flow solver algorithms are validated. Two single-point optimizations are performed in the design condition and in an off-design condition. It is shown that both optimized shapes have overall better performance for both on-design and off-design conditions. An analysis is given regarding how the SCB has changed the wave structure between blade sections resulting in a more favorable flow pattern.

Erratum to: The application of the gradient-based adjoint multi-point optimization of single and double shock control bumps for transonic airfoils

Erratum to: The application of the gradient-based adjoint multi-point optimization of single and double shock control bumps for transonic airfoils

Vortical Structures on Three-Dimensional Shock Control Bumps

Three-dimensional shock control bumps have long been investigated for their promising wave drag reduction capability. However, a recently emerging application has been their deployment as “smart” vortex generators, which offset the parasitic drag of their vortices against their wave drag reduction. It is known that three-dimensional shock control bumps produce streamwise vortices under most operating conditions; however, there have been very few investigations that have aimed to specifically examine the relevant flow structures. In particular, the strength of the vortices produced as well as the factors influencing their production are not well known. This paper uses a joint experimental and computational approach to test three different shock control bump shapes, categorizing their flow structures. Four common key vortical structures are observed, predominantly shear flows, although all bumps also produce a streamwise vortex pair. Both cases with and without flow separation on the bump tails are scrutinized. Finally, correlations between the strength of the main wake vortices and pressure gradients at various locations on the bumps are assessed to investigate which parts of the flow control the vortex formation. Spanwise flows on the bump ramp are seen to be the most influential factor in vortex strength.

Application of the adjoint multi-point and the robust optimization of shock control bump for transonic aerofoils and wings

A shock control bump (SCB) is a flow control method which uses a local small deformation in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, both equally and variably weighted multi-point optimization and a robust adjoint optimization scheme are used to optimize the SCB. The numerical simulation of the turbulent viscous flow and a gradient-based adjoint algorithm are used to find the optimum location and shape of the SCB for two benchmark aerofoils. A multi-point optimization method under a constant-lift-coefficient constraint is implemented to find the optimum design of a two-dimensional (2D) SCB and it is observed that the general results are similar to other optimization algorithms. To show that these results are extendable to real three-dimensional (3D) cases, a 3D bump model with 11 parameters is introduced, and it is optimized using both single- and multi-point optimization procedures. Although the 3D flow structure involves much more complexity, the overall results are shown to be similar to the 2D case.

The Multi-point Optimization of Shock Control Bump with Constant-Lift Constraint Enhanced with Suction and Blowing for a Supercritical Airfoil

Both shock control bump (SCB) and suction and blowing are flow control methods used to control the shock wave/boundary layer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. A SCB uses a small local surface deformation to reduce the shock-wave strength, while suction decreases the boundary-layer thickness and blowing delays the flow separation. Here a multi-point optimization method under a constant-lift-coefficient constraint is used to find the optimum design of SCB and suction and blowing. These flow control methods are used separately or together on a RAE-2822 supercritical airfoil for a wide range of off-design transonic Mach numbers. The RANS flow equations are solved using Roe’s averages scheme and a gradient-based adjoint algorithm is used to find the optimum location and shape of all devices. It is shown that the simultaneous application of blowing and SCB (hybrid blowing/SCB) improves the average aerodynamic efficiency at off-design conditions by 18.2 % in comparison with the clean airfoil, while this increase is only 16.9 % for the hybrid suction/SCB. We have also studied the SWBLI and how the optimization algorithm makes the flow wave structure and interactions of the shock wave with the boundary layer favorable.

The application of the gradient-based adjoint multi-point optimization of single and double shock control bumps for transonic airfoils

A shock control bump (SCB) is a flow control method that uses local small deformations in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, we have used a multi-point adjoint optimization scheme to optimize shape and location of the SCB. Practically, this introduces transonic airfoils equipped with the SCB that are simultaneously optimized for different off-design transonic flight conditions. Here, we use this optimization algorithm to enhance and optimize the performance of SCBs in two benchmark airfoils, i.e., RAE-2822 and NACA-64-A010, over a wide range of off-design Mach numbers. All results are compared with the usual single-point optimization. We use numerical simulation of the turbulent viscous flow and a gradient-based adjoint algorithm to find the optimum location and shape of the SCB. We show that the application of SCBs may increase the aerodynamic performance of an RAE-2822 airfoil by 21.9 and by 22.8 % for a NACA-64-A010 airfoil compared to the no-bump design in a particular flight condition. We have also investigated the simultaneous usage of two bumps for the upper and the lower surfaces of the airfoil. This has resulted in a 26.1 % improvement for the RAE-2822 compared to the clean airfoil in one flight condition.

Optimization and analysis of shock wave/boundary layer interaction for drag reduction by Shock Control Bump

Shock Control Bump (SCB) is a flow control method which reduces the wave drag through introducing a small bump over the wing surface. The present paper is mainly devoted to numerical investigation of shock wave/boundary layer interaction (SWBLI) as the main factor influencing the aerodynamic performance of transonic bumped airfoils. The survey is conducted for three airfoils through detailed SCB shape optimization processes employing differential evolution algorithm (DE). SWBLI is analyzed thoroughly for clean and bumped airfoils and it is shown how the modified wave structure originating from upstream of SCB reduces the wave drag while simultaneously improving the boundary layer velocity profiles downstream of the shock wave. The present work extends the conventional approach for SCB design via detailed interpretation of the decay of mean velocity defect downstream of the bumped airfoils. The numerical analysis of bumped airfoils in case of high transonic Mach number shows that taller SCB required for weakening the strong shock wave results in large separated flow zone and its performance improvement is deteriorated.

Review of research into shock control bumps

Thispaperpresentsareviewofresearchonshock control bumps (SCBs), a class of flow control device with potential for application to transonic wings. Beginning with a brief review of the origins of the SCB concept, the primary focus is on the more recent studies from the last decade. Results from both experimental and numerical work are considered and the synergy between these two approaches to SCB research is critically explored. It is shown that the aerodynamic performance enhancement potential of SCBs, namely their capacity for drag reduction and delaying the onset of buffet for transonic wings, has been widely demon- strated in the literature, as has the high sensitivity of SCB performance toflow conditions including shock strength and position, and post-shock adverse pressure gradient. These characteristic features of SCBs are relatively well explained in terms of the flow physics that have been observed for dif- ferentbumpgeometries.Thisstemsfromanumberofstudies that have focused on the balance of viscous and inviscid flow features and also the mechanism by which finite span SCBs generate streamwise vorticity. It is concluded that our under- standing of SCBs is reaching an advanced level of maturity for SCBs in simple configurations and steady flow fields. However, SCB performance in unsteady flow and on swept wings requires further investigation before the concept can be considered a viable candidate for transonic wings. These investigations should adopt a multi-disciplinary approach combiningcarefullydesignedexperimentsandtargetedcom- putations. Finally, two concepts for future SCB research are suggested: the adaptive SCB and SCBs in engine intakes.

The drag reduction study of the supercritical airfoil with shock control bump considering the robustness

The shock control bump of supercritical airfoil is numerically investigated by Computational Fluid Dynamics in present paper. The influence of the geometry parameters of the bump is studied by considering the drag reduction performance and robustness. The results show that, the bump location strongly affects on the drag reduction. The best performance is obtained when locating the bump crest at the shock position of the clean airfoil. Higher bump is worse for the drag reduction, while longer bump has good effect in a bigger height range. The bump can effectively weaken the shock wave, suppress the boundary layer separation, and extend the buffet onset boundary, but its working lift coefficient range is relatively narrow. The robustness is an important requirement of engineering application. The results of robustness analysis shows that, the longer and lower bump is more engineering acceptable than the shorter and higher bump, while it could not only improve lift-drag ratio in larger lift coefficient range insensitive to the changes of shapes and Reynolds number, but also increase the drag divergence Mach number.

Joint Experimental and Numerical Approach to Three-Dimensional Shock Control Bump Research

Previous studies of transonic shock control bumps have often been either numerical or experimental. Comparisons between the two have been hampered by the limitations of either approach. The present work aims to bridge the gap between computational fluid dynamics and experiment by planning a joint approach from the outset. This enables high-quality validation data to be produced and ensures that the conclusions of either aspect of the study are directly relevant to the application. Experiments conducted with bumps mounted on the floor of a blowdown tunnel were modified to include an additional postshock adverse pressure gradient through the use of a diffuser as well as introducing boundary-layer suction ahead of the test section to enable the in-flow boundary layer to be manipulated. This has the advantage of being an inexpensive and highly repeatable method. Computations were performed on a standard airfoil model, with the flight conditions as free parameters. The experimental and computational setups were then tuned to produce baseline conditions that agree well, enabling confidence that the experimental conclusions are relevant. The methods are then applied to two different shock control bumps: a smoothly contoured bump, representative of previous studies, and a novel extended geometry featuring a continuously widening tail, which spans the wind-tunnel width at the rear of the bump. Comparison between the computational and experimental results for the contour bump showed good agreement both with respect to the flow structures and quantitative analysis of the boundary-layer parameters. It was seen that combining the experimental and numerical data could provide valuable insight into the flow physics, which would not generally be possible for a one-sided approach. The experiments and computational fluid dynamics were also seen to agree well for the extended bump geometry, providing evidence that, even though the bump interacts directly with the wind-tunnel walls, it was still possible to observe the key flow physics. The joint approach is thus suitable even for wider bump geometries.

Multi-objective optimization of shock control bump on a supercritical wing

Based on the supercritical “wing1” which was released in the DPW-III conference, multi-objective optimization has been done to increase the lift-drag ratio at cruise condition and improve transonic buffet boundary and drag-rise performance. Hicks-Henne shape functions are used to represent the bump shape. In the design optimization to increase lift-drag ratio, the objectives involve the cruise point and three other off-design points nearby. In the other optimization process to improve buffet and drag-rise performance, three buffet onset points near the cruise point and one drag-rise point are selected as the design points. Non-dominating sort genetic algorithm II (NSGA-II) is used in both processes. Additionally, individual analysis for every selected point on the Pareto frontier is conducted in order to avoid local convergence and achieve global optimum. Results of optimization for aerodynamic efficiency show a decrease of 11 counts in drag at the cruise point. Drag at nearby off-design points are also reduced to some extent. Similar approaches are made to improve buffet and drag-rise characteristics, resulting in significant improvements in both ways.

The influence of transition onset location on the performance of shock control bumps

AbstractIn order to investigate the robustness of three dimensional bumps on shock control for natural laminar-flow wings, the impact of transition onset location on the overall performance of the shock control device was studied. For a ramp bump, a moderate ramp start angle θr =4° was found to effectively fix the location of the leading leg of the shock lambda, decreasing chord-wise movement in the main shock position resulting from variations in transition onset location. With increasing transition onset length from xtrans =0% chord to 45% chord, little influence was found regarding the overall performance of the shock control device but a down-stream movement of the secondary leg of the shock lambda in a range about 3% chord was observed. Change in the boundary-layer displacement thickness due to varying transition onset locations was identified as the primary mechanism responsible for this secondary shock leg movement.

Shock control bump optimization for a low sweep supercritical wing

Shock control bumps are a promising technique in reducing wave drag of civil transport aircraft flying at transonic speeds. This paper investigates the optimization of 3D shock control bumps on a supercritical wing with a sweep angle of 16° at the 1/4 chord. A similar supercritical wing with a higher sweep angle of 24.5° at the 1/4 chord has been adopted as a baseline for the study. Numerical results show that the drag coefficient of the low sweep wing with the optimized 3D shock control bumps is reduced below that for the high sweep wing, indicating shock control bumps can be used as an effective means to reduce the wave drag caused by reducing the wing sweep angle. From the point of view of the wing structure design, lower sweep angle will also bring the benefits of weight reduction, resulting in further fuel reduction.

Active flow control of airfoil using mesh/meshless methods coupled to hierarchical genetic algorithms for drag reduction design

PurposeThe purpose of this paper is to investigate an active flow control technique called Shock Control Bump (SCB) for drag reduction using evolutionary algorithms.Design/methodology/approachA hierarchical genetic algorithm (HGA) consisting of multi‐fidelity models in three hierarchical topological layers is explored to speed up the design optimization process. The top layer consists of a single sub‐population operating on a precise model. On the middle layer, two sub‐populations operate on a model of intermediate accuracy. The bottom layer, consisting of four sub‐populations (two for each middle layer populations), operates on a coarse model. It is well‐known that genetic algorithms (GAs) are different from deterministic optimization tools in mimicking biological evolution based on Darwinian principle. In HGAs process, each population is handled by GA and the best genetic information obtained in the second or third layer migrates to the first or second layer for refinement.FindingsThe method was validated on a real life optimization problem consisting of two‐dimensional SCB design optimization installed on a natural laminar flow airfoil (RAE5243). Numerical results show that HGA is more efficient and achieves more drag reduction compared to a single population based GA.Originality/valueAlthough the idea of HGA approach is not new, the novelty of this paper is to combine it with mesh/meshless methods and multi‐fidelity flow analyzers. To take the full benefit of using hierarchical topology, the following conditions are implemented: the first layer uses a precise meshless Euler solver with fine cloud of points, the second layer uses a hybrid mesh/meshless Euler solver with intermediate mesh/clouds of points, the third layer uses a less fine mesh with Euler solver to explore efficiently the search space with large mutation span.

Toward Designing with Three-Dimensional Bumps for Lift/Drag Improvement and Buffet Alleviation

The desire to design more efficient transport aircraft has led to many different attempts to minimize drag. One approach is the use of three-dimensional shock control bumps, which have gained popularity in the research community as simple, efficient and robust devices capable of reducing the wave drag of transonic wings. This paper presents a computational study of the performance of three-dimensional bumps, relating key bump design variables to the overall wing aerodynamic performance. An efficient parameterization scheme allows three-dimensional bumps to be directly compared to two-dimensional designs, indicating that two-dimensional bumps are capable of greater design point aerodynamic performance in the transonic regime. An advantage of three-dimensional bumps lies in the production of streamwise vortices, such that, while two-dimensional bumps are capable of superior performance near the design point, three-dimensional bumps are capable of breakingup regions of separated flow at high Mach numbers, suggesting improvement in terms of buffet margin. A range of bump designs are developed that exhibit a tradeoff between design point aerodynamic efficiency and improvementinbuffet margin, indicating the potential for bespoke designs to be generated for different sections of a wing based on its flow characteristics. Copyright © 2012 by Jeremy Eastwood and Jerome Jarrett.

Experimental Study into the Flow Physics of Three-Dimensional Shock Control Bumps

This paper describes a fundamental experimental study of the flow structure around a single three-dimensional (3D) transonic shock control bump (SCB) mounted on a flat surface in a wind tunnel. Tests have been carried out with a Mach 1.3 normal shock wave located at a number of streamwise positions relative to the SCB. Details of the flow have been studied using the experimental techniques of schlieren photography, surface oil flow visualization, pressure sensitive paint, and laser Doppler anemometry. The results of the work build on the findings of previous researchers and shed new light on the flow physics of 3D SCBs. It is found that spanwise pressure gradients across the SCB ramp and the shape of the SCB sides affect the magnitude and uniformity of flow turning generated by the bump, which can impact on the spanwise propagation of the quasi-two-dimensional (2D) shock structure produced by a 3DSCB. At the bump crest, vortices can form if the pressure on the crest is significantly lower than at either side of the bump. The trajectories of these vortices, which are relatively weak, are strongly influenced by any spanwise pressure gradients across the bump tail. Asignificant difference between 2D and 3D SCBs highlighted by the study is the impact of spanwise pressure gradients on 3D SCB performance. The magnitude of these spanwise pressure gradients is determined largely by SCB geometry and shock position. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Robust active shock control bump design optimisation using hybrid parallel MOGA

The paper investigates a robust optimisation for detail design of active shock control bump on a transonic Natural Laminar Flow (NLF) aerofoil using a Multi-Objective Evolutionary Algorithm (MOEA) coupled to Computational Fluid Dynamics (CFDs) software. For MOEA, Robust Multi-Objective Optimisation Platform (RMOP) developed at CIMNE is used. For the active shock control bump design, two different optimisation methods are considered; the first method is a Pareto-Game based Genetic Algorithm in RMOP (denoted as RMOGA). The second method uses a Hybridised RMOGA with Game-Strategies and a parallel computation for high performance computation. Numerical results show not only how the concept of Shock Control Bump (SCB) coupled to CFD can improve aerodynamic performance of classic transonic aerofoil at the variability of flight conditions but also how high performance (parallel/distributed) computation with applying Hybrid-Game increases the efficiency of optimisation in terms of computational cost and results accuracy.

Shock control bump parametric research on supercritical airfoil

High precision of CFD code was used to study supercritical Airfoil RAE2822 superimposed with different shock control bumps under the transonic conditions. A successful improvement was made to current widely used Hicks-Henne functions which describe shock control bumps. Based on improving the airfoil’s lift-drag ratio, the study shows that, (1) the best bump crest position is at the position close to 50% of bump chord, which is almost independent of free stream or pre-shock Mach numbers, but the bump height is highly coupled with the crest position, which means that the higher the bump is, the more obviously the crest position affects the airfoil lift-drag ratio, and it becomes more evident with the increase of free stream or pre-shock Mach numbers; (2) in case that the lift-drag ratio of airfoil with bump is higher than basic airfoil, almost all the optimum distances between bump crest and shock wave are close to 30% of bump chord; (3) almost all the lift-drag ratios of airfoil with bump increase as bump chord length increases, of which this trend becomes more evident as bump height increases; (4) with the increase of the bump height, almost all the lift-drag ratios of airfoil with bump decrease at low free stream or pre-shock Mach numbers. When the Mach numbers are higher, the lift-drag ratio of airfoil increases as the increase of the bump height, and particularly, the trend tends to be visible when the Mach numbers are at a high level.

Double-shock control bump design optimization using hybridized evolutionary algorithms

This study investigates the application of two advanced optimization methods for solving active flow control (AFC) device shape design problem and compares their optimization efficiency in terms of computational cost and design quality. The first optimization method uses hierarchical asynchronous parallel multi-objective evolutionary algorithm and the second uses hybridized evolutionary algorithm with Nash-Game strategies (Hybrid-Game). Both optimization methods are based on a canonical evolution strategy and incorporate the concepts of parallel computing and asynchronous evaluation. One type of AFC device named shock control bump (SCB) is considered and applied to a natural laminar flow (NLF) aerofoil. The concept of SCB is used to decelerate supersonic flow on suction/pressure side of transonic aerofoil that leads to a delay of shock occurrence. Such active flow technique reduces total drag at transonic speeds which is of special interest to commercial aircraft. Numerical results show that the Hybrid-Game helps an EA to accelerate optimization process. From the practical point of view, applying a SCB on the suction and pressure sides significantly reduces transonic total drag and improves lift-to-drag ( L/ D) value when compared to the baseline design.