Efficient polar optimization of transport aircraft in transonic RANS flow using adjoint gradient based approach

A major design requirement for transport aircraft is efficient cruise flight in the transonic region. From the aerodynamic viewpoint, this is achieved by favorable lift-to-drag ratio of the aircraft, both at the main design point and at off-design conditions. We therefore present a method to efficiently perform a multi-point optimization of a representative wing-body configuration. Designs are evaluated with RANS CFD simulations, the wing is parametrized using 40 free-form deformation control points, and a gradient-based method is used to drive the optimization. The gradient of cost functions is computed with a discrete adjoint approach, in which flow and mesh adjoint equations are solved. Compared to single-point optimization, with multi-point optimization we obtain a design with slightly lower best lift-to-drag ratio, but which has improved lift-to-drag polar over the whole range of practical lift coefficients compared to the baseline design

Achieving High Speed CFD simulations: Optimization, Parallelization, and FPGA Acceleration for the unstructured DLR TAU Code

Today, large scale parallel simulations are fundamental tools to handle complex problems. The number of processors in current computation platforms has been recently increased and therefore it is necessary to optimize the application performance and to enhance the scalability of massively-parallel systems. In addition, new heterogeneous architectures, combining conventional processors with specific hardware, like FPGAs, to accelerate the most time consuming functions are considered as a strong alternative to boost the performance. In this paper, the performance of the DLR TAU code is analyzed and optimized. The improvement of the code efficiency is addressed through three key activities: Optimization, parallelization and hardware acceleration. At first, a profiling analysis of the most time-consuming processes of the Reynolds Averaged Navier Stokes flow solver on a three-dimensional unstructured mesh is performed. Then, a study of the code scalability with new partitioning algorithms are tested to show the most suitable partitioning algorithms for the selected applications. Finally, a feasibility study on the application of FPGAs and GPUs for the hardware acceleration of CFD simulations is presented

Flight Dynamic Stability Prediction for an Aircraft in Transonic Separated Flow Conditions with a Linear Frequency Domain Solver

Recent computational methods for more efficient and accurate quantification of unsteady aerodynamic loads on the aircraft

Linear Frequency Domain Method For Aerodynamic Applications

Applications such as load alleviation involve a wide range of parameters including a multitude of different Mach numbers, angles of attack and load cases and therefore create the demand for rapid prediction of unsteady air loads. First, there is a need for an enhanced prediction accuracy including viscous effects and shocks for a more reliable judgement of aerodynamic behavior compared to the classically-used methods based on the potential theory for such applications. Secondly, short turnaround times must be guaranteed, and this in turn means to find a suitable replacement of the tedious and time-consuming un- steady Navier-Stokes solvers. Driven by these requirements for accurate and fast prediction of air loads, a time-linearized unsteady Navier-Stokes method was developed also known as linear frequency domain method (LFD). The LFD in the DLRs TAU suite is based on the modeling of a damped harmonic oscillator, and it has been shown to be accurate and efficient for the evaluation of unsteady air loads at transonic and partly separated flow conditions [1]. Since then, the LFD method has been continuously extended and applied for various applications. The scope of target applications of the LFD has been growing consistently including different topics in aeroelasticity, where the determined surface pressure and surface skin friction distributions make an important contribution. Moreover, the time-linearized method can also be used for the efficient evaluation of flight dynamic (flight mechanical) characteristics relevant for the stability and control behavior of an aircraft. Furthermore, gust loads were successfully predicted which are important for structural and control surface design [2, 3] as well as control system performance. A recent and demanding application was the extension of the LFD method for fluidic actuators. Thus, the LFD was adopted for simulating pulsating blowing to avoid the enormously long transient phase inherently occurring during time-marching Navier-Stokes simulations. Several applications involving industrial relevant configurations are presented and discussed to outline the maturity of the method and to demonstrate the versatility of the technique

Repositioning of the global epicentre of non-optimal cholesterol

High blood cholesterol is typically considered a feature of wealthy western countries(1,2). However, dietary and behavioural determinants of blood cholesterol are changing rapidly throughout the world(3) and countries are using lipid-lowering medications at varying rates. These changes can have distinct effects on the levels of high-density lipoprotein (HDL) cholesterol and non-HDL cholesterol, which have different effects on human health(4,5). However, the trends of HDL and non-HDL cholesterol levels over time have not been previously reported in a global analysis. Here we pooled 1,127 population-based studies that measured blood lipids in 102.6 million individuals aged 18 years and older to estimate trends from 1980 to 2018 in mean total, non-HDL and HDL cholesterol levels for 200 countries. Globally, there was little change in total or non-HDL cholesterol from 1980 to 2018. This was a net effect of increases in low- and middle-income countries, especially in east and southeast Asia, and decreases in high-income western countries, especially those in northwestern Europe, and in central and eastern Europe. As a result, countries with the highest level of non-HDL cholesterol-which is a marker of cardiovascular riskchanged from those in western Europe such as Belgium, Finland, Greenland, Iceland, Norway, Sweden, Switzerland and Malta in 1980 to those in Asia and the Pacific, such as Tokelau, Malaysia, The Philippines and Thailand. In 2017, high non-HDL cholesterol was responsible for an estimated 3.9 million (95% credible interval 3.7 million-4.2 million) worldwide deaths, half of which occurred in east, southeast and south Asia. The global repositioning of lipid-related risk, with non-optimal cholesterol shifting from a distinct feature of high-income countries in northwestern Europe, north America and Australasia to one that affects countries in east and southeast Asia and Oceania should motivate the use of population-based policies and personal interventions to improve nutrition and enhance access to treatment throughout the world.Peer reviewe

Lagrangian Trajectory Simulation of Rotating Regular Shaped Ice Particles

This paper focuses on the numerical simulation of the motion of regular shaped ice particles under the forces and torques generated by aerodynamic loading. Ice particles can occur during landing and take-off of aircraft at ground level up to the lower bound of the stratosphere at cruising altitude. It may be expected that the particle Reynolds number is high because the flow around the aircraft is in certain regions characterized by strong acceleration and deceleration of the flow. In combination with this flow pattern, the rotation of particles becomes important. Applicable translational and rotational equations of motion combined with a drag correlation taking into account rotation will be derived for a Lagrangian type particle tracking. Orientation is described with quaternions to prevent the singularities associated with the description by Euler angles. The influence of regular shaped particles on collection efficiencies is investigated. Test cases are the flow past a cylinder, a NACA0012 airfoil and a NHLP L1/T2 three element airfoil. Due to the increased computational effort compared to the purely translational approach, observed trajectory simulation times are reported

Lagrangian Particle Tracking on Large Unstructured Three-Dimensional Meshes

A prerequisite for the prediction of ice accretion on an aircraft flying through clouds of supercooled liquid water is the accurate determination of the water impingement rate on various components of the aircraft. For this purpose, a droplet impingement module has been developed using the datastructure of the unstructured Navier-Stokes solver TAU. Since nowadays large computational grids are common practice, an efficient algorithm for determination of the droplet trajectories on such grids had to be implemented. This paper describes the physics and details of the implemented numerical algorithm. It summarizes lessons learned during development. The paper concludes with the presentation of code validation results and examples of applications

Comparison between Gradient-free and Adjoint Based Aerodynamic Optimization of a Flying Wing Transport Aircraft in the Preliminary Design.

This paper describes investigations of planform and shape optimizations for a flying wing transport aircraft with an Euler continuous adjoint method. For a prescribed lift the cost function will be the drag, which has to be minimized and implies a maximization of L/D. The results presented for the gradient based method using an adjoint solver are compared to an optimization performed with a gradient free approach. The different workflows and procedures will demonstrate the advantages and disadvantages of each particular optimization approach. The optimization procedure uses a freeform deformation technique for the design parameterization of the shape as well as for the surface mesh deformation required to determine the gradients. This combination of both tasks into one tool is advantageous because performing finite differences for evaluating the mesh sensitivities can be carried out with a constant grid topology. An example design case is also shown for demonstration purposes

LINEAR FREQUENCY DOMAIN PREDICTIONS OF DYNAMIC DERIVATIVES FOR THE DLR F12 WIND TUNNEL MODEL

Structural loads for full aircraft configurations can be represented by evaluating dynamic derivatives over a wide parameter space mainly including different mode shapes, an- gle of attack and Mach numbers. Traditionally, these values are determined by wind tunnel tests applying forced periodic motions to aircraft models. The ability of numerical simula- tions provide an excellent addendum to wind tunnel tests. Instead of time-accurate unsteady Reynolds-averaged Navier-Stokes (URANS) solvers which are recognized as extremely compu- tational expensive this paper considers a linearized frequency domain solver (LFD). With this approach the unsteady simulation reduces to a single steady state computation and a single linear simulation in the frequency domain. By the assumption of small perturbations and har- monic oscillations dynamic derivatives can be computed efficiently within a wide parameter space. In addition, the theoretical background for the LFD will be presented. Based on the linearization of the RANS equations and modeling of small perturbations with Fourier series a complex valued linear system has to be solved

Improvement of the Automatic Grid Adaptation for Vortex Dominated Flows using Advanced Vortex Indicators with the DLR-TAU Code.

Vortex dominated flows appear in many flow simulations such as wake turbulence of an aircraft or a delta wing at a high angle of attack. For detailed investigations of vortex breakdown, vortex interactions or tracing vortex cores, an automated grid adaptation with suitable vortex indicators is essential. Physical indicators, e.g. the vorticity magnitude or the total pressure loss, are in most cases not sufficient for correctly identifying a vortex core. This paper presents advanced vortex core indicators which properly identify a vortical structure independent of the flow case. These vortex indicators are tested in typical flow applications to determine the right cut-off value which is important for an automated adaptation procedure. A grid refinement for a delta wing testcase in combination with the newly introduced vortex indicators will demonstrate the improvements compared to the standard pressure loss indicator