Géza Schrauf

Géza Schrauf
German Aerospace Center (DLR) | DLR · Institute of Aerodynamics and Flow Technology

Dr.

About

63
Publications
9,672
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809
Citations
Citations since 2017
9 Research Items
387 Citations
2017201820192020202120222023020406080100
2017201820192020202120222023020406080100
2017201820192020202120222023020406080100
2017201820192020202120222023020406080100

Publications

Publications (63)
Article
The classical criteria on allowable surface imperfections for laminar flow are slightly modified and applied to an hybrid-laminar-flow-control (HLFC) wing.
Article
We describe a simple pre-design method to estimate the size of an air outlet flap for a passive hybrid laminar flow control (HLFC) system to determine the feasibility of that flap. The method is based on an ingenious application of old experimental results. The computational effort is minimal.
Conference Paper
Within the European AFLoNext project, a simplified HLFC system has been designed for the vertical tail plane of an A320 aircraft. The flight tests with this system were performed in spring 2018. We will give a short overview of design, manufacturing, measuring systems and installation on the aircraft. Then, we will present the current status of eva...
Chapter
We describe a simple pre-design method to estimate the size of an air outlet flap for a passive hybrid laminar flow control (HLFC) system to determine the feasibility of that flap. The method is based on an ingenious application of old experimental results. The computational effort is minimal.
Article
A flight test with a simplified hybrid laminar flow control (HLFC) system on the vertical tail plane (VTP) of an A320 aircraft was performed in April/May 2018. This HLFC system was a prototype for a simplified system that might be attractive for drag reduction of commercial long-range aircraft. The paper presents the design principles of a simplifi...
Conference Paper
A flight test with a simplified HLFC system on the vertical tail plane of an A320 aircraft was performed in April/May 2018. In this paper we discuss the preparation of the flight test data for evaluation with linear stability theory on the basis of sample measurements. Then we present our correlated transition N-factors and compare them with the re...
Article
We describe a simple pre-design method to estimate the size and suction capability of an air outlet flap for a passive hybrid laminar flow control (HLFC) system. The method is based on an ingenious application of old experimental results. The computational effort is minimal.
Conference Paper
Full-text available
A flight test with a simplified HLFC system on the vertical tail plane of an A320 aircraft was performed in April/May 2018. The aerodynamic and system design is discussed and first results of the flight tests are presented.
Conference Paper
Data and observations from F100 and ATTAS flight tests with forward and backward facing steps are presented and a modification of a classical step criterion is proposed.
Conference Paper
Full-text available
The reduction of fuel-consumption is an environmentally relevant priority of the aviation industry. One of the key technologies in this field is the hybrid laminar flow control (HLFC), which is based on perforated sections on the leading edge of aircrafts. Up to now the economic efficiency aswell as the quality of several micro drilling processes,...
Article
Full-text available
To realize a reduced fuel consumption of civil jet transport aircrafts, hybrid laminar flow control (HLFC) is a key technology in aerospace industry. For drag reduction caused by boundary layer suction, small holes at the leading edges of the aircraft wings and tail planes are needed. Much effort has been spend in drilling of small holes into diffe...
Conference Paper
This paper presents a wing design methodology for civil aircraft with hybrid laminar flow control (HLFC), conceived for application in conceptual and preliminary aircraft design. It is based on a quasi-three-dimensional approach that comprises sophisticated methods for estimation of transonic aerodynamic characteristics and transition prediction. I...
Article
Full-text available
Previous flight tests have clearly demonstrated the potential of hybrid laminar flow control (HLFC). However, these HLFC systems were too heavy and too complex for the application on commercial transport aircraft. In this paper we describe the concept and present some design features for a simplified HLFC system for the fin of an Airbus A320.
Conference Paper
In einem multidisziplinären Ansatz wird im Rahmen des DLR-Projektes LamAiR ein aerodynamisch optimier-tes und in Grenzen ein systemtechnisch optimiertes Seitenleitwerk eines Airbus A320 numerisch für die Um-setzung der Hybrid-Laminarhaltung ausgelegt. Die aerodynamische Entwurfsaufgabe soll folgenden wesent-lichen Anforderungen gerecht werden: a....
Conference Paper
Full-text available
Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim of obtaining a laminar flow testing capability in the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number. Results of pre-tes...
Conference Paper
Full-text available
A wind-tunnel experiment on laminar-turbulent transition has been performed in ETW at high Reynolds number and cryogenic conditions. The studied geometry is a swept-wing configuration. The transition location was determined by means of Temperature Sensitive Paint (TSP). The experimental observations were further analysed using different transition...
Conference Paper
Full-text available
The Pathfinder model was designed in the course of the TELFONA European Research Project as a calibration tool to evaluate the transonic, cryogenic ETW facility for laminar flow testing, and assess the possibility for studies of NLF or HLF wings in ETW. The Pathfinder wing is a simplified, low taper, swept wing with an optimized profile allowing al...
Chapter
A Reynolds-averaged Navier-Stokes solver, a laminar boundary-layer code and a fully automated local, linear stability code for the prediction of Tollmien-Schlichting and cross flow instabilities were coupled for the automatic prediction of laminar-turbulent transition on general aircraft configurations during the ongoing flow computation. The proce...
Conference Paper
Full-text available
With the goal of studying Natural Laminar Flow (NLF) wings for future ‘green’ transport aircraft, the aim of the European Research Project TELFONA is to develop and demonstrate the possibility of testing full aircraft models at large Reynolds numbers in the cryogenic Wind Tunnel ETW, with direct measurements of total drag. Two main steps were defin...
Conference Paper
Full-text available
Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim to obtain the capability of laminar flow testing of the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number. Pre-test numeric...
Article
A Reynolds-averaged Navier-Stokes solver, a laminar boundary-layer code and a fully automated local, linear stability code for the prediction of Tollmien-Schlichting and cross flow instabilities were coupled for the automatic prediction of laminar-turbulent transition on general aircraft configurations during the ongoing flow computation. The proce...
Article
A hybrid Reynolds-averaged Navier–Stokes solver, a laminar boundary-layer code, and a fully automated local, linear stability code were coupled to predict the laminar–turbulent transition due to Tollmien–Schlichting and crossflow instabilities using the eN method based on the two-N-factor approach. The coupled system was designed to be applied to t...
Article
This article is the second of two companion papers which document the concept and the application of a coupled computational fluid dynamics system which was designed to incorporate the prediction of laminar–turbulent transition into a hybrid Reynolds-averaged Navier–Stokes solver. Whereas the first part deals with the description of the transition...
Conference Paper
A wind-tunnel experiment on laminar-turbulent transition has been performed in ETW at high Reynolds number and cryogenic conditions. The studied geometry is a swept-wing configuration. The transition location was determined by means of Temperature Sensitive Paint (TSP). The experimental observations were further analysed using different transition...
Conference Paper
Full-text available
A Reynolds-averaged Navier-Stokes solver, a laminar boundary-layer code and a fully automated local, linear stability code for the prediction of Tollmien-Schlichting and cross flow instabilities were coupled for the automatic prediction of laminar-turbulent transition on general aircraft configurations during the ongoing flow computation. The proce...
Conference Paper
A hybrid Reynolds-averaged Navier-Stokes solver, a laminar boundary layer code and a fully automated local, linear stability code were coupled in order to predict the laminar-turbulent transition due to Tollmien-Schlichting and cross flow instabilities using the eN-method based on the two N factor approach. The coupled system was designed to be app...
Conference Paper
For the simulation of low Reynolds- and Mach number flows, a boundary layer code in combination with a database method are coupled with an unstructured RANS code. The technique is validated in 2D using a glider airfoil and in 3D for a glider, showing good agreement with experiments and a well-validated 2D design code.
Article
Full-text available
This document provides a synthesis of recent research studies that have been conducted in the last decade within several European projects from the 5 th and 6 th Framework Programmes. All these studies aimed at a better characterization of aircraft wake vortices and then at their subsequent control. In the latter case, the goal is to minimize the s...
Article
Full-text available
After identifying the ecological and economic drivers for use of laminar flow technology, we outline the mechanisms of laminar-turbulent boundary layer transition and review the status of natural laminar flow (NLF) and hybrid laminar flow control (HLFC). New ways to reduce the complexity of HLFC systems are presented, and the remaining steps to ach...
Article
A short overview of the different ways to apply linear stability theory in the form of the e(N) method for transition prediction in boundary-layer flow is given. The ATTAS/VFW614, the Fokker F100, and the Airbus A320 flight tests are evaluated and compared to two hybrid laminar-flow tests in the SIMA tunnel. N-factor correlations are given for all...
Chapter
We assess linear, local and non-local, as well as non-linear instability theory for transition prediction. After an overview of all linear, local theories, we re-evaluate the transition experiment with the HQ26 profile using non-local theory and obtain an improved N-factor correlation. We propose a hybrid two-N-factor method, using local theory to...
Conference Paper
Wind tunnel and flight tests have clearly demonstrated the potential of hybrid laminar flow control (HLFC) for drag reduction. Additional weight and costs of the suction system reduce the efficiency of the HLFC technology. Within the EC funded ALTTA programme a drastically simplified suction system has been proposed. Characteristic of this system i...
Article
After highlighting the need for laminar flow technology, we give an overview of the large-scale laminar flow wind tunnel and flight tests performed within European programmes and consider the prospects of the latest developments.
Conference Paper
The e N -method is applied to three large-scale experiments performed in the ONERA S1MA wind tunnel and two flight experiments with the ATTAS VFW614 and a Fokker F100 aircraft. N-factor correlations using incompressible as well compressible linear stability theory obtained for natural and hybrid laminar flow surfaces are discussed.
Chapter
For the stability analysis of the ELFIN II HLF half wing measurements which were conducted in the S1Ma wind tunnel the input data for 55 selected test runs have been prepared. The following steps have been treated: Selection of the test cases Smoothing and interpolation of measured wing coordinates and pressures in the nose section Determination of...
Chapter
This paper reports on the evaluation of the ELFIN II HLF experiment in the ONERA S1MA wind tunnel with the e N -method. It is shown that the envelope method can fail for swept wings with leading edge suction. More consistent N-factors are obtained if the amplification of Tollmien-Schlichting and cross-flow waves is described separately by two N-fac...
Article
Full-text available
Flight tests using a Fokker F100 aircraft equipped with a natural laminar flow glove demonstrated that natural laminar now is feasible for transport aircraft with up to 130 passengers. Furthermore, the flight tests generated a wealth of experimental data. These data have been evaluated with all known variations of tbe e<SUP>N</SUP> method. The aim...
Conference Paper
Within the ELFIN I program, flight tests using a Fokker FIDO aircraft equipped with a naturallaminar-flow glove demonstrated that natural laminar flow is feasible for transport aircraft with up to 130 passengers. Furthermore, the flight tests generated a wealth of experimental data. These data have been evaluated with all known variations of the e^...
Article
The VFW 614/ATTAS flight tests have provided an extensive database for the analysis and development of methods to predict transition for aerodynamic design. While previous work has rested on the e(N) method, we re-evaluate two Tollmien-Schlichting-dominated test cases using the linear and nonlinear parabolized stability equations (PSE), We compare...
Article
A potential confusion regarding the signs of the wave-front curvature terms m12, m21 in the linear stability equations is resolved. It is shown that these terms, although denoted by Stuart, Malik, and the author with the same symbols, have different geometrical meanings depending on the underlying coordinate systems.
Article
A FORTRAN 77 implementation of a generalized inverse Rayleigh iteration procedure for the calculation of eigenvalues and left and right eigenvectors of a complex band matrix is described. The core of the procedure is an algorithm that solves systems with the original matrix and with the adjoint matrix by calculating only one LU-decomposition.
Article
A FORTRAN 77 implementation of a Gauss algorithm with partial pivoting for banded matrices is described. The algorithm keeps only part of the matrix that is necessary for the actual computation in memory. This allows large systems to be solved on machine without virtual memory, or if the virtual memory is too small for the problem.
Article
A compressible stability code was developed as a tool for the design of natural-laminar-flow airfoils. The code is based on a general set of stability equations which allows one to examine the influence of non-parallelity or non-zero pressure gradients. It also allows streamline and surface curvature to be included.
Article
In this paper continuation methods are applied to the axisymmetric Navier-Stokes equations in order to investigate how the stability of spherical Couette flow depends on the gap size σ. We find that the flow loses its stability due to symmetry-breaking bifurcations and exhibits a transition with hysteresis into a flow with one pair of Taylor vortic...
Article
The present study is concerned with a calculation of solutions of the Navier-Stokes equations under steady flow conditions, taking into account the flow in a gap between a rotating and stationary spherical shell. It is pointed out that the laminar flow of an incompressible, Newtonian liquid with constant viscosity is described by means of the conti...
Chapter
The transitions of the flow in a spherical gap are investigated by calculating the solution branches of the steady-state axisymmetric Navier-Stokes equations with a continuation method. The first flow instability is explained by a bifurcation of the spherical Couette flow into flows without equatorial symmetry. A hysteresis is predicted for η = R1/...
Article
The Navier-Stokes equations were solved for stationary flow in a gap between two concentric spheres the inner of which rotates and the outer of which is at rest. Rotational and equatorial symmetric solutions for several radii ratios are calculated. Stationary and unsteady solutions which depend on the Reynolds number and the radii ratio are establi...
Article
Full-text available
Wind tunnel and flight tests have clearly demonstrated the potential of hybrid laminar flow control (HLFC) for drag reduction. However, for application on a commercial aircraft, previous HLFC systems were too heavy and complex. In this paper, a simplified system is proposed based on a double skin structure using a micro-perforated outer skin and an...

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