06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
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Item Open Access Thermodynamic analysis and numerical modeling of supercritical injection(2015) Banuti, Daniel; Weigand, Bernhard (Prof. Dr.-Ing. habil.)Although liquid propellant rocket engines are operational and have been studied for decades, cryogenic injection at supercritical pressures is still considered essentially not understood. This thesis intends to approach this problem in three steps: by developing a numerical model for real gas thermodynamics, by extending the present thermodynamic view of supercritical injection, and finally by applying these methods to the analysis of injection. A new numerical real gas thermodynamics model is developed as an extension of the DLR TAU code. Its main differences to state-of-the-art methods are the use of a precomputed library for fluid properties and an innovative multi-fluid-mixing approach. This results in a number of advantages: There is effectively no runtime penalty of using a real gas model compared to perfect gas formulations, even for high fidelity equations of state (EOS) with associated high computational cost. A dedicated EOS may be used for each species. The model covers all fluid states of the real gas component, including liquid, gaseous, and supercritical states, as well as liquid-vapor mixtures. Numerical behavior is not affected by local fluid properties, such as diverging heat capacities at the critical point. The new method implicitly contains a vaporization and condensation model. In this thesis, oxygen is modeled using a modified Benedict-Webb-Rubin equation of state, all other involved species are treated as perfect gases. A quantitative analysis of the supercritical pseudo-boiling phenomenon is given. The transition between supercritical liquid-like and gas-like states resembles subcritical vaporization and is thus called pseudo-boiling in the literature. In this work it is shown that pseudo-boiling differs from its subcritical counterpart in that heating occurs simultaneously to overcoming molecular attraction. In this process, the dividing line between liquid-like and gas-like, the so called Widom line, is crossed. This demarcation is characterized by the set of states with maximum specific heat capacity. An equation is introduced for this line which is more accurate than previous equations. By analyzing the Clausius-Clapeyron equation towards the critical limit, an expression is derived for its sole parameter. A new nondimensional parameter evaluates the ratio of overcoming molecular attraction to heating: It diverges towards the critical point but shows a significant pseudo-boiling effect for up to reduced pressures of 2.5 for various fluids. It appears reasonable to interpret the Widom-line, which divides liquid-like from gas-like supercritical states, as a definition of the boundary of a dense supercritical fluid. This may be used to uniquely determine the radius of a droplet or the dense core length of a jet. Then, a quantitative thermodynamic analysis is possible. Furthermore, as the pseudo-boiling process may occur during moderate heat addition, this allows for a previously undescribed thermal jet disintegration mechanism which may take place within the injector. This thermal jet break-up hypothesis is then applied to an analysis of Mayer’s and Branam’s nitrogen injection experiments. Instead of the constant density cores as predicted by theory, the majority of their cases show an immediate drop in density upon entering the chamber. Here, three different axial density modes are identified. The analysis showed that heat transfer did in fact take place in the injector. The two cases exhibiting a dense core are the cases which require the largest amount of power to reach the pseudo-boiling temperature. After this promising application of pseudo-boiling analysis, thermal break-up is tested numerically. By accounting for heat transfer inside the injector, a non dense-core injection can indeed be simulated for the first time with CFD. Finally, the CFD model is applied to the A60 Mascotte test case, a reactive GH2/LOX single injector operating at supercritical pressure. The results are compared with experimental and other researcher’s numerical data. The flame shape lies well within the margins of other CFD results. Maximum OH* concentration is found in the shear layer close to the oxygen core and not in the shoulder, in agreement with experimental data. The axial temperature distribution is matched very well, particularly concerning position and value of the maximum temperature.Item Open Access Passively mode-locked Tm-lasers for all-fiber high-energy nonlinear chirped pulse amplification(2023) Graf, Florian; Dekorsy, Thomas (Prof. Dr. rer. nat.)Item Open Access Turbulence modeling of complex flows in CFD(2008) Uddin, Naseem; Weigand, Bernhard (Prof. Dr.-Ing. habil.)In the last two decades of the 20th century, the world had witnessed the enormous increase in the computational resources. This has brought in the tremendous increase in human knowledge and understanding of complex phenomenon, like turbulence and its modeling among others. The technical development has brought new challenges in engineering design. Whether we limit ourselves to the earthly matters or indulge in space exploration, the simulation of turbulence has become a routine task. Turbulence is a phenomenon in nature comprising of complex eddy structures which can greatly improve heat and mass transfer. The simplistic approach for the computation of turbulent flows is to compute them by Reynolds Averaged Navier-Stokes (RANS) equations based models. But due to the averaging procedure, the inherent unsteadiness of the flow is compromised. On the other hand, Direct Numerical Simulation (DNS) is the best approach for turbulent flow computations, in which no modeling assumptions are invoked and turbulent eddies as small as of the order of Kolmogorov scale are computed. The middle approach between these extremes is the Large Eddy Simulation (LES), in which part of the turbulence is modeled and rest is computed. However, the computational costs and memory requirement are still too large to take it as a general purpose engineering design tool. In this thesis, the effect of changes in inflow conditions on the heat transfer by an impinging jet is investigated using LES. The Dynamic Smagorinsky model proposed by Germano et al. has been used as a subgrid model. Results of several Large Eddy Simulations are reported in the thesis, which are conducted with use of total 244 processors on high performance computing clusters. The inflow conditions explored are: - The fully developed turbulent jet - Swirling jet - Velocity field active excitation - Velocity field passive excitation - Temperature field excitation An ERCOFTAC recommended benchmark test case of an orthogonally impinging round jet at Reynolds number of 23000 is simulated first. The agreement between the experiments and the LES gives encouragement for further investigations. Therefore in a next step, the effect of inlet velocity and temperature fields excitations of an orthogonally impinging round jet, on the heat transfer are explored. In case of the active control of the impinging jet’s inlet velocity field, it is found that the selection of excitational frequencies is important for heat transfer enhancement. The excitation at the subharmonic frequencies of the preferred mode is found to be a promising approach for heat transfer enhancement. A passively excited inlet velocity field is also investigated. It is found that this approach gives a better heat transfer than an active excitation case. The novel idea of heat transfer enhancement through jet’s inlet temperature field excitation is presented. The LES shows that the excitation at the preferred mode can give surface averaged Nusselt number higher than the non-excited jet impingement case. However the frequencies higher than the preferred mode should be taken with care, as they might cause thermal fatigue. The effect of the addition of the swirl to the impinging jet on the heat transfer is investigated. Also, it is found that the swirl does not give appreciable enhancement in heat transfer for H=D=2 case. The knowledge of flow and passive scalar flux dynamics gained through the simulation has helped in understanding the functional relationship between different turbulence quantities and heat transfer. It is found that the assumption of a constant turbulent Prandtl number (often used in RANS based models) is not a realistic approach. Alternative is to use scalarflux models, which allow the prediction of scalar-fluxes in non-isotropic turbulent state. The knowledge gained through the LES is then used to investigate coefficients in some explicit scalar-flux models (RANS based models). The investigation gives insight in the impingement phenomenon, which could help in the development of advanced turbulence models for heat transfer prediction.Item Open Access Coupled flow field and heat transfer in an advanced internal cooling scheme(2010) Coletti, Filippo; Weigand, Bernhard (Prof. Dr.-Ing. habil.)State-of-the-art gas turbines are designed to operate at turbine inlet temperatures in excess of 1850 K. Such temperature levels are sustainable only by means of an aggressive and efficient cooling of the components exposed to the hot gas path. Not only the maximum metal temperature needs to be kept below the safety limits, but the thermal field must be reasonably uniform, in order to limit the thermal stresses. This requires from the designer the most accurate knowledge of the local heat transfer rate. The need for such detailed information is in conflict with some common practices in the cooling system design: numerical simulations are often compared against area-averaged experimental data; the link between coolant flow field and heat transfer rates is scarcely analyzed; moreover, the coupling between convection and conduction is hardly taken into account. The present thesis aims at the aero-thermal characterization of a trailing edge cooling channel geometry. Cooling the trailing edge, one of the life-limiting parts of the airfoil, represents an especially challenging task since the aerodynamic requirement of high slenderness is conflicting with the need of integrating internal passages. The focus of the study is on three main aspects of the internal cooling technology: (i) the details of the coolant flow field; (ii) the contribution of the obstacles’ surface to the heat transfer; and (iii) the effect of the conduction through the cooling channel walls. The investigated cooling channel geometry is characterized by a trapezoidal cross-section. It has one rib-roughened wall and slots along two opposite walls. The coolant passes through a smooth inlet channel upstream of the investigated cavity; it crosses the divider wall through a first row of inclined slots, producing crossing-jets; the latter impinge on the rib-roughened wall, and the jet-rib interaction results in a complex flow pattern, rebounding the coolant towards the opposite smooth wall; finally the air exits through a second row of slots along the trailing edge. Such a scheme represents a combination of internal forced convection cooling and impingement cooling. An engine-representative Reynolds number equal to 67500 is defined at the entrance of the inlet channel. A comprehensive experimental investigation is carried out on a magnified model of the channel, at a scale of 25 : 1 with respect to engine size (applied to both the cavity volume and the walls thickness). The main flow structures are identified and characterized by means of particle image velocimetry, allowing to deduce a model of the highly three-dimensional mean flow. Each jet is shown to impinge on the three ribs in front of the slot, and the jet-rib interaction produces two upward deflections in each inter-rib domain. Distributions of heat transfer coefficient are obtained by means of liquid crystals thermography on the rib-roughened surface as well as on the opposite smooth wall in a purely convective regime, with a uniform heat flux imposed at the solid-fluid interface. The thermal patterns on the channel walls show the footprints of the flow features detected by the velocity measurements. Globally, the top side of the rib shows the highest Nusselt number among the investigated surfaces. The presence of the ribs enhances the global heat transfer level (averaged on all surfaces) by 14%. The aero-thermal results suggest a definite margin for improvement of the heat transfer performance by varying one or more geometrical parameters. In this perspective, the ribs have been tapered and shifted with respect to the slots position. Both expedients have proven to be useful in reducing the extent and intensity of the aforementioned hot spots in the vicinity of the ribs: an enhancement of about 20% in area-averaged heat transfer rate is achieved with respect to the standard configuration. The thermal behavior of the ribbed wall has also been investigated in conjugate heat transfer regime, in order to study the effect of the wall conduction on the thermal levels. By matching the solid-to-fluid thermal conductivity ratio found in an engine, the correct thermal boundary conditions for the convective problem are attained, which guarantees full similarity between laboratory model and engine reality. Infra-red thermography coupled to a finite element analysis is used to retrieve the whole thermal pattern through the considered rib-roughened wall. Nusselt number levels in conjugate regime differ by up to 30% locally and 25% globally with respect to the purely convective results. Neglecting wall conduction when evaluating the heat transfer coefficient leads to underestimating the maximum surface temperature by 26 to 33 K at engine conditions. Decreasing the wall thermal conductivity increases the overall heat transfer coefficient on the ribbed surface. However lower conductivities amplify local temperature gradients and hot spots.Item Open Access Stability of swirl tube flow(2019) Novotny, Pavel; Weigand, Bernhard (Prof. Dr.-Ing. habil.)This work focuses on detailed investigation of the flow phenomena and flow stability in swirl tubes. In general, a swirl tube is a tube with one or more tangential inlets generating complex swirling flow. This leads to large tangential velocities near the wall and to enhanced turbulent mixing in the tube, which results in a positive influence on the convective heat transfer in the tube. In the present work, a formulation of a condition to investigate stability of a flow is provided. This formulation reflects the definition of the second law of thermodynamics, i.e. the balance of entropy, and also the balance of the total enthalpy. So, the derived condition may serve as a criterion to investigate processes in general flows, for which an incompressible fluid via the Cauchy stress tensor is approximated. The experimental and numerical analysis of flow fields conducted for different Reynolds numbers show an axial backflow region in the tube centre determining possible vortex breakdown. For the lowest Reynolds number, an axial backflow region, in contrast to the higher Reynolds numbers, is observable up to the middle of the tube length. Thus, there is a region where the flow is characterised by no vortex breakdown. Moreover, similar behaviour is observed for the intermediate Reynolds number near the tube outlet. Nevertheless, for strong swirling flows, a possible vortex breakdown may be expected for a Rossby number lower than 0.65. Furthermore, the ratio between the local tangential and axial Reynolds numbers reveals that a vortex breakdown may occur in regions where this ratio is greater than 1. In addition, a connection between the derived stability criterion and the vortex breakdown confirms that the redistribution of flow fields is, due to the highest swirl strength, dominant at the beginning of the tube. Moreover, it is shown that vortex breakdown is accompanied by processes causing flow stabilisation.Item Open Access Experimental and numerical investigations of convective cooling configurations for gas turbine combustors(2008) Maurer, Michael; von Wolfersdorf, Jens (Prof. Dr.)Within the present study, experiments and numerical computations are conducted to analyze the cooling performance of different convective cooling techniques for backside cooled combustor walls. For all investigated configurations, the pressure loss and the heat transfer enhancement is observed. As possible candidates for a convective cooling scheme, rib turbulators, channels with dimples and channels with hemispheres are considered. The data bases for such convective cooling techniques, which have already been reported in literature, arise from the experience in internal blade cooling. Compared to the typical conditions found for backside cooled combustor walls, the Reynolds number and the mass flow rates are lower in the case of internal blade cooling. Additionally, the ribs or other convective cooling techniques are applied to two opposite channel walls within the blade. For backside cooled combustor walls, the heat transfer on only one channel wall needs to be enhanced. For the experimental setup, several measurement techniques are applied. The heat transfer coefficient between two successive ribs is obtained with a steady and a transient measurement technique. A comparison of the two measurement techniques is also provided. Averaged heat transfer coefficients on the rib itself are measured by using the lumped heat capacitance method. For the numerical setup, the commercial solver FLUENTTM is applied together with two different turbulence models. In the case of rib turbulators, a standard k-e turbulence model is used. It could be demonstrated that for dimpled surfaces or surfaces with hemispheres, a Reynolds Stress Model performs better. In general, the experimental results are underpredicted, whereas the trends are predicted correctly. It is concluded, that the present numerical approach is applicable to preliminary design studies. One result of this study is to extend the Reynolds number range of typical rib turbulators to Reynolds number levels found in backside cooled combustor walls. In contrast to internal blade cooling, the design requirements of a backside cooled combustor wall are a moderate pressure loss at higher Reynolds numbers and at the same time a good heat transfer enhancement. It could be demonstrated, that the geometry of rib turbulators need to be adjusted to satisfy the mentioned design requirements. The investigations on V shaped, W shaped and WW shaped ribs revealed the following fact. The existence of a second ribbed wall has an influence on the heat transfer of the opposite wall. It is therefore suggested not to directly use heat transfer correlations, which are derived from experimental data of two sided ribbed channels, for the design of one sided ribbed channels. Additionally, it could be demonstrated, that for higher Reynolds numbers the rib height has to be reduced to obtain lower levels of pressure losses. As the rib geometry is changed from V shaped to W shaped rib, the pressure losses are increased for an equal rib spacing and rib height. WW shaped ribs resulted in even higher pressure losses. For V shaped and W shaped ribs, a reduction of the rib spacing leads to a lower pressure loss. For WW shaped ribs, an opposite trend is observed. In the case of W shaped ribs, the heat transfer enhancement on the rib itself is obtained. It could be demonstrated that a reduction of the rib spacing has no impact on the heat transfer enhancement on the rib. A combination of the heat transfer data between two successive ribs and the data on the rib reveals, that heat transfer levels of around three times higher than the heat transfer of a smooth channel wall are realized for the investigated Reynolds number range. The possibility to replace the commonly used rib turbulators with dimples or hemispheres is also addressed in this study. For channels with hemispheres or dimples on one channel wall, a lower pressure loss and at the same time only moderate heat transfer enhancement levels are observed. For the design of a convective cooling technique for convectively cooled combustor walls, W shaped ribs should be preferred. This configuration shows the best thermal performance for the typical Reynolds numbers found in backside cooled combustor walls. In cases, where the convective cooling has to be achieved with very low pressure losses, dimpled channels represent an interesting alternative to ribbed configurations.Item Open Access Flow and heat transfer investigations in swirl tubes for gas turbine blade cooling(2017) Biegger, Christoph; Weigand, Bernhard (Prof. Dr.-Ing. habil.)A swirl tube is a very effective cooling technique for high thermal loaded components like gas turbine blades. Such a tube consists of one or more tangential inlet jets, which induce a highly 3D swirling flow. This swirling flow is characterized by large velocities near the wall and an enhanced turbulence in the tube which both increase the convective heat transfer. In the present work, the flow phenomena and the heat transfer in swirl tubes are studied experimentally and numerically. Therefore, a generic swirl tube with tangential inlets at the upstream end of the tube and a novel application-oriented swirl tube geometry with multiple tangential inlet jets in axial direction are investigated in detail. In strong swirling flows, the flow field is dominated by the circumferential velocity which is characterized by a Rankine vortex with a solid body vortex in the tube center and a potential vortex in the outer region. A stability analysis reveals that the solid body vortex is unstable and hence explains the transformation of the solid body vortex into a stable potential vortex towards the tube outlet. In addition, the axial velocity shows a backflow region (vortex breakdown) in the tube center over the entire tube length. It is shown that a vortex breakdown occurs in swirl dominated flows. The measurements indicate that the heat transfer in swirl tubes increases with increasing Reynolds number and swirl number, respectively. Near the inlet, the maximum heat transfer occurs due to the large circumferential velocity component. With decreasing swirl and velocity towards the tube outlet, also the heat transfer decreases continuously. The investigation of the swirl tube with multiple tangential inlet jets reveals a very complex axial velocity which changes after each inlet due to the additional mass flow. However, the circumferential velocity stays almost constant since the swirl strength is re-enhanced with each inlet jet, respectively. For each inlet jet, a high heat transfer can be observed. However, the maximum heat transfer is lower than for the swirl tube with only one inlet because of the lower inlet jet velocities. On the other hand, the heat transfer distribution is more homogeneous over the entire tube length at a much lower pressure loss. For the investigated swirl tubes with one, three or five inlets, the thermal performance is in the same order of magnitude and hence all swirl tube configurations are suitable for cooling.Item Open Access Investigation of thermal loads onto a cooled strut injector inside a scramjet combustion chamber(2016) Dröske, Nils Christoph; Wolfersdorf, Jens von (Prof. Dr.-Ing.)For future aviation or space transportation systems, scramjets could provide a complement or even an alternative to conventional propulsion systems. However, due to the high-enthalpy flow environment, scramjet development still implies considerable technical challenges. One of the most relevant issues is the need for an efficient fuel injection and mixing system. It has to guarantee a stable and reliable combustion process, as the flow residence time inside the engine is only in the order of several milliseconds. Strut-based injection systems have proven to be a suitable choice due to their ability to provide fuel directly into the center of the flow. In contrast to wall-based injection systems, however, struts are exposed to the complete aerodynamic heat loads of the flow, which necessitates active cooling to avoid structural damages. As experimental facilities are hardly able to reproduce flight conditions over a long period of time, a numerical approach is inevitable to assess the heat loads onto a strut and to evaluate the internal cooling mechanism. Within the present thesis, a numerical solver for the conjugate simulation of heat transfer in supersonic flows was developed and integrated into the OpenFOAM software package. A thorough validation for a variety of data from both literature and in-house studies was conducted. The accurate prediction of different phenomena relevant for supersonic flows could be verified. The solver was then applied to the evaluation of an internally cooled strut injector. In a first step, the injector was investigated at moderate flow temperatures. Experimental data for different flow temperatures and coolants was obtained using infrared thermography of the injector surface. A comparison to numerical simulations led to the identification of characteristic well and poorly cooled zones along the injector surface, which could be explained by features of either the external or the internal flow field. Finally, the lobed strut injector was studied numerically at hot gas conditions representative for the ITLR model combustor, where no experimental data of the surface is available. Besides the leading edge, a second hot zone was identified towards the trailing edge of the strut, which was attributed to the impact of the reflected leading edge shock wave onto the surface. Activation of internal air cooling was found to lower the general temperature level, but to have only a small effect on the leading edge. Instead, heat conduction towards the cooled combustor side walls provided a considerable part of the cooling in this area. Switching to hydrogen as coolant led to a further reduction of the injector temperature at a considerably lower coolant mass flux, without changing the overall characteristics of the cooled injector. Changing to more realistic, hotter combustor side walls for a hydrogen-cooled strut caused a generally higher injector surface temperature. While the hottest injector regions were found to be near the side walls, the leading edge could still be partially cooled by the internal hydrogen flow.Item Open Access Experimentelle Untersuchung von Strömung und Wärmeübergang in Kühlkanälen mit wirbelerzeugenden Elementen(2007) Henze, Marc; von Wolfersdorf, Jens (Prof. Dr.-Ing.)Die vorliegende Arbeit entstand im Rahmen des Teilprojekts WO-872/4-1, das in das von der DFG (Deutsche Forschungsgemeinschaft) geförderte Paketvorhaben "Experimentelle und Numerische Untersuchungen zum Wärmeübergang bei komplexen Innenströmungen mit wirbelerzeugenden Strukturen" eingegliedert war. Die experimentellen Untersuchungen umfassen sowohl Wärmeübergangs- als auch Strömungsmessungen in einem Windkanal beim Einsatz von längswirbelerzeugenden Geometrien. Hierfür kamen tetraederförmige Vollkörper-Wirbelgeneratoren (VGs) zum Einsatz, die durch ihre erzeugten Wirbelstrukturen eine deutliche Steigerung des Wärmeübergangs bewirken. Zur detaillierten Vermessung des Wärmeübergangs wurden Methoden angewandt, die auf thermochromatischen Flüssigkristallen (TLC) basieren. Die stationäre Methode arbeitet mit Heizfolien und setzt näherungsweise einen konstanten Wandwärmestrom voraus. Dagegen basiert die transiente Methode auf der Auswertung des zeitlichen Verlaufs der Wandtemperatur als Reaktion auf einen Temperatursprung in der Fluidströmung, und entspricht etwa einer konstanten Wandtemperatur. Beide Methoden ermöglichen es, verschiedene thermische Randbedingungen zu simulieren und liefern mit sehr hoher Genauigkeit flächendeckende Wärmeübergangsinformationen. Neben der Charakterisierung der Anströmbedingungen mittels Hitzdrahtmesstechnik fand zur Vermessung des Strömungsfelds die Methode der Particle Image Velocimetry (PIV) Anwendung. Die vorherrschenden Geschwindigkeitsprofile sowie Turbulenzintensitäten wurden detailliert vermessen. Mittels Autokorrelation aus den zeitlich aufgelösten Signalen der Hitzdrahtmessung sowie der örtlich korrelierten Geschwindigkeitsdaten der PIV wurden die turbulenten Längenskalen identifiziert. Im hier eingesetzten Windkanal konnten Reynoldszahlen von 80.000 bis 600.000 und Turbulenzgrade von etwa 1 bis 8 % realisiert werden. Untersucht wurde der Wärmeübergang hinter sowie auch auf Einzel-VGs mit variierenden Geometrieparametern und Anströmverhältnissen. Für einfache Reihen- und Parallelanordnungen von bis zu drei VGs wurde die Interaktion verschiedener Längswirbel verdeutlicht. Anhand zweier Feldanordnungen konnte die erreichbare Wärmeübergangsintensivierung mit dem resultierenden Druckverlust in Verbindung gebracht werden. Mittels PIV wurden die Längswirbelstrukturen hinsichtlich ihrer Position, Rotation und Wirbelstärke vermessen und dem einhergehenden Wärmeübergang gegenübergestellt. Hierbei konnte ein klarer Zusammenhang der Wärmeübergangsverteilung mit den Trajektorien der Längswirbel gefunden werden. Der maximale Wärmeübergang ist stets in den Bereichen zu finden, in denen die induzierte Wirbelströmung eine zur Wand hin gerichtete Komponente aufweist und damit eine Verringerung der hydrodynamischen und thermischen Grenzschicht bewirkt. Die sogenannte Methode der Stereo-PIV wurde eingesetzt, um alle drei Strömungskomponenten zu vermessen. Durch eine hohe Anzahl an Einzelaufnahmen (bis zu 3.000) konnten über statistische Analysen die Turbulenzgrößen bestimmt werden. An ausgewählten Schnittebenen durch einen Längswirbel wurden damit Turbulenzgrade, die kinetische Turbulenzenergie sowie auch die Reynoldsschen Haupt- und Schubspannungen bestimmt. Die vorliegende Arbeit liefert detaillierte Daten hinsichtlich Strömung und Wärmeübergang für komplexe Wirbelströmungen und kann als Benchmark-Datensatz zur Validierung und Weiterentwicklung numerischer Methoden verwendet werden.Item Open Access Untersuchung des Wärmeübergangs in einem Strömungskanal einer Gasturbinenschaufel(2005) Amro, Mahmoud; Weigand, Bernhard (Prof. Dr.–Ing. habil. )Die Kühlung der ersten Stufen von Hochdruckturbinen stellt die anspruchsvollsten Teilgebiete bei der Kühlung von Gasturbinen dar. Die Anforderung nach hohen Turbineneintrittstemperaturen setzt insbesondere die erste Stufe der Turbinenschaufeln enormen thermischen Belastungen aus. Eine Senkung der Oberflächentemperaturen der Schaufel von ca. 10K kann die Lebensdauer der Schaufeln nahezu verdoppeln. Im Rahmen dieser Arbeit wurde der konvektive Wärmeübergang einer internen Strömung experimentell untersucht. Aufgabe war es durch die richtige Wahl von Rippenkonfigurationen im Strömungskanal Sekundärströmungen und Verwirbelungen zu erzeugen, mit der Ziel, eine Geometrieoptimierung derart durchzuführen, dass Wärmeübergang und Druckverlust in einem ausgewogenen Verhältnis zueinander stehen. Zur Auswertung des Wärmeübergangs wurde eine transiente Messmethode mit thermochromatischen Flüssigkristallen TLC benutzt. Die Versuche wurden bei Reynolds-Zahlen von 30000 bis 200000 durchgeführt. Bei den untersuchten Geometrien handelt es sich um verschiedene Rippenanordnungen, Anstellwinkel g [g={45°; 60°, 135°}], Rippenabstand P zu Rippenhöhe e [P/e = {10; 15; 20}], Rippenhöhe e zu Kanalhöhe H [e/H ={0,10; 0,15; 0,167}]. Unter Berücksichtigung der experimentellen Daten wurden Korrelationen für den Wärmeübergang und die Reibungsverhältnisse aufgestellt. Die erzielten Ergebnisse wurden mit Literaturangaben und numerischen Berechnungen verglichen. Mit den Ergebnissen aus der untersuchten Rippenvariationen kann numerische Modelle erstellt werden, mit denen ohne größeren Aufwand verschieden Konfigurationen und Variationen der Rippen untersucht werden können. Als Ergebnis konnten optimale Geometrien hinsichtlich des Wärmeübergangs und der Reibungsverhältnissen ermittelt werden und Korrelationsgleichungen aufgestellt werden. Die experimentellen Untersuchungen haben insgesamt die bedeutende Rolle der Rippen zur Intensivierung von Wärmeübergang im Vergleich zu der glatten Kanal gezeigt.