Ali Gülhan

German Aerospace Center (DLR) | DLR · Department of Supersonic and Hypersonic Technology (HYP)

In the present study, the response of a hypersonic turbulent boundary layer at an inflow of Ma∞ = 6 and Re∞ = 16·10⁶ 1/m to a smooth and rough surface along a sharp cone is examined. The model consisted of three segments with exchangeable parts to consider smooth and rough surfaces with a roughness topology of square bar elements with a nominal wav...

In the frame of the European funded H2020 project RETALT (retro propulsion-assisted landing technologies), the unsteady aerodynamics of vertically descending and landing launchers have been investigated. In this paper, experimental data of the landing burn tested in the Vertical Free-Jet Facility Cologne at DLR in Cologne are presented. The landing...

This paper takes a new look at how the aerodynamic interactions of multiple bodies in high-speed flow affect their motion behaviors. The influence of the body shape and orientation on aerodynamic and stability behavior in the case of shock–shock and wake–shock interactions is the focus of this publication. Experiments were performed in the hyperson...

High uncertainties exist in modelling subsonic retro propulsion flow fields with CFD. For example, the choice of the turbulence model can greatly influence the flow field and the resulting heat loads. Hence, experiments with hot oxygen/hydrogen exhaust plumes and active counterflow are indispensable for the understanding of these flow fields. In th...

This research aims at analysing the particle-laden flow of the hypersonic high-enthalpy wind tunnel L2K, situated in Köln at the German Aerospace Center (DLR). In the L2K wind tunnel, Martian atmosphere can be created, and the facility can simulate heat load conditions encountered during atmospheric entry of Martian missions. In the tests, a simpli...

Experimental and numerical simulation of launcher base flows is crucial for future launcher design. In experiments, the exhaust plume simulation is often limited to cold or slightly heated gases. In numerical simulations, multi-species reactive flow is often neglected due to limited resources. The impact of these simplifications on the relevant flo...

Communication blackouts during the atmospheric reentry phase are a significant challenge, as flight data are lost due to interruptions caused by plasma gas generated by aerodynamic heating. This study explores a novel mitigation method using an air film, a thin insulating coolant layer on the surface. The researchers successfully reduced the reentr...

The presence of particles in supersonic flows can cause significant increases in stagnation point heat fluxes (Dunbar et al. in AIAA J 13:908–912, 1975). This effect is commonly named ‘particle-induced heat flux augmentation’ or just ‘heating augmentation.’ Heating augmentation can be described as the sum of the conversion of kinetic energy of the...

In the frame of the European funded H2020 project RETALT (Retro Propulsion Assisted Landing Technologies) the unsteady aerodynamics of vertically descending and landing launchers have been investigated. In this paper experimental data of the landing burn tested in the Vertical Free-Jet Facility Cologne (VMK) at DLR in Cologne is presented. The land...

This research aims at analyzing thermo-chemical properties of the hypersonic high-enthalpy flow in the L2K wind tunnel, situated in Köln at the German Aerospace Center (DLR). In the L2K wind tunnel, Martian atmosphere can be created, and the facility can simulate heat load conditions encountered during atmospheric entry of Martian missions. The foc...

During the vertical descent and landing of a launcher first stage with the aid of retropropulsion, commonly two main propulsive deceleration maneuvers are performed: the reentry burn in high altitudes at hypersonic to supersonic speeds and the landing burn shortly before touchdown at transonic to subsonic speeds. In the frame of the EU-funded H2020...

Herein, a direct comparison of the thermal conductivity and stability of different silica‐fiber‐reinforced silica aerogels is presented. The thermal performance under high‐temperature exposure within an arc‐heated facility is evaluated by means of thermal propagation and stability. All aerogel materials, tested within this study, outperform the hig...

Particle mass flow rate and particle mass concentration are key parameters for describing two-phase flows, especially for particle-induced heating augmentation analysis. This work addresses the question of how accurate particle mass flow rate can be determined with three non-intrusive measurement approaches, based on shadowgraphy, particle tracking...

This research aims at analysing thermo-chemical properties of the hypersonic high-enthalpy flow in the L2K wind tunnel, situated in Köln at the German Aerospace Center (DLR). In the L2K wind tunnel, Martian atmosphere can be created, and the facility can simulate heat load conditions encountered during atmospheric entry of Martian missions. The foc...

Kostenreduktion unter Beibehaltung der Zuverlässigkeit gehört zu den Hauptanforderungen an zukünftige Raumtransportsysteme. Neben den neuen und effizienteren Fertigungs- und Qualifizierungsmethoden ist die Wiederverwendbarkeit ein Schlüsselelement um dieses Ziel zu erreichen. Die neuesten Studien zeigen, dass im Falle der Wiederverwendbarkeit die e...

The technology of missiles and of their countermeasures is evolving continuously. High-power lasers are an option to encounter these threats. In order to understand their potential in such a scenario, it is vital to investigate the laser effects in the presence of a corresponding aerodynamic environment. Thus, experimental and numerical investigati...

Aerogels itself have already proven their outstanding thermal performances and insulative properties. However, classical silica aerogels often are limited in their application due to melting and/or heavy sintering effects. By these structural changes and reconstructions the properties of the aerogels are lost. New space-related applications require...

The HEXAFLY-INT flight vehicle is a small-scale flight demonstrator of a supersonic passenger aircraft [8,9]. In order to determine the flight angles, Mach number and altitude for this vehicle a set of pressure sensors can be used to derive this data. In the frame of this study such a system, usually called Flush Air Data Sensing system (FADS), was...

Aerodynamic stability is very important for high-speed aircraft configurations, where reaction times to disturbances can become quite short. Six-degree-of freedom measurements have been performed with a wind tunnel model of an air-breathing hypersonic vehicle. Mach numbers ranged between Mach 3.5 and Mach 8, utilizing two different wind tunnels. Th...

The three-stage rocket configuration of the hypersonic experiment STORT with several scientific payloads concerning hypersonic technologies was launched from the Andøya Space launch site in northern Norway on 26th June 2026 successfully. The third stage performed a suppressed trajectory to increase integral heat load on the structures of payloads....

In all sorts of Ramjet engines the intake serves as the major component to compress the flow to sufficiently large pressures. With its location being far upstream, its performance is crucial for all following components such as combustor or nozzle. One major physical effect that influences intake performance is intake starting and unstart. During i...

In the frame of the RETALT (RETro propulsion Assisted Landing Technologies) project, the aerodynamics of reusable launch vehicles reentering the atmosphere and descending and landing with the aid of retro propulsion are studied. In particular, series of wind tunnel tests are performed to assess the aerodynamic properties of such a vehicle in the va...

RETALT (RETro propulsion Assisted Landing Technologies) is a project funded in the frame of the European Union Horizon 2020 program, that is studying critical key technologies for the vertical landing of launcher configurations with the aid of retro propulsion. In particular Aerodynamics, Aerothermodynamics, Flight Dynamics and Guidance Navigation...

The paper focuses on wind tunnel tests of the hypersonic re-entry part of the RETPRO descent trajectory. The re-usable rocket launcher configuration is investigated including active retro-propulsion at Mach 5.3 and 7.0 in the Hypersonic Wind Tunnel (H2K) of DLR, Cologne. Results from high-speed Schlieren imaging, force and unsteady wall pressure me...

The RETALT (RETro propulsion Assisted Landing Technologies) project aims to investigate vertically landing launcher configurations, which decelerate by means of retro propulsion manoeuvres during the descent and final landing phase. One key objective was to understand the complex steady and unsteady flow field and the resulting oscillating pressure...

Since SpaceX successfully demonstrated the vertical landing of launcher first stages and made this way of returning them to earth a routine operation with over 100 successful landings after 6 years, the interest in Europe to develop the key technologies for this approach has drastically increased. It not only promises large cost savings, but also r...

In the frame of the RETALT project a large number of CFD simulations and Wind Tunnel experiments were made for both the RETALT1 and RETALT2 configurations to better understand the physics and mechanisms of retro-propulsion at supersonic flow conditions. For RETALT1, it was found in both CFD and Wind Tunnel experiments that the flow structure (bow s...

The European Union H2020 project EFESTO has been implemented with the main objective to improve the technology readiness level (TRL) of flexible inflatable heat shields for re-entry vehicles in Europe from 3 to 4 or 5. For this purpose, two reference missions with atmospheric entry to Earth and Mars were selected. Both missions were designed to mak...

Blunt capsule shapes have proven to be suitable for atmospheric entry flights on numerous missions. Some concepts like MarcoPolo-R focus on fully passive entry systems without a parachute, demanding for aerodynamic stability of the shape throughout the complete entry flight. These probes are commonly equipped with a Thermal Protection System (TPS)...

Capsule-like shapes are commonly used for Earth return or exploration missions, which experience very high velocities during atmospheric entry. For some of these missions such as sample return, neither aerodynamic stabilizers, like parachutes, nor RCS devices are employed. Therefore, the capsule stability has to be guaranteed solely by the spacecra...

The RETALT (Retro Propulsion Assisted Landing Technologies) project aims at investigating launch system reusability technologies for two different Vertical Take-off Vertical Landing launcher configurations, namely RETALT1 and RETALT2. This paper describes and summarizes the CFD based aerothermal load predictions, aerothermal database generation and...

In this study, the capsule of the EURASTROS study is discussed in terms of its aerodynamic and aerothermal properties, re-entry characteristics, structural design, and thermal protection system. Approximative methods are used to estimate the aerodynamic coefficients for the computation of nominal and off-nominal re-entry trajectories and to determi...

This paper provides an overview of the project ‘RocketHandbrake’, which investigates the reusability of upper stages re-entering the earth’s atmosphere at high angles of attack as a means for aerodynamic braking, using Supersonic Braking Devices. For a maximum benefit, this concept takes so-called Ariane Next and Vega E -like launchers as reference...

The excel file contains the Aerodynamic Data Base for the RETALT1 configuration. The pdf file contains the necessary information to use this data base. the excle file can be found under: https://zenodo.org/record/7027367

The excel file contains the Aerodynamic Data Base for the RETALT2 configuration. The pdf file contains the necessary information to use this data base. The excel file can be found under: https://zenodo.org/record/7081540

Since March 2014, all ESA satellites and launcher upper stages which will be disposed of by atmospheric re-entry at the end of their operational life must demonstrate that the risk from fragments surviving the re-entry and causing casualties on ground is less than 1 in 10,000. This casualty risk is calculated by re-entry tools simulating the uncont...

Supersonic and hypersonic vehicles experience significant aerothermal loads from the exterior flowfield and/or their propulsion system. Thus, reliable prediction of aerothermal heating is important for the design of such vehicles. However, even modest temperature changes can lead to buckling of mechanically constraint lightweight structures. This d...

The particle mass concentration and -mass flow rate are fundamental parameters for describing two-phase flows and are products of particle number, -size, -velocity, and -density. When investigating particle-induced heating augmentation, a detailed knowledge of these parameters is essential. In most of previous experimental studies considering parti...

Static force and moment measurements are performed on the MarcoPolo-R aero shape in the trisonic wind tunnel TMK. The static stability behaviour of the capsule is characterized in the Mach number range 0.5≤M≤3.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \use...

In the RETALT (RETro propulsion Assisted Landing Technologies) project vertical landing launcher configurations are investigated. In the aerodynamic phase of retro propulsion assisted descent and landing, the main devices for control and trim of the vehicle are the aerodynamic control surfaces. In this paper, experimental data of a novel concept wh...

Ultra high-temperature ceramic matrix composites (UHTCMCs) based on carbon fibre (Cf) have been shown to offer excellent temperature stability exceeding 2000 °C in highly corrosive environments, which are prime requirements for various aerospace applications. In C3Harme, a recent European Union-funded Horizon 2020 project, an experimental campaign...

Aerothermoelastic fluid–structure interaction (FSI) is a crucial problem in the design of supersonic and hypersonic vehicles, but modeling capabilities are in many cases quite limited. Insufficient treatment of FSI can limit design options or lead to damage or loss of vehicles. To improve understanding of such problems, we conducted FSI experiments...

View Video Presentation: https://doi.org/10.2514/6.2022-1308.vid In the RETALT (Retro Propulsion Assisted Landing Technologies) project critical technologies for two different vertical landing launcher configurations are investigated. For RETALT1, a Two Stage To Orbit launcher, only the first stage will be recovered using retro propulsion. A large...

View Video Presentation: https://doi.org/10.2514/6.2022-2150.vid The communication blackout, which is the communication cutoff between a reentry vehicle and ground station during the atmospheric reentry, has been observed for many missions. Aerodynamic heating caused by a strong shock wave in front of the reentry vehicle dissociates and ionizes the...

CALLISTO is a demonstrator for a first stage of a reusable vertical take-off, vertical landing rocket and is developed and build within a collaboration of DLR, CNES and JAXA [1]. DLR is leading the aero science team [2] and is in charge of the aerodynamic and aerothermodynamic characterization of the vehicle. Within this task, experimental work has...

To gather information about both particle and gas phase temperatures inside a scaled solid rocket motor plume UV-VIS emission spectroscopy (UVVIS) and infrared emission pectroscopy (FTIR) have been used. Additionally, a position resolving two-color pyrometer technique in the visible spectrum range (Alumina Emission Measurements, AEM) has been devel...

This paper gives a summary of dedicated experiments on the shock interaction induced heat flux augmentation, by means of tests carried out in the hypersonic wind tunnel H2K. The first test case is devoted to the shock boundary layer interaction on a flat plate. The interaction impact has been varied by changing the free stream parameters and the po...

A think tank of DLR space-research institutes and ArianeGroup reflected on the launcher perspectives, broadening the mission capabilities for European access to space including human mission towards LEO, supporting potential future commercial markets. The Ariane 6 launcher is to be evolved with perspective of enhanced versatility and reduced costs....

For avoiding the Kessler syndrome, satellites in low Earth orbits must be removed in due time after the end of their service life by re-entering into the Earth's atmosphere. Active, controlled re-entry requires availability of thrusters and propellant at the end of the mission. Thus, the active re-entry comes at a high cost and reduces the availabl...

Simulation based design of flight hardware is one of the longterm goals of the DLR’s research programs. In case of spacecraft development this task is very challenging, since the number of flight experiment and availability of the flight data is very limited. This requires a complementary validation approach using ground and flight testing for gath...

The ATEK flight experiment was successfully launched on 13th July 2019 from the launch site Esrange in Kiruna and provided valuable flight data. The second stage and the payload reached an apogee of approx. 240 km. The second stage continued the descent on a ballistic trajectory and landed approx. 500 seconds after the take-off at a distance of app...

A compact three-dimensional scramjet intake with a high compression ratio and a movable cowl as a starting device and for the adaption of the internal contraction to respective operating conditions was designed for a parabolic reentry flight experiment. In an extensive measurement campaign, conducted in a blowdown wind tunnel at Mach 7, the operati...

There are many limitations in ground testing in the laboratory, that prohibit fully realistic simulation of the destructive entry-flight. Some of these limitations could be overcome by technical solutions, others are determined by the physics (e.g. gravitational forces acting on the test hardware). The impact of the limitations varies and have been...

Demisable Joint is a technical solution to allow an early break up of satellites structure and payload separation in order to reduce the risk posed by re-entering satellites, improving their demise. The ESA study “ITI – Innovation Triangle Initiative - Demisable Joint” aims at identifying the environment conditions, an then design, manufacturing an...

Usually heat flux measurements in ground test facilities as well as simulations in the hypersonic flow regime are performed at static conditions with non-moving objects. But objects performing an uncontrolled re-entry are quite likely to rotate and/or tumble. This is true for meteorites, satellites and empty stages of launch vehicles. Previous expe...

The influence of the flight attitude on aerodynamic coefficients and static stability of cylindrical bodies in hypersonic flows is of interest in understanding the re/entry of space debris, meteoroid fragments, launch-vehicle stages and other rotating objects. Experiments were therefore carried out in the hypersonic wind tunnel H2K at the German Ae...

Buffet/buffeting as load imposing mechanism on the base structures of space launcher has been of strong interest ever since it was found as partially responsible for the failed flight 157 of Ariane 5. Several studies suggested that the base region is most excited at Mach 0.8. A preceding study of the current series on base flow effects revealed a d...

The analysis of the risk from re-entry objects has become an important topic. Concerning the uncertainties and different flow regimes, the object-oriented tools have been developed and used for various re-entry mission scenarios because of the simplified computation process and low calculation burden, which allow a probabilistic analysis. In this s...

Retropropulsion, a deceleration technique where the thrust is directed along the flight path, is the driving technology for vertically landing, reusable launchers. Experiments, which are indispensable for the full comprehension of retropropulsion flows, pose serious challenges to the operability of wind tunnels and interpretation of these subscale...

After the failure of maiden flight 157 of Ariane 5 Evolution Cryotechnique type A (ECA), the inquiry board responsible for the investigation reported as one of the probable causes the “non-exhaustive definition of the loads to which the Vulcain 2 engine is subjected during flight.” As a result, many research activities were set up with the objectiv...

To protect the copper liners of liquid-fuel rocket combustion chambers, a thermal barrier coating can be applied. Previously, a new metallic coating system was developed, consisting of a NiCuCrAl bond-coat and a Rene 80 top-coat, applied with high velocity oxyfuel spray (HVOF). The coatings are tested in laser cycling experiments to develop a detai...

Mastering aerothermal fluid-structure interaction (FSI) is crucial for the efficient and reliable design of future (reusable) launch vehicles. However, capabilities in this area are still quite limited. To address this issue, a multidisciplinary experimental and numerical study of such problems was conducted within SFB TRR 40. Our work during the l...

Experiments have shown that a high-enthalpy flow field might lead under certain mechanical constraints to buckling effects and plastic deformation. The panel buckling into the flow changes the flow field causing locally increased heating which in turn affects the panel deformation. The temperature increase due to aerothermal heating in the hyperson...

Rocket wake flows were under investigation within the Collaborative Research Centre SFB/TRR40 since the year 2009. The current paper summarizes the work conducted during its third and final funding period from 2017 to 2020. During that phase, focus was laid on establishing a new test environment at the German Aerospace Center (DLR) Cologne in order...

The current paper provides an outline and first results of the ESA-EMAP project. This project pursues activities regarding the experimental modeling of alumina particulates in solid boosters (EMAP). The issue regards the particles residing in the atmosphere after the passage of a launch vehicle with solid rocket propulsion, which might contribute t...

ZURAM is an ablative carbon–phenolic thermal protection material, developed by the DLR, German Aerospace Center (DLR) in cooperation with the Institute of Space Systems, University of Stuttgart. In addition to building up a basic competence in the sector of ablative thermal protection materials, an objective of the development was to provide a nonc...