K. Nübler's research while affiliated with Universität Stuttgart and other places

Publications (8)

Article
Full-text available
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 b...
Article
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...
Article
This article presents a numerical investigation on the influence of three-dimensional shock control bumps (SCB) on the effect of transonic buffet. Three different types of SCBs are generated by an optimization for low drag in steady flow conditions at a medium lift coefficient. The impact of these SCB types is then investigated for two different Ma...
Chapter
A method allowing a detailed investigation of the flow physics of shock control bumps (SCBs) on an unswept airfoil has been developed by comparison of the results of experiments and computations. A simple wind tunnel set-up is proposed which is shown to generate representative baseline conditions, allowing fine details of the flow to be measured us...
Conference Paper
Previous research on the behavior of shock control bumps (SCBs) on transonic airfoils has been largely limited to numerical studies, with experimental investigations primarily limited to basic flow fields in small wind tunnels. This paper examines the possibility of simulating the conditions on a wing in a blow-down supersonic wind tunnel to allow...
Conference Paper
Robustness enhancement for Shock Control Bumps (SCBs) on transonic wings is an ongoing topic because most designs provide drag savings only in a relatively small band of the airfoil polar. In this paper, different bump shapes are examined with CFD methods which are validated first by comparison with wind tunnel results. An evaluation method is intr...
Chapter
Corner flow effects prove to have a significant influence on the results obtained in wind tunnels. During the SCBOPT project discrepancies between experiments and numerical investigations occurred. 3D numerical studies considering the wind tunnel were performed to show the effect of wind tunnel walls on the obtained results in both subsonic and tra...

Citations

... The pressure in the separated flowfield varies from 29 − 57 kPa; this range of pressures is sufficiently large to provide reliable measurements (Sajben 1993). In order to determine the values of A(T) and B(T) in the Stern-Volmer relation, in-situ calibration is performed using five 0.3 mm diameter static pressure taps connected to a differential pressure transducer (error: ±1% ) (Colliss et al 2016). This calibration enables absolute pressure values on the target surface to be extracted from the measured light intensity. ...
... They operate as 'smart' vortex generators 17 , thus the design location is upstream of the SBLI region. Their performance is still not well defined; previous studies show that they can suppress the shock oscillation 16 or decrease the angle of buffet onset 19 . The main drawback is that the optimal position for wave drag control is different from the one for shock buffet control. ...
... 21 proposed an analytical model for expansion fan/oblique shock interactions studies and verified the model with numerical results. Bruce et al. 22 and Colliss et al. 23 conducted shock control bump (SCB)-based drag reduction studies. They reported that if the normal shock impinges the SCB away (ahead or behind) from the crest region then flow features like expansion waves and second lambda shock may appear leading to the unfavorable case of drag enhancement. ...
... A complete overview of Shock Control Bumps is given in [16]. A crucial aspect that is gaining more attention recently is the need for a robust SCB configuration for industrial applications [17], [18]. The robustness of shock control bumps, i.e., its ability to effectively reduce wave drag at different flight conditions, is of primary concern as they are highly sensitive to the shock wave location [16]. ...
... In the beginning, 2D-shape bumps were investigated and led to significant wave drag reductions with moderate viscous penalties, but were found to perform very badly at off-design conditions (Birkemeyer et al. 2002). More recent studies were performed with 3D bumps, which have a limited spanwise extent, to enhance the off-design performance (Wong et al. 2008, Ogawa et al. 2008, Colliss et al. 2012. The λ shock structure has been found to propagate between the bumps, giving total pressure decreases across the span. ...
... An imaginary rotor is build up using copies of the one evaluated blade. In (Kamruzzaman, et al., 2011) the modelling approach from 2D to 3D is described. For the determination of the directivity of each section pitch and twist angle as well as azimuthal position of the blade on an imaginary rotor are considered. ...