Force and Moment Measurements on a Free-Flying Capsule in a Shock Tunnel

Laurence, Stuart J.; Butler, Cameron; Schramm, Jan Martinez; Hannemann, Klaus

doi:10.2514/1.a33820

Cited by 14 publications

(5 citation statements)

References 28 publications

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“…Details of the free flight technique applied in HEG are discussed in Laurence et al. (2017), who used this technique combined with optical-tracking for aerodynamic testing of a reduced-scale blunted-cone ExoMars entry capsule. Drag, lift and pitching-moment coefficients were determined and excellent agreement was obtained between the optical tracking technique and internally mounted accelerometer measurements.…”

Section: Experimental and Numerical Techniquesmentioning

confidence: 99%

“…Detailed discussion of the algorithm concept and its development is given by Laurence & Hornung (2009), Laurence & Karl (2010), Laurence (2012) and Laurence et al. (2017).…”

Section: Experimental and Numerical Techniquesmentioning

confidence: 99%

“…It is terminated by the arrival of expansion waves in the reservoir, resulting in steadily decreasing pressures thereafter. As discussed in Laurence et al (2017) the unsteadiness in the reservoir pressure during the test period is typically of the order of 3.5 % standard deviation about the mean pressure. Estimated single-run uncertainties at this low-enthalpy condition in HEG are 5 % in p 0 and 4 % in h 0 , with run-to-run variability being of the same order; corresponding uncertainties in the free stream properties are estimated as 5 % in p ∞ and ρ ∞ , 3 % in T ∞ , 2 % in u ∞ , and 0.3 % in M ∞ .…”

Section: The Hegmentioning

confidence: 99%

“…Here, both quantities are determined based on high-speed schlieren cinematography of freely flying capsule models in the HEG test section. Details of the free flight technique applied in HEG are discussed in Laurence et al (2017), who used this technique combined with optical-tracking for aerodynamic testing of a reduced-scale blunted-cone ExoMars entry capsule. Drag, lift and pitching-moment coefficients were determined and excellent agreement was obtained between the optical For the free-flight force measurement technique, the capsule models are integrated in the test section prior to a run by suspending them from the test section ceiling with two 150 μm diameter Kevlar threads.…”

Section: Diagnostic Techniquesmentioning

confidence: 99%

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Hypersonic flow over spherically blunted cone capsules for atmospheric entry. Part 2. Vibrational non-equilibrium effects

2023

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Atmospheric entry capsules shaped as spherically blunted, large apex-angle cones are widely used in space missions. In Part 1 of this study (Hornung, Martinez Schramm & Hannemann, J. Fluid Mech., vol. 871, 2019, pp. 1097–1116) we explored flows over the two elements of the capsule shape, the sphere and the sharp cone with detached shock, theoretically and computationally. Using a large number of inviscid, perfect-gas computations, analytical functions of two independent variables, the normal-shock density ratio $\varepsilon$ and a cone-angle parameter $\eta$ (which is a function of $\varepsilon$ and the cone half-angle $\theta$ ) were found for the dimensionless shock wave stand-off distance and the drag coefficient of a sharp cone. An analytical description was found for the shock stand-off distance in the transition from the 90 $^\circ$ cone (flat-faced cylinder) to the sphere. In Part 1, it was speculated that the perfect-gas results have relevance to non-equilibrium situations if the normal-shock density ratio is replaced by the density ratio based on the average density along the stagnation streamline. In Part 2, the investigation is extended to blunted-cone capsule shapes. High-precision force measurements and schlieren image analysis are performed in the High-Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Centre using air as the test gas, at conditions where vibrational non-equilibrium effects are significant. Accordingly, results are compared with viscous numerical predictions using different physico-chemical models. A theoretical model is constructed for the density profile along the stagnation streamline that is determined by the free stream conditions and gives the average density. Comparisons of the experimental and numerical results for the dimensionless shock stand-off distance and the drag coefficient, with the extension of the analytical functions of Part 1 to vibrationally relaxing flow, exhibit very good agreement in all of a range of geometries.

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Section: Experimental and Numerical Techniquesmentioning

confidence: 99%

“…Detailed discussion of the algorithm concept and its development is given by Laurence & Hornung (2009), Laurence & Karl (2010), Laurence (2012) and Laurence et al. (2017).…”

Section: Experimental and Numerical Techniquesmentioning

confidence: 99%

Section: The Hegmentioning

confidence: 99%

Section: Diagnostic Techniquesmentioning

confidence: 99%

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Hypersonic flow over spherically blunted cone capsules for atmospheric entry. Part 2. Vibrational non-equilibrium effects

2023

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“…In addition, the FFT was very susceptible to flow establishment. This is because the response time of the FFT was very short, and the unexpected motion of the free-flying model could be induced easily For the heavy and large test model, internal mounting accelerometers in the test model [54] or improved image-based optical tracking [55,56] could be applied to measure the accurate acceleration of the free-flying model. Compared to the FFT, the MST had larger size factor due to the movable support, which has higher rigidity than the detachable support.…”

Section: Comparison Of the Test Environment Between Drag Measurement ...mentioning

confidence: 99%

Assessment of drag measurement techniques in a shock tunnel

et al. 2022

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Three force measurement techniques in a shock tunnel, the free-flight, movable-support force balance, and stress-wave force balance techniques were employed, and each technique’s characteristics were assessed. For each force measurement technique, the system setup, data processing method, measurement uncertainties, and applied range of the test model size-flow establishment time were described in detail and compared. For a comparison and discussion, the drag coefficients of a circular pointed cone model with a semi-angle of 18.4° at a nominal freestream Mach number of 6 were measured. As a result, three force measurement techniques yield similar drag coefficients. However, the measurement uncertainties were increased in the order of the free-flight, the stress-wave force balance, and the movable-support force balance techniques. The main causes of the measurement uncertainties were the corner detection uncertainties for the free-flight techniques, and the propagation of the internal or external vibrations for the movable-support and stress-wave force balance techniques. To estimate the appropriate range of the test model size and flow establishment time for each technique’s application, the force measurement systems of the present work and the available literature were compared. As a result of comparative discussion, force measurement environments that can be advantageous for each technique are suggested.

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