Rolf A. Guenther

Elastic Launch Vehicle Response to Sinusoidal Gusts

Separated flow and time lag effects on sinusoidal gust penetration loads and elastic launch vehicle response of Apollo-Saturn class

Analytic Difficulties in Predicting Dynamic Effects of Separated Flow

The purpose of the paper is to demonstrate how a simple analytic theory that uses static experimental data as an input, can predict the observed large adverse effects of separated flow on the vehicle dynamics of heat-sink type re-entry bodies and elastic launch vehicles. The theory is based on quasi-steady-flow concepts in which the time history effects are lumped to one discrete past time event. The analytic difficulties consist largely of insufficient capability in predicting the composition of static loads in regions of separated flow, even when static experimental data are available. If more basic knowledge were available about nonsymmetric stationary separated flow, very substantial improvement in existing capability to predict dynamic effects of separated flow would result.

Effect on Slender Vehicle Dynamics of Change from Spherical to Conical Nose Bluntness

It is by now well established that spherical nose bluntness has a large effect ort vehicle dynamics. However, comparatively little data are available for the effect of nonspherical nose bluntness of the shapes resulting from ablative nose tip recession. As the conical nose tip geometry approximates the nose shape expected after ablation under turbulent heating conditions, a previously developed analytical theory for the hypersonic unsteady aerodynamics of spherically blunted cones has been extended to account for the effects of conical nose bluntness. It is found that (ablative) changes from spherical to conical nose bluntness can have significant effects on stability and trim characteristics of slender cones. The theoretical predictions are shown to agree well with available experimental data. It is shown by the theory and verified by experiments that the effects of conical nose bluntness can be represented by universal scaling laws involving two scaling parameters. These scaling laws demonstrate that there exists a critical nose bluntness for which the ablation change from spherical to conical nose-tip has no effect on the vehicle stability derivatives.

Launch Vehicle Gust Penetration Loads

The gust penetration loads on Saturn launch vehicles in sinusoidal gusts have been investigated. An analytic theory is presented that includes the effects of separated flow and associated convective time lag, and which accepts static experimental data as an input, thereby providing realistic gust load predictions. It is shown that the commonly used quasi-steady treatment that neglects the separated flow time lag can give very unconservative estimates of the gust induced loads even when experimental static load distributions are used. It will, however, give realistic gust load predictions for many launch vehicle geometries of practical interest. Nomenclature a = speed of sound, m/sec c = reference length (maximum body diameter) m f = gust function of inertial space coordinate X Lb and Lg = body length and gust wavelength, m M = Mach number, M = U/a MA = axial force generated pitching moment, kg-m coefficient CmA - MA/(pU2/2)Sc M, N = maximum number of summation terms, Eqs. (14) and (16) N = normal force, kg coefficient CN = N(/pU2/2)S P = generalized force, kg-m/m, defined in Eq. (15) q(t) = amplitude, m of normalized bending deflection, 8 = 9000(0

Scale Effects on Fluctuating Pressures in Spike-Induced Flow Separation

Data for 40% and 100% wind-tunnel models are compared with flight results. The separated region was found to increase in size with increasing Reynolds number even though the Reynolds number at reattachment was always turbulent. Futhermore, critical Reynolds number effects in the flow recirculation region caused the most severe fluctuating pressure on the spike to shift to the leeward side. Evidence of the excitation of a fundamental breathing mode of the spike-induced flow separation was observed on a second flight.

Factors Affecting the Fluctuating Pressures on Ablated and Unablated Re-entry Nosetips

t time; sec Fluctuating pressure measurements have been obtained a t M = 5.0 on hemispherical, blunt-conic, and indented nosetips that simulate the evolution of an ablating graphite nosetip during reentry. An analysis of the fluctuating pressure distribution data on hemispherical and blunt conic nosetips show that when the flow i s attached, a s i t is for these noses, the fluctuating pressure spectra can be successfully collapsed using free s t ream flow parameters rather than boundary layer parameters. The spectra from the indented nosetip a r e collapsed with free stream flow parameters and the maximum thickness of the region of flow separation. It is postulated that entropy gradient effects, not the boundary shear, dominate the fluctuating pressures when the flow i s attached and that flow separation effects dominate the fluctuating pressures when the flow i s separated.

Analysis of Normal Shock Noise Measurements on Nose-Cylinder Bodies

Aerodynamic noise measurements have been obtained on three nose-cylinder configurations (15 deg cone-cylinder, biconic nose-cylinder and biconic nose-corrogated cylinder) in transonic flow. The noise environment at the foot of the terminal normal shock and its associated separated flow bubble were examined in detail. A peak in the frequency spectra of the separated flow region was observed which compares well with the predicted resonance frequency of the separated pocket using Trillings incident shock model. As a consequence of the observed sound spectra and noise level, a flow model is postulated which consist of a cellular separated flow region. In the central portion of the cell the flow resembles the classical two-dimensional recirculating bubble, but each cell is vented by a pair of counter rotating vortices, which start at the surface and steam downstream.