Roger L. Simpson

Effects of a Fillet on the Flow Past a Wing-Body Junction

Measurements are presented to demonstrate the effects of a single fillet on the flow of a turbulent boundary layer past an idealized wing-body junction. The time-averaged flow structure in the vicinity of the wing and in the wake of the wing-body junction is considered, as well as the unsteadiness of the horseshoe vortex. The effects of angle of attack and approach boundary-layer thickness are also examined.

Two-Dimensional Turbulent Separated Flow

TkJTANY different flow cases with nominally twolYJLdimensional turbulent separated flow regions are discussed in Refs. 1 and 2. Because intermittent flow reversal and backflow occur in the near-wall region, directionally sensitive measurement techniques must be used to examine the flow structure. The experimentally-observed structure of detached flows on streamlined surfaces and around sharp-edged corners is discussed in detail for steady and unsteady incompressible and compressible cases. In all cases, large-scale structures dominate the flow behavior, producing large shearing stresses in the middle of the detached shear flow and strongly influencing the local intermittent backflow. The turbulence structure strongly lags the mean flow behavior in the detachment and reattachment processes. For unsteady periodic separation, there is considerable hysteresis of the flow during a cycle. A number of differential and integral calculation methods are discussed. Traditional attached flow turbulence models and correlations do not describe detached flows well. Methods that include experimentally-observed features and/or correlations of detached flow parameters seem to perform best, although further improvements are still needed.

Interpreting Laser and Hot-Film Anemometer Signals in a Separating Boundary Layer

• RECENTLY an experimental study of a separating in-I^compressible turbulent boundary layer produced by an adverse pressure gradient was completed. A directionally sensitive fringe-type laser anemometer with a Bragg cell was used to measure the mean streamwise velocity £7, the meansquare fluctuation w, and the fraction of time the flow was moving in the downstream direction yp. In addition, a constant-temperature single-sensor cylindrical hot-film probe (Thermo-Systems, Inc., model 1274-10) was used to compare the behavior of this directionally insensitive sensor with the laser anemometer results. The purpose of the Note is to discuss the interpretation of signals from these two instruments in a separation region, i.e., when yp < 1. Sampling spectrum analysis of the laser anemometer signals was used because of the high-signal dropout level encountered in this flow with a relative low-particle seeding level and the high-signal frequencies produced by frequency shifting one incident beam. Most frequency trackers cannot handle either of these signal conditions. The signal from the photomultiplier tube or detector is input to a swept filter spectrum analyzer (HP 8558B). For each sweep of the analyzer when a particle (about 1 in size) is in the focal volume, a vertical voltage distribution proportional to the filter output is displayed. The simultaneous horizontal sweeping voltage is proportional to the signal frequency. The peak of the vertical voltage distribution marks the frequency of the passing particle signal and can be used as a gating signal to allow the instantaneous value of the horizontal sweep voltage to be sampled. This instantaneous voltage value is related to the instantaneous velocity £7 of the particle through the equation

Backflow structure of steady and unsteady separating turbulent boundary layers

Recent LDA measurements in unsteady separating turbulent boundary layers by the authors have revealed some new information on the phase-ensemble-averaged backflow behaviour. In the large-amplitude unsteady flows studied, very large backflow velocities exist in the detached flow at some phasees of the oscillation cycle. In some cases even grater than the freestream velocity. The Reynolds shearing stress and turbulence-energy production near the wall in the backflow region are not negligible at these phases. Under such conditions Simpsons backflow velocity profile model is not applicable and a normal turbulent boundary-layer type of structure appears to be present in the phase-ensemble-averaged near-wall backflow. These new features of backflow are discussed and a new concept of a re-entrainment velocity of the backflow into the outer region downstream flow is introduced.

Features of separating turbulent boundary layers

In the present study of two strong adverse pressure gradient flows, mean flow and turbulence characteristics are measured, together with frequency spectra, using hot-wire and laser anemometry. In these separating flows, reattachment occurs over a shorter distance than separation. It is noted that the outer flow variables form a unique set of scaling parameters for streamwise power spectra in adverse pressure gradient flows. The inner flow scaling of Perry et al. (1985) for streamwise spectra does not hold in the backflow region unless the value of the downstream-upstream intermittency in the flow is unity.

Comment on "Prediction of Turbulent Boundary Layers at Low Reynolds Numbers"

tion equations. In one special case [B] is [A T ] , but the result is very poor for most practical truss problems. Thus, although the solution (3) satisfies the conditions (1), (2), (4), and (6), it does not necessarily give the best values for the Xj in applications. It can be used as a starting point for the solution and can be taken as a solution if nothing other than Eq. (1) is known about the system. Obviously, in applications it is desirable to have sufficient known conditions to solve the problem, or m = n.

Some effects of oscillation waveform and amplitude on unsteady turbulent shear flows

Some physical features of several unsteady separating turbulent boundary layers are presented for practical Reynolds numbers and reduced frequencies such as for helicopter and turbomachinery flows. The effects of unsteadiness amplitude and waveform are examined for flows along the floor of a converging and diverging wind tunnel test section. At the end of the converging portion, the mean skin friction coefficient normalized on the mean dynamic pressure is independent of the waveform and amplitude within low experimental uncertainties. In the detaching and detached portions of the flow, wall values of the fraction of time that the flow moves downstream of gamma sub pu, which is a separated flow state variable, shows that oscillation waveform and amplitude strongly influence the detached flow behavior. Distributions of gamma sub pu during a cycle indicate hysteresis within the detached flow and the effects of the higher harmonics of pressure gradient and velocity. 19 refs.