Gerald C. Lauchle

Wall‐pressure fluctuations in turbulent pipe flow

Wall‐pressure fluctuation measurements are reported for the fully developed turbulent flow of glycerine in a long pipe. Because of the relatively large viscous scales associated with glycerine, it has been possible to perform pressure fluctuation spectral measurements for 0.7≤d+≤1.5, where d+ is the transducer diameter expressed in wall units. The data presented are for d+ values smaller than ever before reported.

Aerodynamic lift and drag fluctuations of a sphere

An experimental and theoretical investigation is made of the unsteady lift and drag exerted on a sphere in a nominally steady, high Reynolds number, incompressible flow. The net force on the sphere has previously been ascribed to fluctuations in the bound vorticity in the meridian plane normal to the force, produced by large-scale coherent structures shed into the wake. A simplified model of vortex shedding is proposed that involves coherent eddies in the form of a succession of randomly orientated vortex rings, interconnected by pairs of oppositely rotating line vortices, and shed at quasi-regular intervals with a Strouhal number ∼ 0.19. The rings are rapidly dissipated by turbulence diffusion, but it is shown that only the nascent vortex ring makes a significant contribution to the surface force, and that the force spectrum at Strouhal numbers exceeding unity is effectively independent of the shape of the fully formed vortex. Predictions of the lift and drag spectra at these frequencies are found to be in good accord with new towing tank measurements presented in this paper.

Underwater acoustic intensity probe

An underwater probe for determining true acoustic intensity by the direct asurement of true acoustic velocity and true acoustic pressure in a neutrally buoyant package, utilizes a moving-coil geophone embedded in a casting of syntactic foam and a pair of hydrophones on the exterior of the casting.

Development of an accelerometer-based underwater acoustic intensity sensor

An underwater acoustic intensity sensor is described. This sensor derives acoustic intensity from simultaneous, co-located measurement of the acoustic pressure and one component of the acoustic particle acceleration vector. The sensor consists of a pressure transducer in the form of a hollow piezoceramic cylinder and a pair of miniature accelerometers mounted inside the cylinder. Since this sensor derives acoustic intensity from measurement of acoustic pressure and acoustic particle acceleration, it is called a p-a intensity probe. The sensor is ballasted to be nearly neutrally buoyant. It is desirable for the accelerometers to measure only the rigid body motion of the assembled probe and for the effective centers of the pressure sensor and accelerometer to be coincident. This is achieved by symmetric disposition of a pair of accelerometers inside the ceramic cylinder. The response of the intensity probe is determined by comparison with a reference hydrophone in a predominantly reactive acoustic field.

Development of a velocity gradient underwater acoustic intensity sensor

A neutrally buoyant, underwater acoustic intensity probe is constructed and tested. This sensor measures the acoustic particle velocity at two closely spaced locations, hence it is denoted a “u-u” intensity probe. A new theoretical derivation infers the acoustic pressure from this one-dimensional velocity gradient, permitting the computation of one component of acoustic intensity. A calibration device, which produces a planar standing-wave field, is constructed and tested. In this calibrator, the performance of the u-u intensity probe compares favorably to that of an acoustic intensity probe which measures both pressure and velocity directly.

Vector intensity field scattered by a rigid prolate spheroid

The short-wavelength, steady-state vector intensity field scattered by a rigid prolate spheroid (10:1 fineness ratio) is investigated analytically. The intensity field is the product of the scalar acoustic pressure and the acoustic particle velocity fields which are computed from the Helmholtz equation in prolate spheroidal coordinates. Particular emphasis is placed on results in the forward-scattered direction. It is found that the equivalent plane wave intensity varies by less than ±0.5dB (relative to the incident acoustic intensity) in the far-forward-scattered direction with the selected parameters. This illustrates that the forward-scattered pressure is masked by and interferes with the incident wave. The reactive intensity in the forward-scattered direction is found to be −25dB relative to the incident active intensity, and the computed phase difference between pressure and particle velocity is 4° at ranges approaching 10 spheroid lengths at a reduced frequency of h=41.7; in the absence of the spher...

Flow‐induced noise on a bluff body

Flow noise measurements were made on inertial type pressure gradient hydrophones, configured as three‐dimensional cylinders in cross flow, over a diameter‐based Reynolds number range of 4×103 to 1.8×104. The measurements were made at frequencies from 4.2 to 50 Hz as the bodies were towed in a quiescent body of water. Systematic changes were made in the cylinder geometry as to affect the flow noise level and to aid in the identification of dominant flow noise sources. The cylinder aspect ratio was varied from 0.5 to 2.5, and the endcap geometry was altered by relieving the 90° edge with radii that ranged from 0.0315D to 0.5D, where D is the diameter of the cylinder. The data from these (and other flow visualization) experiments shows that the presence of a radius at the corner between the endcap and the cylinder results in a significant reduction of the separated flow over the endcap, and that the flow noise levels decrease accordingly. The flow noise levels are also observed to decrease as the body aspect...

Short‐wavelength acoustic diffraction by prolate spheroids

The scattering of a plane acoustic wave by a rigid prolate spheroid of large fineness ratio is investigated analytically. The solution for the diffracted field is presented in terms of the classic modal series of spheroidal harmonics. The series are numerically evaluated for wavelengths much smaller than the length of the spheroid, but comparable to the minor radius. For this range of wavenumbers, use was made of available asymptotic formulas of the spheroidal wave functions, where the convergence of the double infinite series is discussed in terms of the value of the product of wavenumber and various characteristic lengths of the spheroid. The directivity functions are presented for several values of plane‐wave incidence, reduced frequency, and fineness ratio. The total scattering cross section is evaluated and compared to the scattering cross section of rigid spheres. An estimate is given to the size sphere required to scatter approximately the same power as the spheroid of given size and orientation wi...

Laminar flow performance of a heated body in particle-laden water

The effects of small uniformly sized spherical particles seeded into the freestream flow of a water tunnel on the delayed transition of a heated laminar flow control body is examined experimentally. In separate trials, four different mean diameter particle seedings were added to the flow and the approach flow velocity was cycled from subcritical to supercritical conditions at three different body heating conditions. The transition Reynolds number based on the body arc length and the approach flow velocity decreases monotonically with increasing d/δ*, where d is the particle diameter and δ* is the displacement thickness at a critical location. The location of initial turbulent spot formation defines the critical location, and, within the range of experimental conditions reported here, is independent of particle size, heating condition and the approach velocity. For the high unit Reynolds numbers considered (Reu⩽ 1.88 × 107 per metre), there is no observed critical particle diameterbased Reynolds number threshold; all sizes of particles considered in the experiments (d = 37 to 218 μm) have some effect on transition. In a second set of experiments, particles were injected into the laminar boundary layer from a small orifice located at the forward stagnation point. These injected particles have no observable effect on the laminar layer or transition, which suggests that the injected particles fail to produce wakes or vorticity within the laminar layer that may lead to turbulent spot production.

Noise generated by axisymmetric turbulent boundary layer flow

The noise generated by hydrodynamic flow over an axisymmetric body with a blunt nose is described quantitatively. Flush‐mounted piezoceramic hydrophones were used to measure that part of the turbulent boundary‐layer pressure fluctuations that propagates as true sound. Power spectra of the sound pressure were measured in a 3–50‐kHz frequency range over a wide range of Reynolds numbers (U∞D/ν ⩽ 3.03 × 106, where D is the diameter of the body) for the model operating in the Garfield Thomas Water Tunnel. The use of flush‐mounted hot‐film probes to locate turbulence transition is also described. The power spectra of the noise measured in the laminar flow regions correspond closely to those measured in the transition and fully developed turbulent regions of the flow, The exceptions were those spectra measured on the flat part of the nose, but correction for diffraction loss effects suggests that the noise measured there is due to the noise generated by the turbulent part of the flow. Nondimensionalization of th...