Laser Velocimeter Measurements Research Articles

Response of a shell structure subject to distributed harmonic excitation

Previously, a coupled, two-dimensional structural-acoustic ring model was constructed to simulate the dynamic and acoustical behavior of pneumatic tires. Analytical forced solutions were obtained and were experimentally verified through laser velocimeter measurement made using automobile tires. However, the two-dimensional ring model is incapable of representing higher order, in-plane modal motion in either the circumferential or axial directions. Therefore, in this paper, a three-dimensional pressurized circular shell model is proposed to study the in-plane shearing motion and the effect of different forcing conditions. Closed form analytical solutions were obtained for both free and forced vibrations of the shell under simply supported boundary conditions. Dispersion relations were calculated and different wave types were identified by their different speeds. Shell surface mobility results under various input distributions were also studied and compared. Spatial Fourier series decompositions were also performed on the spatial mobility results to give the forced dispersion relations, which illustrate clearly the influence of input force spatial distribution. Such a model has practical application in identifying the sources of noise and vibration problems in automotive tires.

Response of a shell structure subject to distributed harmonic excitation

Previously, a coupled, two-dimensional structural-acoustic ring model was constructed to simulate the dynamic and acoustical behavior of pneumatic tires. Analytical forced solutions were obtained and were experimentally verified through laser velocimeter measurement made using automobile tires. However, the two-dimensional ring model is incapable of representing higher order, in-plane modal motion in either the circumferential or axial directions. Therefore, in this paper, a three-dimensional pressurized circular shell model is proposed to study the in-plane shearing motion and the effect of different forcing conditions. Closed form analytical solutions were obtained for both free and forced vibrations of the shell under simply supported boundary conditions. Dispersion relations were calculated and different wave types were identified by their different speeds. Shell surface mobility results under various input distributions were also studied and compared. Spatial Fourier series decompositions were also performed on the spatial mobility results to give the forced dispersion relations, which illustrate clearly the influence of input force spatial distribution. Such a model has practical application in identifying the sources of noise and vibration problems in automotive tires.

Effects of coincidence window and measuring volume size on laser Doppler velocimetry measurement of turbulence

The effects of coincidence window and measuring volume size on two-component laser velocimeter measurement of turbulence in an isothermal liquid flow through a concentric annular channel were studied. Three different coincidence windows (100–500 μs) and three different measuring volume sizes (diameter, 5–9 wall units; spanwise length, 24–91 wall units) were used in a flow of Reynolds number 31,500 and data density spanning the high end of intermediate to the low end of high (3–6). While no significant effects of the coincidence window and measuring volume size were found on the time-mean velocity and turbulence intensities, the streamwise Reynolds shear stress measured near a wall was found to be markedly affected by both. The smallest feasible measuring volume along with an appropriate coincidence window provides good measurement of the shear stress.

Laser Velocimeter Measurements in the Stator of an Automotive Torque Converter

The flow field in the stator of a clear torque converter was studied using laser velocimetry. Five planes in the stator were studied at a speed ratio of 0.800 and three planes were studied at a speed ratio of 0.065. Data complements previously available pump and turbine data. Flow in the stator inlet plane is highly non‐uniform due to the complicated flow exiting the turbine. At the 0.800 speed ratio, separation regions are located in the 1/4 and mid‐planes in the corepressure corner region. In the 3/4 and exit planes, separation regions are located in the shellsuction corner. In the inlet plane a region of high velocities is located along the shell near the pressure side for a speed ratio of 0.800. The high velocity region migrated to the shell‐suction corner and suction side in the 1/4 and mid‐planes. The overall velocity field for the speed ratio of 0.065 changes significantly from the inlet plane to the mid‐plane. The velocity magnitude generally decreases from the suction to the pressure side of the inlet plane and the general direction of the tangential velocity is from pressure‐to‐suction surface. At the speed ratio of 0.065 a strong secondary flow in the inlet from suction surface to pressure surface was seen. However, at the high speed ratio a moderate secondary flow in the inlet from pressure surface to suction surface was observed. Mass flow rates at the different planes are within the experimental uncertainty and also within the uncertainty of pump and turbine mass flow rates. The flow in the stator inlet plane are significantly influenced by the turbine relative blade position. The turbine influence on the mid‐plane data is significantly less than on the inlet plane data. The influence of the pump blade position on the stator exit plane is small.

Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter Part II – Effect of Pump Speed and Oil Viscosity

The velocity field inside a torque converter pump was studied for two separate effects: variable pump rotational speed and variable oil viscosity. Three‐dimensional velocity measurements were taken using a laser velocimeter for both the pump mid‐ and exit planes. The effect ofvariable pump rotational speed was studied by running the pump at two different speeds and holding speed ratio (pump rotational speed]turbine rotational speed) constant. Similarly, the effect of viscosity on the pump flow field was studied by varying the temperature and]or using two different viscosity oils as the working fluid in the pump. Threedimensional velocity vector plots, through‐flow contour plots, and secondary flow profiles were obtained for both pump planes and all test conditions. Results showed that torque converter mass flows increased approximately linearly with increasing pump rotational speed (and fixed speed ratio) but that the flow was not directly proportional to pump rotational speed. However, mass flows were seen to decrease as the oil viscosity was decreased with a resulting increased Reynolds number; for these conditions the high velocity regions were seen to decrease in size and low velocity regions were seen to increase in size. In the pump mid‐plane strong counter‐clockwise secondary flows and in the exit plane strong clockwise secondary flows were observed. The vorticities and slip factors were calculated from the experimental results and are presented. The torque core‐to‐shell and blade‐to‐blade torque distributions were calculated for both planes. Finally, the flow fields were seen to demonstrate similitude when Reynolds numbers were matched.

Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter Part I – Effect of Speed Ratio

A torque converter was tested at four turbine/pump rotational speed ratios (0.200, 0.400, 0.600, and 0.800) all with a constant pump rotational speed in order to determine the effect of speed ratio on the torque converter pump flow field. Laser velocimetry was used to measure three components of velocity within the pump and a shaft encoder was employed to record the instantaneous pump angular position. Shaft encoder information was correlated with measured velocities to develop flow field blade‐to‐blade profiles and vector plots. Measurements were obtained in both the pump mid‐ and exit planes for all four speed ratios. Results showed large separation regions and jet/wake flows throughout the pump. The midplane flow was found to have strong counter‐clockwise secondary components and the exit plane flow had strong clockwise secondary components. Mass flows were calculated from the velocity data and were found to decrease as the speed ratio was increased. Also, the vorticity and slip factors were calculated from the experimental data and are included. The mid‐plane slip factors compare favorably to those for conventional centrifugal pumps but less slip was present in the exit plane than the mid‐plane. Neither the slip factor nor the vorticity were seen to be strongly affected by the speed ratio. Finally, the torque core‐to‐shell and blade‐to‐blade torque distributions are presented for both planes.

Laser Velocimeter Measurements in the Turbine of an Automotive Torque Converter: Part I—Average Measurements

The three-dimensional average velocity field in an automotive torque converter turbine was examined. Two significantly different operating conditions of the torque converter were tested: the 0.065 and 0.800 turbine/pump speed ratio. Velocities were measured using a one-directional, frequency-shifted laser velocimeter. The instantaneous angular positions of the torque converter turbine and pump were recorded using digital shaft encoders. Shaft encoder information and velocities were correlated to generate average velocity blade-to-blade profiles and velocity vector plots. Measurements were taken in the inlet, quarter, mid, and exit planes of the turbine. From the experimental velocity measurements, mass flows, turbine output torque, average vorticities, viscous dissipation, inlet incidence flow angles, and exit flow angles were calculated. Average mass flows were 23.4 kg/s and 14.7 kg/s for the 0.065 and 0.800 speed ratios, respectively. Velocity vector plots for both turbine/pump speed ratios showed the flow field in the turbine quarter and midplanes to be highly nonuniform with separation regions and reversed flows at the core-suction corner. For the conditions tested, the turbine inlet flow was seen to have a high relative incidence angle, while the relative turbine exit flow angle was close to the blade angle.

Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter: Part I—Average Measurements

A torque converter was tested for two turbine/pump rotational speed ratios, 0.065 and 0.800, and a laser velocimeter was used to measure three components of velocity within the pump. Shaft encoders were used to record the instantaneous pump angular position, which was correlated with the velocities. Average flow velocity profiles were obtained for the pump inlet, mid-, and exit planes. Large separation regions were seen in the mid- and exit planes of the pump for a speed ratio of 0.800. Strong counterclockwise secondary flows were observed in the midplane and strong clockwise secondary flows were seen in the exit plane of the pump for all conditions; vorticities were evaluated and are reported. Velocity data were also used to find the torque distribution. For both speed ratios the torque was approximately evenly distributed between the inlet and exit. Finally, slip factors were evaluated at the mid-and exit planes. At the midplane they were approximately the same as for conventional centrifugal pumps; however, at the exit plane the slip factors are larger than for centrifugal pumps.

Simultaneous velocity and temperature measurements in a premixed dump combustor

Experimental measurements of velocity and temperature were made in a low-speed turbulent flowfield following an axisymmetric sudden expansion with and without combustion. The combustion case considered here used a lean, completely premixed propane-air mixture whose flame was stabilized by the recirculation zone present in this flow. Simultaneous two-component laser velocimeter measurements were made giving the mean axial and radial velocities and the Reynolds stresses throughout the flowfield. In addition, simultaneous timeresolved temperature measurements were made in the reacting flow using a fast response thermocouple. Velocitytemperature correlations were formed from the velocity and temperature measurements. The reacting flow case was found to have a shorter and stronger recirculation zone, and the turbulence intensity level was found to be suppressed over most of the flowfield when compared with the cold flow case.

The effect of spatial wandering on experimental laser velocimeter measurements of the end-wall vortices in an axial-flow pump

In a high Reynolds number axial-flow pump, laser velocimeter (LV) measurements were made to study the size and structure of the end-wall vortex. The time mean measurements show that the core size of the end-wall vortex increased with decreasing tip clearance, which is contrary to existing theory. Observations of cavitation in the vortex showed that the flow was unsteady. The vortices emanating from the smaller clearances were observed to wander or meander spatially and to develop kinks more than the vortices emanating from the larger tip clearances. This observed unsteadiness has a significant effect on the time mean size and velocity distribution of the vortex as measured with the LV employing the field point measurement technique. In order to obtain an estimate of the true size and velocity distribution, computational experiments were conducted which modelled a periodically wandering vortex and the LV measurement process. The computational and experimental results show good agreement, including a broadened and reduced tangential velocity distribution. In this paper, the end-wall vortex LV measurements are presented, and the method of analyzing the vortex wandering is described.

Laser Velocimeter Measurements in a Centrifugal Pump With a Synchronously Orbiting Impeller

Velocity profiles were measured in the impeller of a centrifugal pump with a two-directional laser velocimeter. Blade-to-blade profiles were measured at four circumferential positions and four radii within and one outside the four-bladed impeller. Data are presented herein at two circumferential and three radial locations. The pump was tested in two configurations; with the impeller running centered within the pump, and with the impeller orbiting with a synchronous motion (ε/r2 = 0.016). Variation in velocity profiles among the individual passages in the orbiting impeller were found. At design flow rate, these variations ranged from 30 to 60 percent for the radial component, and 15 to 25 percent for the tangential component. Tangential velocity profiles near the impeller exit (r/r2 = 0.973) were near uniform across each individual passage. Differences in the magnitude of the exit tangential velocities among the passages however, were detected. Systematic differences in the velocity profile shapes of the centered and orbiting impellers were in general not measured, the only exception being at r/r2 = 0.973 at 40 percent of the design flow rate. At this condition, two distinct radial velocity profiles were measured. Two of the impeller passages of the orbiting impeller contained a recirculation region covering 20-30 percent of the blade passage while the other two passages contained no recirculation region. The centered impeller also contained this region of reverse flow. Finally, velocity data were numerically integrated to find the forces and stiffnesses due to momentum fluxes on the impeller for the orbiting condition.

Effect of Helmholtz resonators on boundary-layer turbulence

HELMHOLTZ resonators were investigated as a passive device for the purpose of modifying a turbulent boundary layer. Resonators, imbedded in a wall, also occur inadvertently when porous walls are used to reduce boundarylayer growth or as acoustic control devices in inlet ducts and combustors. In all cases it is of interest to know the effect of the resonators on the boundary layer. Helmholtz resonators are formed by cavities that are vented by a small orifice (see Fig. 1). They respond to excitation from the shear layer at the orifice as well as from incident acoustic waves. Previous experimental work '~4 has focused on the conditions for resonance in a single resonator. In the present study, a row of 10 resonators was positioned across the span of a wind-tunnel wall. Separate studies5'6 were conducted to determine the response of the resonator row to the boundary layer and the interaction that occurred between adjacent resonators. The relevant results are that peak response was achieved at a freestream velocity of 26.5 m/s, and the frequency and amplitude of the cavity pressure oscillations were 570 Hz and 143 dB (equivalent to 80% of the freestream dynamic pressure). In addition, adjacent resonators showed a strong antiphase locking with an average coherence coefficient of 70% and a phase lag of 150 to 180 deg. The phase locking between resonators was localized, and coherence decreased rapidly with resonators that were further away. Contents Experiments were conducted in a wind tunnel with a test section of 0.71 m x 1.0 m and 2.7 m long (28 in. x 40 in. x 9 ft). Ten resonators were formed with orifices of diameter D = 1.03 cm (0.406 in.) and 0.305 cm (0.120 in.) thickness. They were spaced 3.05 cm (1.20 in) on centers occupying the central 27.5 cm (10.8 in) of the 1.0 m (40 in.) span. At the location of the resonators, with flow parameters chosen to produce a resonant condition, the boundary layer had a thickness of d = 2.8 cm (1.1 in.), friction velocity UT = 1.0 m/s, and freestream speed of 26 m/s (58 mph). The corresponding Ret> was 5500. Measurement locations were chosen at the streamwise (X) positions X/D= -3,-0.5, 0.5, 3, 10,20,40, and 80 together with six spanwise (Z) positions, three directly in line with the resonator orifices and three half-way between the orifices. Laser velocimeter measurements of the streamwise and vertical velocity were obtained and processed to yield values of the

Turbulent structure in a channel flow with polymer injection at the wall

Two-component laser velocimeter measurements in a fully developed turbulent water channel flow with polymer injection were used to examine the effect of polymer injection on the Reynolds stresses and the production terms in the Reynolds stress transport equations. These measurements show that while the root-mean-square fluctuation level of the streamwise velocity was increased, the r.m.s. of the wall-normal velocity and the Reynolds shear stress were reduced.

Investigation of turbulent transport in an axisymmetric sudden expansion

Simultaneous two-component laser velocimeter measurements were made in the incompressible turbulent flowfield following an axisymmetric sudden expansion. Mean velocities, Reynolds stresses, and triple products were measured and are presented at axial positions ranging from x/H = 0.2-14. A balance of the turbulent kinetic energy in the flow was performed. The production, convection, and diffusion of turbulent kinetic energy were computed directly from the experimental data using central differencing. A specially designed correction lens was employed to correct for optical aberrations introduced by the circular tube. This lens system allowed the accurate simultaneous measurement of axial and radial velocities in the test section. The experimental measurements were compared to predictions generated by a code that employed the k-epsilon turbulence model. Agreement was good for mean axial velocities, turbulent kinetic energy, and turbulent shear stresses. However, the modeled turbulent normal stresses where in poor agreement with the measured values. The modeled diffusion of turbulent kinetic energy was underpredicted in the region between the shear layer and the centerline of the flow giving lower values of turbulent kinetic energy downstream of the potential core than measured.

Effect of measuring volume length on two-component laser velocimeter measurements in a turbulent boundary layer

The effects of finite measuring volume length on laser velocimetry measurements of turbulent boundary layers were studied. Four different effective measuring volume lengths, ranging in spanwise extent from 7 to 44 viscous units, were used in a low Reynolds number (Reθ=1440) turbulent boundary layer with high data density. Reynolds shear stress profiles in the near-wall region show that 〈u v〉 strongly depends on the measuring volume length; at a given y-position, 〈u v〉 decreases with increasing measuring volume length. This dependence was attributed to simultaneous validations on the U and V channels of Doppler bursts coming from different particles within the measuring volume. Moments of the streamwise velocity showed a slight dependence on measuring volume length, indicating that spatial averaging effects well known for hot-films and hot-wires can occur in laser velocimetry measurements when the data density is high.

Laser sheet technique for visualizing a periodic rotor wake

Introduction L sheets have been used to illuminate cross sections of steady flowfields for several years. Intense sheets of light only a few millimeters in thickness can be produced by either expanding a single laser beam with a cylindrical lens or by rapidly sweeping the beam by means of a vibrating mirror or other optical device.' Generally, smoke or other seed particles which scatter light as they pass through the laser sheet are introduced upstream of the region of interest. Streamlines and vortical structures are identified respectively as streaks and swirl patterns in the illuminated region.' Recent experiments conducted in the John J. Harper 2.31 m x 2.74 m (7 x 9 ft) low-speed wind tunnel at the Georgia Institute of Technology employed a strobed laser sheet to visualize the periodic flowfield between a model rotor and an airframe in forward flight. A nonintrusive method was developed to determine accurately tip vortex trajectories in a uniformly seeded flow. Unlike Schlieren, shadowgraphic, or interferometric methods, the laser sheet technique is well-suited for visualizing the incompressible (low Mach number) flows common to rotorcraft. Quantitative data valuable for use in the interpretation of vortex/airframe interaction measurements were gathered using this technique, as reported in Ref. 5. Used in conjunction with laser velocimeter measurements, the laser sheet flow visualization approach provides a powerful means for documenting vortex jitter or other flow instabilities that can affect measurements. The methods described are adaptable to many situations requiring visualization of a periodic flow structure.

Influence of cardiac flow rate on turbulent shear stress from a prosthetic heart valve.

Elevated turbulent shear stresses associated with sufficient exposure times are potentially damaging to blood constituents. Since these conditions can be induced by mechanical heart valves, the objectives of this study were to locate the maximum turbulent shear stress in both space and time and to determine how the maximum turbulent shear stress depends on the cardiac flow rate in a pulsatile flow downstream of a tilting disk valve. Two-component, simultaneous, correlated laser velocimeter measurements were recorded at four different axial locations and three different flow rates in a straight tube model of the aorta. All velocity data were ensemble averaged within a 15 ms time window located at approximately peak systolic flow over more than 300 cycles. Shear stresses as high as 992 dynes/cm2 were found 0.92 tube diameters downstream of the monostrut, disk valve. The maximum turbulent shear stress was found to scale with flow rate to the 0.72 power. A repeatable starting vortex was shed from the disk at the beginning of each cycle.

Laser Velocimeter Measurements in Shrouded and Unshrouded Radial Flow Pump Impellers

Shrouded and unshrouded versions of a four-vaned radial flow impeller with a design flow coefficient of 0.063 were tested in a volute pump using a two-component frequency-shifted laser velocimeter. Velocity profiles were measured at six flow rates and at four radial and six circumferential positions in the volute. The variations of the velocity from blade to blade and in the axial direction were measured and are presented. A passage vortex caused by tip leakage and relative casing wall velocity was found in the unshrouded impeller. The tip leakage did not accumulate in the suction wake region; the suction wake region was only 30 to 50 percent as large in the unshrouded impeller as compared to the shrouded impeller. The slip was 30 percent higher in the unshrouded impeller and the variation of slip with flow rate is presented. At no measured position in the impellers did the slip factor reach unity; the closest approach was 0.90. Reverse loadings of the vanes at outer radii were found for flow rates below the impeller/volute matching point for both impellers.

Computation of transonic flow about helicopter rotor blades

An inviscid, nonconservative, three-dimensional full-potential flow code, ROT22, has been developed for computing the quasi-steady flow about a lifting rotor blade. The code is valid throughout the subsonic and transonic regime. Calculations from the code are compared with detailed laser velocimeter measurements made in the tip region of a nonlifting rotor at a tip Mach number of 0.95 and zero advance ratio. In addition, comparisons are made with chordwise surface pressure measurements obtained in a wind tunnel for a nonlifting rotor blade at transonic tip speeds at advance ratios from 0.40 to 0.50. The overall agreement between theoretical calculations and experiment is very good. A typical run on a CRAY X-MP computer requires about 30 CPU seconds for one rotor position at transonic tip speed.

Cold Flow and Combustion Experiments With a New Burner Air Distribution Concept

Experiments were conducted with a JT8D-engine sized can combustor modified such that all the combustion and dilution air entered through the burner front face from a single plenum through counter-rotating annular swirlers. Cold flow experiments were conducted to visualize and to develop a mixing and recirculation flow pattern within the combustor which contained annular and central recirculation cells and featured rapid mixing in the downstream section of the combustor. Laser velocimeter measurements, downstream of the air inlet configuration used in the combustion experiments, showed the largest velocity gradients in the radial direction were in the tangential velocity profile. Low-pressure combustion experiments were conducted with three flat spray fuel nozzle orientations and three air inlet geometries to determine the general air inlet and fuel injection characteristics required to produce acceptable combustion characteristics with the selected swirler configuration. The combustion experiments included emission, total pressure and total temperature measurements at the burner exit plane. Low emission levels and temperature pattern factors with relatively low burner pressure losses were demonstrated.