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We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our “Preston-static” device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.

Zebra mussels adhere tenaciously and gregariously to hard surfaces, thereby fouling water‐processing facilities and equipment. At present, there are few data on zebra mussel adhesion strength to common substrates. A rotating disk test system (RDTS) was used to measure the adhesion strength of small mussels (≈1 mm) to four materials [polyvinylchloride (PVC), polymethylmethacrylate (PMMA), stainless steel (SS), and aluminum (AL)].Adhesion strength varied significantly with material but only marginally with residence time (one, two, seven, 14, 21, and 28 days). The estimated shear stress required to remove 95&percent; of mussels (τ95&percent;) averaged 62±5 Pa (mean±standard error, n = 6 disks) on PVC, 50±3 Pa on PMMA, 48±4 Pa on SS, and 31±1(n = 4) Pa on AL. τ95&percent; peaked on the second day (85 Pa on PVC, 65 Pa on PMMA, 57.5 Pa on SS, 32.5 Pa on AL), then decreased to a constant level. Ultimately, this research should provide insight into material selection and designs that minimize attachment and facilitate removal of zebra mussels.

We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our “Preston-static” device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.