Axisymmetric air jet impinging on a hemispherical convex plate

Author

• Salahuddin Qureshi, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

5-31-1985

Degree Name

Master of Science in Mechanical Engineering - (M.S.)

Department

Mechanical Engineering

First Advisor

P. Hrycak

Second Advisor

Gerald Jaffe

Third Advisor

E. S. Geskin

Abstract

This experimental study was carried out on an axisymmetric air jet impinging normally on a smooth, hemispherical convex plate. Three different nozzles of diameters 0.5in.(12.7mm), 0.375in.(9.525mm) and 0.25in.(6.35mm) were used and the nozzle exit Reynolds number varied from 14,000 to 80000.

The impingement hemispherical plate was made of brass and had a nominal outer diameter of 7.48in (189.99mm).

Calibrated Pitot tubes, U-tube manometer and a micromanometer were used for pressure and velocity measurements. The Pitot tubes were mounted on Precision position mechanisms permitting the accurate traversing in any direction in space. The test air flow rate was measured with calibrated rotameters.

The following results are obtained:

1. 1. The length of the Potential Core was found to be 6 by plotting the centerline jet velocity Um/Uoc vs. the distance from the nozzle exit, X/ D.
2. 2. The velocity profiles of a free jet at different locations from the nozzle exit were plotted and found that the velocity remains constant to some distance away from the centerline and then decreases to zero. This constant velocity is found to decrease inversely with the distance from the nozzle exit. However, the spread of the jet increases directly proportionally with the distance from the nozzle exit, and indicates the presence of a virtual origin inside the nozzle. There is no effect of Reynolds number and nozzle diameter.
3. 3. The static pressure along the jet centerline is found to be lower than the surrounding pressure and varies with the axial distance from the nozzle exit. The static pressure across the jet centerline was studied and found that it is minimum at the centerline of the jet and then increases gradually to that of the ambient at the outer portion of the jet. There is no observable effect of ReD.
4. 4. The maximum velocity decay in the wall jet was determined to be more rapid than that of either the flat plate or the concave hemisphere.
5. 5. The mean velocity profile at a given wall distance from the stagnation point is similar to those of the flat plate and the concave hemispherical plate; but it deviates from them at the outer envelop where the decay rate is maximum, followed by the curves of the flat plate and of the concave surface, in that order.
6. 6. The inner and outer boundary layer profiles obtained were compared with those of the flat plate and concave hemisphere and found that the inner boundary layer grows at a slightly higher rate with the wall distance, while the outer boundary layer grows at a slightly lower rate.
7. 7. The static pressure across the wall jet is found to increase negatively from some value close to ambient at the wall surface to a maximum at Z/Z_1/2 of about 10 before it increases to ambient at Z/Z_1/2 > 4. Also, its maximum value is a function of S/D and z/D.
8. 8. The skin friction coefficient was determined to be around 0.009 using Clauser's method.

These results are in good agreement with those of the previous investigators with 1/ deviation.

Recommended Citation

Qureshi, Salahuddin, "Axisymmetric air jet impinging on a hemispherical convex plate" (1985). Theses. 3465.
https://digitalcommons.njit.edu/theses/3465