# Questions tagged [fluid-mechanics]

Questions relating to fluids at rest (fluid statics) or the forces and effects of fluids in motion (fluid dynamics).

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### Buoyancy force problem

I'm trying to design a kind of water valve with inexpensive materials as a first prototype. The water flow from the PVC pipe (1) reach the body of the valve and pass through an aluminum grid (3) to ...
140 views

I have questions about a well pump application I am working on. It consists of a well that with a submersible pump that fills a reservoir tank. As far as I know, the tank is not pressurized. Here are ...
22 views

### How (mathematically) does pressure in the intake manifold vary based on size of throttle opening?

I have the intuitive picture somewhat down: the intake manifold is partially opened; during the intake stroke of a four-stroke process, the piston moves rapidly moves downwards creating a short-term ...
41 views

### Pressure variation through reduction (Bernoulli) and pipe wall design

Let's say I have a pipe followed by a reduction and then another smaller diameter pipe continues. Using conservation of mass, the flow through the smaller diameter pipe will have higher velocity. If I ...
24 views

### Employing a deforming mesh, inlet, and no shear wall in ANSYS

I am interested in running a simulation in ANSYS Fluent (or CFX, whichever is more useful) that combines the following. Update: A rotating wing in the air, similar to a turbine blade. After ...
59 views

### Interpretation of dx/dt and u in CFD

I am currently studying CFD and I have a question about how I should interpret the term u and dx/dt. I would like to find that out in the textbook, but I could not. When I solve 1D Euler Equation with ...
59 views

### Increasing airflow of fan

I learned at at young age from a physics kit that one can blow up a large bag with your mouth by blowing into it from a distance and letting the air pick more air with it. Later in life when Dyson ...
1 vote
53 views

### Airflow visible over the airplane wing

What's that visible airflow over the airplane wing and what causes it?
630 views

### How to calculate the viscous damping coefficient given drag force

Force due to drag at low velocities, is equal to some constant times negative velocity $$F_{d}=-c_{1}V$$ The viscous damping coefficient equals decay constant divided by 2 times mass \gamma = \...
56 views

### Component selection type for fluid-mechanical system

I am creating an enclosure and need to get a water supply through a plastic wall inside to the core device. I imagine this water line will be a flexible tube and will screw on or snap to an adapter on ...
1 vote
746 views

### Find Torque and Force on Pipe with Bend

I did a Civil Engineering course some years ago and from my textbook I had a question on a pipe with a bend. Now I think I have the part of the question on force correct, but I am not sure how the ...
170 views

### What is the force needed to exert on the piston for a certain extrusion rate of a syringe tube?

I am trying to design a syringe pump for microfluidic extrusion uses. I have a 5cc syringe tube that I will use as the cartridge. We would be using it to extrude a variety of materials so the ...
19 views

### Consistent Fluid or powder flow through an orifice

This is a really odd and specific question, and I'm not sure this is even where to ask. A few weeks ago I thought about making a clock based on water flowing from an orifice. The obvious issue is that ...
1 vote
155 views

### Boundary Layer Thickness for Flat Plate

I did a Civil Engineering course some years ago and from my textbook I had a question on boundary layer thickness. So far I have been able to calculate the transition distance, but I am not sure how ...
1 vote
221 views

### Pipe network analysis: static pressure of a closed-loop pipe

I've learned fluid dynamics but does not have much knowledge about its real-world applications. My question is about the static pressure of a closed-loop pipe. [Fig. 1. Pipe network. Source: ...
1 vote
88 views

### Can I create a whirlpool/vortex around a horizontal axis in a flat bottle using motor?

I am using this flat bottle: I fixed a motor at the centre of one of the flat sides and attached an impeller. I thought this will create some kind of whirlpool effect but as you can guess, since the ...
225 views

### Boundary layer thickness decreases as fluid velocity increases, so why is the boundary layer thicker in the turbulent region for higher velocities?

I am modelling transitional fluid flow over a flat plate, and investigating the effects of free stream velocity on boundary layer thickness. From what we have been told, increasing free stream ...
1k views

### Free falling fluid pressure distribution

Consider a free falling tank of fluid. The goal is to find the pressure distribution. My intuition says that there should be no pressure distribution; the pressure should be uniform since the ...
53 views

### Could a hybrid system of mechanical levers and hydrostatic/hydraulic cylinders be able to lift 200+ kg with the force of an arm?

I don't know much about levers and hydrostatic/hydraulics myself, so I hope I don't make too many misconceptions. The idea: Hypothetically, if you had a 40km+ long indestructible lever on a ...
1 vote
90 views

### Pressure drop in a CFD simulation of an air flow too small

I am simulating a turbulent air flow through a rectangular channel with the goal to match measured velocity profiles and the static pressure at certain points. My problem is that the pressure drop in ...
661 views

### Direction of fluid flow

Consider water flowing in a pipe, and I don't know the direction of flow. How to determine the direction of flow? My approach- I can use a pitot tube but for that I have to drill a hole in the pipe ...
58 views

### Low-Flow Nozzles for Corrosion Spray Testing

So, for a cyclic corrosion test system, I need a nozzle or arrangement of nozzles that provides a flow rate of 45ml-140ml of salt solution per hour to an area 60cm square. All commercial nozzles I've ...
64 views

### Imposing/ensuring a constant mass flow rate in turbulent flow simulation

I'm trying to simulate using Finite Elements (non commercial software) the Tube Bundle benchmark problem: http://cfd.mace.manchester.ac.uk/ercoftac/doku.php?id=cases:case078&s[]=tube&s[]=...
47 views

### Flow of fluid in branched pipes

Could any one please tell me if there is any flow possible into pipe 2. What I believe is that as pipe 1 and pipe 3 are of same diameter and applying Bernoulli's equation between points 1 and 3 gives ...
30 views

### Ball immersed into a fluid

A plastic ball is pushed inside the tank and then released, can anyone plot velocity vs time and velocity vs height as long as ball is completely inside the water? For simplicity we can assume no ...
31 views

### What is a good working fluid in the temperature range of 150 - 180 °F?

I am looking for a good working fluid whose boiling point is in the range of 150 - 180 °F for a waste heat recovery system. The fluid should be minimally flammable, preferably nontoxic, and low in ...
14 views

### Meshing edges in Star CCM+ for CFD simulation

I am doing a CFD study on a bluff body to study the drag variation. During the meshing process in Starccm+ I came across a stage where the mesh does end smoothly at the edge (see figures). Which ...
19 views

### Analytical / Experimental calculation of pressure loss for simple crossflow of air across a simple cylinder

I need a way to find pressure loss of air flowing across a single tube for both laminar and turbulent flows. I have referred to several sources (Y. Cengel Heat and Mass Transfer and Fluid Dynamics ...
8 views

### At what location in a ducted centrifugal fan, the discharge of which is turned from radial to axial via the duct, is the force of thrust applied?

I am optimizing the structure of the duct for weight savings and need to know where the force of thrust (load) will be located. Assume the inlet is at the top, the fan axis of rotation is vertical. ...
1 vote
211 views

### Calculating Minimum Pipe Pressure Requirement for an Irrigation System

I am setting up an irrigation system for my ranch and I have a hard time calculating the minimum pipe pressure requirements to reduce cost. I need to know the maximum pressure the pipe has to cope ...
### Why is the exit loss $\frac{u^2}{2g}$ is small for laminar flow?
I have done some calculations: My lecturer just said that exit loss $\frac{u^2}{2g}$ is small for laminar flow so ignore it. But never explains why it is small?